Dr Rajiv Desai

An Educational Blog

HOLOGRAM

HOLOGRAM:

_____

Typical laser-lit transmission hologram

____

Prologue:

Suppose you want to take a photograph of an apple. You hold a camera in front of it and, when you press the shutter button to take your picture, the camera lens opens briefly and lets light through to hit the film (in an old-fashioned camera) or the light-sensitive CCD chip (in a digital camera). All the light traveling from the apple comes from a single direction and enters a single lens, so the camera can record only a two-dimensional pattern of light, dark, and color. To be more accurate camera records wave length (color) and intensity (amplitude) of light waves. If you move your head slightly, the photograph remains same i.e. it is two dimensional. The physical world around us is three-dimensional (3D), yet traditional display devices can show only two-dimensional (2D) flat images that lack depth (i.e., the third dimension) information. This fundamental restriction greatly limits our ability to perceive and to understand the complexity of real-world objects. Nearly 50% of the capability of the human brain is devoted to processing visual information. Flat images and 2D displays do not harness the brain’s power effectively. Now if you look at an apple, something different happens. Light reflects off the surface of the apple into your two eyes and your brain merges their two pictures into a single stereoscopic (three-dimensional) image. If you move your head slightly, the rays of light reflected off the apple have to travel along slightly different paths to meet your eyes, and parts of the apple may now look lighter or darker or a different color. Your brain instantly recalculates everything and you see a slightly different picture. This is why your eyes see a three-dimensional image. A hologram is a cross between what happens when you take a photograph and what happens when you look at something for real. Like a photograph, a hologram is a permanent record of the light reflected off an object. But a hologram also looks real and three-dimensional and moves as you look around it, just like a real object. That happens because of the unique way in which holograms are made where holographic film (media) not only records wave length and intensity of light waves but also records phase of light waves. If a 2D picture is worth a thousand words, then a 3D image is worth a million. With holography, it is possible to reconstruct 3D images using holograms, and the process is unlike anything found in traditional display technology. However, the term “hologram” gets thrown around loosely, simply because many people don’t know the true definition. What media commonly identifies as ‘hologram’ is not actually a hologram; it is Pepper’s Ghost illusion or its variants or a volumetric display or reconstructed tomograms. Actual holograms are 3D images on 2D surfaces, and not visible from arbitrary angles. People use the term ‘hologram’ loosely as it is easier to say hologram than volumetric display, Pepper’s Ghost and many other techniques and tricks. 2D/3D holograms are by far the most common type of holograms seen on credit cards and driver licenses but they are multilayer images and not real holograms.

_______

Glossary of Terms:

Amplitude – The height of a wave crest or depth of a wave trough, measured from the wave’s mid-point.

Phase – The position of a wave in space, measured at a particular point in time.

Coherent light – Light which is of the same frequency and is vibrating in phase. The laser produces coherent light.

Beamsplitter – A device used to divide the light from the laser into two separate beams – the reference and object beams. It consists of a partially transparent mirror which reflects part of the laser beam and transmits the rest.

Film – Whether photographic or holographic, film consists of light sensitive chemicals (the emulsion) spread on a surface. A film’s resolution measures its ability to distinguish between details. Because holographic films must be able to record very detailed information, they have a resolving power of 50 or more times that of photographic film. They require either exposure to a high intensity pulsed or a long exposure to a continuous wave laser. Holographic film is developed in a manner similar to photographic film, by bathing it in a series of chemical agents.

Interference pattern – When two waves overlap, their amplitudes add at every point. This results in an interference pattern which records the relative phase relationships between the two waves, storing each individual wave’s characteristics. This is how a hologram works.

Laser – An acronym for “Light Amplification by Stimulated Emission of Radiation.” A laser is a device that produces a concentrated beam of coherent light. Some, called continuous wave lasers, produce a continuous beam of light. Others, called pulsed lasers, emit more light in brief pulses which are able to freeze motion.

Lenses – Lenses are devices which redirect light. In photography, lenses are used to focus an image for the film. Holographers use lenses to widen the lasers beam to illuminate all of the subject which is to be holographed.

Object beam – The light from the laser beam that illuminates the object, and is reflected to the holographic film.

Reference beam – The portion of the laser beam that goes directly to the holographic film. The interference pattern which results from the object beam meeting the reference beam at the holographic film is recorded on the film.

Reflection hologram – One that forms an image by reflected light. Reflection holograms are lit from the front, reflecting the light to the viewer.

Transmission hologram – One that forms an image from the light passing through the holographic emulsion. Transmission holograms are lit from the rear, bending the light as it passes through the hologram to your eyes.

White light – Light which contains most of the wavelengths in the visible spectrum, such as light from the sun or a spotlight. White light is incoherent, while laser light is coherent. A white light transmission hologram (or rainbow hologram) is one which can be displayed using ordinary white light. Early holograms required viewing with coherent laser light.

_____

Abbreviations and synonyms:

2D = two dimensional

3D = three dimensional

4D = 3D + time

CGH = computer generated holography

DH = digital holography

AH = analog holography

SLM = spatial light modulator

LCD = liquid crystal device

CRT = cathode ray tube

DHM = digital Holographic Microscopy

HVD = holographic versatile disc

HDS = holographic data storage

LED = light-emitting diode

VMETH = volumetric multiple exposure transmission holography

CCD = charge-coupled device

4K = horizontal resolution of 4,096 pixel

HOE = holographic optical elements

_____

_____

D means dimension:

Each dimension is a way of seeing or sensing something.

1D (one dimensional) is mostly a theoretical idea or the domain of the very small world of quantum mechanics.  Everything we can see has 2 dimensions. Even a very thin long line has at least some width.

2D is a flat representation of a scene or object. Its size can be described as height and width, like a square, picture  or image on a standard TV.

3D is a recreation of an object or scene in three dimensions.  So height, width and depth like a cube or sphere. We have two eyes so we have great depth perception and experience the world in 3D.

4D is basically 3D plus movement over time. So Time is the fourth dimension.

5D and above are not viewable or detectable by us in our Universe. These extra dimensions are the playground of theoretical physicists.

____

Parallax:

_

Figure above shows a simplified illustration of the parallax of an object against a distant background due to a perspective shift. When viewed from “Viewpoint A”, the object appears to be in front of the blue square. When the viewpoint is changed to “Viewpoint B”, the object appears to have moved in front of the red square.

_

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects have a larger parallax than more distant objects when observed from different positions, so parallax can be used to determine distances. To measure large distances, such as the distance of a planet or a star from the earth, astronomers use the principle of parallax. Here, the term “parallax” is the semi-angle of inclination between two sight-lines to the star, as observed when the Earth is on opposite sides of the Sun in its orbit. These distances form the lowest rung of what is called “the cosmic distance ladder”, the first in a succession of methods by which astronomers determine the distances to celestial objects, serving as a basis for other distance measurements in astronomy forming the higher rungs of the ladder. Parallax also affects optical instruments such as rifle scopes, binoculars, microscopes, and twin-lens reflex cameras that view objects from slightly different angles. Many animals, including humans, have two eyes with overlapping visual fields that use parallax to gain depth perception; this process is known as stereopsis. In computer vision the effect is used for computer stereo vision, and there is a device called a parallax rangefinder that uses it to find range, and in some variations also altitude to a target.

____

2D to 3D:

3D stands for three-dimensional. “Regular” movies are 2D, or two-dimensional. Dimensions are properties of space. They refer to extension in a particular direction. For example, two-dimensional (2D) images have two dimensions: length and width. Think of a picture drawn on a piece of paper. The paper has length and width. Many things in the real world, however, have three dimensions. The third dimension is depth. Think of a cube. Not only does it have length and width, but it also has depth. When you watch a movie, the screen is two-dimensional. It has length and width, but not depth. That’s why “regular” 2D movies appear as if all the action is happening up there on the big screen. 3D movies, on the other hand, add depth and make you feel like you’re part of the experience. You see cars flying toward you or snowflakes floating in the air all around you.

_

People perceive depth and see the real world in three dimensions thanks to binocular vision as we have two eyes that are about three inches apart. The separation of our eyes means that each eye sees the world from a slightly different perspective. Our powerful brains take these two slightly-different images of the world and do all the necessary calculations to create a sense of depth and allow us to gauge distance. Try these simple experiments to test your binocular vision. Hold one arm straight out in front of you with your thumb pointing up. Close one eye and stare at your thumb. Now close the other eye. What do you see? As you close one eye and then the other, you should see your thumb appear to move slightly against the background. This binocular vision does make much of a difference.  Grab a ball and ask a friend to toss it to you. Practice catching the ball a couple of times. Then, keep one eye closed and try to catch the ball. Do you notice how much harder it is to gauge distance and catch the ball? Scientists have a fancy word for how your eyes and your brain work together to see in three dimensions. It’s called stereoscopy. Stereoscopy is what modern 3D technology tries to duplicate.

_

There are several different types of 3D technology in use today, but they basically do the same thing. 3D movies and those 3D glasses work together to send each of your eyes different perspectives of the same image. Depending upon the exact type of technology used, the 3D glasses you wear will either use special shutters, color filters, or polarized lenses to receive the images. Your brain takes care of the rest! For example, older (and some newer) 3D movies have to be viewed through special red and blue (sometimes red and green) glasses. Images are projected in those colors — red and blue — and the special glasses make sure each eye only receives one of the images. As always, your brain puts the 3D effect together. Newer movies use polarized glasses that take advantage of the fact that light can be polarized, or given different orientations. Newer 3D glasses with polarized lenses don’t need separate colors and can give a much more lifelike experience. Your incredible brain does all this 3D processing automatically.  The hardest part for 3D movie makers is getting a camera to do the same thing, so that they have the right images to send to your eyes via the movie screen. To get a good 3D image, you have to have two versions of the same image filmed from the exact angle as your eyes would see it. To accomplish this, filmmakers use special film rigs that use two cameras bolted into position to mimic human eye position. To make an animated movie in 3D, animators do basically the same thing. They create two versions of each individual picture to duplicate the perspective of each individual eye. Although it’s easier to get perfect images, it also takes a lot of extra time to create all the extra images.

_

The earliest forms of 3D glasses were not glasses at all. In the mid-19th century, Charles Wheatstone discovered that simply viewing a pair of similar (but not exact) images side-by-side can give the impression of three-dimensionality. The images are taken by two cameras that are slightly separated. This way, the photographs mimic what each one of our two eyes would see in reality.  This method is far from ideal, however. It requires people to “cross” their eyes, which some people cannot do or find uncomfortable. In the late 19th and early 20th century, the stereoscope was invented to address these issues. The stereoscope used lenses that merged the two distinct images into one, giving the effect of a 3D scene without straining the eyes.  The stereoscope was a popular novelty in bars and arcades until around the 1930s, when film became the dominant media for entertainment. Surprisingly, even today most people are probably familiar with the technology. The View-Master, a ubiquitous childhood toy for over 65 years, is a version of the stereoscope. When most people hear the term ‘3D,’ they don’t think of stereoscopes or View-Masters. Instead, flimsy plastic glasses with red and blue lenses usually come to mind. These glasses, when used with special photographs called anaglyph images, create the illusion of depth.

_

Traditionally, anaglyph images were taken using two slightly separated cameras, one with a red filter and one with a blue filter. Recently, the filtering is being done afterwards with a processing program like Adobe Photoshop. In both cases, the images are then combined to form a single picture, or anaglyph image. When viewed without 3D glasses, these images will look blurry and discolored.  Using a red and blue lens ‘tricks’ the brain into seeing a 3D image. Each eye sees a slightly different image. The eye covered by the red lens will perceive red as “white” and blue as “black,” and vice versa for the other eye. This disparity mimics what each eye would see in reality, as with most 3D technology.  Because the traditional red-blue glasses are inexpensive to produce, anaglyph images remain popular in modern media. Anaglyph images can be found everywhere from Disney’s feature film Spy Kids 3D to the latest Sports Illustrated Swimsuit Edition.  While anaglyph images prevail in print media, a new technology has eclipsed the venerable red-and-blue lenses in motion pictures. Relying on the optical phenomenon of polarization, these new 3D glasses allow for more accurate color viewing than anaglyph images.

_

To understand polarization, think of a garden hose. If you shake the hose up and down, you will generate vertical ‘waves’ that also move up and down. We would say this wave is vertically polarized. Similarly, shaking the hose left to right will generate waves we call horizontally polarized. Light is a wave made up of electric and magnetic fields that vary in time and, like the garden hose, it can be made to be vertically or horizontally polarized.  Like with anaglyph images, special glasses are needed to view these new 3D movies. One lens allows only vertically polarized light to pass through, while the other allows only horizontally polarized light. Two projectors show slightly different images, using light polarized in one or the other direction. In this way, each eye sees a different image, just like you would if you were viewing the scene in real life.  Because only the polarization and not the color of light is changed, polarized lenses produce much more lifelike images than their red-and-blue predecessors.  This polarized lens system is used at Disneyworld and Universal Studios and in IMAX 3D theaters across the country.

_

3D film:

A three-dimensional stereoscopic film (also known as three-dimensional film, 3D film) is a motion picture that enhances the illusion of depth perception, hence adding a third dimension. The most common approach to the production of 3D films is derived from stereoscopic photography. In it, a regular motion picture camera system is used to record the images as seen from two perspectives (or computer-generated imagery generates the two perspectives in post-production), and special projection hardware and/or eyewear are used to limit the visibility of each image in the pair to the viewer’s left or right eye only. 3D films are not limited to theatrical releases; television broadcasts and direct-to-video films have also incorporated similar methods, especially since the advent of 3D television and Blu-ray 3D. The “automultiscopic displays” is a 3D enabler that presents “multiple angular images of the same scene” and doesn’t require glasses.

_

Stereoscopy:

Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision.  Any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of stereo images which could be viewed using a stereoscope. Most stereoscopic methods present two offset images separately to the left and right eye of the viewer as discussed earlier. These two-dimensional images are then combined in the brain to give the perception of 3D depth. This technique is distinguished from real 3D displays that display an image in three full dimensions, by allowing the observer to increase information about the 3-dimensional objects being displayed by head and eye movements.

_

Stereoscopy creates the illusion of three-dimensional depth from given two-dimensional images. Human vision, including the perception of depth, is a complex process, which only begins with the acquisition of visual information taken in through the eyes; much processing ensues within the brain, as it strives to make sense of the raw information. One of the functions that occur within the brain as it interprets what the eyes see is assessing the relative distances of objects from the viewer, and the depth dimension of those objects. The cues that the brain uses to gauge relative distances and depth in a perceived scene include:

  • Stereopsis
  • Accommodation of the eye
  • Overlapping of one object by another
  • Subtended visual angle of an object of known size
  • Linear perspective (convergence of parallel edges)
  • Vertical position (objects closer to the horizon in the scene tend to be perceived as farther away)
  • Haze or contrast, saturation, and color, greater distance generally being associated with greater haze, desaturation, and a shift toward blue
  • Change in size of textured pattern detail

(All but the first two of the above cues exist in traditional two-dimensional images, such as paintings, photographs, and television.)

Stereoscopy is the production of the illusion of depth in a photograph, movie, or other two-dimensional image by the presentation of a slightly different image to each eye, which adds the first of these cues (stereopsis). The two images are then combined in the brain to give the perception of depth. Because all points in the image produced by stereoscopy focus at the same plane regardless of their depth in the original scene, the second cue, focus, is not duplicated and therefore the illusion of depth is incomplete. There are also mainly two effects of stereoscopy that are unnatural for human vision: (1) the mismatch between convergence and accommodation, caused by the difference between an object’s perceived position in front of or behind the display or screen and the real origin of that light; and (2) possible crosstalk between the eyes, caused by imperfect image separation in some methods of stereoscopy. Stereoscopic viewing may be artificially created by the viewer’s brain, as demonstrated with the Van Hare Effect, where the brain perceives stereo images even when the paired photographs are identical. This “false dimensionality” results from the developed stereoacuity in the brain, allowing the viewer to fill in depth information even when few if any 3D cues are actually available in the paired images.

_

Types of 3D display:

3-D displays can be categorized by the technique used to channel the left and right images to the appropriate eyes: some require optical devices close to the observer’s eyes, while others have the eye-addressing techniques completely integrated into the display itself. Displays of the latter category are called autostereoscopic and are technically much more demanding than the type with viewing aids (stereoscopic displays).

_

Autostereoscopy:

Autostereoscopic display technologies use optical components in the display, rather than worn by the user, to enable each eye to see a different image. Because headgear is not required, it is also called “glasses-free 3D”. The optics split the images directionally into the viewer’s eyes, so the display viewing geometry requires limited head positions that will achieve the stereoscopic effect. Automultiscopic displays provide multiple views of the same scene, rather than just two. Each view is visible from a different range of positions in front of the display. This allows the viewer to move left-right in front of the display and see the correct view from any position. The technology includes two broad classes of displays: those that use head-tracking to ensure that each of the viewer’s two eyes sees a different image on the screen, and those that display multiple views so that the display does not need to know where the viewers’ eyes are directed. Examples of autostereoscopic displays technology include lenticular lens, parallax barrier, volumetric display, holography and light field displays.

_

Stereoscopy vs. real 3D display:

The basic technique of stereo displays is to present offset images that are displayed separately to the left and right eye. Both of these 2D offset images are then combined in the brain to give the perception of 3D depth. Although the term “3D” is ubiquitously used, it is important to note that the presentation of dual 2D images is distinctly different from displaying an image in three full dimensions. The most notable difference to real 3D displays is that the observer’s head and eyes movements will not increase information about the 3-dimensional objects being displayed. For example, holographic displays and volumetric displays do not have such limitations. Similar to how in sound reproduction it is not possible to recreate a full 3-dimensional sound field merely with two stereophonic speakers, it is likewise an overstatement of capability to refer to dual 2D images as being “3D”. The accurate term “stereoscopic” is more cumbersome than the common misnomer “3D”, which has been entrenched after many decades of unquestioned misuse. It is to note that although most stereoscopic displays do not qualify as real 3D display, all real 3D display are also stereoscopic displays because they meet the lower criteria as well.

_

Types of stereoscopic displays:

Stereoscopic displays can be divided into autostereoscopic displays and goggle-bound displays. While goggle-bound displays require the aid of additional glasses to support a proper separation of the stereo images, autostereoscopic displays do not.

_

Real 3D displays:

Each element (voxel or hoxel) in a true 3D display should consist of multiple directional emitters: if tiny projectors radiate the captured light, the plenoptic function of the display is an approximation to that of the original scene when seen by an observer. A 3D display mimics the plenoptic function of the light from a physical object. The accuracy to which this mimicry is carried out is a direct result of the technology behind the spatial display device. The greater the amount and accuracy of the view information presented to the viewer by the display, the more the display appears like a physical object. On the other hand, greater amounts of information also result in more complicated displays and higher data transmission and processing costs.

_

Why 3D display?

Conventional 2D display devices, such as cathode ray tubes (CRTs), liquid crystal devices (LCDs), or plasma screens, often lead to ambiguity and confusion in high-dimensional data/graphics presentation due to lack of true depth cues. Even with the help of powerful 3D rendering software, complex data patterns or 3D objects displayed on 2D screens are still unable to provide spatial relationships or depth information correctly and effectively. Lack of true 3D display often jeopardizes our ability to truthfully visualize high-dimensional data that are frequently encountered in advanced scientific computing, computer aided design (CAD), medical imaging, and many other disciplines. Essentially, a 2D display apparatus must rely on humans’ ability to piece together a 3D representation of images. Despite the impressive mental capability of the human visual system, its visual perception is not reliable if certain depth cues are missing.

_

Real 3D displays displaying an image in three full dimensions. The most notable difference from stereoscopic displays with only two 2D offset images is that the observer’s head and eyes movement will increase information about the 3-dimensional objects being displayed.

  1. Volumetric 3D display:

Volumetric displays use some physical mechanism to display points of light within a volume. Such displays use voxels instead of pixels. Volumetric displays include multiplanar displays, which have multiple display planes stacked up, and rotating panel displays, where a rotating panel sweeps out a volume.

  1. Holographic displays:

Holographic display is a display technology that has the ability to provide all four eye mechanism: binocular disparity, motion parallax, accommodation and convergence. The 3D objects can be viewed without wearing any special glasses and no visual fatigue will be caused to human eyes. In 2013, a Silicon valley Company LEIA Inc started manufacturing holographic displays well suited for mobile devices (watches, smartphones or tablets) using a multi-directional backlight and allowing a wide full-parallax angle view to see 3D content without the need of glasses.

  1. Integral imaging:

Integral imaging is an autostereoscopic or multiscopic 3D display, meaning that it displays a 3D image without the use of special glasses on the part of the viewer. It achieves this by placing an array of microlenses (similar to a lenticular lens) in front of the image, where each lens looks different depending on viewing angle. Thus rather than displaying a 2D image that looks the same from every direction, it reproduces a 4D light field, creating stereo images that exhibit parallax when the viewer moves.

  1. Compressive Light Field Displays:

A new display technology called “compressive light field” is being developed. These prototype displays use layered LCD panels and compression algorithms at the time of display. Designs include dual and multilayer devices that are driven by algorithms such as computed tomography and Non-negative matrix factorization and non-negative tensor factorization.

__

Figure below shows evolution of displays:

_______

_______

Brief History of holography:

_

In 1947, Hungarian born British physicist Dennis Gabor (1900–1979) tried to improve the image-producing capability of electron microscopes, which use streams of electrons rather than light to magnify objects. His solution was to take an electron “picture” of an object. The technique as originally invented is still used in electron microscopy, where it is known as electron holography, but optical holography did not really advance until the development of the laser in 1960. Optical holography process required a coherent light source—something that did not exist at the time. It wasn’t until the early 1960s, when the first working laser was produced, that 3-D images could be created. For developing the basic principles of holography, Gabor was awarded the Nobel Prize in 1971. The development of the laser enabled the first practical optical holograms that recorded 3D objects to be made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks at the University of Michigan, USA. Early holograms used silver halide photographic emulsions as the recording medium. They were not very efficient as the produced grating absorbed much of the incident light. Various methods of converting the variation in transmission to a variation in refractive index (known as “bleaching”) were developed which enabled much more efficient holograms to be produced.

_

Another major advance in display holography occurred in 1968 when Dr. Stephen A. Benton invented white-light transmission holography while researching holographic television at Polaroid Research Laboratories. This type of hologram can be viewed in ordinary white light creating a “rainbow” image from the seven colors which make up white light. The depth and brilliance of the image and its rainbow spectrum soon attracted artists who adapted this technique to their work and brought holography further into public awareness.  Benton’s invention is particularly significant because it made possible mass production of holograms using an embossing technique. These holograms are “printed” by stamping the interference pattern onto plastic. The resulting hologram can be duplicated millions of times for a few cents apiece. Consequently, embossed holograms are now being used by the publishing, advertising, and banking industries.

_

In 1972 Lloyd Cross developed the integral hologram by combining white-light transmission holography with conventional cinematography to produce moving 3-dimensional images. Sequential frames of 2-D motion-picture footage of a rotating subject are recorded on holographic film. When viewed, the composite images are synthesized by the human brain as a 3-D image.  In 70’s Victor Komar and his colleagues at the All-Union Cinema and Photographic Research Institute (NIFKI) in Russia, developed a prototype for a projected holographic movie. Images were recorded with a pulsed holographic camera. The developed film was projected onto a holographic screen that focused the dimensional image out to several points in the audience.

_

Holographic artists have greatly increased their technical knowledge of the discipline and now contribute to the technology as well as the creative process. The art form has become international, with major exhibitions being held throughout the world. In its early days, holography required high-power expensive lasers, but nowadays, mass-produced low-cost semi-conductor or diode lasers, such as those found in millions of DVD recorders and used in other common applications, can be used to make holograms and have made holography much more accessible to low-budget researchers, artists and dedicated hobbyists.

______

______

Overview of hologram and holography:

_

If you want to see a hologram, you don’t have to look much farther than your wallet. There are holograms on most driver’s licenses, ID cards and credit cards. If you’re not old enough to drive or use credit, you can still find holograms around your home. They’re part of CD, DVD and software packaging, as well as just about everything sold as “official merchandise.”  Unfortunately, these holograms — which exist to make forgery more difficult — aren’t very impressive. You can see changes in colors and shapes when you move them back and forth, but they usually just look like sparkly pictures or smears of color. Even the mass-produced holograms that feature movie and comic book heroes can look more like green photographs than amazing 3-D images. On the other hand, large-scale holograms, illuminated with lasers or displayed in a darkened room with carefully directed lighting, are incredible. They’re two-dimensional surfaces that show absolutely precise, three-dimensional images of real objects. You don’t even have to wear special glasses or look through a View-Master to see the images in 3-D.  If you look at these holograms from different angles, you see objects from different perspectives, just like you would if you were looking at a real object. Some holograms even appear to move as you walk past them and look at them from different angles. Others change colors or include views of completely different objects, depending on how you look at them.  Holograms have other surprising traits as well. If you cut one in half, each half contains whole views of the entire holographic image. The same is true if you cut out a small piece -­- even a tiny fragment will still contain the whole picture. On top of that, if you make a hologram of a magnifying glass, the holographic version will magnify the other objects in the hologram, just like a real one. Once you know the principles behind holograms, understanding how they can do all this is easy.

_

When taking a photograph, one light reference is reflected directly off the object and recorded as a two dimensional image. When viewing a photograph, we imply a third dimension based upon our past perceptions of similar situations. Holograms are 3 or 4 dimensional. Height, width, depth, and motion (time), are all recorded in a holograph.

_

Light is an amazing form of energy that zaps through our world at blistering speeds: 300,000 km (186,000 miles) per second—enough to whip from the Sun to Earth in just over 8 minutes. We see things because our eyes are sophisticated light detectors: they constantly capture the light rays bouncing off nearby objects so our brain can construct an ever-changing impression of the world around us. The only trouble is that our brain can’t keep a permanent record of what our eyes see. We can recall what we thought we saw, and we can recognize images we’ve seen in the past, but we can’t easily recreate images intact once they’ve disappeared from view. Back in the 19th century, ingenious inventors helped to solve this problem by discovering how to capture and store images on chemically treated paper. Photography, as this became known, has revolutionized the way people see and engage with the world—and it gave us fantastic forms of entertainment in the 20th century in the form of movies and TV. But no matter how realistic or artistic a photograph appears, there’s no question of it being real. We look at a photo and instantly see that the image is dead history: the light that captured the objects in a photograph vanished long ago and can never be recaptured. Holograms are a bit like photographs that never die. They’re sort of “photographic ghosts”: they look like three-dimensional photos that have somehow got trapped inside glass, plastic, or metal. When you tilt a credit-card hologram, you see an image of something like a bird moving “inside” the card.

__

Light as a wave:

To explain what light is, we want to start at a very low level—at an atomic level. Illustrated by the well-known planetary model by Niels Bohr (1913), atoms consist of a nucleus and electrons that orbit the nucleus. They are held in the orbit by an electrical force. The nucleus itself consists of protons (having a positive electrical charge) and neutrons (having no electrical charge). The electrons have a negative electrical charge and can move from atom to atom. The level at which an electron orbits the nucleus (i.e., the distance of the electron to the nucleus) is called its energy state. By default, an electron exists at the lowest energy state—that is the orbit closest to the nucleus. If excited by external energy (e.g., heat) the electron can move from lower to higher energy states (i.e., further away from the nucleus). This shift from a lower to a higher energy state is called quantum leap. Since all energy is always preserved (it might be converted, but it is never lost), the electrons have to release energy when they drop back to lower energy states. They do so by releasing packages of energy. Albert Einstein called these packages photons.

Photons have a frequency that relates to the amount of energy they carry which, in turn, relates to the size of the drop from the higher state to the lower one. They behave like waves—they travel in waves with a specific phase, frequency, and amplitude, but they have no mass. These electromagnetic waves travel in a range of frequencies called electromagnetic (EM) spectrum, which was described by J. C. Maxwell (1864–1873). A small part of this spectrum is the EM radiation that can be perceived as visible light. Since light behaves like waves, it shares many properties of other waves. Thomas Young showed in the early 1800s that light waves can interfere with each other. Depending on their phase, frequency, and amplitude, multiple light waves can amplify or cancel each other out. Light that consists of only one wavelength is called monochromatic light. Light waves that are in phase in both time and space are called coherent. Monochromaticity and low divergence are two properties of coherent light. If a photon passes by an excited electron, the electron will release a photon with the same properties. This effect—called stimulated emission— was predicted by Einstein and is used today to produce coherent laser light. In general, “normal” light consists of an arbitrary superimposition of multiple incoherent light waves that create a complex interference pattern. Light travels in a composition of waves with a variety of different orientations. It can be polarized by selecting waves with a specific orientation. The filtered portion is called polarized light. Augustine Fresnel explained this phenomenon in the 19th century. Depending on the material properties, light can be reflected, refracted, scattered, or absorbed by matter. If reflected, light is bounced off a surface. Imperfections on the reflecting surface causes the light to be scattered (diffused) in different directions. Light can also be scattered when it collides with small particles (like molecules). The amount of scattering depends on the size of the particle with respect to the wavelength of the light. If the particle (e.g., a dust particle) is larger than the wavelength, light will be reflected. If the particle (e.g., a gas molecule) is smaller, then light will be absorbed. Such molecules will then radiate light at the frequency of the absorbed light in different directions. John Rayleigh explained this effect in the 1870s, thus this process is called Rayleigh scattering. Light can also be absorbed and its energy converted (e.g., into heat). Refraction occurs when light travels across the boundaries of two mediums. In a vacuum, light travels at 300,000 km/s (the speed of light). If travelling through a denser medium, it is slowed down which causes it to alter its direction. The amount of refraction also depends on the wavelength of the light—as described by Isaac Newton who showed that white light splits into different angles depending on its wavelength.

_

To understand how interference fringes form on film, you need to know a little bit about light. Light is part of the electromagnetic spectrum — it’s made of high-frequency electrical and magnetic waves. These waves are fairly complex, but you can imagine them as similar to waves on water. They have peaks and troughs, and they travel in a straight line until they encounter an obstacle. Obstacles can absorb or reflect light, and most objects do some of both. Reflections from completely smooth surfaces are specular, or mirror-like, while reflections from rough surfaces are diffuse, or scattered.  The wavelength of light is the distance from one peak of the wave to the next. This relates to the wave’s frequency, or the number of waves that pass a point in a given period of time. The frequency of light determines its color and is measured in cycles per second, or Hertz (Hz). Colors at the red end of the spectrum have lower frequencies, while colors at the violet end of the spectrum have higher frequencies. Light’s amplitude, or the height of the waves, corresponds to its intensity. White light, like sunlight, contains all of the different frequencies of light traveling in all directions, including ones that are beyond the visible spectrum. Although this light allows you to see everything around you, it’s relatively chaotic. It contains lots of different wavelengths traveling in lots of different directions. Even waves of the same wavelength can be in a different phase, or alignment between the peaks and troughs. Laser light, on the other hand, is orderly. Lasers produce monochromatic light — it has one wavelength and one color. The light that emerges from a laser is also coherent. All of the peaks and troughs of the waves are lined up, or in phase. The waves line up spatially, or across the wave of the beam, as well as temporally, or along the length of the beam.

__

For a better understanding of the process of holography, it is necessary to understand interference and diffraction. Interference occurs when one or more wavefronts are superimposed. Diffraction occurs whenever a wavefront encounters an object. The process of producing a holographic reconstruction is explained purely in terms of interference and diffraction. It is somewhat simplified but is accurate enough to provide an understanding of how the holographic process works.

_

In physics, a wave is defined to be a process of disturbance travelling throughout a medium. How is it performed, it depends on the kind of disturbance and on the medium-disturbance coupling. Wave transfers energy from one particle of medium to another one without causing a permanent displacement of the medium itself. Let us have a look at a light wave, being modelled by an electromagnetic wave.  Before starting with the basic phenomena of interference and diffraction of light, remember the simple wave model, describing the propagation of light wave through a space. The Dutch physicist Christian Huygens formulated a principle. It says that each point on the leading wave front may be regarded as a secondary source of spherical waves, which themselves progress with the speed of light in the medium and whose envelope constitutes the new wave front later. The new wave front is tangent to each wavelet at a single point.

_

Interference of light:

Let us add two waves, i.e. illuminate a surface by two light beams. The observable result depends on what light beams were used. Mostly, one can observe a brighter surface comparing to that illuminated by one-beam only. However, there are situations, when one can see both, parts of the surface with very high brightness, and parts with very low one, even dark. Just that case, when a kind of redistribution of all the incident energy can be observed, represents what is said to be the interference of light.

Diffraction of light:

Any deviation from rectilinear propagation of light that cannot be explained because of reflection or refraction is included into diffraction. When light passes through a narrow slit, it seems as it “bends” and incidents on the screen behind the slit also where darkness was expected to be according a geometric construction. This bending called “diffraction,” is most noticeable for longer wavelengths. When the wavelength of a wave is comparable to or smaller than the size of an obstacle or aperture, diffraction is sometimes difficult to detect. When the wavelength of a wave is large compared to the size of an obstacle or aperture, diffraction is so extreme that it may not be evident that an obstacle even existed.

_

The simple example of diffraction and interference is Thomas Young’s Double Slit. To understand holography, it is first necessary to understand one of the most important studies of wave theory known as Young’s double-slit experiment conducted in 1801 by Thomas Young. His apparatus consisted of a sheet of material with two close spaced slits with a viewing screen. If light consisted of particles, one would expect two bright lines on the screen.

Here we see diffraction, plus superposition, resulting in both constructive and destructive interference.

_

_

When two waves of identical wavelength are in phase, they form a new wave with an amplitude equal to the sum of their individual amplitudes (constructive interference). When two waves are of completely opposite phase, they either form a new wave of reduced amplitude (partial destructive interference) or cancel each other out (complete destructive interference). Much more complicated constructive and destructive interference patterns emerge when waves with different wavelengths interact. To fully understand the history of holography you need to have a basic idea of what a hologram is. Light is an electromagnetic wave. Holography uses the wave nature of light. Unlike a normal photograph that uses a lens to focus an image on an electronic chip or a piece of film and simply records where there is light or no light, holography is a photographic technique that records the shape a light wave takes after it bounces off an object, much like the impression you would see if a key were pressed into clay. It uses interfering waves of light to capture images that can be fully three dimensional. When waves of light meet they interfere in the same way waves of water interfere to make the kind of patterns you see when you throw rocks into a pond. It is the information in this type of wave pattern that is used to make holograms.

__

Holography was discovered in 1947 by Hungarian physicist Dennis Gabor, for which he received the Nobel Prize in Physics in 1971. The discovery was an unexpected result of research into improving electron microscopes. He carried out his experiments using visible light from a filtered mercury arc. Because of the limited coherence of that source his holographic images were restricted to transparencies little larger than a pinhead. The field did not really advance until the development of the laser in 1962. The laser provides a powerful source of coherent light which enabled recording holograms of diffusely reflecting objects with appreciable depth. Holography is the science of producing holograms. It is an advanced form of photography that allows an image to be recorded in three dimensions. The technique of holography can also be used to optically store, retrieve, and process information. A common misunderstanding is that a hologram is simply some sort of a three dimensional photograph. Certainly, both photography and holography make use of photographic film, but that is about all they have in common. The difference is in the way the image is produced. A photographic image produced by a camera lens can be described using a simple geometric or ray model for the behaviour of light, whereas the holographic image cannot be described by wave propagation in geometrical optics. Its existence depends on diffraction and interference, which are wave phenomena. With photography we only store information about the amplitude of light. In a hologram we store information about the phase and amplitude. Information about the phase is stored in a form of fringe pattern that is created by two interfering beams falling on a photographic plate. The relative phase (difference between the wave vectors) between the two beams varies across the photographic plate and is encoded as the maxima and minima of the fringe pattern.

_

Standard photography is widely used to conserve moments, but it has the disadvantage that only a two-dimensional projection of the three-dimensional world is stored. Conventional recording media (e.g. CCD-chip, photo plate) only respond to the intensity of the light waves. Therefore the phase information is lost in the image storing process. If the amplitude as well as the phase of a wave front in an image can be reproduced, a perfect image of the object is generated which is impossible to distinguish from the original. A normal photograph records the amount and wavelength (or colour) of light reflected from an object. Hologram records additionally phase of light. A hologram requires a coherent energy source, normally a laser, to produce it rather than white light. The holographic imaging process results in an image that rather than being a two dimensional representation of the object, is three dimensional and contains all the information about the object.

_

In the framework of the wave theory, the monochromatic light wave is characterized by an amplitude and a phase of a vector in every point of the light field. The classic photography records only amplitude of the wave, therefore the viewer can perceive only a flat picture without parallax. You can make and view a photograph using unorganized white light, but to make a hologram, you need the organized light of a laser. This is because photographs record only the amplitude of the light that hits the film, while holograms record differences in both amplitude and the phase. In order for the film to record these differences, the light has to start out with one wavelength and one phase across the entire beam. All the waves have to be identical when they leave the laser. Holography is a method of recording the complete information about the light field at a photographic plate. It means that both amplitude and phase of the wave are stored. So recorded picture is the hologram with which an observer can view an image with all of its three-dimensional details with parallax.

_

Hologram basics:

The hologram is actually a recording of the difference between two beams of coherent light. Ordinary monochromatic light is composed of waves that are all the same length and that travel in all directions. Coherent light is in phase, meaning its waves are vibrating and traveling together in the same direction. To create a hologram, a laser beam (coherent light) is split in two: one beam that stays undisturbed, called the reference beam, strikes a photographic plate. The second beam, called the object beam, strikes the subject and then bounces onto the plate. The subject’s interfering with the second beam causes the two beams to become out of phase. This difference—called phase interference—is what is recorded on the photographic plate. These two beams interfere with each other, causing a specific pattern of bright and dark spots where there has been constructive and destructive interference, spots where the waves added and subtracted. This creates areas of high amplitude and low amplitude, or bright and dark bands. These bands are recorded on the holographic surface, and preserved through the developing process. The bands of bright and dark act as an extremely sophisticated diffraction grating, so that when light passes through the plate or film, it interferes to form the exact image of the object that was recorded.  It’s the interference pattern that the photographic film records, unlike a regular photograph, which records the amount of light from a specific point. Also, unlike the photograph, each point of the hologram contains all of the information from the object. So we could destroy almost all of our hologram and still reconstruct the image from a small piece. When a hologram is later illuminated with coherent light of the same frequency that created it, a three-dimensional image of the subject appears. The hologram is illuminated with laser light (transmission) or white light (reflection). The reflected or transmitted light is scattered by the interference patterns into your eye. At this point, the eye-brain system interprets the light rays and reconstructs the image of the original object. It is able to do this because all the space-time information has been captured by the interference patterns on the hologram. Hence, the eye-brain mechanism cannot distinguish any difference between the light scattering off the original object and the light being redirected (via the diffraction pattern) by the hologram. In either case the “image” is the same. A regular photograph is only two-dimensional (2D) because it only records the intensity of the light hitting the film, recording shades of brightness and darkness. A hologram is three-dimensional (3D) because it records both the intensity and the direction of the light that hits the film. This additional information is recorded in the interference pattern, and allows you to “look around” the recorded object as if it were really there. Unlike photography or painting, holography can render a subject with complete dimensional fidelity. A hologram creates everything your eyes see — depth, size, shape, texture, and relative position – from many points of view.

____

The technique of holographic imaging is unique in that it records both the amplitude and phase information of an object. A photosensitive medium is one which responds to incident light via a change in its physical properties. There are some holographic recording materials such as anisotropic recording media which are sensitive to the state of polarisation of the incident light, however most photosensitive materials respond to variations in the intensity of the incident light only. It should be noted that most photosensitive film can only record the distribution of the amplitude (or intensity), and cannot directly record the phase distribution. The phase information of an object can be converted to variations in intensity by creating an interference pattern between the light scattered from the object (i.e. the object beam) and a second reference beam which originates from the same coherent light source. The intensity at any point in this interference pattern depends on the phase of the object wave; therefore, the intensity variation recorded in the photosensitive medium (i.e. the hologram) contains both the phase and amplitude information of the object. If the hologram is then illuminated with the same reference beam, the original object wave will be reconstructed and can be viewed by an observer looking through the hologram.

__

The photography records only the intensity of dispersed light, i.e. its amplitude characteristics. Information about the phase difference of the beams, i.e. about the distances between various points of the object characterising its three-dimensionality, vanishes. Holography means recording of the three-dimensional structure of the light wave dispersed by the object. This record is obtained by the interference image that keeps the amplitude ratio of the dispersed light, i.e. relative intensities on which the rate of blackening of dark areas in the interference image depends, as well as its phase ratio defining the mutual distribution of dark and light areas.

___

On-axis and off-axis holography:

Holography is based on recording both the amplitude and phase of the wavefront of light from an object. This is done by combining the wavefront of light from the object with a coherent reference beam from the same source to produce an interference pattern, which is called a hologram. Illuminating the recorded hologram with an identical reference beam reconstructs the original wavefront, which the eyes perceive as showing the original object as if it were present. In Dennis Gabor’s original concept, the object and reference beams followed the same path, and the object itself was two-dimensional. This approach, called on-axis holography, is easy to implement and is still used for some applications, but it is inherently limited to small objects and produces troublesome twin images that overlap. Leith’s invention of off-axis holography, in which the object and reference beam follow separate paths, allowed holography of larger objects and removed the twin image from the reconstructed scene.

_

Where the light source, the object and the photographic plate are located along an axis it is also called an in-line (on-axis) hologram. The problem with this approach is that the waves overlap which results in twin images. An observer viewing one image sees it superposed on the out of-focus twin image and strong coherent background. The problem is solved with off-axis hologram technique where the reference beam is diverted by a beam splitter and is incident on the photographic plate under an offset angle. The difference is that the real and virtual image are formed at different angles and there are no more twin images and wave overlapping.

_

On-axis hologram recording:

In this method, a semi-transparent object is illuminated with a single, collimated, monochromatic, coherent beam perpendicular to the photosensitive medium along the z-axis, as shown in figure below. Due to the semi-transparent nature of the object, the incident light is then split into two components; the transmitted light which becomes the reference beam and the light scattered from the object, which is the object beam.

_

On-axis hologram reconstruction:

In order to reconstruct the hologram, it is illuminated with the same monochromatic, coherent beam of light used to record it.

_

While this technique allowed for the first objects to be imaged holographically, the inline holographic recording method has some problems. The presence of both virtual and real reconstructed images in the same viewing plane (i.e. a twin image) is one of the main-drawbacks of in-line holography, as it degrades the quality of the reconstructed image. Secondly, the object must have a high average transmittance. This limits greatly the range of objects that can be imaged using this holographic technique. Thirdly, holograms recorded in this manner are transmission holograms, as both beams illuminate the photosensitive medium from the same side. In order to reconstruct the hologram, it is therefore necessary to use the same wavelength as used to record the hologram; thus the in-line holograms cannot be viewed with white light.

_

Off-axis holography:

The twin-image problem was solved in 1962 by Leith and Upatneiks with the development of the off-axis holographic recording method. For this method, a separate reference beam was used for the first time. The object and reference beams were separated at a large enough angle that the resultant images did not overlap. This was a huge step for the field of holography, and together with the production of the first working laser at Hughes Research Laboratories in 1960, allowed the field of holography to expand and diversify. For this holographic recording configuration, the points on the real and virtual images are located at equal distances from the hologram, but on opposite sides to it. The real image formed is therefore a pseudoscopic image, as the image depth has been inverted. As long as the angle between the recording beams is large enough, the two reconstructed images can be independently viewed. In this article holography means off-axis holography.

________

Defining hologram and holography:

Holography is the science and practice of making holograms. Typically, a hologram is a photographic recording of a light field, rather than of an image formed by a lens, and it is used to display a fully three-dimensional image of the holographed subject, which is seen without the aid of special glasses or other intermediate optics. The hologram itself is not an image and it is usually unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of seemingly random variations in the opacity, density, or surface profile of the photographic medium. When suitably lit, the interference pattern diffracts the light into a reproduction of the original light field and the objects that were in it appear to still be there, exhibiting visual depth cues such as parallax and perspective that change realistically with any change in the relative position of the observer. Holography is a technique that enables a light field, which is generally the product of a light source scattered off objects, to be recorded and later reconstructed when the original light field is no longer present, due to the absence of the original objects. Holography can be thought of as somewhat similar to sound recording, whereby a sound field created by vibrating matter like musical instruments or vocal cords, is encoded in such a way that it can be reproduced later, without the presence of the original vibrating matter.

_

Holography is a method to record and to reconstruct whole wave fields with amplitude and phase. Recording is done by taking the object wave scattered or reflected by the object or the scene and superposing a mutually coherent reference wave. The resulting intensity distribution (interference pattern) was originally was captured by high resolution photographic emulsion, however in digital holography it is recorded by a CCD-or CMOS-target. When interference patterns on the holographic plate/film/emulsion are illuminated by original coherent light a three-dimensional image is produced. Holography is a 3D display technique that involves using interference and diffraction to record and reconstruct optical wavefronts. Holography’s unique ability to generate accurately both the amplitude and phase of light waves enables applications beyond those limited by the light manipulation capabilities of lens- or mirror-based systems. Holography is visual recording and playback process that can record our 3 dimensional worlds on a 2 dimensional recording medium, playback the original object or scene to the unaided eyes as a 3 dimensional image. The image demonstrates complete parallax and depth of field and floats in space either behind, in front of, or straddling the recording medium. In both the types whether it is reflection or transmission the formations of holograms have same nature and dimensions.

_

Holograph is a related term of hologram. As nouns the difference between holograph and hologram is that holograph is a hologram while hologram is a three-dimensional image of an object created by holography. As nouns the difference between holography and hologram is that holography is (physics) a technique for recording, and then reconstructing, the amplitude and phase distributions of a coherent wave disturbance; used to produce three-dimensional images or holograms while hologram is a three-dimensional image of an object created by holography.

_

In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram. In a side-by-side comparison under optimal conditions, a holographic image is visually indistinguishable from the actual subject, if the hologram and the subject are lit just as they were at the time of recording. A microscopic level of detail throughout the recorded volume of space can be reproduced. In common practice, however, major image quality compromises are made to eliminate the need for laser illumination when viewing the hologram, and sometimes, to the extent possible, also when making it. Holographic portraiture often resorts to a non-holographic intermediate imaging procedure, to avoid the hazardous high-powered pulsed lasers otherwise needed to optically “freeze” living subjects as perfectly as the extremely motion-intolerant holographic recording process requires. Holograms can now also be entirely computer-generated and show objects or scenes that never existed.

___

When the two laser beams reach the recording medium, their light waves, intersect and interfere with each other.  It is this interference pattern that is imprinted on the recording medium. The pattern itself is seemingly random, as it represents the way in which the scene’s light interfered with the original light source but not the original light source itself. The interference pattern can be considered an encoded version of the scene, requiring a particular key the original light source in order to view its contents. This missing key is provided later by shining a laser, identical to the one used to record the hologram, onto the developed film. When this beam illuminates the hologram, it is diffracted by the hologram’s surface pattern. This produces a light field identical to the one originally produced by the scene and scattered onto the hologram. The image this effect produces in a person’s retina is known as a virtual image.

_

You need the right light source to see a hologram because it records the light’s phase and amplitude like a code. Rather than recording a simple pattern of reflected light from a scene, it records the interference between the reference beam and the object beam. It does this as a pattern of tiny interference fringes. Each fringe can be smaller than one wavelength of the light used to create them. Decoding these interference fringes requires a key — that key is the right kind of light. The light-sensitive emulsion used to create holograms makes a record of the interference between the light waves in the reference and object beams. When two wave peaks meet, they amplify each other. This is constructive interference. When a peak meets a trough, they cancel one another out. This is destructive interference. You can think of the peak of a wave as a positive number and the trough as a negative number. At every point at which the two beams intersect, these two numbers add up, either flattening or amplifying that portion of the wave. In a hologram, the two intersecting light wave fronts form a pattern of hyperboloids — three-dimensional shapes that look like hyperbolas rotated around one or more focal points. The holographic plate, resting where the two wave fronts collide, captures a cross-section, or a thin slice, of these three-dimensional shapes.

______

Making hologram:

The L.A.S.E.R. (Light Amplified by Stimulated Emission of Radiation) was invented to produce coherent light. Incoherent light travels in different frequencies and in different phases. Coherent light travels in the same frequency and in the same phase. (100% coherent light is rare) It is important to use light which is coherent because the information is carried on the crest of each wave. The more points of intersection, the more information.  Unlike a camera, which has only one point of light reference, a hologram has two or more points of light references. The intersection points of the two light waves contain the whole information of both reference points. A LASER is used as the light source so the waves are coherent.

______

Hologram recording:

It would be useful to stop for a while at physical meaning of the process of recording. To record light a recording medium is used. It can be any medium, optical properties of which vary with the intensity of incident light. The intensity distribution we would like to record causes similar optical property distribution in the medium. It can be either transparency of the recording medium (amplitude hologram is made) or its optical thickness/index of refraction (a phase hologram is made). Which one is relevant depends on the used light, its intensity and the kind of recording medium. The commonly known one is the photographic material. The photographic film gets darker where the original image was lighter. On that case, mostly the transparency of the medium is changed. Bleaching may transform it into a phase hologram.

_

The recording of hologram is based on the phenomenon of interference.  It requires a laser source, a half-mirror or beam splitter, an object and a photographic plate. You make a hologram by reflecting a laser beam off the object you want to capture. In fact, you split the laser beam into two separate halves by shining it through a half-mirror (a piece of glass coated with a thin layer of silver so half the laser light is reflected and half passes through—sometimes called a semi-silvered mirror). One half of the beam bounces off a mirror, hits the object, and reflects onto the photographic plate inside which the hologram will be created. This is called the object beam. The other half of the beam bounces off another mirror and hits the same photographic plate. This is called the reference beam. A hologram forms where the two beams meet up in the plate. The superposition of these two beams produces an interference pattern (in the form of dark and bright fringes) and this pattern is recorded on the photographic plate. The photographic plate with recorded interference pattern is called hologram. Photographic plate is also known as Gabor zone plate in honour of Denis Gabor who developed the phenomenon of holography. Each and every part of the hologram receives light from various points of the object. Thus, even if hologram is broken into parts, each part is capable of reconstructing the whole object.

Figure above shows the process of storing a hologram by making two laser beams interfere.

Laser light is much purer than the ordinary light in a torch beam. In a torch beam, all the light waves are random and jumbled up. Light in a torch beam runs along any old how, like schoolchildren racing down a corridor when the bell goes for home time. But in a laser, the light waves are coherent: they all travel precisely in step, like soldiers marching on parade. When a laser beam is split up to make a hologram, the light waves in the two parts of the beam are traveling in identical ways. When they recombine in the photographic plate, the object beam has travelled via a slightly different path and its light rays have been disturbed by reflecting off the outer surface of the object. Since the beams were originally joined together and perfectly in step, recombining the beams shows how the light rays in the object beam have been changed compared to the reference beam. In other words, by joining the two beams back together and comparing them, you can see how the object changes light rays falling onto it—and that’s simply another way of saying “what the object looks like.” This information is recorded permanently into the photographic plate by the laser beams. So a hologram is effectively a permanent record of what something looks like seen from any angle.

_

Figure below shows how interference pattern looks on holographic plate:

The hologram itself is not an image (it doesn’t look anything like the recorded objects), and it is not three-dimensional, either. A holographic image is the three-dimensional image that is reconstructed by shining (coherent) light onto a hologram i.e. onto interference pattern on holographic plate. Most people refer to the holographic images as “holograms” somewhat confusingly.

______

Reconstruction of a hologram:

While recording a hologram, no optical system to create the image of the object was used. This way, after processing the recording medium, nothing can be seen by naked eye. Only a microscope would show us a very tiny interference structure (maxims and minima).  To record a hologram of an object the interference of two waves (object wave and reference one) is recorded. In other words, an interference structure is recorded. To reconstruct the hologram, certainly it is necessary to illuminate the hologram. In the reconstruction process, the hologram is illuminated by laser beam and this beam is called reconstruction beam. This beam is identical to reference beam used in construction of hologram. Huygens’ Principle might be the simplest way. When recording a hologram, two waves overlap, interfere and create a resulting wave with special intensity distribution in all the space of overlapping. In one of the planes, the interference pattern is recorded. When one of the waves creating the hologram (usually the reference one) illuminates the hologram the same intensity distribution as during the hologram recording appears just behind the hologram. We get the same point light sources distribution as during the interference of former object and reference waves. That means, following the Huygens’ Principle, – the same waves have to spread from them as before, i.e. the reference wave and the object wave. It is said – the object wave was reconstructed, object can be observed, again. The reconstructed object wave is the diffracted maximum of the first order, created when reference beam is diffracted by the hologram. The hologram acts a diffraction grating. This reconstruction beam will undergo phenomenon of diffraction during passage through the hologram. The reconstruction beam after passing through the hologram produces a real as well as virtual image of the object. One of the diffracted beams emerging from the hologram appears to diverge from an apparent object when project back. Thus, virtual image is formed behind the hologram at the original site of the object and real image in front of the hologram. Thus an observer sees light waves diverging from the virtual image and the image is identical to the object. If the observer moves round the virtual image then other sides of the object which were not noticed earlier would be observed. Therefore, the virtual image exhibits all the true three dimensional characteristics. The real image can be recorded on a photographic plate.

_

When you develop the holographic plate and look at it, what you see is a little unusual. Developed film from a camera shows you a negative view of the original scene — areas that were light are dark, and vice versa. When you look at the negative, you can still get a sense of what the original scene looked like. But when you look at a developed piece of film used to make a hologram, you don’t see anything that looks like the original scene. Instead, you might see a dark frame of film or a random pattern of lines and swirls. Turning this frame of film into an image requires the right illumination. In a transmission hologram, monochromatic light shines through the hologram to make an image. In a reflection hologram, monochromatic or white light reflects off of the surface of the hologram to make an image. Your eyes and brain interpret the light shining through or reflecting off of the hologram as a representation of a three-dimensional object. Because holograms can reconstruct the 3D scene from different points of view, the hologram looks 3D when viewed. The stereo vision of humans sees two different points of view in each eye, causing the image to appear to have depth. The holograms you see on credit cards and stickers are reflection holograms. You need the right light source to see a hologram because it records the light’s phase and amplitude like a code. Rather than recording a simple pattern of reflected light from a scene, it records the interference between the reference beam and the object beam. It does this as a pattern of tiny interference fringes. Each fringe can be smaller than one wavelength of the light used to create them. Decoding these interference fringes requires a key — that key is the right kind of light.

_

Fidelity of the reconstruction beam:

To replicate the original object beam exactly, the reconstructing reference beam must be identical to the original reference beam and the recording medium must be able to fully resolve the interference pattern formed between the object and reference beams. Exact reconstruction is required in holographic interferometry, where the holographically reconstructed wavefront interferes with the wavefront coming from the actual object, giving a null fringe if there has been no movement of the object and mapping out the displacement if the object has moved. This requires very precise relocation of the developed holographic plate. Any change in the shape, orientation or wavelength of the reconstruction beam gives rise to aberrations in the reconstructed image. For instance, the reconstructed image is magnified if the laser used to reconstruct the hologram has a shorter wavelength than the original laser. Nonetheless, good reconstruction is obtained using a laser of a different wavelength, quasi-monochromatic light or white light, in the right circumstances.

_

Exact reconstruction is required in holographic interferometry, where the holographically reconstructed wavefront interferes with the live wavefront, giving a null fringe if there has been no movement of the object and mapping out the displacement if the object has moved. This requires very precise relocation of the developed holographic plate. The recording medium should be able to resolve fully all the fringes arising from interference between object and reference beam. In an off-axis holographic recording, these fringe spacings can range from tens of microns to less than one micron, i.e. spatial frequencies ranging from 200-1200 cycles/mm so ideally, the recording medium should have a response which is flat over this range – see recording media below. If the response of the medium to these spatial frequencies is low, the diffraction efficiency of the hologram will be poor, and a dim image will be obtained. If the response is not flat over the range of spatial frequencies in the interference pattern, then the resolution of the reconstructed image will also be degraded. It should be noted that standard photographic film has a very low, or even zero, response at the frequencies involved and cannot be used to make a hologram.

_

Recording motion:

To add motion (time) to your holograph, you would turn the object, or move the mirrors and lenses, and shoot again onto the same film. The original waves recorded on the film, will intersect with the waves from the new perspective.

_

Multiple Images:

In movies, holograms can appear to move and recreate entire animated scenes in midair, but today’s holograms can only mimic movement. You can get the illusion of movement by exposing one holographic emulsion multiple times at different angles using objects in different positions. The hologram only creates each image when light strikes it from the right angle. When you view this hologram from different angles, your brain interprets the differences in the images as movement. It’s like you’re viewing a holographic flip book. You can also use a pulsed laser that fires for a minute fraction of a second to make still holograms of objects in motion. Multiple exposures of the same plate can lead to other effects as well. You can expose the plate from two angles using two completely different images, creating one hologram that displays different images depending on viewing angle. Exposing the same plate using the exact same scene and red, green and blue lasers can create a full-color hologram. This process is tricky, though, and it’s not usually used for mass-produced holograms. You can also expose the same scene before and after the subject has experienced some kind of stimulus, like a gust of wind or a vibration. This lets researchers see exactly how the stimulus changed the object. Although holograms don’t currently move like they do in the movies, researchers are studying ways to project fully 3-D holograms into visible air. In the future, you may be able to use holograms to do everything from watching TV to deciding which hair style will look best on you.

______

Only a hologram is hologram: it is remarkably different to anything else:

Consider you have just taken a photo of a scene. You have taken your camera, pointed, clicked, and captured some information. From an optics point of view, you have stored some time-averaged amplitude of the light-field emanating from that scene using some form of sensor. As a result, a vast amount of information within that light field has just been thrown away. Collecting just this information is effectively capturing a tiny percentage of what is there. A hologram in its most basic sense, is recording then reconstruction of all the light-field information such that when viewed, the observer is unable to tell the difference from the original scene because the hologram is giving the observer all of the original information.

_

The simplest hologram is a reflection hologram.  This hologram is formed when the reference beam and the object beam meet on opposite sides of the holographic surface. They interfere and record an image. To reconstruct the image, a point source of white light illuminates the hologram from the proper angle, and the viewer looks at it from the same side as the light source. Reflection holograms require the simplest setup, and are visible without laser light. The other type of hologram is a transmission hologram, where you look through the film and see the three dimensional image suspended in midair at a point which corresponds to the position of the real object which was photographed. This type of hologram is created when the reference beam and the object beam meet on the same side of the holographic surface. They are viewed by shining a spread out laser light through the emulsion side (dull side) of the hologram at the same angle that the hologram was recorded with the viewer looking on from the opposite side. Transmission holograms must be viewed with laser light, and they appear the same color as the laser used to view and create them. Two types of holography are available: Conventional and dynamic. Conventional holography represents static images of 3D objects whereby a change in viewing angle of the viewer results in a change of perspective of the holographic object. Dynamic holograph, meanwhile, adds motion to the 3D object. This addition of motion represents a significant advancement to current 3D displays, which can only show 3D static images.

____

Holography should not be confused with lenticular and other earlier autostereoscopic 3D display technologies, which can produce superficially similar results but are based on conventional lens imaging. Stage illusions such as Pepper’s Ghost and other unusual, baffling, or seemingly magical images are also often incorrectly called holograms. In its early days, holography required high-power expensive lasers, but nowadays, mass-produced low-cost semi-conductor or diode lasers, such as those found in millions of DVD recorders and used in other common applications, can be used to make holograms and have made holography much more accessible to low-budget researchers, artists and dedicated hobbyists.

_

Holography is a much broader field than most people have perceived. Recording and displaying truly three-dimensional images are only small parts of it. Holographic optical elements (HOE) can perform the functions of mirrors, lenses, gratings, or combinations of them, and they are used in myriad technical devices. Holographic interferometry measures microscopic displacements on the surface of an object and small changes in index of refraction of transparent objects like plasma and heat waves. Future photonic devices such as electro-optical chips will undoubtedly incorporate micro-lasers and HOEs for optical computations, free-space interconnects, and massive analog and digital memory systems.

__

It was thought that it would be possible to use X-rays to make holograms of very small objects and view them using visible light. Today, holograms with x-rays are generated by using synchrotrons or x-ray free-electron lasers as radiation sources and pixelated detectors such as CCDs as recording medium. The reconstruction is then retrieved via computation. Due to the shorter wavelength of x-rays compared to visible light, this approach allows to image objects with higher spatial resolution.  As free-electron lasers can provide ultrashort and x-ray pulses in the range of femtoseconds which are intense and coherent, x-ray holography has been used to capture ultrafast dynamic processes.

_____

Real and virtual image:

If an image appears to be on the other side of the hologram, like looking through a window, it is called virtual. If an image jumps right out of the hologram and appears in front of the film, it is called real, since it has left the “virtual” world inside the film and entered the “real” world. When you flip a hologram over, the image is inside out and called pseudoscopic. Flip it back over and view it normally, right side out, and it is called orthoscopic. An image can be orthoscopic and real or orthscopic and virtual. Or an image can be pseudoscopic and real or pseudoscopic and virtual. An image can be both real and virtual, as in the case of an image that starts behind the film and then protrudes right out of it. Holograms can be made (especially by artists) that have both orthoscopic and pseudoscopic images in them. Any combination of these terms is possible.

_

Remember images that protrude out in front of a piece of holographic film are called real images. Virtual image holograms are used as the masters for real image holograms. Most real image holograms are holograms of holograms. The basic concept is like the idea that a negative of a negative is a positive. In effect, when you typically make a hologram it is orthoscopic (right side out) and virtual (the image appears behind the film). If you turn this orthoscopic and virtual image hologram over, the image you see is both pseudoscopic (inside out) and real (in front) since the spatial relationship of where the image is seen has flipped. If you use this image to record a second hologram, that image will be pseudoscopic (inside out) because you are recoding the pseudoscopic image of the first hologram and virtual. If you then turn it over it is orthoscopic (right side out) because an inside out image of an inside out image is right side out and real because each time you flip a hologram over you reverse from virtual image to real image.

________

________

Characteristics of hologram:

  1. Three dimensionality of hologram:

Every point in a hologram catches light waves that travel from every point in the object. That means wherever you look at a hologram you see exactly how light would have arrived at that point if you’d been looking at the real object. The images are true three-dimensional images, showing depth and parallax and continually changing in aspect with the viewing angle. This is evidenced by the fact that you can move your head while viewing the image and see it in a different perspective. This includes revealing part of the image which was hidden at another viewing angle. Shown below are three images from the same hologram, obtained by looking through it at different angles. Note that the pawn appears in different perspective in front of the king behind it.

Holography is the only visual recording and playback process that can record our three-dimensional world on a two-dimensional recording medium and “playback” the original object or scene to the unaided eyes as a three dimensional image. So the same wave, as propagating from the 3D scene/object while recording the hologram, is reconstructed. We can see the scene/object like through a window in the hologram size.

_

  1. Scaling Holographic Images:

One of the unique properties of holograms is that the size of the viewed image scales with the wavelength of the viewing light.

Above is a view of a hologram of the end of a pipe formed with light from a mercury vapor tube. The mercury source has three prominent wavelengths and you can see three distinct images of different size. Measuring the relative size of the images compared to the blue image (435.8 nm) gives 1.26 for the green (546.1 nm) and 1.36 for the yellow-orange image (576.9 and 579.1 nm). The scaling of the wavelengths relative to the blue wavelength gives 1.25 for the green and an average of 1.33 for the yellow-orange lines, so the image sizes appear to scale with the wavelength.

_

The holograms can “jump” mediums, that is, a hologram made using X rays can be viewed later in white light with increased magnification and depth. This initially caused great excitement because one could imagine making holographic images with x-rays and viewing them with visible light, getting three-dimensional views of things on the scale of molecules. X-ray holograms are in research labs, and there are practical difficulties with the scaling, but there is still the possibility that this feature of holograms will prove to be of great benefit.

_

  1. Divisible property:

Any part of the hologram contains the whole image! Hologram shows divisible property i.e. if you cut one in half, each half contains whole views of the entire holographic image:

When a piece is the whole:

The interference patterns captured on film are not focused by a lens and therefore the information thus recorded is evenly distributed over the recording surface. If you cut the original film in half, each part will still produce the whole image, when illuminated by the laser. If you cut the film in quarters, or eighths or sixtyfourths, each part will still produce the whole image when lit by the laser, although detail is lost with the decrease in total information. Every part of a hologram contains the image of the whole object. You can cut off the corner of a hologram and see the entire image through it. For every viewing angle you see the image in a different perspective, as you would a real object. Each piece of a hologram contains a particular perspective of the image, but it includes the entire object.

_

There are a couple of things to keep in mind about the object beam. One is that the object is not 100 percent reflective — it absorbs some of the laser light that reaches it, changing the intensity of the object wave. The darker portions of the object absorb more light, and the lighter portions absorb less light. On top of that, the surface of the object is rough on a microscopic level, even if it looks smooth to the human eye, so it causes a diffuse reflection. It scatters light in every direction following the law of reflection. In other words, the angle of incidence, or the angle at which the light hits the surface, is the same as its angle of reflection, or the light at which it leaves the surface. This diffuse reflection causes light reflected from every part of the object to reach every part of the holographic plate. This is why a hologram is redundant — each portion of the plate holds information about each portion of the object. If you tore a hologram of a mask in half, you could still see the whole mask in each half. But by removing half of the hologram, you also remove half of the information required to recreate the scene. For this reason, the resolution of the image you see in half a hologram isn’t as good.

_

If you break a hologram into tiny pieces, you can still see the entire object in any of the pieces: smash a glass hologram of a cup into bits and you can still see the entire cup in any of the bits!

Remember each broken piece would let you see the image from its own unique perspective. Think of a hologram as a window. Anywhere you look through a window you see what’s on the other side. If you were to paint the window black and scratch a hole in the paint on the left side of that window just big enough to look through, you would see everything on the other side of the window. Like looking through a peephole. If you then scratch another viewing peephole somewhere on the right side of the window, you still can see through, but from a different perspective. This is the same effect that each broken piece of a hologram would display. Just remember that if you have two broken pieces taken from opposite sides of the hologram, and you are looking at an object that looks differently from each side, one piece may let you see just one of those sides while the other piece will let you view the other side. So, you might say that each piece of a hologram stores information about the whole image, but from its own viewing angle. No two pieces will give you a view that is exactly the same.

_

Reconstruction of broken hologram:

Since each point in the object illuminates all of the hologram, the whole object can be reconstructed from a small part of the hologram. Thus, a hologram can be broken up into small pieces and each one will enable the whole of the original object to be imaged. One does, however, lose information and the spatial resolution gets worse as the size of the hologram is decreased — the image becomes “fuzzier”. The field of view is also reduced, and the viewer will have to change position to see different parts of the scene.

Figure above shows reconstructions from two parts of a broken hologram. Note the different viewpoints required to see the whole object.

_

Quoted from, “The Holographic Universe”, by Michael Talbot:

The “whole in every part” nature of a hologram provides us with an entirely new way of understanding organization and order. For most of its history, science has laboured under the bias that the best way to understand a physical phenomenon, whether a frog or an atom, is to dissect it and study its respective parts. A hologram teaches us that some things in the universe may not lend themselves to this approach. If we try to take apart something constructed holographically, we will not get the pieces of which it is made, we will only get smaller wholes.

__

  1. Multiple images on same holographic plate:

Many records can be made on the same recording medium and they can be reconstructed without interfering each other. The holographic record is a record of a structure. It can be reconstructed only when proper orientation of the reconstructing (usually reference) beam towards the hologram is chosen. In hologram, the image is recorded by a single laser beam split into two parts – one reflected back from the object, and the other serving as a reference. These are combined on a photographic plate. Light striking the developed hologram at the same angle as the reference beam, projects an image of the object. Multiple holograms can be recorded on one photographic plate and the viewer will see only one image at a time, depending on the angle of the beam illuminating the plate.  We can record more images on the same holographic plate and each of them can be reconstructed without any failures of the other records. When making more records on the same recording medium, the orientation of the medium is gradually changed. However, the number of records is limited by the state when all the structures overlap so that they cannot be distinguished.

_

  1. If you make a hologram of a magnifying glass, the holographic version will magnify the other objects in the hologram, just like a real one. A hologram of a glass lens can easily magnify other objects within the same hologram. Holography hobbyists perform a common demonstration by making a hologram of several small 3D objects including a small glass lens. In the finished hologram, you can see through the lens and see other objects behind it magnified. This works because a hologram reproduces the entire scene from many different viewpoints.

Think about it like this:

If you take a photograph of a magnifying glass which is being held near an object, you’ll have a picture of the magnifying glass and also the magnified object in the photo.

Now if you use holography, the hologram essentially records billions of separate pictures,  each taken from a different viewpoint.  Each picture will depict the magnifying glass and the magnified objects behind it. The magnifying glass isn’t really magnifying.  You’re just looking at a 3D picture of a magnifying glass, and also a 3D picture of the blurry image within the magnifying glass.

There are two situations where a lens within a hologram can create genuine magnified images of objects which lie in the real world OUTSIDE the hologram:

First: If you make a conventional hologram of a glass lens, and then you illuminate a darkened room with laser light, you can position the hologram so it bends the light like a lens.  The holographic lens will both magnify and also miniaturize the objects being viewed.  This does not work under normal illumination.  You must illuminate your room with laser light and position the hologram-lens in just the right way.

Second: If you make a “reflection hologram” of a curved, polished object (such as an eyeball), you will see some miniature images reflected in its holographic surface.  Reflection holograms of very shallow objects can behave as lenses even for incoherent white light.

Remember all holograms are lenses.  They are called “Gabor Zoneplate Lenses,” and they magnify and minify at the same time. Whenever you make a hologram, you are actually making a very complicated lens that bends the incoming light into the image of the original 3D object.  Because all holograms form both a positive and negative lens at the same time, they also create two images: the virtual image of the object being photographed, and also an “inside-out” real image (also called the “pseudoscopic” image.)

_

  1. Hologram always creates positive images (no negative like photography). During the reconstruction only positive images are created. A negative hologram merely produces a wave field that is shifted 180 degree in phase with respect to that of positive hologram. Since the eyes are insensitive to this phase difference, the view seen by the observer is identical in the two cases.

_

  1. Holograms can also be entirely computer-generated and show objects that never existed.

_____

_____

Types of hologram:

A hologram contains various information. This information is stored in a very microscopic and complex pattern of interference. The interference pattern is made possible by the properties of light generated by a laser. There are various types of holograms like custom holograms, 3D holograms, security hologram, promotional holograms, hologram with variable, holograms pouch, pharma protect, hot stamped hologram, scratch holograms, hologram seals, holographic shrink sleeves, hologram labels etc. Several types of holograms can be made. Transmission holograms, such as those produced by Leith and Upatnieks, are viewed by shining laser light through them and looking at the reconstructed image from the side of the hologram opposite the source.  A later refinement, the “rainbow transmission” hologram, allows more convenient illumination by white light rather than by lasers. Rainbow holograms are commonly used for security and authentication, for example, on credit cards and product packaging. Another kind of common hologram, the reflection or Denisyuk hologram, can also be viewed using a white-light illumination source on the same side of the hologram as the viewer and is the type of hologram normally seen in holographic displays. They are also capable of multicolour-image reproduction. Specular holography is a related technique for making three-dimensional images by controlling the motion of specularities on a two-dimensional surface. It works by reflectively or refractively manipulating bundles of light rays, whereas Gabor-style holography works by diffractively reconstructing wavefronts. Most holograms produced are of static objects but systems for displaying changing scenes on a holographic volumetric display are now being developed.

_

Types of Hologram:

Let us now discuss in details the various types of holograms produced under different processes and methods. These holograms are:

  • Reflection Hologram: It forms an image by reflected light.
  • Transmission Hologram: It forms an image from the light that passes through the holographic emulsion.
  • Embossed Holograms: The most commonly used hologram.
  • Integral Hologram: A type of hologram formed from series of photographs of an object.
  • Rainbow Holograms: A popular type of hologram, viewed in white light.
  • Computer Generated Holograms (vide infra): Computers are used to create images and patterns for developing holograms. There is no need for a real object. Interference pattern is calculated digitally, using algorithms. The time-varying light field of a scene with all its physical properties is to be recorded and then regenerated.
  • Multiplex Hologram: It is a type of hologram produced by combining a large number of photographs.
  • Stereogram: An optical illusion of depth created from flat, two-dimensional image.
  • Volume Holograms: A hologram in which the angle difference between the object beam and reference beam is greater than 90 degrees.
  • Plane Holograms: A hologram in which the angle difference between the object beam and reference beam is less than 90 degrees.

_______

Transmission and reflection hologram:

A transmission hologram is one where the object and reference beams are incident on the recording medium from the same side. In practice, several more mirrors may be used to direct the beams in the required directions. Normally, transmission holograms can only be reconstructed using a laser or a quasi-monochromatic source, but a particular type of transmission hologram, known as a rainbow hologram, can be viewed with white light. In a reflection hologram, the object and reference beams are incident on the plate from opposite sides of the plate. The reconstructed object is then viewed from the same side of the plate as that at which the re-constructing beam is incident. Only volume holograms can be used to make reflection holograms, as only a very low intensity diffracted beam would be reflected by a thin hologram.

_

The transmission hologram was one the first holograms made. A transmission hologram is formed when the light from the object and the reference beam enters the recording material from the same side. Like a photographic transparency, transmission holograms are lit from the back and bend light as it passes through the hologram to our eyes to form the holographic image. In order to reconstruct the holographic image, the hologram is placed in its original position in the reference beam as during its recording. We see an image of the object if we look along the reconstructed object beam. We see object from different perspectives as we shift viewpoints. Thus the object gives a three-dimensional effect. In reconstructing transmission hologram, the light does not actually pass through the image, but it creates a wave front that makes it appear as though the light had been generated in the position of the object. This image is called virtual image.

_

Figure above shows set-ups for recording transmission and reflection hologram. The difference is the direction of the reference beam.

_

Reflection holograms are viewed with the light source on the same side as the viewer. In comparison to a transmission hologram, the recording of a reflection hologram requires 10 to 100 times more power. This leads to longer exposure time. During the process of hologram recording, the two beams-the reference beam and the object beam-illuminates the film plate from opposite sides and interfere on it. The fringes form flat layers more or less parallel to the emulsion’s surface. The reflection hologram selects the appropriate band of wavelengths to reconstruct the image if it is illuminated by a highly directed beam of white light like a spotlight or sun light. This is because a reflection hologram reflects light within a narrow band while the rest of the light passes straight through.

_

There are two basic types of holograms — reflection and transmission. They can be distinguished by the way in which they are illuminated. Reflection holograms are lit from the front, reflecting the light to you as you view it, like a painting or photograph hung on a wall. Transmission holograms are lit from the rear (like a photographic transparency) and bend light as it passes through the hologram to your eyes to form the image.

In a transmission hologram, monochromatic light shines through the hologram to make an image. In a reflection hologram, monochromatic or white light reflects off of the surface of the hologram to make an image. Your eyes and brain interpret the light shining through or reflecting off of the hologram as a representation of a three-dimensional object.

_

The reflection hologram, in which a truly three-dimensional image is seen near its surface, is the most common type shown in galleries. The hologram is illuminated by a “spot” of white incandescent light, held at a specific angle and distance and located on the viewer’s side of the hologram. Thus, the image consists of light reflected by the hologram. If a mirror is the object, the holographic image of the mirror reflects white light; if a diamond is the object, the holographic image of the diamond is seen to “sparkle.” Reflection holograms can also be as elaborate as the transmission holograms. There are lots of object and laser setups that can produce these types of holograms. A common one is an inline setup, with the laser, the emulsion and the object all in one line. The beam from the laser starts out as the reference beam. It passes through the emulsion, bounces off the object on the other side, and returns to the emulsion as the object beam, creating an interference pattern. You view this hologram when white or monochrome light reflects off of its surface. You’re still seeing a virtual image — your brain’s interpretation of light waves that seem to be coming from a real object on the other side of the hologram.

_

The holograms you see on credit cards and stickers are reflection holograms. The holograms you can buy as novelties or see on your driver’s license are reflection holograms. These are usually mass-produced using a stamping method. When you develop a holographic emulsion, the surface of the emulsion collapses as the silver halide grains are reduced to pure silver. This changes the texture of the emulsion’s surface. One method of mass-producing holograms is coating this surface in metal to strengthen it, then using it to stamp the interference pattern into metallic foil. A lot of the time, you can view these holograms in normal white light. You can also mass-produce holograms by printing them from a master hologram, similar to the way you can create lots of photographic prints from the same negative. Holograms on credit cards can also be transmission hologram. Although mass-produced holograms such as the eagle on the VISA card are viewed with reflected light, they are actually transmission holograms “mirrorized” with a layer of aluminum on the back.

_

Bragg effect:

Reflection holograms are often thicker than transmission holograms. There is more physical space for recording interference fringes. This also means that there are more layers of reflective surfaces for the light to hit. You can think of holograms that are made this way as having multiple layers that are only about half a wavelength deep. When light enters the first layer, some of it reflects back toward the light source, and some continues to the next layer, where the process repeats. The light from each layer interferes with the light in the layers above it. This is known as the Bragg effect, and it’s a necessary part of the reconstruction of the object beam in reflection holograms. In addition, holograms with a strong Bragg effect are known as thick holograms, while those with little Bragg effect are thin. The Bragg effect can also change the way the hologram reflects light, especially in holograms that you can view in white light. At different viewing angles, the Bragg effect can be different for different wavelengths of light. This means that you might see the hologram as one color from one angle and another color from another angle. The Bragg effect is also one of the reasons why most novelty holograms appear green even though they were created with a red laser.

_

______

Hybrid holograms:

Between the reflection and transmission types of holograms, many variations can be made.

  1. Embossed holograms: To mass produce cheap holograms for security application such as the eagle on VISA cards, a two-dimensional interference pattern is pressed onto thin plastic foils. The original hologram is usually recorded on a photosensitive material called photoresist. When developed, the hologram consists of grooves on the surface. A layer of nickel is deposited on this hologram and then peeled off, resulting in a metallic “shim.” More secondary shims can be produced from the first one. The shim is placed on a roller. Under high temperature and pressure, the shim presses (embosses) the hologram onto a roll of composite material similar to Mylar.
  2. Integral holograms: A transmission or reflection hologram can be made from a series of photographs (usually transparencies) of an object—which can be a live person, an outdoor scene, a computer graphic, or an X-ray picture. Usually, the object is “scanned” by a camera, thus recording many discrete views. Each view is shown on an LCD screen illuminated with laser light and is used as the object beam to record a hologram on a narrow vertical strip of holographic plate (holoplate). The next view is similarly recorded on an adjacent strip, until all the views are recorded. When viewing the finished composite hologram, the left and right eyes see images from different narrow holograms; thus, a stereoscopic image is observed. Recently, video cameras have been used for the original recording, which allows images to be manipulated through the use of computer software.
  3. Multichannel holograms: With changes in the angle of the viewing light on the same hologram, completely different scenes can be observed. This concept has enormous potential for massive computer memories.

______

Thin and thick (volume) hologram:

A thin hologram is one where the thickness of the recording medium is much less than the spacing of the interference fringes which make up the holographic recording. The thickness of a thin hologram can be down to 60 nm by using a topological insulator material Sb2Te3 thin film. Ultrathin holograms hold the potential to be integrated with everyday consuming electronics like smartphone. A thick or volume hologram is one where the thickness of the recording medium is greater than the spacing of the interference pattern. The recorded hologram is now a three dimensional structure, and it can be shown that incident light is diffracted by the grating only at a particular angle, known as the Bragg angle. If the hologram is illuminated with a light source incident at the original reference beam angle but a broad spectrum of wavelengths; reconstruction occurs only at the wavelength of the original laser used. If the angle of illumination is changed, reconstruction will occur at a different wavelength and the colour of the re-constructed scene changes. A volume hologram effectively acts as a colour filter.

____

Amplitude and phase modulation holograms:

An amplitude modulation hologram is one where the amplitude of light diffracted by the hologram is proportional to the intensity of the recorded light. A straightforward example of this is photographic emulsion on a transparent substrate. The emulsion is exposed to the interference pattern, and is subsequently developed giving a transmittance which varies with the intensity of the pattern – the more light that fell on the plate at a given point, the darker the developed plate at that point. A phase hologram is made by changing either the thickness or the refractive index of the material in proportion to the intensity of the holographic interference pattern. This is a phase grating and it can be shown that when such a plate is illuminated by the original reference beam, it reconstructs the original object wavefront. The efficiency (i.e., the fraction of the illuminated object beam which is converted into the reconstructed object beam) is greater for phase than for amplitude modulated holograms.

_

A given hologram can be amplitude modulated thin transmission hologram, or a phase modulated thick reflection hologram.

_______

_______

Static versus Dynamic (real time) holography:

In static holography, recording, developing and reconstructing occur sequentially, and a permanent hologram is produced. There also exist holographic materials that do not need the developing process and can record a hologram in a very short time. This allows one to use holography to perform some simple operations in an all-optical way. Examples of applications of such real-time holograms include phase-conjugate mirrors (“time-reversal” of light), optical cache memories, image processing (pattern recognition of time-varying images), and optical computing. The amount of processed information can be very high (terabits/s), since the operation is performed in parallel on a whole image. This compensates for the fact that the recording time, which is in the order of a microsecond, is still very long compared to the processing time of an electronic computer. The optical processing performed by a dynamic hologram is also much less flexible than electronic processing. On one side, one has to perform the operation always on the whole image, and on the other side, the operation a hologram can perform is basically either a multiplication or a phase conjugation. In optics, addition and Fourier transform are already easily performed in linear materials, the latter simply by a lens. This enables some applications, such as a device that compares images in an optical way. The search for novel nonlinear optical materials for dynamic holography is an active area of research. The most common materials are photorefractive crystals, but in semiconductors or semiconductor heterostructures (such as quantum wells), atomic vapors and gases, plasmas and even liquids, it was possible to generate holograms.

_

A particularly promising application is optical phase conjugation. It allows the removal of the wavefront distortions a light beam receives when passing through an aberrating medium, by sending it back through the same aberrating medium with a conjugated phase. This is useful, for example, in free-space optical communications to compensate for atmospheric turbulence (the phenomenon that gives rise to the twinkling of starlight). It is possible, using nonlinear optical processes, to exactly reverse the propagation direction and phase variation of a beam of light. The reversed beam is called a conjugate beam, and thus the technique is known as optical phase conjugation. One can interpret this nonlinear optical interaction as being analogous to a real-time holographic process. In this case, the interacting beams simultaneously interact in a nonlinear optical material to form a dynamic hologram (two of the three input beams), or real-time diffraction pattern, in the material. The third incident beam diffracts off this dynamic hologram, and, in the process, reads out the phase-conjugate wave. In effect, all three incident beams interact (essentially) simultaneously to form several real-time holograms, resulting in a set of diffracted output waves that phase up as the “time-reversed” beam. In the language of nonlinear optics, the interacting beams result in a nonlinear polarization within the material, which coherently radiates to form the phase-conjugate wave.

_____

_____

White light hologram:

Laser transmission holograms are made with lasers, like all holograms, but also must be lit with lasers to be viewed. Therefore, the images appear in the color of the laser used in illuminating them for viewing, usually red (helium neon laser). Other types of holograms use a laser transmission hologram as the master, from which copies are made. White light transmission holograms are illuminated with incandescent light (white light) and produce images that contain the rainbow spectrum of colors. The colors change as the viewer moves up and down and are often called “rainbow” holograms. Holographers have developed considerable control over the colors displayed in this type hologram to produce images in a specific color or in near full, natural color.

__

__

White light consists of light of a wide range of wavelengths. Normally, if a hologram is illuminated by a white light source, each wavelength can be considered to generate its own holographic reconstruction, and these will vary in size, angle, and distance. These will be superimposed, and the summed image will wipe out any information about the original scene, as if superimposing a set of photographs of the same object of different sizes and orientations. However, a holographic image can be obtained using white light in specific circumstances, e.g. with volume holograms and rainbow holograms. The white light source used to view these holograms should always approximate to a point source, i.e. a spot light or the sun. An extended source (e.g. a fluorescent lamp) will not reconstruct a hologram since its light is incident at each point at a wide range of angles, giving multiple reconstructions which will “wipe” one another out. White light reconstructions do not contain speckles.

_

Standard holography uses single wavelength for reconstruction, hence no white light reconstruction possible and reconstruction possible with Laser. White light reconstruction is possible in three ways.

  1. Reflection type volume hologram
  2. Transmission type rainbow hologram
  3. Stereogram

_

Volume holograms:

A reflection-type volume hologram can give an acceptably clear reconstructed image using a white light source, as the hologram structure itself effectively filters out light of wavelengths outside a relatively narrow range. In theory, the result should be an image of approximately the same colour as the laser light used to make the hologram. In practice, with recording media that require chemical processing, there is typically a compaction of the structure due to the processing and a consequent colour shift to a shorter wavelength. Such a hologram recorded in a silver halide gelatin emulsion by red laser light will usually display a green image. Deliberate temporary alteration of the emulsion thickness before exposure, or permanent alteration after processing, has been used by artists to produce unusual colours and multicoloured effects.

Reflection-type “Denisyuk” Hologram:

Here, a multi colored image is first copied and later on white-light source is added. This technology negates use of backlight coating. But, these hologram stickers are costly option for product manufacturing companies.

_

Rainbow hologram:

In this method, parallax in the vertical plane is sacrificed to allow a bright, well-defined, gradiently colored reconstructed image to be obtained using white light. The rainbow holography recording process usually begins with a standard transmission hologram and copies it using a horizontal slit to eliminate vertical parallax in the output image. The viewer is therefore effectively viewing the holographic image through a narrow horizontal slit, but the slit has been expanded into a window by the same dispersion that would otherwise smear the entire image. Horizontal parallax information is preserved but movement in the vertical direction results in a color shift rather than altered vertical perspective. This means that if the viewer eye is moved vertically, no parallax is seen and the image colour moves through the rainbow spectrum from blue to red. It is seen that when a rainbow hologram is viewed at an average height, the image appears yellowgreen. Viewed higher the colour changes from orange or red and viewed lower it becomes blue or violet. That is why it is referred to as a rainbow hologram. The colour changes when we view it at different angle, but the hologram is still monochromatic. Because perspective effects are reproduced along one axis only, the subject will appear variously stretched or squashed when the hologram is not viewed at an optimum distance; this distortion may go unnoticed when there is not much depth, but can be severe when the distance of the subject from the plane of the hologram is very substantial. Stereopsis and horizontal motion parallax, two relatively powerful cues to depth, are preserved. The holograms found on credit cards are examples of rainbow holograms. These are technically transmission holograms mounted onto a reflective surface like a metalized polyethylene terephthalate substrate commonly known as PET.

Figure above is an example of rainbow hologram from MIT.

Holograms cannot (normally) be in color because monochromatic (single frequency) laser light must be used to reconstruct them. The holograms on credit cards are called “rainbow holograms” and use a trick to be able to be visible without lasers, i.e. under “white” light. A side-effect of this trick is that the 3D depth is only visible when the hologram is viewed upright. If you rotate a credit card 90 degrees, the 3D hologram effect goes away.

____

Stereogram:

A stereogram is a type of hologram that reconstructs a three-dimensional image from a series of two-dimensional views of an object recorded from different angles. A series of photographs of the object is taken from equally spaced positions along a horizontal line. Contiguous, vertical strip holograms are then recorded of these photographs of a photographic plate. When we illuminate the stereogram with a point source of monochromatic light, the viewer sees a three-dimensional image. The image lacks vertical parallax, but it exhibits horizontal parallax over the range of angles covered by the original photographs. The method is widely used for simple presentations of objects. In medicine we can use computer tomography shots to create a stereogram and so we can present the internal organ more clearly.

______

______

Smart holograms (Holographic sensors):

Holograms can be modified to detect and quantify environmental changes, such as changing temperature or humidity, and also the presence of certain substances such as harmful gases and metals. This is advancing field of holographic sensors, also called smart holograms. Smart holograms are a new branch of holography usage resulting from extensive researches in the field of “portable” diagnostics and new sensors. In a smart hologram, a suitable complementary receptor is attached to the polymer matrix of the photographic emulsion. When a particular substance (called the analyte) reacts with a polymer physical or chemical changes occur, and polymer responds to them. This means that smart polymer will generate observable changes in the wavelength (i.e. colour), intensity (brightness) or encoded image of the reflection hologram. The active component in such a “smart” hologram is normally a 3D polymer network called a hydrogel, which is a material that is very good at absorbing water and can swell anywhere up to 1000% of its original volume. By incorporating a hologram throughout the volume of a hydrogel, holographic gratings can be fabricated that respond to, for example, humidity, water, solvents, dissolved gases, ions, metabolites, drugs, antibiotics, sugars or enzymes. The structure of the interference fringes indicate the extent of hydrogel expansion accompanied with visible changes. Combined with their rapid response times, smart holograms offer great potential for monitoring changes in analyte concentrations in real time. For example, a green smart hologram sprayed with ethanol to simulate a Breathalyser test for alcohol on expired breath turns blue when the polymer contracts.

_

One of the simplest application of holographic sensors are measurements of water quantity in immiscible liquids. Immersing gelatin-based holograms in “wet” solvents cause water from the bulk solution to move into the holographic phase. The hydrogel swells and consequently imposes increase in the diffraction wavelength, which is directly proportional to the water containing in the sample. Holographic sensors thus can serve as power-free sensors of water activity in the petrochemical, food, textile, electronics and pharmaceutical industries, where water contamination can cause physical or financial damage. The potential of smart holograms is huge. First product a moisture-sensitive sensor called H2No has been developed to control water contamination in aviation fuel. Water contamination can cause the fuel to freeze at high altitude, which can block filters with potentially disastrous consequences. It is usually identified by performing a somewhat subjective “clear-and-bright” test, in which a hazy visual appearance indicates water contamination. On the other hand, this device — a hand-held syringe that contains a holographic sensor some 1 cm in diameter — instantly generates an easily discernible red cross if the water content of the fuel is above acceptable limit of 30 ppm.  Other devices in development are blood glucose monitor, monitor for architectural glazes and ion detectors.

_

The principle of operation of holographic sensors is straightforward. Dimensional and other changes in the hologram occur in response to some external influence. For example, a change in the refractive index modulation of the hologram due to a physical/chemical interaction between a hologram constituent and some analyte would allow for the detection of the analyte. Alternatively a change in the spacing of a recorded fringe pattern due to shrinkage or swelling of the material results in a change in the angular position of the Bragg peak for transmission holograms, or a change in the spectral position of the Bragg peak in reflection holograms. The IEO has developed humidity and temperature holographic sensors based on this principle using an AA-based photopolymer. Reflection holograms are used as any changes in the hologram are easily observed by eye under white light, such as a change in colour. For transmission mode sensors, laser light or a photodetector is required to observe any change. Nanoparticles can be used in conjunction with photopolymer materials to produce some interesting sensing properties. Zeolite nanoparticles have been added to the AA photopolymer to act as analyte traps. The refractive index of the material is then altered by the presence of the analyte. This principle has been used for a humidity sensor, where the porous zeolite nanoparticles trap water molecules inside. This causes the material to swell and the colour of the hologram changes due to a shift in the spectral position of the Bragg peak. Lowe et al have developed several sensors in their polymer-based system, designed to detect metal ions, monitor glucose levels and quantify the pH of solutions.

______

______

Security holograms:

According to conservative estimates, around the world every year, due to counterfeit payment instruments like currency, checks, credit cards, and counterfeiting of all kinds of high-end goods caused nearly $ 100 billion loss to the world economy and industry. Security holograms are the most common type of holograms used in many industries. Security hologram products like stickers, labels, cards are found on a lots of products and packaging, certificates, tickets, passes, bank notes and many kinds of identification and membership cards. Security holograms are an essential method of protection against forgery. They are produced on special materials and with more complicated techniques resulting that products cannot be copied by standard printing techniques or replicated by colour copiers or computer scanning equipment. As a result, the use of security holograms virtually guarantees product authenticity. More details are hard to find because the exact procedures are confidential otherwise the forgery wouldn’t be a problem.  Security holograms are labels with a hologram printed onto it for sale security reasons. Security holograms are very difficult to forge because they are replicated from a master hologram which requires expensive, specialized and technologically advanced equipment. They are used widely in several banknotes around the world, in particular those that are of high denominations. They are also used in passports, credit and bank cards as well as quality products.

_

Security Holograms are classified into different types with reference to the degree of level of optical security incorporated in them during the process of master origination.

  1. 2D / 3D “hologram” images:

These are by far the most common type of hologram – and in fact they are not holograms in any true sense of the words. The term “hologram” has taken on a secondary meaning due to the widespread use of a multilayer image on credit cards and driver licenses. This type of “hologram” consists of two or more images stacked in such a way that each is alternately visible depending upon the angle of perspective of the viewer. The technology here is similar to the technology used for the past 50 years to make red safety night reflectors for bicycles, trucks, and cars. These holograms (and therefore the artwork of these holograms) may be of two layers (i.e. with a background and a foreground) or three layers (with a background, a middle ground and a foreground). In the case of the two-layer holograms, the matter of the middle ground is usually superimposed over the matter of the background of the hologram. These holograms display a unique multilevel, multi-colour effect. These images have one or two levels of flat graphics “floating” above or at the surface of the hologram. The matter in the background appears to be under or behind the hologram, giving the illusion of depth.

  1. Dot matrix:

These holograms have a maximum resolution of 10 micrometres per optical element and are produced on specialized machines making forgery difficult and expensive. To design optical elements, several algorithms are used to shape scattered radiation patterns.

  1. Flip Flop:

Flip Flop Hologram Masters Origination is a technique used to produce holograms that display flip flop effect. They are produced used 2D/3D master shooting system. This two channel effect of 2D/3D holograms displays two different images from different angles. These holograms are often fabricated using supreme quality material. The final master obtained from this flip flop mastering technique are used to manufacture holograms which gives flip-flop effects. Having an excellent blend of 2D/3D and flipping images offers holographic images an excellent depth and a dazzling appeal.

  1. Electron-beam lithography:

These types of hologram are created using highly sophisticated and very expensive electron-beam lithography systems. This kind of technology allows the creation of surface holograms with a resolution of up to 0.1 micrometres (254,000 dpi). This technique requires development of various algorithms for designing optical elements that shapes scattered radiation patterns. This type of hologram offers features like the viewing of four lasers at a single point, 2D/3D raster text, switch effects, 3D effects, concealed images, laser readable text and true colour images. These kind of holograms enhance your hologram security a lot because only few company can make good pattern released.

  1. Computer-synthesized 2D/3D and 3D images:

This technology allows 2D / 3D images to be combined with other security features (microtexts, concealed images, CLR etc.) – this combination effect cannot be achieved using any other traditional technologies of origination. 2D / 3D hologram masters are developed in 2D/3D master shooting lab that incorporates highly sensitive machines and advanced equipment like Microprocessor-Controlled Automatic Positioning Equipment, Optical Table, He-Cd laser, laser power controller, silver coatings and other related technologies. The final master obtained from 2D / 3D Mastering is used to manufacture 2D/ 3D hologram stickers. These stickers consist of a multitude of two-dimensional layers with images placed on behind the other thereby offering excellent depth. These stickers are colorful images with 3D depth between different layers.

  1. True colour images:

True colour images are very effective decorative pictures. When synthesized by a computer, they may include microtexts, hidden images, and other security features, yielding attractive, high-security holograms. True Color hologram masters can be produced using 2D/3D master shooting system. The final master obtained from this mastering technique comprises true photographic images like images of people, animals, flags, etc. This type of holograms can’t be duplicated if in case they can’t obtain the original photo. True color holograms are one of the best ways to prevent counterfeiters from duplicating.

______

______

Frequently asked questions (FAQ) on hologram:

Q – Can I make a hologram using my favorite photograph?

A-Yes and no. It is possible to make a hologram of photograph, but photograph itself contains flat, 2-D image information. Therefore on the hologram it will also look flat. It would look just like a flat photograph floating in the space on front, or behind the frame. The third missing dimension of a photograph cannot be reconstructed by holographic process.

_

Q – Can the holographic image be enlarged or reduced?

A – Once the hologram is made it cannot be reduced or enlarged. Hologram made from 3 dimensional models are recorded in identical size as the original object and the image size cannot be changed. However the size of the viewed image scales with the wavelength of the viewing light. The computer generated holograms can be reduced or enlarged; stereogram holography which is created on computer from movie footage, can be varied in size.

_

Q – How about full-color holography?

A – Most of holograms are made in one color – similar to black and white holography. The typical greenish – yellow color of a hologram is formed there because of interference of white light on holographic emulsion, development provides colour variations (from red to bluish). Multi-color holograms are available, but as it takes extremely complicated process and is time consuming, they are still rare and expensive. The embossed holograms are like multi-color, but it is not the “original” color – just a “rainbow” effect. True-colour holograms can be made, but the true colours are viewable only at one specific angle and once you shift your view point the image will cycle through the rainbow spectrum.

_

Q – Will a hologram last long?

A – Holograms are very durable, and with proper care will outlive any regular photographs or prints.

_

Q – How can I view a hologram?

A – If you purchased your hologram in one of the shops across your country, chances are it is a “white-light reflection” hologram. Reflection holograms are popular because you can mat and frame them, and hang them on your wall. In order to view your reflection hologram, you must provide a light source to light up the hologram. This light source is commonly located on your ceiling, such as track lighting. If you do not have track lighting, you may also use one of the inexpensive “clip-on” lamps.  You should place your hologram on the wall at a comfortable height – taking into consideration both adults and children. It is much easier for a tall person to bend down a little than it is for a shorter person to stretch up to see. A good starting point would be to have the center of your hologram placed between 150 cm and 170 cm on your wall, measured from the base of the wall. Your light source should come into the hologram at a starting angle of approx. 45 degrees. Different holograms light up at different angles, but 45 degrees is a good place to start. Have someone hold the light in place, and then view the hologram from around 2 meters or so away from the wall. Adjust the incoming angle until you get the best view of the hologram. It is very important that you provide the right bulb to light the hologram. The best bulb to use is a clear halogen bulb. If a halogen bulb is not possible, you should use a clear incandescent bulb. It is important that the bulb is clear and not frosted. A frosted light source will create a blurred hologram – as will any flourescent lighting. If you’d like to display your hologram on a lamp table, replace your lamp bulb with a clear bulb and have the hologram angled at a 45-degree angle. While this will not give the quality effect of having the hologram on the wall with track lighting, it will allow you to enjoy your hologram if the other methods are not possible. Anyway, clear and pointed light source is preferable.

_

Q – How does a hologram differ from a photograph?

A – The hologram records an infinite number of views of the object, whereas a photograph records only one view. Thus, when viewing a hologram, the left eye sees a different set of information than the right eye so that the image appears three dimensional, and as head and eyes of observer moves, another 3D view of object is seen.

_

Q – Why can’t the hologram be copied?

A – Hologram is very difficult to copy. Generally what passes as copies of holograms are not holograms at all, but diffractive material with screen printing and or hot stamping with various foils. To the untrained eye they appear like holograms because they have some form of rainbow colours. They are crude pass offs that do not stand any scrutiny and cannot be called holograms. Holograms cannot be copied by any known printing technique. All printing is done with ink whereas hologram is an inkless optical process that cannot be scanned, photocopied, or electronically transmitted. A properly specified and executed hologram is impossible to duplicate. Every hologram has a signature and it is not possible to replicate it well that is why holograms are used on over 90 currencies around the world such Pound Sterling, Euro, Japanese Yen, Swiss Frank, etc.

_

Q – Can moving holograms be made?

A -Yes. Specially filmed motion pictures of 3 to 10 second lengths can be used to create animated holographic images. This process is known as stereogram and the resultant image can be viewed under tungsten (point source) light.

_______

Uses for holograms in brief:

Holograms have many uses in art, science and technology. Holograms are used on product packaging at many stores. Several magazines have featured holograms on their covers. Holograms are found on credit cards, drivers licenses, and even clothing to help stop counterfeiting. Computer-generated holograms allow engineers and designers to visually see their creations like never before.  Engineers also use holography to test for fractures and also for quality control during manufacturing. It is called holographic non-destructive testing. Holograms are used in many airplanes, both civilian and military. These holograms provide the pilot with critical information while looking through the cockpits window. It is called a heads-up display. Artists use holography for artistic expression. Many artists feel that exploring the three-dimensional space and pure light that holography offers allows them to convey images and messages that were never before possible with traditional media. The medical field was also quick to find a use for holograms. A holographic picture could be taken for research, enabling many doctors to examine a subject in three dimensions. Holography has also been instrumental in the development of acoustical (sound) imaging and is often used in place of X-ray spectroscopy, especially during pregnancies.  A critical application of holography is in computer data storage. Magnetic disk, the most common storage device for home and small-frame computers, is two dimensional, so its storage capacity is limited. Because of its three-dimensional nature, a hologram can store much more information. Optical memories store large amounts of binary data (with series of zeroes and ones representing bits of information) on groupings of small holograms. When viewed by the computer using coherent light, these groupings reveal a 3-D image full of information. Holography is also used in microscopy and interferometry.

_______

Hologram is costly:

Although holography can solve many problems, it still is a relatively expensive procedure. It has been used—or misused—in applications more amenable to simpler and cheaper methods. The laser system by itself is a fairly complex and costly piece of equipment, and costs are aggravated further by the additional equipment and the long exposure times required to produce holograms and reconstruct images. Aside from its uses in microscopy and interferometry, holography is therefore applied only when other methods have failed or are not precise enough.

The figure below shows cost of holographic system:

_______

The Future of holography:

Today, the most common use of holograms is in consumer products and advertising materials. There are some unusual applications too. For example, in some military aircraft, pilots can read their instruments while looking through the windshield by using a holographic display projected in front of their eyes. Automobile manufacturers are considering similar displays for their cars. Holograms can be created without visible light. Ultraviolet, x-ray, and sound waves can all be used to create them. Microwave holography is being used in astronomy to record radio waves from deep space. Acoustical holography can look through solid objects to record images, much as ultrasound is used to generate images of a fetus within a woman’s womb. Holograms made with short waves such as x rays can create images of particles as small as molecules and atoms. Holographic television sets may project performers into viewers’ homes within the next decade. Fiber optic communications systems will be able to transmit holographic images of people to distant homes of friends for realistic visits. Just as CD-ROM technology used optical methods to store large amounts of computer information on a relatively small disk, three-dimensional holographic data storage systems will further revolutionize storage capacities. It is estimated that this technology will store an amount of information equivalent to the contents of the Library of Congress in a space the size of a sugar cube.

______

______

Technological requirements of holography:

_

To make a hologram, the following are required:

  • a suitable object or set of objects
  • part of the laser beam to be directed so that it illuminates the object (the object beam) and another part so that it illuminates the recording medium directly (the reference beam), enabling the reference beam and the light which is scattered from the object onto the recording medium to form an interference pattern
  • a recording medium which converts this interference pattern into an optical element
  • a laser beam that produces coherent light with one wavelength.
  • an environment which provides sufficient mechanical and thermal stability that the interference pattern is stable during the time in which the interference pattern is recorded.

These requirements are inter-related, and it is essential to understand the nature of optical interference to see this. Interference is the variation in intensity which can occur when two light waves are superimposed. The intensity of the maxima exceeds the sum of the individual intensities of the two beams, and the intensity at the minima is less than this and may be zero. The interference pattern maps the relative phase between the two waves, and any change in the relative phases causes the interference pattern to move across the field of view. If the relative phase of the two waves changes by one cycle, then the pattern drifts by one whole fringe. One phase cycle corresponds to a change in the relative distances travelled by the two beams of one wavelength. Since the wavelength of light is of the order of 0.5 μm, it can be seen that very small changes in the optical paths travelled by either of the beams in the holographic recording system lead to movement of the interference pattern which is the holographic recording. Such changes can be caused by relative movements of any of the optical components or the object itself, and also by local changes in air-temperature. It is essential that any such changes are significantly less than the wavelength of light if a clear well-defined recording of the interference is to be created.

_

The exposure time required to record the hologram depends on the laser power available, on the particular medium used and on the size and nature of the object(s) to be recorded, just as in conventional photography. This determines the stability requirements. Exposure times of several minutes are typical when using quite powerful gas lasers and silver halide emulsions. All the elements within the optical system have to be stable to fractions of a μm over that period. It is possible to make holograms of much less stable objects by using a pulsed laser which produces a large amount of energy in a very short time (μs or less). These systems have been used to produce holograms of live people. A holographic portrait of Dennis Gabor was produced in 1971 using a pulsed ruby laser. Thus, the laser power, recording medium sensitivity, recording time and mechanical and thermal stability requirements are all interlinked. Generally, the smaller the object, the more compact the optical layout, so that the stability requirements are significantly less than when making holograms of large objects.

_

Another very important laser parameter is its coherence. This can be envisaged by considering a laser producing a sine wave whose frequency drifts over time; the coherence length can then be considered to be the distance over which it maintains a single frequency. This is important because two waves of different frequencies do not produce a stable interference pattern. The coherence length of the laser determines the depth of field which can be recorded in the scene. A good holography laser will typically have a coherence length of several meters, ample for a deep hologram.

_

The objects that form the scene must, in general, have optically rough surfaces so that they scatter light over a wide range of angles. A specularly reflecting (or shiny) surface reflects the light in only one direction at each point on its surface, so in general, most of the light will not be incident on the recording medium. A hologram of a shiny object can be made by locating it very close to the recording plate.

_

Laser holography, in its original “pure” form of the photographic transmission hologram, is the only technology yet created which can reproduce an object or scene with such complete realism that the reproduction is visually indistinguishable from the original, given the original lighting conditions. It creates a light field identical to that which emanated from the original scene, with parallax about all axes and a very wide viewing angle. The eye differentially focuses objects at different distances and subject detail is preserved down to the microscopic level. The effect is exactly like looking through a window. Unfortunately, this “pure” form requires the subject to be laser-lit and completely motionless—to within a minor fraction of the wavelength of light—during the photographic exposure, and laser light must be used to properly view the results. Most people have never seen a laser-lit transmission hologram. The types of holograms commonly encountered have seriously compromised image quality so that ordinary white light can be used for viewing, and non-holographic intermediate imaging processes are almost always resorted to, as an alternative to using powerful and hazardous pulsed lasers, when living subjects are photographed.

_

Although the original photographic processes have proven impractical for general use, the combination of computer-generated holograms (CGH) and optoelectronic holographic displays, both under development for many years, has the potential to transform the half-century-old pipe dream of holographic 3D television into a reality; so far, however, the large amount of calculation required to generate just one detailed hologram, and the huge bandwidth required to transmit a stream of them, have confined this technology to the research laboratory.

_

Laser:

In laser holography, the hologram is recorded using a source of laser light, which is very pure in its color and orderly in its composition. Various setups may be used, and several types of holograms can be made, but all involve the interaction of light coming from different directions and producing a microscopically fine interference pattern which a plate, film, or other medium photographically records. In one common arrangement, the laser beam is split into two, one known as the object beam and the other as the reference beam. The object beam is expanded by passing it through a lens and used to illuminate the subject. The recording medium is located where this light, after being reflected or scattered by the subject, will strike it. The edges of the medium will ultimately serve as a window through which the subject is seen, so its location is chosen with that in mind. The reference beam is expanded and made to shine directly on the medium, where it interacts with the light coming from the subject to create the desired interference pattern. Like conventional photography, holography requires an appropriate exposure time to correctly affect the recording medium. Unlike conventional photography, during the exposure the light source, the optical elements, the recording medium, and the subject must all remain perfectly motionless relative to each other, to within about a quarter of the wavelength of the light, or the interference pattern will be blurred and the hologram spoiled. With living subjects and some unstable materials, that is only possible if a very intense and extremely brief pulse of laser light is used, a hazardous procedure which is rare and rarely done outside of scientific and industrial laboratory settings. Exposures lasting several seconds to several minutes, using a much lower-powered continuously operating laser, are typical.

_

Projection using HELIUM-NEON LASER:

Helium-neon lasers are versatile devices that have many useful applications. They are often found in integrated bar code readers (the hand-held bar code readers use red semiconductor lasers or red LEDs.) Because they can emit visible light, helium-neon lasers are used in laser surgery to position the powerful infrared cutting beams. Surveyors take advantage of the helium-neon laser’s good beam quality to take precise measurements over long distances or across inaccessible terrain. Red helium-neon lasers are also used in holography. The typical helium-neon laser consists of three components: the laser tube, a high-voltage power supply, and structural packaging. The laser tube consists of a sealed glass tube which contains the laser gas, electrodes, and mirrors. Depending on the power output of the laser, the tube may vary in size from one to several centimeters in diameter, and from five centimeters to several meters in length. The laser gas is a mixture of helium and neon in proportions of between 5:1 and 14:1, respectively. Electrodes situated near each end of the tube, discharge electricity through the gas. Mirrors, located at each end of the tube, increase efficiency. The power supply provides the high voltages needed (10kV to start laser emission and 1-2kV to maintain it.) The structural packaging consists of mounts for the laser tube and power supply. The laser may also include safety shutters to prevent random exposure and external optics to fine-tune the beam.

_______

_______

The continuous-wave (CW) laser and the pulsed laser holography:

Of the many kinds of laser beam, two have especial interest in holography: the continuous-wave (CW) laser and the pulsed laser. The CW laser emits a bright, continuous beam of a single, nearly pure colour. The pulsed laser emits an extremely intense, short flash of light that lasts only about 1/100,000,000 of a second.

_____

Continuous-wave laser holography:

In a darkened room, a beam of coherent laser light is directed onto object from source. The beam is reflected, scattered, and diffracted by the physical features of the object and arrives on a photographic plate. Simultaneously, part of the laser beam is split off as an incident, or reference beam and is reflected by mirror onto plate. The two beams interfere with each other; that is, their respective amplitudes of waves combine, creating on the photographic plate a complex pattern of stripes and whorls called interference fringes. These fringes consist of alternate bright and dark areas. The bright areas result when the two beams striking the plate are in step—when crest meets crest and trough meets trough in the waves from the two beams; the beams are then in phase, and so reinforce each other. When the two waves are of equal amplitude but opposite phase—trough meeting crest and crest meeting trough—they cancel each other and a dark area results. The plate, when developed, is called a hologram. The image on the plate bears no resemblance to the object photographed but contains a record of all the phase and amplitude information present in the beam reflected from the object. The two parts of the laser beam—the direct and the reflected beams—meet on the plate at a wide angle and are recorded as very fine and close-packed interference fringes on the hologram. This pattern of fringes contains all the optical information of the object being photographed.

_

By reversing the procedure, an image of the original object can be reconstructed. The coherent light of a laser beam illuminates the hologram negative. Most of the light from the laser passes through the film as a central beam and is not used. The close-packed, fine-detailed fringes on the hologram negative act as a diffraction grating, bending or diffracting the remaining light to exactly reverse the original condition of the coherent light waves that created the hologram. The diffracted light is transmitted at a wide angle from that of the laser’s reference beam.

_

On the light source side of the hologram, a virtual image visible to the eye is formed. On the other side, a real image that can be photographed is formed. Both these reconstituted images have a three-dimensional character because in addition to amplitude information, which is all that an ordinary photographic process stores, phase information also has been stored. This phase information is what provides the three-dimensional characteristics of the image, as it contains within it exact information on the depths and heights of the various contours of the object. It is possible to photograph the reconstituted real image, by ordinary photographic means, at a selected depth, in exact focus.

_

The real image from a hologram—that is, the one that can be photographed—appears pseudoscopic, or with a reversed curvature. This reversal can be eliminated by making a double hologram, first by preparing the single hologram and then by using it as an object in the creation of a second hologram. With a double reversal the image becomes normal again, as when a mirror image of writing is made legible by viewing it in a second mirror. The real image of a hologram has valuable properties. A viewing camera or microscope can be positioned and focused on various selected positions in depth. The original object also can be brought into the position in space.

_

The hologram not only offers images at different depths (different cross-sections of the object) but also images seen along different directions if the viewer moves off the axis on which the principal image is viewed. Direct images can be seen under these conditions. In holography it is also possible to record on the same plate a succession of numerous multiple images that can be reconstructed as one image, leading to the possibility of holography in colour. Three holograms could be superimposed on the same plate, using three lasers of different colours. Reconstruction with the three different lasers would produce an image in its natural colour, even though the hologram plate itself is black-and-white.

_____

Pulsed-laser holography:

A moving object can be made to appear to be at rest when a hologram is produced with the extremely rapid and high-intensity flash of a pulsed ruby laser. The duration of such a pulse can be less than 1/10,000,000 of a second; and, as long as the object does not move more than 1/10 of a wavelength of light during this short time interval, a usable hologram can be obtained. A continuous-wave laser produces a much less intense beam, requiring long exposures; thus it is not suitable when even the slightest motion is present. With the rapidly flashing light source provided by the pulsed laser, exceedingly fast-moving objects can be examined. Chemical reactions often change optical properties of solutions; by means of holography, such reactions can be studied. Holograms created with pulsed lasers have the same three-dimensional characteristics as those made with CW sources. Pulsed-laser holography has been used in wind-tunnel experiments. Usually high-speed air flow around aerodynamic objects is studied with an optical interferometer (a device for detecting small changes in interference fringes, in this instance caused by variations in air density). Such an instrument is difficult to adjust and hard to keep stable. Furthermore, all of its optical components (mirrors, plates, and the like) in the optical path must be of high quality and sturdy enough to minimize distortion under high gas-flow velocities. The holographic system, however, avoids the stringent requirements of optical interferometry. It records interferometrically refractive-index changes in the air flow created by pressure changes as the gas deflects around the aerodynamic object.

_______

Uses of Lasers in Holography:

In order to determine the best criteria for lasers for any given application, the applications may be split into three classes:

  1. Holographic Optical Elements or technical applications (vide infra)
  2. Holographic Interferometry (vide infra)
  3. Display Holography (vide infra)

_

Preferred Laser Characteristics Holographic Optical Elements Holographic Interferometry Display Holography
Power 300 mW Pulse/1W 100 mW or more
Stability Good for short periods Good for short periods Very good for long periods
Beam shape Round Round Round
Coherence length 1m 1m 5m
Mode TEM00 TEM00 TEM00
Polarization Polarized Polarized Polarized
Automatic power adjustments Necessary for periods ~ 10 mins Necessary for periods ~ seconds Necessary for extended period (> 8 hrs)
Cooling Air Air Air
Power Supply 110/240 110/240 110/240
Size small Very small small
Wavelength (nm) 457, 488 442, 457, 488 457
Warm-up time less than 1hr 15 mins 15 min

_______

_______

Holographic recording media:

The recording medium has to convert the original interference pattern into an optical element that modifies either the amplitude or the phase of an incident light beam in proportion to the intensity of the original light field. The recording medium should be able to resolve fully all the fringes arising from interference between object and reference beam. These fringe spacings can range from tens of micrometers to less than one micrometer, i.e. spatial frequencies ranging from a few hundred to several thousand cycles/mm, and ideally, the recording medium should have a response which is flat over this range. If the response of the medium to these spatial frequencies is low, the diffraction efficiency of the hologram will be poor, and a dim image will be obtained. Standard photographic film has a very low or even zero response at the frequencies involved and cannot be used to make a hologram – see, for example, Kodak’s professional black and white film whose resolution starts falling off at 20 lines/mm — it is unlikely that any reconstructed beam could be obtained using this film. If the response is not flat over the range of spatial frequencies in the interference pattern, then the resolution of the reconstructed image may also be degraded.

_

The table below shows the principal materials used for holographic recording. Note that these do not include the materials used in the mass replication of an existing hologram. The resolution limit given in the table indicates the maximal number of interference lines/mm of the gratings. The required exposure, expressed as millijoules (mJ) of photon energy impacting the surface area, is for a long exposure time. Short exposure times (less than  1⁄1000 of a second, such as with a pulsed laser) require much higher exposure energies, due to reciprocity failure.

_

General properties of recording materials for holography:

Material Reusable Processing Type Theoretical max. efficiency Required exposure (mJ/cm2) Resolution limit (mm−1)
Photographic emulsions No Wet Amplitude 6% 1.5 5000
Phase (bleached) 60%
Dichromated gelatin No Wet Phase 100% 100 10,000
Photoresists No Wet Phase 30% 100 3,000
Photothermoplastics Yes Charge and heat Phase 33% 0.1 500–1,200
Photopolymers No Post exposure Phase 100% 10000 5,000
Photorefractives Yes None Phase 100% 10 10,000

_

Material requirements for holographic recording:

There are many requirements that a material must meet in order to be suitable for holographic recording and therefore for holographic applications. An ideal holographic material will have the following properties:

  • Large dynamic range to ensure sufficient modulation during exposure
  • High spatial resolution for improved quality recording
  • Does not suffer from shrinkage during holographic recording
  • Low noise i.e. have a fine grain structure to reduce unwanted scatter effects
  • Inexpensive to produce
  • Sensitive to the available commercial wavelengths
  • Straightforward and safe production process
  • Unaffected by ambient environmental conditions

There are many different materials available for holographic recording. The recording material chosen will depend largely on the requirements of the holographic application.

_

Several different materials can be used as the recording medium. Holograms can be recorded on a range of different image recording media. These include photographic emulsions, photoresists, photopolymers, photothermoplastics, photochromics and photorefractives. One of the most common is a film very similar to photographic film (silver halide photographic emulsion), but with a much higher concentration of light-reactive grains, making it capable of the much higher resolution that holograms require. A layer of this recording medium (e.g., silver halide) is attached to a transparent substrate, which is commonly glass, but may also be plastic. These are excellent for wall pictures, portraits, etc. Silver halide materials have to date been the most successful for full colour holography, as they do not suffer from shrinkage, can achieve high sensitivities and demonstrate low scattering. However, silver halide is expensive and requires chemical processing after recording. Meka et al have developed a panchromatic AA-based photopolymer which can be used for full colour holography also. Dichromate hologram (DCG) is made of special gelatin emulsion sealed between two glass plates. It is mainly used for small earrings, holo-watches, pendants, etc. It offers really bright and sharp imaging. Embossed holograms are the ones on plastic with “silver foil”. Embossed holograms are the lowest priced in large runs. They are used on credit cards, security applications, sports cards, stickers, etc. Embossed or “rainbow” holograms often are like multi-color. Color information is computer-generated before embossing process. Photo-polymer is relatively new material. It gives very bright image on a flexible surface and requires easy development procedure. Used for bright wall holograms, keyrings, etc.  It may be transparent – which opens new possibilities.

_

Holographic Film is the same as photographic film, except often a thicker emulsion is used and it is attached to glass or plastic. The emulsion (regular film and holographic film) is made of a mixture of gelatin and silver halide crystals (e.g. silver bromide and silver chloride). When light strikes the silver halide crystals in the gelatin, it gets absorbed by the outermost electrons. This causes a valence electron (outermost electron) to go up to a higher allowed energy level, which happens to be in the conduction band (almost removed from the atom). Silver ions, within the silver halide crystal, can then capture this electron, causing microscopic congregations of four or more silver atoms to form in the silver halide crystals. The areas where these silver atoms congregate cause a change in the film’s surface. A thin hologram is one in which the thickness of the emulsion is much less than the spacing between the interference fringes produces. When a thick emulsion is used – one whose thickness is much greater than the spacing of the interference pattern created by the reference beam mixing with the beam from the object – it is called a volume hologram. This type of hologram has a three dimensional structure due to the change in the emulsion from the silver atoms congregating. In this case, many different frequencies of incident light are diffracted from this 3-dimensional structure, which acts like a grating. This reproduces the hologram in a variety of colors when viewed under white light — creating a rainbow or white light hologram.

_

And this leads us back to the how they make those great reflective holograms on the back of credit cards and on your driver’s license. For the thick emulsion, the information for the hologram is embedded within the surface features of the emulsion. All the surface structures (where atoms have clumped together and collapsed) form a 3-dimensional structure that can be coated in metal to make an embossing tool. This metal embosser can be used to stamp (or emboss) the topographic pattern into another material such as thin piece of metal foil, which is then coated with a thin piece of plastic. When white light strikes the plastic over embossed foil, it goes through the plastic and reflects off the foil, and is affected in the same way as viewing the hologram in the emulsion. The different colors depend on the angle of viewing.

_

By definition, a hologram is a complete record of the phase and amplitude of an object’s wavefront. This principle lends itself to a huge variety of applications, from everyday items like embossed security holograms on passports and credit cards to holographic data storage (HDS) systems, sensors, 3-D displays, non-destructive interferometric testing methods and advanced scientific tools such as holographic tweezers and electro-optical switching holographic devices. In order to develop such a large range of applications, it is crucial that suitable holographic recording media are readily available. For years silver halide was the medium of choice for holographers. In the past few decades a large variety of alternative media have been developed for holography, such as dichromated gelatin, photoresists, photodicroics, photorefractives, photothermoplastics and photopolymers. Of these, photopolymer materials have been the subject of much study for holographic applications such as HDS, sensors and holographic optical elements (HOEs). Their large dynamic range, high sensitivity, self-processing nature, low cost and ease of production make them an attractive candidate.

____

Primary Support Options for holograms:

Film:

Most holographic film is just like photographic film in many ways. It often contains photosensitive silver halide crystals. The major difference in holographic film is that it is capable of very high resolution. Holographic film is also specially designed to be sensitive to a particular wavelength of light.

Film (photopolymer):

Photopolymer is the newest of the recording materials. Developed by Polaroid and Dupont, photopolymers have a plastic backing and are suitable for long production runs. The image depth of photo polymers is slightly less than that of silver halide; however, the images are brighter, with a wider angle of view.

Foil:

Foil is often the support material for embossed holograms.

Glass:

Sometimes emulsion is applied to glass, which provides greater stability than film during the exposure process.

Hard Plastic:

Sometimes used as a support material for embossed holograms (such as record albums). Holographers occasionally apply emulsion to thick plastic just as they would to glass. Film can be made sturdier after being developed if it is laminated onto plastic sheets. This technique is most often used in large format holography, since heavy glass plates would be difficult to safely manage.

Metal:

Anything that is solid enough to retain an imprint image can be used to record a hologram. Metal is often used as a master shim, from which other holograms are embossed onto plastic or other material

___

Non-photographic holography:

Holographic images are also recorded on materials other than photographic plates. Most of these nonphotographic materials, however, are still in the experimental stage, and the photographic production of holograms remains the only widely used process.

_

High resolution holograms from carbon nanotubes:

Researchers from the University of Cambridge’s Department of Engineering have demonstrated the novel utilisation of carbon nanotubes for making high resolution holograms.  Carbon nanotubes – a manmade material – have been the focus of an enormous amount of research during the last decade due to their extraordinary electrical and optical properties. These tubes are many times thinner than a wavelength of visible light which makes them promising candidates for being used as pixels. The researchers have produced holograms using the smallest pixels yet – carbon nanotubes. Due to the nanoscale dimensions of the carbon nanotube array, the image presented a wide field of view and high resolution. This work is a breakthrough in the field of holographic technology as it reports the original use of nanostructures for producing holograms.

____

____

Copying and mass production of holograms:

An existing hologram can be copied by embossing or optically.

Embossing:

Most holographic recordings (e.g. bleached silver halide, photoresist, and photopolymers) have surface relief patterns which conform with the original illumination intensity. Embossing, which is similar to the method used to stamp out plastic discs from a master in audio recording, involves copying this surface relief pattern by impressing it onto another material. The first step in the embossing process is to make a stamper by electrodeposition of nickel on the relief image recorded on the photoresist or photothermoplastic. When the nickel layer is thick enough, it is separated from the master hologram and mounted on a metal backing plate. The material used to make embossed copies consists of a polyester base film, a resin separation layer and a thermoplastic film constituting the holographic layer. The embossing process can be carried out with a simple heated press. The bottom layer of the duplicating film (the thermoplastic layer) is heated above its softening point and pressed against the stamper, so that it takes up its shape. This shape is retained when the film is cooled and removed from the press. In order to permit the viewing of embossed holograms in reflection, an additional reflecting layer of aluminum is usually added on the hologram recording layer. This method is particularly suited to mass production. Embossed holograms are used widely on credit cards, banknotes, and high value products for authentication purposes. It is possible to print holograms directly into steel using a sheet explosive charge to create the required surface relief. The Royal Canadian Mint produces holographic gold and silver coinage through a complex stamping process.

Optically:

A hologram can be copied optically by illuminating it with a laser beam, and locating a second hologram plate so that it is illuminated both by the reconstructed object beam, and the illuminating beam. Stability and coherence requirements are significantly reduced if the two plates are located very close together. An index matching fluid is often used between the plates to minimize spurious interference between the plates. Uniform illumination can be obtained by scanning point-by-point or with a beam shaped into a thin line.

_

Holographic print:

A holographic print is a rendition of a hologram on a flat surface, producing 3-D (three-dimensional) effects when viewed. A holographic print differs from a traditional hologram in that the print does not require any special lighting arrangements to yield the 3-D effect. The viewer does not need any task-specific eyewear to view the image. Holographic prints are extensively used for identification and security purposes. Credit cards, driver licenses, passports, and security badges commonly have small holographic prints embedded on their surfaces. Holographic prints work especially well in these applications because the image cannot be duplicated with a scanner or photocopier, and counterfeiting such an image has proven exceptionally difficult and expensive. Engineers and architects use large holographic prints to demonstrate or promote their projects in a more enhanced fashion than conventional photographs can do. In some situations, holographic prints can take the place of cumbersome video demonstrations. Holographic printing cannot be done on ordinary paper. In order to facilitate the process, the paper or other printing surface must be coated with a layer of metal (usually aluminum or steel) or reflective plastic. The hologram is embossed into the shiny metal or plastic, forming a complicated, extremely detailed, pixelated image in relief. When viewed under a microscope, the metal or plastic surface seems to have hills, gullies, ridges, and valleys. These irregularities produce the 3-D effect by scattering reflected light and diffracting it into its constituent color wavelengths. The reflected waves interfere with each other in such a way as to give a vivid, realistic 3-D portrayal of perspective and parallax. Small holographic prints, such as those found on identification documents and credit cards, can be produced at moderate cost. Large holographic prints, such as engineers might use, can range upwards of $3000 apiece. Holographic printing should not be confused with lenticular printing, which involves a different format and can be done with simpler equipment.

__

Hologram Master:

Film Holograms, Photopolymer and Embossed Holograms are the three basic kinds of Holograms available in the commercial world. Embossed Holograms are the majorly produced holographic products which are produced by embossing. Purposes for which they are used are for packaging, security and display purposes. In order to produce these basic kinds of holograms holography nickel master has to be developed. This most basic process of producing holograms is known as hologram master origination. Holograms are normally produced with the aid of laser beams, starting by creating a prototype from photosensitive material such as Fotoresist. However, this template is too soft to be able to act as an embossing or injection-moulding tool for holograms.  Consequently, the filigree relief pattern is copied onto a harder material such as nickel by means of electroplating. Mounted on a roller, this nickel shim transfers the hologram onto a plastic film of the kind that can be seen on EC cards and concert tickets.

_

The ‘explosive embossing’ method:

Researchers at the Fraunhofer Institute for Chemical Technology ICT in Pfinztal have now adopted a more radical method. The scientists are using explosives to impress holograms in steel. With the right dosage, explosives enable a template to be copied with far greater accuracy than by conventional methods. The ‘explosive embossing’ method achieves a resolution in the two-figure nanometer range. “Nobody believed such a thing could be possible,” raves ICT project manager Günter Helferich. Almost any structure, be it wood, leather, textiles or sand, can be rapidly and accurately impressed on metal in perfect detail with the aid of a sheet explosive. The scientists are now working with industrial partners to create steel tools with holographic structures – as a ‘stamp’ for applying holograms to plastic parts. The challenge is tremendous: The structures that have to be imprinted into the steel are so tiny that they cannot even be discerned under an optical microscope. The experts have optimized the method to the desired image sharpness through numerous series of experiments.  The advantage of this method over electroplating is that it does not produce a soft nickel piece that quickly wears out, but a hard steel stamp. Steel treated in this way is also in demand in the plastics industry: Many plastic parts are designed to look decorative and attractive, particularly if they are placed in elegant surroundings.

_____

_____

Display Holography:

Display holography covers those applications of holography where a 3D image of a real object or a photographic recording of an object or scene is recorded into a holographic medium, such as silver halide. Viewing the hologram involves lighting the medium which then reveals the image or scene recorded.  Display holograms are widely used as a powerful tool wherever an audience needs to be reached. They are popular and used frequently for eye-catching displays at trade fairs or presentations-a truly unique and amazing way to present objects, corporate images, educational materials and many more. This type of hologram is recorded on to a photographic glass or film plate. The photograph of a virtual object reproduces real 3D magic in display hologram. Display holography is basically a large-scale holography which can play a vital role to get the impact and attention you have been seeking. As it is, we all know that holograms are used for that “extra” effect and look, and display holography enlarges this effect many times over. If you need to grab anyone’s attention then display holography is your all-time solution.

Advantages of display hologram:

The striking three dimensional properties of holograms make them ideal for displays. Display holograms can produce spectacular displays for educational, medical, scientific, artistic and commercial purposes. Holographic displays have one great advantage of avoiding the risk of theft of art objects. The same object can be displayed at several places at the same time, which in turn implies that there is much wider exposure of rare items.

Requirement of a Display Hologram:

An ideal display hologram should meet certain requirements, such as follows:

  • White Light Viewable Image: The display holograms should be preferably viewed with a light source which is white. Finite size of the source creates blur in the image. When we talk about a typical white light source, it is the sun. The sun light is equivalent to the case of reconstructing a hologram from a distance or length of one meter using a white light source of 9 mm diameter. The blurred image is around 0.6 mm for an image point at distance of 10 cm from the hologram. In other light sources, the apparent size of the source can be reduced.
  • Focused Image: When the hologram is viewed by a white light source, the image should appear to be well focused. The image is blurred due to the finite size of the source and its spectral bandwidth. The blurring of the image increases with the increase in the distance of the image point from the hologram. The average distance of the image from the hologram can be minimized. This is done when the image straddles the hologram plane.
  • Wide Field-of-View: The field-of-view of the hologram should be wide to allow a large parallax. The vertical field-of-view may be restricted but the horizontal field must be large.
  • High Resolution: The display hologram should produce an image with excellent sharpness.
  • Low Image Aberrations: The image of the display hologram must be aberration free and without distortions. The image should not move as the observer moves up or down or sideways in the field.
  • Low Background Noise: Background noise has a drawback of reducing the contrast of the image. The processing chemistry should not introduce scattering noise. Background noise (flare light) is also introduced by Interference between light scattered by different parts of the body.
  • True Color: The display hologram should produce the image with true color. For monochrome object, while a display with only one color gives satisfactory results for many purposes, the addition of false colors can improve the display.
  • Ambience: Another important requirement is that hologram should display the image as acceptably bright-with proper contrast in high ambient light brightness.
  • Hologram Durability: The display hologram medium should be resistant to shrinkage and unaffected by ambient environmental conditions.

______

______

Holography versus photography:

Holography may be better understood via an examination of its differences from ordinary photography:

  • A hologram represents a recording of information regarding the light that came from the original scene as scattered in a range of directions rather than from only one direction, as in a photograph. This allows the scene to be viewed from a range of different angles, as if it were still present. If you look at these holograms from different angles, you see objects from different perspectives, just like you would if you were looking at a real object.
  • A photograph can be recorded using normal light sources (sunlight or electric lighting) whereas a laser is required to record a hologram.
  • A lens is required in photography to record the image, whereas in holography, the light from the object is scattered directly onto the recording medium.
  • A holographic recording requires a second light beam (the reference beam) to be directed onto the recording medium.
  • A photograph can be viewed in a wide range of lighting conditions, whereas holograms can only be viewed with very specific forms of illumination.
  • When a photograph is cut in half, each piece shows half of the scene. When a hologram is cut in half, the whole scene can still be seen in each piece. This is because, whereas each point in a photograph only represents light scattered from a single point in the scene, each point on a holographic recording includes information about light scattered from every point in the scene.
  • Photograph lacks depth perception. A photograph is a two-dimensional representation that can only reproduce a rudimentary three-dimensional effect, whereas the reproduced viewing range of a hologram adds many more depth perception cues that were present in the original scene. These cues are recognized by the human brain and translated into the same perception of a three-dimensional image as when the original scene might have been viewed.
  • A photograph clearly maps out the light field of the original scene. The developed hologram’s surface consists of a very fine, seemingly random pattern, which appears to bear no relationship to the scene it recorded.

_

The figure below shows difference in recording of photograph and hologram.

_

The figure below shows difference in viewing of photograph and hologram.

______

Holography versus Shearography:

Holography and Shearography are similar techniques. Holography employs interferometry by using two beams of laser light.  Shearography on the other hand, employs a single beam of laser light which is reflected off the specimen. Shearography is the preferred choice for industrial applications of relatively large objects due to its vibration insensitivity. The technique is primarily used for qualitative interpretation. Holography would be preferred for smaller objects and as Gabor had initially proposed for microscopic imaging. Recently with the advent of digital holographic interferometry, quantitative measurement become possible without any phase shifting.  One example of an interferometric measurement used for non-destructive characterization of materials in mechanical engineering is shearography, a method similar to holographic interferometry.  It is widely used in production and development in aerospace, wind rotor blades, automotive, and materials development and testing research. Shearography uses coherent light for nondestructive testing of materials, strain measurement, and vibration analysis. Advantages of shearography are high area throughput, non-contact interrogation, relative insensitivity to environmental disturbances, and good performance on honeycomb materials.

_______

Holography vs. virtual reality (VR) vs. augmented reality (AR):

Both virtual reality and augmented reality have reached a point that we are seeing them practically implemented throughout our lives. Pokemon Go was perhaps the biggest way we have seen augmented reality used and we’ve probably all seen virtual reality video games or even amusement park rides.

_

Augmented reality:

Augmented reality (AR) is a live direct or indirect view of a physical, real-world environment whose elements are “augmented” by computer-generated sensory input such as sound, video, graphics or GPS data. It is related to a more general concept called computer-mediated reality, in which a view of reality is modified (possibly even diminished rather than augmented) by a computer. Augmented reality enhances one’s current perception of reality, whereas in contrast, virtual reality replaces the real world with a simulated one. Augmentation techniques are typically performed in real time and in semantic context with environmental elements, such as overlaying supplemental information like scores over a live video feed of a sporting event. With the help of advanced AR technology (e.g. adding computer vision and object recognition) the information about the surrounding real world of the user becomes interactive and digitally manipulable. Information about the environment and its objects is overlaid on the real world. This information can be virtual or real, e.g. seeing other real sensed or measured information such as electromagnetic radio waves overlaid in exact alignment with where they actually are in space. Augmented reality brings out the components of the digital world into a person’s perceived real world. One example is an AR Helmet for construction workers which display information about the construction sites.  Augmented Reality is also transforming the world of education, where content may be accessed by scanning or viewing an image with a mobile device.

_

AR layers a virtual world on the real world but the user never loses touch with the real, physical, world during use of AR technology. For example, Pokemon Go allowed users to catch Pokemon that appeared to be in the real world, but only through the lens of a smartphone. More complex AR technologies use glasses or the like to fully immerse the user in an augmented reality, but the physical world is still what is being altered. AR needs glasses or camera to see the augmented view. The camera is capturing the video in the traditional manner. In the AR system a marker appears in the video and wherever you hold the marker the system super-imposes the 3D model of the object on the marker. To the viewer it appears as though the image has materialized by magic. The size and movement of the image is tracked by the computer via the placement and positioning of the marker.

_

Virtual Reality:

Virtual reality (VR) is the use of computer-generated technology to create an artificial three dimensional simulated environment or to recreate a real life environment or situation. Such created environment can be explored and interacted with. In simple terms we can say that virtual reality is a simulated artificial 3D environment and the person becomes a part of this new world. The person is so much immersed in the 360-degree view of this new world that he has little or no sensory input from the room his body is in. Virtual reality can be seen only through the use of headsets like Oculus, Sony, HTC etc. and requires 3 things. A PC, console or smartphone to run the app or game, a headset which secures a display in front of your eyes and some kind of input – head tracking, controllers, hand tracking, voice, on-device buttons or trackpads. A video is sent from the console or computer to headset via HDMI cable in case of headsets and for gears like Samsung and google the smartphone is fitted in the headset.

VR is used to affect and influence our experience.

1) It is used to create a new world and enhance the user’s experience of a game or entertainment through 3D virtual spaces.

2) It is used to enhance training for real life situations through simulation.

These 2 approaches segment VR into two different main categories, recreational or practical. VR can be used for gaming or other recreational activities purely to add fun to the experience. VR is also being used for practical training of employees or even for use as a design space for engineers. While the recreational side of VR drives the public’s interest, development of the technology relies heavily on more practical and monetizable applications of the technology.

_

Mixed reality:

Mixed Reality (sometimes called Hybrid Reality or MR) aims to combine the best aspects of both virtual reality and augmented reality. Mixed reality is the merging of real and virtual worlds to produce new environments and visualizations where physical and digital objects co-exist and interact in real time. Mixed reality takes place not only in the physical world or the virtual world, but is a mix of reality and virtual reality, encompassing both augmented reality and augmented virtuality via immersive technology.  In mixed reality environments, users seamlessly navigate through both the real and virtual environments at the same time. Instead of residing in an entirely virtual world (i.e. virtual reality), virtual objects are anchored into a user’s real world space and augment their real world environment, making virtual interactions appear to be “real.” These interactions mimic our natural behavior of interaction, such as objects getting bigger as you get closer and the changing of perspectives as you move around an object.

_

A hologram is an augmented reality device; it adds something into reality that wasn’t otherwise there. More specifically, AR is defined as an enhanced version of reality created through technology to incorporate more information into the physical world. Augmented reality is more than just holograms. Holographic headsets are a central theme to augmented reality (AR) today, but the recent AR in Action Conference demonstrated the diversity of the field and the potential to include many more technologies to augment humans.  The AR in Action Conference, held at the MIT Media Lab, expanded the definition of AR through a TED conference-like lens, delivering 70 diverse curated talks and 32 panels over two days to over 1,000 experts and practitioners in the field.  A liberal definition of AR focuses on the way data is presented to users and how they interact with it. The popular definition of the AR platform as a holographic projection system like the Hololens, Meta and ODG headsets limits what AR can be. The value of these holographic projection headsets is represented by surgical AR applications, and by enhanced 360-degree field of views that let the pilot look down, through his body, and the fuselage underfoot to see adversaries below.  AR can be visual, fitting the popular paradigm of holographic projections overlayed onto reality using a headset. But in its essence, it is the overlay of a data sources impacting human perception. It is not necessarily visual, but it could be sound or haptic perception of interactions with electromechanical stimulus, though this is still somewhat limiting to the definition of this emerging field.  AR can also change human perception of the surrounding space when a digitally augmented human interacts with a data source, such digitally enhanced senses or accumulated data from surrounding IoT infrastructure.  AR augments people’s cognitive capabilities and perceptions through their interconnecting data acquired from bio- sensors, worn sensors and the space around them.

_

My view:

Augmented reality is an enhanced version of reality created through technology by incorporating more information into the physical world to enhance one’s current perception of reality. Some authors label hologram as an augmented reality device because it adds something into reality that wasn’t otherwise there. In my view, hologram is three dimensional depiction of reality but it does not add anything to reality. Holographic projection system like the Hololens, Meta and ODG headsets are augmented reality platforms that superimpose data onto reality using a headset impacting human perception but they are not true holograms.

How do you differentiate between true real holograms and its lookalike?

Read next segment.

_______

_______

True real Hologram and its lookalike:

We seem to be fascinated by holograms or at least the promise of what they can do. Think the famous Princess Leia projection in Star Wars; holographic fashion shows in New York, Hamburg and Beijing; the massive success of synthetic pop star Hatsune Miku in Japan, or recent reports of holographic politicians in France. Technically, all of these are misrepresentations of holography – either special cinematic effects, video projections onto water and smoke, or a hi-tech version of an old Victorian stage trick called Pepper’s Ghost. Effects produced by lenticular printing, the Pepper’s Ghost illusion (or modern variants such as the Musion Eyeliner), tomography and volumetric displays are often confused with holograms.

_

First off, the words “holography,” “hologram,” and “holographic image” have very precisely defined meanings.

  • Holography is a technique, based on coherent (laser) light and interference, to record and view images, that, when presented properly, precisely recreate the three-dimensional visual appearance of recorded real objects that are no longer there.
  • A hologram is the imprint on a recording medium (such as photographic film) that is created during holographic recording. The hologram itself is not an image (it doesn’t look anything like the recorded objects), and it is not three-dimensional, either.
  • A holographic image is the three-dimensional image that is reconstructed by shining (coherent) light onto a hologram. Some sources, and pretty much everyone who is not a holography expert, refers to the holographic images as “holograms” as well, somewhat confusingly. Based on the strict definition, the hologram is not the floaty 3D thing, but the flat transparent plate behind it (or in front of it).

That’s all nice and precise, but when non-experts think about holograms, they don’t think about lasers and interference, i.e., about the technology that was used to record and view them, but about the experience, i.e., the fact that holograms, or, more precisely, holographic images, are apparently solid three-dimensional objects floating in thin air. In other words, the most remarkable thing about holograms is not how they’re made, but the illusion they create. And how do holographic images create the illusion of solid three-dimensional objects?  That has nothing to do with lasers and interference patterns, but with how the visual system in our brains sees the physical world.

When viewing close-by objects, there are six major depth cues that help us perceive three dimensions:

  1. Perspective foreshortening: farther away objects appear smaller
  2. Occlusion: nearer objects hide farther objects
  3. Binocular parallax / stereopsis: left and right eyes see different views of the same objects
  4. Monocular (motion) parallax: objects shift depending on how far away they are when head is moved
  5. Convergence: eyes cross when focusing on close objects
  6. Accommodation: eyes’ lenses change focus depending on objects’ distances

Reality covers all possible depth cues for unlimited numbers of viewers at the same time.  Real holographic viewing system (hologram plus proper illumination) also covers all six depth cues for any number of viewers. As it turns out, holographic images recreate all six of these cues (yes, even accommodation), perfectly fooling our brains into seeing things that aren’t really there. Based on this, wouldn’t it make sense to call display systems that are not based on lasers and interference, but create the same illusion, “holographic” as well, given that they quack like real holographic images? A large class of specific devices that have visual capabilities similar to true holograms are enumerated below with total depth cues 5 to 6:

List of lookalike holographic displays:

  • Volumetric displays: depth cues 1-6 for any number of viewers, but small display volume, and some have problems with cue 2 (occlusion).
  • Project Vermeer: depth cues 1-6 for any number of viewers, but small display volume/viewing angle.
  • CAVE: depth cues 1-5 for a single viewer. Requires eye wear.
  • Head-tracked 3D TV: same as CAVE, but smaller field of view.
  • zSpace and HP’s Zr Virtual Reality Display (which appears functionally identical): same as head-tracked 3D TV, but smaller field of view.
  • Head-tracked auto-stereoscopic display: covers depth cues 1-5 for a single viewer, does not require head gear.
  • Oculus Rift DK2: depth cues 1-5 for a single viewer. Obviously requires pretty involved head gear.
  • CastAR: depth cues 1-5 for a single viewer, and multiple viewers can potentially see the same virtual objects in the same place when wearing their own headsets.
  • Magic Leap and HoloLens: if these really work as implied by marketing, they will cover at least depth cues 1-5, maybe even 6.
  • Near-eye light field display: depth cues 1-3 and 5-6, and cue 4 if combined with some positional head tracking mechanism.
  • Holovision: covers depth cues 1-6 for any number of viewers, but the only virtual object it can show is a flat display screen plus whatever 2D image happens to be on that screen.
  • Multi-zone auto-stereoscopic display: provides only a crude approximation of depth cue 4, but can be viewed by more than one person at a time. It’s a borderline holographic case as severe parallax artifacts break the illusion of solid objects.

_

Real holographic display:

Light propagates in space in the form of waves – similar to waves visible on a water surface. Laser light has the special property of being coherent. That means light waves from a laser have a fixed wavelength (for instance red only) and also a fixed relation of their phases, so all waves propagate in sync. With 3 lasers in red, green and blue, one can generate all other colors. If several coherent light waves meet at a certain position in space they interfere: that means their amplitudes can either sum up to a larger value (constructive interference) or cancel out each other to a smaller or even 0 value (destructive interference). Coherent light from lasers differs in this regard from incoherent light sources (e.g. your incandescent light bulb or a LED) where the intensities can also sum up to larger values but never cancel each other out. In a holographic display, which is illuminated by a laser, each pixel of the display sends out light waves – the phase of the light wave is modulated by driving the display. Changing the phase basically is a defined delay of light from one pixel compared to other pixels. One can do this for instance with a suitable LCD. By choosing certain phase values for neighboring pixels then, similar to focusing light with a lens, light waves from these pixels can be made to interfere constructively at certain positions in space. At those positions light from all those pixels sums up in order to generate a bright point in space – a 3D pixel if you like. The 3D space seen from an observer position towards the holographic display and beyond can be completely filled with 3D pixels at any depth position in front or behind the physical display screen, all in the same high resolution you know from HDTV. So different from other types of displays that generate flat images on the screen, for holography it is possible to really generate 3D points in space, each with its own color and brightness. Regular flat panel displays generate flat 2D images. Stereo 3D does the same but with individual images for each eye (each gets its own perspective) – but the flat images differ from what one is used from seeing in real life. Real objects are not on a flat surface. They are anywhere in space – some very close, some far away. So real 3D provides additional visual information to the brain, like eye focus or motion parallax. The deeper the 3D, the more sensitive people get to the missing visual information of Stereo 3D. This may show in eye fatigue or even headaches, or one simply cannot fuse the two views and sees double images. The fact that holographic 3D generates the same visual information as a real environment is the key motivator for realizing holographic displays. Once it’s perfectly done, one cannot distinguish between a real object and a holographically reconstructed virtual object.

_

There are important differences between holographic displays of lookalike holograms and real holographic display. Most currently-existing holographic displays don’t provide for proper accommodation, leading to accommodation/ vergence conflict and decoupling, only work for a single viewer, and require some headgear (though, granted, for a large percentage of the population, even reality requires glasses to view). There is popular misconception that holographic images are free-standing. A CAVE, for example, requires several large display screens to prop up the illusion of virtual objects. Even real holographic images need something behind them, namely hologram plates. In a CAVE or head-tracked 3D TV, virtual objects are cut off the moment they leave the pyramid-shaped volume between the viewer’s eyes and the screen(s), and the exact same thing is true for real holograms. If you want a life-size holographic image, you need an at least life-size hologram plate. Holographic projectors, like those familiar from science fiction (“Help me, Obi-Wan Kenobi”), are just that — science fiction.

_

Non-holographic displays with few depth cues (fake holograms):

  • Oculus Rift DK1: misses depth cue 4 due to lack of positional head tracking.
  • GearVR: same as Oculus Rift DK1.
  • 3D TV: no depth cue 4
  • Desktop 3D monitor: same as 3D TV.
  • Head-tracked desktop 2D monitor (TrackIR or similar): has depth cue 4, but misses 3 and 5.
  • Two-zone auto-stereoscopic display: misses depth cue 4.
  • Tupac Shakur at Coachella: just 2D video back-projected onto a transparent screen. Misses depth cues 3, 4, and 5, looks completely flat from the side.
  • Will.I.Am on CNN: just green-screen compositing between synchronized cameras. Was completely invisible to Anderson Cooper on-stage, and missed depth cues 3, 4, and 5 when viewed via regular TV.

______

Note:

We have true holograms (real holograms), lookalike holograms (e.g. volumetric display, hololens) and fake holograms (e.g. Tupac) depending on technology and visual depth cues offered by them to create illusion of three dimensional images.

____

Hololens:

HoloLens doesn’t create holograms by itself. The so-called holograms are actually 3D objects made entirely out of light. By using Microsoft’s special goggles, these virtual 3D objects are projected onto our field of vision. Microsoft introduced Windows Holographic, which, when paired with the company’s HoloLens augmented reality headset, will allow users to see and interact with 3D images. With all forms of immersive virtuality (iV) – including augmented, mixed and virtual reality – finding applications in a wide variety of settings, companies worldwide are developing holographic displays that could fundamentally change how humans work, learn and interact. HoloLens leverages mixed reality, so users see holograms pinned to specific physical locations or objects in their surrounding environment. They can also interact with holograms using voice and hand gestures, as they would with real objects. HoloLens has many exciting use cases. Cleveland Clinic, for instance, will use HoloLens to teach anatomy at their joint Health Education Campus when it opens in Cleveland, Ohio, in mid-2019.  With HoloLens, the students and the professor can all look at the same holographic image of the body and, at the same time, still see each other, even if the professor is in a different city.  In terms of the hologram itself, students can see an organ in three dimensions, from all sides, and all of the shapes and pathways inside it. In addition, the faculty member can present different conditions – for example, a tumor inside the brain, or fluid in a lung or a blocked artery leading to the heart. The NASA Jet Propulsion Laboratory (JPL) in Pasadena, California, has collaborated with Microsoft to develop several HoloLens-based applications. ProtoSpace, for example, enables engineers to design space equipment using full-scale holographic visualizations rather than computer-aided designs. With Sidekick, astronauts on the International Space Station can access a “holographic instruction manual” and work in tandem with experts on Earth when completing complex tasks. A third project, OnSight, enables Earth-based scientists to virtually walk around and explore Mars using images and data taken by the Curiosity Mars Rover. Studies show dramatic improvements in scientists’ understanding of a scene and spacecraft design when they view it via a head-mounted display instead of a computer screen. Feedback has been very positive because holographic visualizations engage humans’ innate ability to explore, allowing them to investigate Mars in a similar way to Earth.

____

DAQRI hologram:

The holograms we use today are very different from the holograms of science fiction. You might find a hologram on your passport or your driving licence, but not as an ethereal, moving representation. At the moment, innovative display includes headsets, smart glasses and other wearables powered by Virtual and Augmented Reality.  Without a VR or AR headset, the sci-fi concept of a hologram doesn’t exist… Yet. As advanced as they may be, these devices are just a step towards integrated displays that don’t rely on physical enablers. That is where AR developer DAQRI comes in. The company has devised a new concept called ‘Software Defined Light’, which alters the properties of light via an algorithm. By creating the right conditions, DAQRI has slowed the speed of light to a point where it can be harnessed and manipulated. In other words, they have created a functioning hologram or rather, millions of them. But what can you use them for, and how will they change the way we see the world around us? Simply put, a hologram is a 3D image formed by photographic projection. DAQRI’s holograms are quite different from the stamp in your passport because they react to environments via sensors and algorithms. Their flagship product is a Sat-Nav-like display called HUD (head-up display), which does exactly what it says on the tin. The projections will eventually replace the need for navigation devices by overlaying route info onto the road.

______

Hologram table:

Australian company Euclideon has created the first real multi-user hologram table in the world, and it’s going to change gaming, business, and so much more. This new tech solves previous problems with holographic images using motion-tracking glasses.

Wearing only a small pair of glasses, up to four people can interact with the table’s holographic images and each other, making this a major advancement from the experience provided by current AR technology. The company estimates that in 2018, the table will be up for sale for $60,000 Australian. The concept of the hologram table in film and science fiction is hardly new, but because of the many technical difficulties inherent to executing the concept, the idea has yet to be realized. This difficulty originates from the fact that holograms are computer-generated stereo images, dependent on the perspective of the viewer. When a group of people in different positions look at a hologram, the illusion “breaks” as they don’t get the same perspective on it and it doesn’t change as they move. Computer-generated holograms work by tracking the viewer — but which viewer does the computer track when there’s more than one? Euclideon’s table requires that users wear only a small, light pair of motion-trackable glasses, which look and feel a lot like 3D glasses. These are much more practical for meetings and social events than huge VR/AR helmets, not to mention more comfortable. As users wear the glasses, the table tracks their eye positions, building a custom image for a potential total of eight user eyes. The table itself is a screen, and the device is made up of projectors that rest beneath a unique film which is sandwiched between two pieces of glass. The result is a mass of mixed up, colored images that the glasses separate out for users, enabling them to see binocular stereo holograms specific to their location. The glasses themselves have special crystal film layers over them, which can change the frequencies of light waves. When users wear the glasses, the computer can tell which light waves belong to which users. The glasses have small boxes at the temples which contain tiny microcomputers and microchips similar to the VR headset’s tracking jiggers, signalling the user’s position to the table.

______

______

Fake holograms:

Pepper’s ghost illusion:

Other methods of projecting and reflecting images are often described as holographic – or even misleadingly holograms, because they have an optical presence and spatial quality. For example the Pepper’s ghost technique, which uses a partially reflective surface to mix a reflection with the scene beyond. John Henry Pepper demonstrated the technique in the 1860s with it being used to overlay visual elements (often a figure – ‘ghost’) onto a physical set or stage.

Despite what your eyes might lead you to believe, most of the “holograms” you’ve seen rely on optical illusions instead of real holographic technology. Figure above shows Pepper’s ghost with a 2D video.  The video image displayed on the floor is reflected in an angled sheet of glass. The Pepper’s ghost technique, being the easiest to implement of these methods, is most prevalent in 3D displays that claim to be (or are referred to as) “holographic”. For example, the “hologram” of Tupac that appeared at Coachella in 2012 was just a two-dimensional image projection. It relied on a 19th century optical illusion called Pepper’s Ghost that makes use of glass mirrors and a bit of stage magic. While the original illusion, used in theater, involved actual physical objects and persons, located offstage, modern variants replace the source object with a digital screen, which displays imagery generated with 3D computer graphics to provide the necessary depth cues. The reflection, which seems to float mid-air, is still flat, however, thus less realistic than if an actual 3D object was being reflected. Examples of this digital version of Pepper’s ghost illusion include the Gorillaz performances in the 2005 MTV Europe Music Awards and the 48th Grammy Awards.

_

When 23rd French presidential election approached, candidates were predictably stumping to bring voters out, but far-left candidate Jean-Luc Mélenchon had the most effective strategy: using an optical illusion, he beamed “holograms” of himself to six cities around the country. As Le Parisien reports, Mélenchon, who is often compared to Bernie Sanders, uses a technique known as Pepper’s Ghost (and not technically a hologram) to broadcast a 2-D version of himself. From Dijon, he simultaneously appeared in seven places at once yesterday. In 2014, over a five week period, now Indian Prime Minister Narendra Modi, delivered a series of campaign speeches across all of India reaching up to 126 sites simultaneously. His political exposure was unrivalled by using our newest designed mobile platforms, enabling his message to reach millions. Modi and his campaign staff use “Pepper’s Ghost” technology. One use of Pepper’s Ghost is to simply project imagery onto reflective glass in order to achieve the perception of a hologram (under the right viewing and lighting conditions). This is exactly what was done by Modi’s campaign during the 2012 and 2014 elections, allowing him to be “transported” to hundreds of locations simultaneously. The company behind the hologram campaign is Musion, the same outfit that startlingly “resurrected” Tupac Shakur during a simulated concert at the Coachella Valley Music and Arts Festival in 2012. The Musion website says the illusion requires 400 satellite dishes; 1,300 lights; 500 audio speakers; 200 sound mixers and power amps; and 14,000 meters of speaker and power cables to create the effect.  Most of the technologies calling themselves “holographic” do not produce actual holograms—including the specters of Vargas Llosa, Kimmel, Modi, Tupac, and MJ, which are created via computer-generated images and high-definition video projection.  An even simpler illusion can be created by rear-projecting realistic images into semi-transparent screens. The rear projection is necessary because otherwise the semi-transparency of the screen would allow the background to be illuminated by the projection, which would break the illusion. Crypton Future Media, a music software company that produced Hatsune Miku, one of many Vocaloid singing synthesizer applications, has produced concerts that have Miku, along with other Crypton Vocaloids, performing on stage as “holographic” characters. These concerts use rear projection onto a semi-transparent DILAD screen to achieve its “holographic” effect.

__

3D holographic projection:

Holographic projection is a 3-D technology where audiences can view 3-D virtual figures without wearing glasses. The technology is at present mainly used in museums and entertainment stages. There are two basic types of 3D: stereoscopic, which requires glasses, and auto-stereoscopic, which doesn’t, but requires a 3D TV screen. Both are shot using special camera lenses, and with the help of the required hardware, create the desired 3D effect. Holograms are created not in the filming, but in the projection. By using the correct projectors, angles and surfaces (there’s a lot of math involved here), an image can be made to appear almost as real. There are also ways to create the hologram look without creating true holograms, via rear projection onto die-cut acrylic material or clear surfaces, but that cuts down the effective field of view. The uses of 3D holographic projections include mass publicity, product launch, keynote presentation, education, live events and onstage performances.  High definition, 3D photographic projection & three dimensional life-size illusions all are brought together to bring your brand alive. This illusion can be either of a person or product, which can be enabled to move and interact with the audience. This technology can be used to craft real time projections for live presentations, live stage performance and for teleconferences which are conducted all across the globe or country.

How 3D holographic projection works?

It is known as ”Musion Eyeliner’‘. It is based on an illusionary technique called Pepper’s Ghost. It has unique Hi Definition 3D Projection Technology where image is captured in 3 dimensional aspect with a Special Hi Definition Camera on a specially built stage projected at various distant locations. It starts with the patented foil, completely invisible to the naked eye, right at 45° across the stage. Holographic display is based on a Spatial Light Modulator, a setup for Musion Eyeliner and viewed without wearing any kind of 3D glasses. These 3D holographic projections are not real holographic projections.

__

Tupac:

The famous appearance of the deceased rapper Tupac Shakur at the 2012 Coachella music festival was a 3D projection, but not an actual hologram. Tupac Shakur was killed more than 15 years ago — three years before the first Coachella Valley Music & Arts festival was held. But thanks to a trick of light, he’s probably the single most talked about musician who performed at 2012 festival.  The image looked shockingly good, but how did it work? There’s an overhead projector that sort of reflects down onto basically a tilted piece of glass that’s sort of on the stage floor. That then reflects onto a screen, and it projects in this sort of 3D kind of thing where it allows the other performers to sort of walk in front of Tupac and basically interact [with] him.

_______

No-logram:

Almost all modern attempts to simulate the effect of an actual three-dimensional object made purely out of light are merely tricks that make your eyes and brain think you’re seeing something you’re really not, and most of them aren’t really all that convincing. This new technique, developed by a French artist named Joanie Lemercier, uses two dimensional projections paired with a motion sensor to make the image appear to be fully 3D. Lemercier calls it the “no-logram.” It works without glasses, using a motion camera to detect where the viewer is in the space and adjust the projection in real time to match their perspective. The result is an extremely convincing image that looks like it has depth and volume despite being completely flat. Unfortunately, due to the nature of the motion tracking and the projection itself, the image can only display correctly for one viewer at a time. Lemercier hopes so solve that in the future by developing a system that uses water particles and pressurized gas to create something that actually has three dimensional depth that the “no-logram” can only simulate.

____

Hologram box:

A hologram box creates a space for interactive, holographic illusions. Essentially, a hologram box is a little box that can be peered into from all sides. Hologram boxes use the latest film technology – holographic technology – to show moving objects, or holograms. Unlike films on a normal monitor, which remain two-dimensional, and 3D films, for which 3D or virtual reality glasses are needed, a three-dimensional hologram can be seen immediately by all observers and from all sides. The hologram box is a continuation of an illusion technique from the 19th century. “Pepper’s Ghost” used mirrors and special lighting to make objects appear and disappear, as if by magic. The hologram box uses a projector to display holograms. There is a glass pyramid inside the hologram box. The projector at the top of the hologram box projects the content on to this. The light is dispersed pyramidally, with the projected objects appearing three-dimensional. The result is a spatial, digital world created within the pyramid, which can even be interacted with. Other terms for projectors which show holograms include holographic displays and holographic pyramids. Holograms are a great way of drawing attention. Therefore, hologram boxes can be used wherever attention should be focused on something in particular. Ideal venues include trade fairs, events, museums, exhibitions, showrooms and stores. With the possibility of controlling and interacting with the content using, e.g. hand movements, observers can also be involved in the product presentation. However, holograms can also be combined with real objects. For example, premium products such as jewellery can be displayed in a virtual shower of gold to highlight their quality. At the same time, useful products can be displayed in everyday use. For example, the effects of various weather conditions on a waterproof jacket can be shown. 3D holograms are also flexible in terms of size – mini-holograms are as achievable as life-sized projections. There are practically no limits to the possibilities.

_____

Specular holography:

The trick is to control the curvature of the reflecting surface so that all sightlines through glints meet at a point somewhere off the surface in 3D space: Since your eyes always see a glint when looking at that point, your brain decides that the light is coming from the 3D point itself.  To make the 3D illusion work for many viewpoints without distortion, each mirror has to have a unique doubly-curved shape. A typical specular hologram has 10,000-1,000,000 of these optics, all multiplexed into a host 2D surface. Each optic is uniquely shaped to keep a perceived 3D point steady (or moving predictably) as the viewpoint or light or hologram moves. The shape depends on the point, its motion, and the curvature of the host surface. Shaping and multiplexing the optical surfaces is essentially a big math problem that mixes differential geometry and combinatorial optimization.

______

How to turn your smartphone into a 3D hologram projector:

Imagine a prism (Pyramid) with the top chopped off; what you get is a plateau prism. We are trying to create something exactly like that as seen in the figure below.

The way it works is deceptively simple. The CD case provides just enough reflection to bounce the light from the image shown on the screen. Because the plastic is transparent, you can also see straight through it, creating the illusion that the reflected object is hovering in mid-air. Because the video plays on all sides of the reflector, it can be viewed from any angle in the room, further adding to the illusion of a physical object being projected.  You’ll need to find an old plastic CD case and a sharp knife or glass cutter to build the sides of your holographic projector.

_

The hologram pyramid is a simple device that can be made by manipulating a sheet of plastic into the shape of a pyramid with its top cut off. The device creates a 3D like illusion for the viewer and makes an image or video appear as if it were in mid-air. It works on the principle of Pepper’s Ghost. Four symmetrically opposite variations of the same image are projected on to the four faces of the pyramid. By principle, each side projects the image falling on it, to the centre of the pyramid. These projections work in unison to form a whole figure which creates a 3D illusion. There’s really nothing strange going on there, it’s simply light from a source, in this case the smartphone’s screen, being reflected on 4 sides of a reflective material, the angles of the sides are only to assure that the entire image is reflected. For instance if the angles of the pyramid were close to 90°, most of the light you want to project wouldn’t even go through the reflective material and if it were close to 0°, most light you would be able to see would be transmitted through the material and you wouldn’t see any effect whatsoever. The three-dimensionality effects are only the result of your brain seeing four different perspectives of the same object being projected in different sides of the pyramid and interpreting that information as a 3D object. It is merely a matter of human perception. Light is only being reflected. When you build the transparent, upside-down pyramid, you are actually building four mirrors, that will show a reflection from the screen, placed as if the object was floating in the center of the pyramid.  When you move to see the next face of the pyramid, you will see the next image – again placed in the center. So it gives the illusion of a three dimensional display that you can move around.

_

Figure below shows smartphone turning into a 3D hologram projector:

_____

3D hologram:

Real hologram is 3D image on 2D surface. Then what is 3D hologram? A 3D hologram is defined as a 3D projection that exists freely in space and is visible to everyone without the need for 3D glasses as seen in the figure above. A 3D hologram displays products, objects, and animated sequences three-dimensionally and enables seemingly real objects or animations to appear to float completely freely in space. Unlike a conventional film on a standard screen, a 3D hologram is visible from all sides, which means the observer can walk around the hologram, enabling an absolutely realistic-looking image to form. A particularly interesting point – unlike 3D television or Virtual Reality, a 3D hologram can be seen by everyone without 3D glasses, which is an incredible advantage for use at trade fairs, exhibitions, and similar events. This method of using 3D holograms opens up a completely new, revolutionary way of presenting products. The products are displayed in a high-quality, exclusive and innovative way and the needs of the corresponding target groups are precisely taken into account at the same time. It is also recommendable to use an acoustic backdrop perfectly coordinated to suit the 3D hologram, including background sound and special sound effects. It lengthens the attention span and sub-consciously embeds the product being presented even more deeply in the minds of the audience.

_

To display a 3D hologram, three things are usually required:

  1. A hologram projector (also known as a holography pyramid), which makes the holographic 3D projection possible.
  2. A 3D hologram that is projected straight into the room and displays the content.
  3. A real object or product that is displayed by the hologram.

_

3D holograms make it possible to display products in a fully unique way. For instance, a hologram can be used to create a visually appealing and stylistically perfectly coordinated environment that precisely matches the product. A backdrop of virtual golden rain is an ideal way of displaying precious jewellery such as watches or colliers; it can cause rain or snow to fall on an all-weather tire, or the sun to shine on it; industrial machines can be created live as if by magic before the very eyes of the audience – the possibilities are endless and there are visualization options to suit every product. No other technology manages to similarly present the advantages of a product like 3D holograms. Observers feel that they are being directly and emotionally appealed to and the incomparable display draws them to the products being presented.

______

2D/3D Hologram (discussed vide supra):

These are by far the most common type of hologram – and in fact they are not holograms in any true sense of the words. The term “hologram” has taken on a secondary meaning due to the widespread use of a multilayer image on credit cards and driver licenses.

Tilt this banknote hologram and you can see the picture change. Tilt it one way and you can see the number 10 (it’s a British £10 note); tilt it the other way and you can see the image of a mermaid.

_

2D/3D Hologram is made up of multiple two dimensional layers with hologram images visually placed one behind another with visual depth to produce an effect of three-dimensional hologram structure. It has very good visual depth between different layers and shininess on first layer. Most existed hologram stickers in the market are made by 2D/3D because this technology has been widely used for more than 20 year and yield very good security features and good result. To achieve good 3D effect, we can make some design with very good depth in background or floating.

_

2D hologram:

2D design has one layer hologram image on surface which is made up of one layer two dimensional images. The images are assigned different colors and position in one layer. It just has only one layer, without visual hologram depth as 2D/3D hologram. But 2D hologram text and image can be very shining, colourful.  2D hologram has the highest brightness and sharpness in colorful text and logo.

______

______

Computer generated hologram (CGH):

Holography was born as an analog technology, and the development of laser holography by Emmett Leith and Juris Upatnieks drew heavily from Leith’s earlier work on optical signal processing, a form of analog computing. Holograms were long recorded on special photographic emulsions applied as coatings to glass plates or film. The idea of computer generation of holograms dates back to 1966, but that technology long was limited by practical issues of computing capacity, and early computer-generated holograms often were recorded on photographic media. Now a new generation of digital technology has replaced photographic media for recording holograms, and has created new options for processing and displaying holographic images. As in photography, the digital approach offers important advantages, including real-time response, and convenient processing and storage. Applications include 3D microscopy, displays, and video or “telepresence.”

_

Computer engineers can describe all of the interactions between the object and reference beams, as well as the shapes of the interference fringes, using mathematical equations. The mathematics of holography is now well understood. Essentially, there are three basic elements in holography: the light source, the hologram, and the image. If any two of the elements are predetermined, the third can be computed. For example, if we know that we have a parallel beam of light of certain wavelength and we have a “double-slit” system (a simple “ hologram”), we can calculate the diffraction pattern. Also, knowing the diffraction pattern and the details of the double-slit system, we can calculate the wavelength of the light. Therefore, we can dream up any pattern we want to see. After we decide what wavelength we will use for observation, the hologram can be designed by a computer. “Computer-generated holograms,” “synthetic holograms,” and “computer holograms” are terms used to refer to a class of holograms that are produced as graphical output from a digital computer. Now it is possible to program a computer to print a pattern onto a holographic plate, creating a hologram of an object that doesn’t actually exist. This computer-generated holography (CGH) has become a sub-branch that is growing rapidly. For example, CGH is used to make holographic optical elements (HOE) for scanning, splitting, focusing, and, in general, controlling laser light in many optical devices such as a common CD player. The computer-generated holograms have their greatest potential in the area of interferometry. They have been shown to be useful in supplementing existing methods of optical testing. Laser beam scanning is another promising area for computer-generated holograms. Holographic grating scanners are in many ways better than other mechanical mirror scanners.

_

Computer generated holography: 3D imaging of virtual and real objects:

In classical holography, light waves from a real object are recorded on light-sensitive films by interference with reference waves. Object waves are reconstructed by diffraction of the interference fringes after chemical processing of the films. Thus, classical holography requires a real object to create its 3D holographic image. It is, therefore, impossible to create holograms of virtual 3D scene such as provided by modern computer graphic and edit the 3D scene after recording the interference fringes. An interference fringe is just a 2D image, and the reference wave can be expressed by a simple theoretical framework. In principle, therefore, we could easily produce the fringe pattern by numerical simulations of optical interference if we could obtain numerical data of the object waves from the 3D scene. However, calculating object waves from virtual 3D scenes is very hard work, even for modern computers. It sometimes takes several hundreds of hours or days to calculate object waves by conventional methods. Capturing light waves from real objects is also not easy, because the resolution and sizes of currently available image sensors do not meet the requirements for computer holography. Researchers have developed a novel computer algorithms that enables synthesis of holograms of completely virtual, computer-generated 3D scenes in only several tens of hours. In addition, they developed a technique to capture light waves from real objects at high resolution and over a wide area to meet computer-holography conditions. This enables digitization of the entire process of classical holography. The resulting computer holograms give viewers a strong sensation of depth that has never been achieved with conventional 3D images.

_

Computer-generated holography is an emerging technology, made possible by increasingly powerful computers, that avoids the interferometric recording step in conventional hologram formation. Instead, as figure below shows, a computer calculates a holographic fringe pattern that it then uses to set the optical properties of a spatial light modulator, such as a liquid crystal microdisplay. The SLM then diffracts the readout light wave, in a manner similar to a standard hologram, to yield the desired optical wavefront.

_

Computer Generated Holograms have been around for a few decades now, and the devices necessary to generate them dynamically (Spatial Light Modulators) have also been around for quite some time – you will know them as LCDs. Now you can get a holographic image out of a low resolution LCD, but lower the resolution  greater the error in your final image, and this generally manifests as random noise in the generated holographic image. This means that greater the number of pixels you can use to generate your CGH pattern the better, because it will result in a more noise-free and accurate final reproduction. The other factor that affects final image fidelity is the mode that is used to modulate the light that illuminates the SLM. Light can be modulated in amplitude, phase, or both by an SLM. Modulating amplitude or phase alone will get you an image, but a noisier one. What most people don’t know is that LCDs can modulate the phase or the amplitude of light, even though we normally see them in displays where they are being used to modulate amplitude (to vary the brightness of a pixel). To modulate the phase, you just remove one of the polarizers! If you’re really smart, you can figure out how to modulate phase and amplitude simultaneously with an LCD in a maximally error-free way to get the best image you can possibly get with the least amount of noise.

_

Digital holographic image processing:

_

Computer Generated Holography (CGH) is the method of digitally generating holographic interference patterns. A holographic image can be generated e.g. by digitally computing a holographic interference pattern and printing it onto a mask or film for subsequent illumination by suitable coherent light source. Computer-generated holography used computers to calculate the interference pattern that a virtual object would produce. That computer-generated hologram was then printed, often on photographic media, and illuminated with a reference beam that produced a 3D image of the virtual object. Alternatively, the holographic image can be brought to life by a holographic 3D display (a display which operates on the basis of interference of coherent light), bypassing the need of having to fabricate a “hardcopy” of the holographic interference pattern each time. Consequently, in recent times the term “computer generated holography” is increasingly being used to denote the whole process chain of synthetically preparing holographic light wavefronts suitable for observation.

_

Computer generated holograms have the advantage that the objects which one wants to show do not have to possess any physical reality at all (completely synthetic hologram generation). On the other hand, if holographic data of existing objects is generated optically, but digitally recorded and processed (digital holography), and brought to display subsequently, this is termed CGH as well. Ultimately, computer generated holography might serve all the roles of current computer generated imagery: holographic computer displays for a wide range of applications from CAD to gaming, holographic video and TV programs, automotive and communication applications (cell phone displays) and many more.

_

Compared to conventional holographic approaches, CGH

  • does not rely on the availability of specialized holographic recording materials;
  • can synthesize optical wavefronts without having to record a physical manifestation of them—for example, it can generate 3D images of nonexistent objects; and
  • offers unprecedented wavefront control by making it easy to store, manipulate, transmit, and replicate holographic data.

Although CGH-based display systems can be built today, their high cost makes them impractical for many applications. However, as compute power and optical hardware costs decrease, CGH displays will become a viable alternative in the near future. CGH provides flexible control of light, making it suitable for a wide range of display types, including 2D, stereoscopic, autostereoscopic, volumetric, and true 3D imaging. CGH-based display technology can produce systems with unique characteristics impossible to achieve with conventional approaches.

______

______

Digital holography:

According to Huang digital holography (DH) is “the computer generation and reconstruction of holograms”. However, in the last decades the term “digital holography” was generally used in a less rigorous way, describing only parts of the holographic chain from hologram generation to the reconstruction of the wave fields. Optical holography is a two-step process: (1) the interferometric recording of a wavefield in a hologram and (2) the reconstruction of the wavefield stored in the hologram by diffraction. In digital holography, the hologram recording step is performed synthetically supported by digital computer means, and the reconstruction step remains the same as in optical holography. Digital holography is a subtype of CGH. By replacing the photochemical procedures of conventional holography with electronic imaging, a door opens to a wide range of new capabilities. Although many of the remarkable properties of holography have been known for decades, their practical applications have been constrained because of the cumbersome procedures and stringent requirements on equipment. A real-time process is not feasible, except for photorefractives and other special materials and effects. In digital holography, the holographic interference pattern is optically generated by superposition of object and reference beams, which is digitally sampled by a charge-coupled device (CCD) camera and transferred to a computer as an array of numbers. The propagation of optical fields is completely and accurately described by diffraction theory, which allows numerical reconstruction of the image as an array of complex numbers representing the amplitude and phase of the optical field. Digital holography offers a number of significant advantages, such as the ability to acquire holograms rapidly, availability of complete amplitude and phase information of the optical field, and versatility of the interferometric and image processing techniques. Indeed, digital holography by numerical diffraction of optical fields allows imaging and image processing techniques that are difficult or not feasible in real-space holography. Digital imaging and display technology opens new possibilities for holography. Digital holographic microscopes can display 3D images of living cells in real time on computers, and digital holographic telepresence is emerging on the technological horizon.

_

Digital holography replaces the analog photographic film or plate used to record early holograms with a digital detector array that records the hologram, as shown for off-axis holography in figure below. The resulting digital version of the hologram then goes to a computer for further processing.

_

One possibility is using the computer to extract phase and intensity data from the digitized hologram and further process that data to create a 3D digital model of the original object viewable on a computer display.

_

Digital hologram display:

A digitally recorded hologram also can be reconstructed by displaying it on a spatial light modulator (SLM) or photorefractive medium and illuminating it with a reference beam. Diffraction of the input light by the displayed hologram produces a 3-D image, as shown in figure below:

Images can be recorded and displayed singly, as fixed images, or in sequence to produce holographic videos, movies, or telepresence.

____

Pixel, Voxel and Hogel (hoxel):

Holography permits a light field, which generally results from a light source scattered off objects, to be recorded and later reconstructed when the original light field and original object is no longer present.  Digital holograms are made up of holographic elements (hogels) rather than pixels. In contrast to normal pixels used in photography, hogels contain 3D information from multiple perspectives. Hogel means holographic pixel (hoxel) which is 3 dimensional pixel containing or generating part of holographic image. Most 2D display screens produce pixels that are points emitting light of a particular color and brightness. They never take on a different brightness or color hue no matter how or from where they are viewed. This omnidirectional emission behavior prevents 2D display screens from producing a true 3D sensation. The profound insight offered by plenoptic function and light field theories reveals that picture components that form 3D display images, often called voxels (volumetric picture elements) or hogels (holographic picture elements) must be directional emitters—they appear to emit directionally varying light. Directional emitters include not only self-illuminating directional light sources, but also points on surfaces that reflect, refract, or transmit light from other sources. The emission of these points is dependent on their surrounding environment. Voxel was the name originally coined for a three-dimensional (or volume) pixel. Just as “pixel” stands for “picture element”, a “voxel” is a “volume element” — the basic building block of a 3D display.  Voxel and hogel are not same thing. A Voxel is a volumetric pixel: it says that this volume of space is this colour (or whatever). A hogel is different from a voxel in that it contains information that is specific to displaying it in a hologram. In particular diffraction patterns that holograms are composed of. This eases the computational burden of working out the diffraction fringe pattern you need in order to display it.  A Hogel is more like a big pile of sprites: it says what this point looks like from these angles. A hogel is a part of a light-field hologram, in particular a computer-generated one. In contrast to 2D pixels, hogels contain the direction and intensity of light rays from many perspectives, and is in essence what is referred to as a micro-image in plenoptic imaging terms.

HPU:

The Hogel processing unit (HPU) is a highly parallel homogeneous computation device dedicated to rendering hogels for a holographic light-field display and encompasses the 3D scene conversion into hogels, the 2D post processing filters on hogels for spatial and color corrections and framebuffer management tasks. Hogels are similar to a sub-aperture image in a plenoptic radiance image, in that a hogel represents both the direction and intensity of light within a frustum from a given point on the light-field display plane. The resulting projected light-field is full parallax, allowing the viewer a perspective correct visualization within the light-field display view volume. The HPU is separated from the host CPU (or GPU) by an expandable, interconnect framework and provides many views (hogels) into a scene per scene frame. The HPU is physically located in close proximity to the photonic modulation layer of a light-field display and has direct write access to the modulation driver back-buffers. This reduces the complexity of an HPU interconnect framework and allows the HPU processing pipeline to be as short and efficient as possible. Synthetic light-field rays are typically rendered as part of a hogel (2D array of rays/RGB pixels) using double-frustum rasterization or ray-tracing/ray-casting algorithms. These hogel rendering algorithms are greatly accelerated by the use of off-the-shelf (OTS) GPUs, however, there exists a substantial gap between real-time light-field rendering needs in terms of frame-rate, power and form factor requirements and modern GPU capability. The computed hogel light-field display requires as input a streaming 3D scene and a modelled/virtual display plane for visualization. The light-field display plane is a 2D array of microlens; hogels are computed at the center of every lens from the perspective of a virtual display plane in model space. 3D operations such as pan, scale, zoom, tilt and rotate are accomplished by transforming the virtual display plane through model space. For every light-field display update, every hogel must be updated or rendered. Therefore, if a light-field display had an array of 600 × 600 hogels, then the HPUs would have to compute 360,000 hogels per update. If each hogel had a directional/angular resolution of 512×512 rays/pixels, then the HPU array would be generating 94,371,840,000 pixels (283,115,520,00 bytes) per update. At 30 display updates per second (DPS), this equates to 2,831,155,200,000 unique pixels every second for dynamic scenes.

_____

Digital hologram:

The scientific definition of holography is image creation using the physical principles of diffraction. Most of us are familiar with the notion of reflections off a mirror and the refraction or bending of light in water. Diffraction occurs when light scatters from structures that are the same size or smaller than the light.  Diffraction can reproduce both refraction and reflection effects, making it a powerful optical phenomenon.

Digital hologram technology is constantly improving where state of the art machines have holopixels a quarter of a millimetre wide, making it possible to create photo-realistic digital holograms. As we can control each ray of light emitted from the surface of the hologram, it’s possible to include some limited animation within the hologram so we can view different images from different angles as seen in the figure above. The holograms produced in this manner are high-quality, full-colour reflection holograms, and it is even possible to produce digital holograms that can lie flat, allowing the viewer to walk 360 degrees around the image. In principle, it is possible to create a digital hologram from any kind of 3D dataset. This could be a medical scan, a simulation, an engineering design or a computer graphics model.  For replay (viewing), digital holograms behave just like any other reflection hologram, only requiring a bright lamp for illumination to bring out the 3D image. Current applications of digital holograms include military terrain visualization, medical imaging (figure above), scientific data presentation and architecture. They are used for education and training; often presented at universities, conferences, trade shows, museums and science festivals. Although current holoprinters are somewhat bulky and expensive devices with large and powerful lasers, portable machines are on the horizon. There is every reason to expect desktop-sized holoprinters no larger than a typical laser printer within the next few years.

_____

Advantages of digital holography:

Compared to a conventional optical holography, digital holograms have many advantages. These are as follows:

  • Digital holograms have strong anti-disturb property.
  • They are easy to be modified.
  • They are difficult to be imitated.
  • By using the pixel holograph and embossment, hologram films can be fabricated by transforming digital holograms. This can make digital hologram anti-counterfeiting identifiers.
  • Digital holography uses holographic printers, exposing the photosensitive emulsion with computer generated images. This leads to the creation of conventional holograms with digital content rather than real scenery.
  • 2D/ 3D graphics or digital photographs and movies can be printed which helps in the holographic recording of real outdoor scenes, completely synthetic objects, and objects in motion. This is impossible to achieve with optical holography.
  • Digital holograms can be multiplexed.
  • Another basic advantage is that the content for digital holograms can easily be created by non-experts and the printing process is not very expensive compared to conventional holograms.
  • A series of digital photographs or a short movie of a real object is enough for producing digital holograms.

____

Applications of digital holography

The applications of digital holograms can be seen in the following areas:

  • Holographic optical elements (HOEs): Holograms are used as lenses.
  • Holographic interferometry: To detect form deformations.
  • Optical data storage: In the area of security applications.
  • They have a good application prospect in laser holography anti-counterfeiting field.
  • 3D displays
  • Optical data processing.

_____

_____

Comparisons of Analog and Digital Holography:

There are a number of significant distinctions between analog (AH) and digital (DH) holographies. Most obviously, DH does not involve photochemical processing. Therefore, DH is orders of magnitude faster and can be performed at video rates. Additional hardware required in DH is the CCD camera and a computer, while the need for dark room facilities and a supply of chemicals is unnecessary. Furthermore, because of the high sensitivity of CCD compared to photographic emulsion, the exposure time is reduced by orders of magnitude. For example, a CCD pixel area of 100 μm2 can detect as few as several photons, whereas a similar area of a high-sensitivity photographic plate requires many millions of photons. Short exposure time in turn implies much reduced requirement on the mechanical stability of the apparatus. Heavy optical tables with vibration isolation are often not critical. On the other hand, the main issue of DH is low resolution. A typical CCD pixel is several microns across, while the grains on a photographic emulsion may be 2 orders of magnitude finer. This limits the spatial frequency of the fringes and therefore the angular size of the object to a few degrees for DH, while a full 180 deg is possible for AH. The familiar parallax effect of display holograms of AH is currently not feasible in DH. The real strength of DH, however, is the whole range of powerful numerical techniques that can be applied once the hologram is input into a computer. Once the computer reads the hologram into an array, one only needs to specify the dimension of the hologram and the wavelength, and proceed to compute the numerical diffraction. In AH, however, to properly read out the magnified or demagnified hologram, the wavelength also needs to be scaled proportionately, a task that is highly cumbersome at the least and infeasible in most cases. Another example is holographic interferometry using multiple wavelengths. In AH interferometry, multiple holograms are produced and repositioned exactly, and ideally each hologram needs to be illuminated with a different wavelength, which can be physically impossible. Most often the superposed holograms are illuminated with a single wavelength, and the resulting aberrations are unavoidable. In DH, however, the superposition simply consists of an addition of several numerical arrays. There is no limitation on the number of arrays, and furthermore, there are ways to preprocess the arrays to compensate for chromatic and other aberrations if present.

______

______

Holoprinter:

Holoprinters are holographic printing machines developed over the past 15 years by companies such as Zebra Imaging, Geola and Ceres Holographics. These devices can print digital holograms. It’s a dot-matrix printer that uses red green and blue lasers to print tiny sub-millimetre holographic dots into a light-sensitive polymer sheet. Each holopixel is encoded with a unique view of the scene. It takes a couple of hours to produce a page-sized digital hologram in this way. Each holopixel contains around 6M bytes of data and a page-sized hologram requires hundreds of Giga bytes of information to be computed, making it a graphics-intensive process.

_

Inkjet hologram printing now possible:

Vivid holographic images and text can now be produced by means of an ordinary inkjet printer. This new method, developed by a team of scientists from ITMO University in Saint Petersburg, is expected to significantly reduce the cost and time needed to create the so-called rainbow holograms, commonly used for security purposes — to protect valuable items, such as credit cards and paper currency, from piracy and falsification. The results of the study were published in the scientific journal Advanced Functional Materials. The team, led by Alexander Vinogradov, senior research associate at the International Laboratory of Solution Chemistry of Advanced Materials and Technologies (SCAMT) in ITMO University, developed colorless ink made of nanocrystalline titania, which can be loaded into an inkjet printer and then deposited on special microembossed paper, resulting in unique patterned images. The ink makes it possible to print custom holographic images on transparent film in a matter of minutes, instead of days as with the use of conventional methods. The new nanocrystalline ink makes it possible to cut the expenditures related to the production of rainbow holograms by several times. The ink is applied with a simple inkjet printer on a microembossed surface, which is afterwards covered by varnish. As a result, the holographic image is exclusively seen in those areas, where the protective ink was deposited. The peculiarity of our ink lies in its high refractive index in all visible range of light. The use of nanocrystalline ink forms a layer with high refractive index that helps preserve the rainbow holographic effect after the varnish or a polymer layer is applied on top.

__

MIT researchers have developed a new kind of 3D hologram that is printed with an inkjet printer. Using an image-processing algorithm, Lummi’s technology prints a scanned image into layers on transparent sheets that are then stacked to create a 3D effect.

______

______

Digital Holographic Microscopy (DHM):

Because the real image from the hologram can be viewed by a camera or microscope, it is possible to examine difficult and even inaccessible regions of the original object. This feature renders holography useful for many purposes. A deep, narrow depression on a plane, for example, cannot often be reached by a microscope objective because of working distance limitations. If the detail can be reached by coherent light, however, a hologram can be taken and its image reconstructed. Since this image is aerial, the microscope can be positioned in such a way that it can focus on the required region. In the same way, a camera also can be focused at the required depth and can photograph objects inside a deep transparent chamber.

_

Imaging of microscopic objects is an essential art, especially in life sciences. Rapid progress in electronic detection and control, digital imaging, image processing, and numerical computation has been crucial in advancing modern microscopy. At present the 3D imaging of biological samples is done by confocal microscopes. Their ability to image biological events in real time is limited by the time necessary to capture stacks of images taken through a certain plane in cells or tissues from which a 3D view is calculated. Digital holographic microscopy is a new imaging technology applied to optical microscopy. The digital holographic microscopy is a very advanced imaging technique because it yields a 3D volume image from a single image capture.

_

Digital Holographic Microscopy (DHM) is digital holography applied to microscopy. Digital holographic microscopy distinguishes itself from other microscopy methods by not recording the projected image of the object. Instead, the light wave front information originating from the object is digitally recorded as a hologram, from which a computer calculates the object image by using a numerical reconstruction algorithm. The image forming lens in traditional microscopy is thus replaced by a computer algorithm. Other closely related microscopy methods to digital holographic microscopy are interferometric microscopy, optical coherence tomography and diffraction phase microscopy. Common to all methods is the use of a reference wave front to obtain amplitude (intensity) and phase information. The information is recorded on a digital image sensor or by a photo detector from which an image of the object is created (reconstructed) by a computer. In traditional microscopy, which do not use a reference wave front, only intensity information is recorded and essential information about the object is lost.

_

Actually, DHM has been mostly applied to light microscopy. This field enables quantitative characterization of living cells. In material Science, DHM are used routinely for research in academic and industrial labs, depending of the application microscopes can be configured both in transmission and in reflection. DHM is a unique solution for 4D (3D + time) characterization of technical samples, when information needs to be grabbed very quickly. It is the case for measurements in noisy environment, in presence of vibrations, when the samples move, or when the shape of samples change due to external stimuli, such as mechanical, electrical, or magnetic forces, chemical erosion or deposition, and evaporation. In life sciences, DHM are usually configured in transmission mode. They enable label free Quantitative Phase Measurement (QPM), also called Quantitative Phase Imaging (QPI), of living cells. Measurements do not affect the cells, enabling long term studies. It provides information that can be interpreted into many underlying biological processes. Digital holographic microscopy does have its limits. A major one is the relatively low spatial frequency response of digital cameras, which limits resolution of reconstructed holograms. That arises from the spacing of detector elements and their larger size than the grains in photographic media.

_

Advantages of DHM:

  1. Phase shift images:

Besides the ordinary bright field image, a phase shift image is created as well. The phase shift image is unique for digital holographic microscopy and gives quantifiable information about optical distance. In reflection DHM, the phase shift image forms a topography image of the object. Transparent objects, like living biological cells, are traditionally viewed in a phase contrast microscope or in a differential interference contrast microscope. These methods visualize phase shifting transparent objects by distorting the bright field image with phase shift information. Instead of distorting the bright field image, transmission DHM creates a separate phase shift image showing the optical thickness of the object. Digital holographic microscopy thus makes it possible to visualize and quantify transparent objects and is therefore also referred to as quantitative phase contrast microscopy. Traditional phase contrast or bright field images of living unstained biological cells have proved themselves to be very difficult to analyze with image analysis software. On the contrary, phase shift images are readily segmented and analyzed by image analysis software based on mathematical morphology, such as CellProfiler.

_

  1. 3-Dimensional information:

An object image is calculated at a given focal distance. However, as the recorded hologram contains all the necessary object wave front information, it is possible to calculate the object at any focal plane by changing the focal distance parameter in the reconstruction algorithm. In fact, the hologram contains all the information needed to calculate a complete image stack. In a DHM system, where the object wave front is recorded from multiple angles, it is possible to fully characterize the optical characteristics of the object and create tomography images of the object.

  1. Digital autofocus:

Conventional autofocus is achieved by vertically changing the focal distance until a focused image plane is found. As the complete stack of image planes may be calculated from a single hologram, it is possible to use any passive autofocus method to digitally select the focal plane. The digital auto focusing capabilities of digital holography opens up the possibility to scan and image surfaces extremely rapidly, without any vertical mechanical movement. By recording a single hologram and afterwards stitch sub-images together that are calculated at different focal planes, a complete and focused image of the object may be created.

  1. Optical aberration correction:

As DHM systems do not have an image forming lens, traditional optical aberrations do not apply to DHM. Optical aberrations are “corrected” by design of the reconstruction algorithm. A reconstruction algorithm that truly models the optical setup will not suffer from optical aberrations.

  1. Low cost:

In optical microscopy systems, optical aberrations are traditionally corrected by combining lenses into a complex and costly image forming microscope objective. Furthermore, the narrow focal depth at high magnifications requires precision mechanics. The needed components for a DHM system are inexpensive optics and semiconductor components, such as a laser diode and an image sensor. The low component cost in combination with the auto focusing capabilities of DHM, make it possible to manufacture DHM systems for a very low cost.

_____

Applications of DHM:

Digital holographic microscopy has been successfully applied in a range of application areas.

  1. Living Cells Imaging
  2. Surface 3D topography
  3. Metrology
  4. Micro optics
  5. 3D particle tracking

_______

______

Digital Planar Holography:

Digital Planar Holography (DPH) is a method for designing and fabricating miniature components for integrated optics. It was invented by Vladimir Yankov and first published in 2003. The essence of the DPH technology is embedding computer designed digital holograms inside a planar waveguide. Light propagates through the plane of the hologram instead of perpendicularly, allowing for a long interaction path. Benefits of a long interaction path have long been used by volume or thick holograms. Planar configuration of the hologram provides for easier access to the embedded diagram aiding in its manufacture.

_

Biomedical applications of holographic microspectroscopy:

The identification and quantification of specific molecules are crucial for studying the pathophysiology of cells, tissues, and organs as well as diagnosis and treatment of diseases. Recent advances in holographic microspectroscopy, based on quantitative phase imaging or optical coherence tomography techniques, show promise for label-free noninvasive optical detection and quantification of specific molecules in living cells and tissues (e.g., hemoglobin protein).

_

Holographic Optical tweezers:

Optical tweezers use forces of light in order to move about small particles (mainly for biological applications) and create optical traps. By using computer generated holograms, researchers can manipulate large arrays of particles over small distances.

______

______

Holographic data storage (HDS):

We now generate huge amounts of data. Digital storage capacity increases (and becomes cheaper) every year and we have an insatiable desire to store our data and keep it for a lifetime. Just think about your own computer and the hundreds of gigabytes of information it can store, from family photos to videos and documents. Now consider your storage disc – and everyone else’s – being corrupted and the vast losses involved.  A holographic image is stunningly realistic because the recording process stores all of the information about the light reflected from the recorded subject. That is a massive amount of information. But holograms don’t have to record information about a visual object – they can also record pure data, pages and pages of it. This means that holograms can, potentially, store unthinkable amounts of information. Not only can the prototype systems store 4.4m individual pages of information on a disc similar to a DVD, but they offer long-term security, too. If you make an optical hologram of a page of information and then smash it, for example, you can reconstruct it from any of the pieces. This makes holographic data storage extremely reliable. Unlike CDs and DVDs, which store their data on the disc’s surface, holograms store data in three dimensions and those pages can overlap in the storage space. Researchers have been suggesting the possibilities of holographic data storage for over 50 years and it looks like they are getting closer to a usable system.

_

Holographic storage is computer storage that uses laser beams to store computer-generated data in three dimensions. It has been discovered that in addition to their other capabilities, holograms possess an astounding capacity for information storage–simply by changing the angle at which the two lasers strike a piece of photographic film, it is possible to record many different images on the same surface. It has been demonstrated that one cubic centimeter of film can hold as many as 10 billion bits of information. Besides the angle, changing the wavelength or phase of the laser makes it possible to store even more data.

_

Holography can be put to a variety of uses other than recording images. Holographic data storage is a technique that can store information at high density inside crystals or photopolymers. The ability to store large amounts of information in some kind of medium is of great importance, as many electronic products incorporate storage devices. Limitations on digital data storage are imposed by the fact that the space required to store a single bit of data on an optical disk cannot be reduced below a limit set by the wavelength of the light used. Holography overcomes this by storing a large number of holograms in the same place. As current storage techniques such as Blu-ray Disc reach the limit of possible data density (due to the diffraction-limited size of the writing beams), holographic storage has the potential to become the next generation of popular storage media. The advantage of this type of data storage is that the volume of the recording media is used instead of just the surface. Currently available SLMs can produce about 1000 different images a second at 1024×1024-bit resolution. With the right type of medium (probably polymers rather than something like LiNbO3), this would result in about one-gigabit-per-second writing speed. Read speeds can surpass this, and experts believe one-terabit-per-second readout is possible.

_

Holographic Memory:

It is a memory that can store information in form of holographic image.  It is a technique that can store information at high density inside crystals or photopolymers. It has more advantages than conventional storage systems. It is based on the principle of holography. Unlike magnetic storage mechanisms which store data on their surfaces, holographic memories store information throughout their whole volume. In holographic data storage, data are first turned into a two-dimensional pattern of light by a spatial light modulator (SLM; an array of light switches that can store as many as one million bits or pixels). Laser light is beamed through the SLM to the recording medium, such as a photopolymer, while a reference beam also illuminates the medium so that interference patterns are created. These expose the medium by generating corresponding differences in optical properties such as refractive index or absorption. Many pages of holograms can be multiplexed onto the same medium, either by varying the angle or phase of the reference beam, or by using different frequencies, among other techniques.

_

A double-sided, double-layer DVD can hold 15.9 GB of data, which is about eight, hours of movies. These conventional storage mediums meet today’s storage needs, but storage technologies have to evolve to keep pace with increasing consumer demand. In order to increase storage capabilities, scientists are now working on a new optical storage method, called holographic memory, that will use the volume of the recording medium for storage, instead of only the surface area. Holographic memory offers the possibility of storing 1 terabyte (TB) of data in a sugar-cube-sized crystal. The basic components that are needed to construct a holographic data storage systems are: laser, beam splitter, mirrors, lenses, lithium-niobate crystal or photopolymer and detector. Light from a single laser beam is split into two beams, the signal beam (which carries the data) and the reference beam. The hologram is formed where these two beams intersect in the recording medium. The process for encoding data onto the signal beam is accomplished by a device called a spatial light modulator (SLM). The SLM translates the electronic data of zeros and ones into an optical “checkerboard” pattern of light and dark pixels. The data are arranged in an array or page of over one million bits. The exact number of bits is determined by the pixel count of the SLM. At the point where the reference beam and the data carrying signal beam intersect, the hologram is recorded in the light sensitive storage medium. A chemical reaction occurs causing the hologram to be stored. By varying the reference beam angle or media position hundreds of unique holograms are recorded in the same volume of material. In order to read the data, the reference beam deflects off the hologram thus reconstructing the stored information. This hologram is then projected onto a detector that reads the entire data page of over one million bits at once. This parallel read out of data provides holography with its fast transfer rates. Holographic storage uses circular media similar to a blank CD or DVD that spins to accept data along a continuous spiral data path. Once the media is written, data is read back using the reference beam to illuminate the refraction.  This three-dimensional aspect of data recording is an important difference between holographic storage and conventional CD/DVD recording. Traditional optical media uses a single laser beam to write data in two dimensions along a continuous spiral data path. In contrast, prototype holographic storage products save one million pixels at a time in discrete snapshots, also called pages, which form microscopic cones through the thickness of the light-sensitive media. Today’s holographic media can store over 4.4 million individual pages on a disc. There are still many technical problems that need to be solved. If there are too many holograms stored on a crystal, and the reference laser used to retrieve a hologram is not perfectly aligned, a hologram will pick up a lot of background from the other holograms stored around it. It is also a challenge to pack all of these components in a low-cost system.

_

While many holographic data storage models have used “page-based” storage, where each recorded hologram holds a large amount of data, more recent research into using submicrometre-sized “microholograms” has resulted in several potential 3D optical data storage solutions. While this approach to data storage cannot attain the high data rates of page-based storage, the tolerances, technological hurdles, and cost of producing a commercial product are significantly lower.

_

The ideal material for HDS should have several physical properties, including a large dynamic range, high photosensitivity, undergo no dimensional changes and be capable of forming thick layers. Of all holographic recording media, photopolymers and photorefractive materials appear to be the most promising for HDS. Photorefractive materials such as LiNbO3 have many features that making them suitable for HDS; the recorded holograms are rewriteable, they can achieve large refractive index modulation, and the material does not suffer from shrinkage during recording. However, the photosensitivity of photorefractive media is reported to be low. Unlike photorefractives, photopolymers demonstrate high photosensitivity. However, photopolymers also face problems such as thickness limitations (approximately 1 mm) and shrinkage. For HDS, a thick, photosensitive material is required. The commercial upper limit on shrinkage for data storage applications is 0.5 %. Research into the suitability of photopolymers and polymer composites for holographic data storage is currently a hot topic, being investigated by many different research groups worldwide. In 2008 InPhase Technologies launched their photopolymer-based holographic disk drive, which is considered to be a huge mile stone in the field. Since then commercial companies such as Bayer, DuPont, General Electric and Sony are also becoming more involved in its development.

_

Holographic Versatile Disc (HVD):

Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which would hold up to 3.9 terabyte (TB) of information. It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used as the reference beam and to read servo information from a regular CD-style aluminum layer near the bottom. These discs have the capacity to hold up to 3.9 terabyte (TB) of information, which is approximately 6000 times the capacity of a CD-ROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray-Discs, and about 8 times the capacity of standard computer hard drives. The HVD also has a transfer rate of 1gigabyte/s .

_

Advantages of HVD:

  1. Resistance to damage – If some parts of the medium are damaged, all information can still be obtained from other parts.
  2. Efficient retrieval – All information can be retrieved from any part of the medium.
  3. These discs have the capacity to hold up to 3.9 terabyte (TB) of information. While reading a page the entire page of data can be retrieved quickly and at one time

Disadvantages of HVD:

  1. Manufacturing cost HVD is very high and there is a lack of availability of resources which are needed to produce HVD.
  2. A difficulty with the HVD technology had been the destructive readout. The re-illuminated reference beam used to retrieve the recorded information, also excites the donor electrons and disturbs the equilibrium of the space charge field in a manner that produces a gradual erasure of the recording.
  3. You would be unable to locate the data if there’s an error of even a thousandth of an inch.

_

For decades, holographic optical data storage has been losing in a race with silicon-based memories and magnetic and optical disks. As researchers have developed ways to make holographic methods more practical and data storage denser, conventional techniques have progressed faster, pushing the technical hurdles to commercialization ever higher. However, accelerating progress in multiple-frequency holography, based on spectral hole burning, offers at least the theoretical and perhaps practical potential for leapfrogging to such high data densities and readout speeds that the holographic turtle may still win the race. Practical prototypes of more modest systems also have shown that holographic data storage does not have to be trapped in the laboratory forever.

______

______

Holographic interferometry:

Interferometry is a family of techniques in which waves, usually electromagnetic waves, are superimposed causing the phenomenon of interference in order to extract information. Many holographic applications exploit the fact that composite repeat holograms of a surface tilted slightly after each exposure can be treated as composite, repeat wave patterns. If two such patterns are matched, a condition arises that is effectively the same as that which exists in ordinary classical two-beam interferometry, in which a single light source is split into two beams and the beams recombined to form interference patterns. Such an arrangement can be set up in several ways; in one, a holographic exposure is made of a surface, then, before the hologram is removed or developed, the surface is slightly tilted and a repeat hologram is made, superimposed on the first hologram. When this double hologram is reconstructed, the object as well as the surface covered by the interference fringes caused by surface irregularities can be seen. These fringes reveal microtopographic information about the object.

_

Holographic interferometry can be applied successfully to any situation in which the wave front is modified slightly, no matter how complex the surface may be. Elastic deformation effects can be studied by superimposing the two wave fronts on the hologram, reflected before and after the elastic distortion effect has been introduced. When reconstructed, the hologram provides a clear picture of the object, crossed by interference fringes. Even highly complex shapes respond to this approach in a manner that would be impossible in classical interferometry. There is also great flexibility in the choice of methods used to apply distortions, and even these conditions alone often completely exclude optical interferometry. Not only static distortion but also slow dynamic variations can be studied in this manner. And with pulsed ruby lasers, very fast, short-time variations can be studied.

_

Microscopic changes on an object can be quantitatively measured by making two exposures on a changing object. The two images interfere with each other and fringes can be seen on the object that reveal the vector displacement. In real-time holographic interferometry, the virtual image of the object is compared directly with the real object. Even invisible objects, such as heat or shock waves, can be rendered visible. There are countless engineering applications in this field of holometry.

_

Time variations in the shape of an object are not usually studied with a single, double-exposure hologram but by an alternative method. First, a hologram is made of the object in its free, unstressed condition. Then the object is stressed and a new hologram made. The stressed hologram is viewed through the original unstressed hologram, and the superposition provides the interference fringe pattern that would have been produced by a double exposure. By such means, time variations can be studied. Valuable studies have been made of mechanically vibrating systems, such as diaphragms, musical instruments (e.g., the belly of a violin), vibrating steam-turbine blades, and the like. The examination of large engineering components, measuring as much as one metre (about three feet) in length, imposes special problems. The distance between the hologram plate and the object must be great enough to ensure that all of the object can be seen at once. In turn, laser power must be increased, high demands on the coherence of light are imposed, and mechanical stability of the whole setup must be exceptionally good.

_

Holographic interferometry (HI) is a technique that enables static and dynamic displacements of objects with optically rough surfaces to be measured to optical interferometric precision (i.e. to fractions of a wavelength of light). It can also be used to detect optical-path-length variations in transparent media, which enables, for example, fluid flow to be visualized and analyzed. It can also be used to generate contours representing the form of the surface. It has been widely used to measure stress, strain, and vibration in engineering structures. Here scientists can make a hologram of something like an engine part and store it as a “three-dimensional photograph” for later reference. If they make another hologram of the engine part at some later date, comparing the two holograms quickly shows up any changes in the engine that may indicate signs of wear or impending failure.

_

Holography is the two-step process of recording a diffracted light field scattered from an object, and performing image rendering. This process can be achieved with traditional photographic plates or with a digital sensor array, in digital holography. If the recorded field is superimposed on the ‘live field’ scattered from the object, the two fields will be identical. If, however, a small deformation is applied to the object, the relative phases of the two light fields will alter, and it is possible to observe interference. This technique is known as live holographic interferometry. It is also possible to obtain fringes by making two recordings of the light field scattered from the object on the same recording medium. The reconstructed light fields may then interfere to give fringes which map out the displacement of the surface. This is known as ‘frozen fringe’ holography. The form of the fringe pattern is related to the changes in surface position or air compaction. Many methods of analysing such patterns automatically have been developed in recent years.

_

With interferometry we can discover a flaw in a tire.

_

From Laser vibrometry to Laser Doppler imaging, from spectroscopy to remote sensing, from mechanical and optical metrology to oceanography and seismology, from quantum mechanics to nuclear and plasma physics, the range of holographic interferometry applications is extremely broad. To accommodate the broad spectrum of applications, a diverse range of continuous wave and pulsed lasers are produced suitable for interferometric measurements.

_

Interferometric microscopy:

The hologram keeps the information on the amplitude and phase of the field. Several holograms may keep information about the same distribution of light, emitted to various directions. The numerical analysis of such holograms allows one to emulate large numerical aperture, which, in turn, enables enhancement of the resolution of optical microscopy. The corresponding technique is called interferometric microscopy. Recent achievements of interferometric microscopy allow one to approach the quarter-wavelength limit of resolution.

______

______

Holographic optical elements (HOEs):

A HOE is a hologram of a light wave converter (lens, prism, mirror etc.) which performs the function of the recorded object with up to 100 % efficiency. They are in general wavelength dependent i.e. they operate best at the wavelength used to record them. It is possible to create HOEs with very large aperture size, and they can be recorded in lightweight materials. This is advantageous as the HOE will be low cost and less bulky than the converter counterpart. A number of HOEs can also be combined into a single layer of photosensitive material to produce a multifunction device. There are a huge number of applications of HOEs, one of which is use in solar concentrators in order to increase energy output. By surrounding photovoltaic cells with HOE lenses, increased concentrations of light may be focussed on to the cells, hence increasing the energy output of the device. This is a low cost technique which is essential for production on a large scale as would be the case for solar cells. It also removes the need for expensive solar tracking systems. Research into the suitability of an AA-based photopolymer material for recording HOE lenses for solar concentrations is currently being carried out by researchers in the IEO centre, and by other research groups worldwide. Another application of HOEs is in interferometric and shearographic systems for non-destructive testing. Both transmission and reflection mode HOEs have been used to reproduce both reference and diffracted beams, removing the typical complications in interferometric systems associated with alignment of bulky optical components, which can be a time-consuming and difficult process.

Optic and Electronic Elements:

Different  kinds of holograms arise according to the holographic optical elements (HOE) such as lenses, mirrors, filters, prisms and etc. and holographic electronic elements(HEE) such as electrons, crystal  displays, cameras, computers, etc. which are used in hologram recording and re-construction.

____

_____

Real 3D holographic technologies:

  1. Electro-holography:

There are some really trendy technologies that belong to the 3D holographic niche. One of them is the electro-holographic display. This technology uses electro-holography to record 3D objects and reconstruct them. Electro-holographic displays are digital displays that transmit stored image data using an electromagnetic resonator. These signals are then read by an acoustic-optic modulator and converted into a legible image and displayed on an RGB laser monitor. Electro-holographic displays hold an advantage over traditional displays in terms of picture accuracy and range of color. This display is distinct from other 3D displays. For example, when the technology reconstructs 3D images, it captures the parallax. Holographic techniques can record and reproduce the properties of light waves – amplitude (luminance), wavelength (chroma) and phase differences – almost to perfection, making them a very close approximation of an ideal free viewing 3-D technique. Recording requires coherent light to illuminate both the scene and the camera target (used without front lenses). For replay, the recorded interference pattern is again illuminated with coherent light. Diffraction (amplitude hologram) or phase modulation (phase hologram) will create an exact reproduction of the original wavefront.  Video-based holographic techniques are still in their infancy, although they have received much attention over the past five years. Organised by TAO (Telecommunications Advancement Organization), several Japanese research institutes are working towards adapting the principle of holography to an LCD-based video electronics environment. However, the spatial resolution of today’s LC-panels is a serious bottleneck (minimum requirements are 1000 lp/mm). A possible solution is to partition the hologram among several LC-panels and to reassemble the image with optical beam combiners. It is yet an open question how to store and transmit the enormous amount of data contained in a hologram. The source rate is estimated to exceed 1012 bit/sec . Specific data compression methods are required. Currently, the scope of this approach is limited to very small and coarse monochromatic holograms (width of field 1 cm).  Holograms cannot be recorded with natural (incoherent) lighting – a decisive shortcoming. Therefore, they will remain confined to applications where the scene is available in the form of computer generated models. An approach based on computer generated holograms has been pursued since the late 1980s at MIT’s Media Lab.  The MIT approach makes intense use of data reduction techniques (elimination of vertical parallaxes, subsampling of horizontal parallaxes). Yet, the pixel rate for a monochrome display with a diameter of 15 cm, a depth of 20 cm, and a viewing zone of 30 degrees amounts to 2 Gigapixel/sec (at 30 Hz frame rate). The hologram is displayed with acousto-optical modulators (tellurium dioxide crystals transversed by laser light). At any one instant, the information of nearly 5000 pixels travels through a crystal. For optical stabilization, synchronized oscillating mirrors are interposed between the modulator and the observer’s eyes. Vertical sweep is accomplished with a nodding mirror. Current work aims at increasing the image diameter to 25 cm by assembling multiple basic elements in parallel.

  1. Holographic telepresence and TV (vide infra) is perhaps going to be the biggest of surprises. Researchers at MIT are anticipating holographic TV could enter our drawing room in just ten years down the line. If it turned into a valid anticipation, then today’s 2D TV sets would be obsolete from the market.
  2. The plasma laser technology (vide infra) could give 3D an altogether new shape. Aerial Burton has used plasma laser to have 3D images floated in the air. The technology is in its nascent stage currently but it has plenty of rooms to prosper in the future. Technologies such as plasma laser work in a fascinating way, it accounts for opaqueness. Using this technology, light could be viewed without it having to bounce off a surface.

_______

_______

Holographic telepresence:

The next step beyond dynamic digital holography is holographic television or telepresence. The idea is to record digital holograms at a video-like frame rate, transmit them, then display them in their full three-dimensional glory at the same frame rate. So far, the most impressive “holographic” demonstrations have not involved any real holograms. The famed “hologram” of Princess Leia pleading for help in Star Wars: Episode I in 1977 was a nonholographic special effect. A series of recent demonstrations of “holographic telepresence” including futurist Ray Kurzweil and long-dead rapper Tupac Shakur were also fakes, based on the “Pepper’s Ghost” illusion, which projects a 2D image onto a clear screen on stage. Holographic motion pictures or television has been a dream since the 1960s, but years of development with analog technology faded away in the mid-1990s. In the past few several years, digital real-time holography has made major progress. “Capture and computation are proving not to be the barriers that people have been assuming they would be,” says V. Michael Bove of the MIT Media Laboratory. “The display itself is the limiting factor.” Developers are using inexpensive cameras to capture images in incoherent light, then using computers to generate the holograms, with much of the computation done at the display. The results have included some eye-catching demonstrations. Nasser Peyghambarian of the University of Arizona (Tucson, AZ) and colleagues in 2010 demonstrated telepresence at one frame per second using a new photorefractive material.

_

Holographic telepresence is an evolving technology for full-motion, three-dimensional (3D) video conferencing. Holographic telepresence systems can project realistic, full-motion, real-time 3D images of distant people and objects into a room, along with real-time audio communication, with a level of realism rivalling physical presence. Images of remote people and surrounding objects are captured, compressed, transmitted over a broadband network, decompressed, and finally projected using laser beams in much the same way as a conventional hologram is produced. Holographic telepresence has the potential to revolutionize many diverse types of communications. Telepresence represents the future of communication, enabling you to connect more effectively and make an incredible impact on your audience. The technology reduces your carbon footprint, saving travel time and expense. In telemedicine, for example, telepresence can allow medical professionals to advise and assist colleagues thousands of miles away in real time. The technology can also reduce the necessity of travel for business meetings and facilitate distance education. Other potential applications include enhanced movies and television programming, advertising, gaming, 3D mapping, aerospace navigation, robot control, and various other forms of simulation. While this emerging technology is still in its infancy and is cost prohibitive today, it is probably a pretty reasonable assumption that it will become increasingly affordable and commonplace in years to come, following the natural path of many powerful technologies.

____________

CNN debuts election-night ‘hologram’

CNN’s Jessica Yellin appears live as a hologram before anchor Wolf Blitzer in New York. “Hi Wolf!” said Yellin, waving to Blitzer as she stood a few feet in front of him in the network’s New York City studios. Or at least, that’s the way it appeared at first glance. In reality, Yellin — a correspondent who had been covering Sen. Barack Obama’s campaign in 2008 Presidential elections   — was at president-elect’s mega-rally along the lakefront in Chicago, Illinois, more than 700 miles away from CNN’s Election Center in New York.

__

How did they manage to send 3D 360 degree footage of virtual correspondent Jessica Yellin from Chicago all the way to the station’s election center in NY?

 

A magic made possible from technology Vizrt and SportVu with the help of forty-four HD cameras and twenty computers.

On the subject’s side:

  • 35 HD cameras pointed at the subject in a ring
  • Different cameras shoot at different angles (like the matrix), to transmit the entire body image
  • The cameras are hooked up to the cameras in home base in NY, synchronizing the angles so perspective is right
  • The system is set up in trailers outside Obama and McCain HQ
  • Not only is it mechanical tracking via camera communication, there’s infrared as well
  • Correspondents see a 37-inch plasma where the return feed of the combined images are fed back to them. Useful for a misplaced hair or an unseemly boogar
  • Twenty “computers” are crunching this data in order to make it usable

On the HQ side:

  • Only used on two out of 40-something total camera feeds that CNN has
  • The delay is either minimal, or we’ve gotten used to satellite delay that we don’t even notice now
  • An array of computers takes the crunched info feed from the subject’s side in order to mesh it with the video from Wolf’s side.
  • Unfortunately, it doesn’t look like the images are actually “projected” onto the floor of the CNN studio so that Wolf can actually talk to the person, you know, in a face to face. Only after computers merge the video feeds together do you get a coherent hologram + person scenario

With all of the good that this new technology is giving off what could be the possible disadvantages??  The disadvantage of this technology is the costs of installing several cameras and the computer power needed to process all of the information is extremely high at its present time.

_

CNN hologram was not true real hologram:

The CNN anchors were not really speaking to three-dimensional projected images, but rather empty space. The images were simply added to what viewers saw on their screens at home, in much the same way computer-generated special effects are added to movies. The images were tomograms, which are images that are captured from all sides, reconstructed by computers, then displayed on screen. The technology of capturing and projecting holograms of big objects like people is still a ways off. Holographic images are generally captured and projected using coherent light such as lasers. A laser would need to be more than six feet in diameter to capture a person’s image, which is impossible because such a light would be blinding. It may soon be possible to capture and project large objects using other sources of coherent light, such as light-emitting diodes. LEDs are considerably cheaper and safer than lasers.

_______

3D holographic video machine:

In the mid of 2014, two artists from Scotland introduced a new technology. The machine has been identified as the first of its kind and it can generate a powerful and highly realistic 3D video. The machine debuted at the Edinburgh Art Festival and it showcases top quality 3D holographic effects. The first video made by the duo featured the space investigation carried out by NASA Voyager. The voyager featured in the video wasn’t real, it was a holographic image of the original voyager. The video also featured a conversation between a holographic baby and a 5-year-old child. The child is real, he is the son of Helson and Jackets, the Scottish artists. The holographic baby is the same child. The artists were inspired by a piece called ‘Help me Obi’ from the legendary Star Wars. Details about the project are indeed astonishing. The two artists worked on the project for almost seven years and the objects, projected by them can have the length of up to 12-inches. The project has given a boost to 3D holographic image rendering industry.

_____

Telehuman: taps Kinect for 3D holographic videoconferencing:

A Queen’s University researcher has created a Star Trek-like human-scale 3-D videoconferencing pod that allows people in different locations to video conference as if they were standing in front of each other. Researchers at the Human Media Lab at Queen’s University in Kingston, Ontario, have developed a life-sized hologram-like telepod that uses Microsoft’s Kinect System and a cylindrical display for live, 3D videoconferencing.  The system, called “TeleHuman,” allows two people to simply stand in front of their own pods and talk to 3D hologram-like images of each other. The setup basically creates a life-size rendering of its subject by using six Kinect sensors, a 3D projector and a cylindrical display. This allows the viewer to walk around the cylinder for a 360-degree view of the subject. The TeleHuman is a cylindrical pod that stands just under two-meters tall and has a 3D projector hidden inside its base. This projects your image onto a convex mirror, which then reflects it onto the wrap-around acrylic screen. An array of six Kinect sensors mounted at the top of the display capture track 3D video and converts it into the lifesize image.  Since the 3D image is visible 360 degrees around the pod, the person can walk around it to see the other person’s side or back, a key advantage over flat displays.  “Why Skype when you can talk to a lifesize 3D holographic image of another person?” said professor Roel Vertegaal, director of the Human Media Lab. TeleHuman was built primarily with existing hardware, including a 3D projector installed at the base of the 1.8 meter-tall translucent acrylic cylinder and a convex mirror. While 3-D holographic video is not a new technology (Cisco and Musion Systems created an on-stage holographic video conference 5 years ago), TeleHuman demonstrates that it can be done for a lot cheaper using the versatile Kinect platform and off-the-shelf hardware. Unlike most holography-like projections, TeleHuman accurately preserves motion parallax— the changing appearance of an object as we move around it. So, the TeleHuman brings use one step closer to making our sci-fi communication dreams a reality, but there are a couple of drawbacks. First, one still has to wear 3D glasses to see the image in three dimensions, which will dim the image even more; and second, it’s quite expensive.

_____

_____

3D TV versus 3D Holographic TV:

First let us discuss 3D TV:

3D television (3DTV) is television that conveys depth perception to the viewer by employing techniques such as stereoscopic display, multi-view display, 2D-plus-depth, or any other form of 3D display. Most modern 3D television sets use an active shutter 3D system or a polarized 3D system, and some are autostereoscopic without the need of glasses. When we say “a 3D TV” what we mean is “an HDTV with 3D compatibility.” 3D compatibility is a feature on higher-end LED LCD and plasma TVs released since 2010. It allows those TVs to display specialized, made-in-3D video with the right accessories — namely 3D glasses and a 3D source device. With that in mind, here are a few basic points about 3D TV. All 3D TVs are first and foremost 2D TVs. All 3D TVs will display current 2D high-def and standard-def content with no problem and no glasses required. In fact, for the foreseeable future we expect most 3D TVs to spend the vast majority of their time showing the same 2D video delivered by other HDTVs. Moreover, the 2D picture quality of 3D TVs is not affected in any negative way we’ve noticed by their 3D capabilities. That’s why we prefer to think of 3D compatibility as “just another feature,” like Internet streaming or a fancy remote control. You can take it or leave it, but for most TV shoppers it’s not the most important feature on a modern television. To view 3D on a 3D TV, you need 3D glasses, a 3D source device, and 3D video content. A screen showing 3D content displays two separate images of the same scene simultaneously, one intended for the viewer’s right eye and one for the left eye. When viewed without the aid of 3D glasses, the two full-size images appear intermixed with one another, fuzzy and basically unwatchable. When viewers don the glasses, they perceive these two images as a single 3D image, a process known as “fusing.” The system relies on a phenomenon of visual perception called stereopsis, so it’s not “true” 3D like real life or a hologram. The current TV is HD, either 720p or, more likely, 1080p. New 4K Ultra HD TVs have four times as many pixels as 1080p. Technically, “4K” means a horizontal resolution of 4,096 pixels.  Here’s where I remind you that more pixels doesn’t necessarily mean a better picture. There are other aspects of picture quality, such as contrast and color, that are far more important than resolution. 3D TV are to be discontinued in 2017 due to low consumer demand. LG and Sony were the last manufacturers to build the product.  However, only limited 4K TVs with 3D capability still exist.

Hologram Glasses versus 3D glasses:

Hologram glasses are actually an improved version of 3D Glasses which have multiple purposes. The glasses as we know help in surrounding every point of bright light with amazing images suspended in the air. Hologram glasses, just like sunglasses in common parlance, give an immersed three-dimensional visual environment. The experience is quite different & superior when compared to conventional virtual reality glasses. The sickening flicker which one has to face is restricted to the minimum in hologram glasses. Holographic glasses have digital computer generated hologram lenses, as found in diffractive optical elements. Hologram glasses generally have the ability to generate diffractive optical elements in the form of binary amplitude and binary phase. The three dimensional effect is produced when a still picture with a red composite image in its right component is superposed on the left component having a contrasting color. The effect takes place when they are viewed through glasses with corresponding colored filters. The brain helps the eyes which are about two inches apart to correlate the picture which are otherwise from slightly different angles.  Holographic glasses with 3D effect make 3D films worth watching, thus, eliminating blurriness & fuzziness completely. These colored filters help separate the different colored images (as red and cyan, blue or green) being projected from different angles simultaneously.

Advantages of Hologram Glasses:

  • There is no difference between real & virtual when viewed through holographic 3D glasses. Fantasy world becomes real when seen through a hologram glasses
  • The glasses help the eyes to correlate the two different images as one, thus, making it easier to grasp the essence.
  • Allows color viewing.
  • Technology used in 3D or stereoscopic movies is quite simple.
  • Recreates the users with their amazing plus points.

_

Microsoft’s new hologram glasses replace traditional eyeglasses:

In a new paper, a Microsoft Research team unveiled a prototype pair of glasses that use digital holography to build more realistic near-eye displays for VR and AR experiences. The glasses prototype offers a fuller range of vision in a smaller space than bulky VR/AR headsets currently on the market, and can even correct users’ vision problems. According to Microsoft researchers, the new display would allow users to view the holographic display without the assistance of their eyeglasses. The display can correct for near-sightedness, far-sightedness, and astigmatism.

_____

3D holographic TV:

Television (TV) holography is a technique which uses a laser, CCD camera and digital processing to generate holograms at TV frame rate. Several different names have been used to describe it. The earliest is probably ‘electronic speckle pattern interferometry’ (ESPI), due to Butters and Leendertz (1971). Recently, a proliferation of names has appeared for slight variations on the same theme, such as ‘electronic holography’ and ‘electro-optic holography’. The name TV holography highlights the real-time operating mode of the technique and also serves as a reminder of its holographic roots.

_

_

The best attempt at a holographic TV was done a decade ago and cost a fortune.  Qinetiq developed a holographic display prototype based on spatial light modulation technology 12 years ago. It used an active tiling system with two different spatial light modulators to provide all the depth cues needed to produce a 3D image. It was expensive to produce and was discontinued shortly after development, yet still is the closest true holographic display to be demonstrated. Recently MIT unveiled holographic TV system. Using a single Xbox Kinect and standard graphics chips, the researchers say they’ve demonstrated the highest frame rate yet for streaming holographic video. The first video depicts a paper crane. The new MIT system uses only one data-capture device — the new Kinect camera designed for Microsoft’s Xbox gaming system — and averages about 15 frames per second. Given that they achieved this in just a couple of weeks, they say, they reckon they’ll soon be able to double that, giving the same illusion of continuous motion as TV. The Kinect feeds data to an ordinary laptop, which relays it over the internet. At the receiving end, a PC with three commercial GPUs computes the diffraction patterns for the final image. The one component of the system that can’t be bought at an electronics store for a couple of hundred dollars is the holographic display itself. The resolution of the real hologram isn’t nearly as high as that of the special-effects hologram in the movie.

_

SeeReal’s Holographic 3D Solution:

A typical set-up for Holographic 3D viewing – a new HDTV panel will be needed which carries twin cameras and refresh speeds of around 480Hz to keep around four people happy. To achieve quality 3D real-time holography – realistic and comfortable to view – the images transmitted to the eye must be reduced to the essentials. Wasted information is also wasted image processing and this slows down replication and spoils image quality. So the breakthrough technology developed by SeeReal banks on highly logical yet keep-it-simple solutions. First of all, rather than boosting resolutions and intensifying display needs to unbearable levels, SeeReal has introduced Viewing Window technology. This actually limits display needs and corresponding diffraction angles. The benefit: a much larger display pitch, so for a 40 inch display the pixel size is in the range of at 25 – 50 microns. This is well within today’s state-of-the-art. Another benefit are smaller encoded hologram areas per scene point, with the shape and size of the sub-hologram closely linked to the 3D scene being viewed (sub-holograms are freely super-positioned, to accurately represent any 3D scene point distribution). Overall, the combination of these two basic principles means that it only takes today’s computing capabilities to create full parallax colour 3D HDTV images in real-time. For example, a 40 inch holographic TV would consume only approx three TFLOPS. Producing these viewing windows then limits the amount of computing power needed to see Holographic 3D. But what happens when there is more than one viewer? This is dealt with by faster displays and these are slowly coming to market. The information is multiplexed in real time and then doubled and tripled for each viewer. For a single user you will need a 120Hz display which are the standard now and for four users you need 480Hz displays. SeeReal’s initial designs with manufacturers in Asia will be able to serve four to five viewers in the first generation of panels. Of course for PC monitors you never need more than one or two so the gaming world will be one of the first industries to benefit from Holographic 3D. So the key here is the eye tracking technology that SeeReal already had which then allows for less computing power to serve up full resolution holography to four or five viewers.

_____

3D Holographic TV versus 3D TV:

While 3D TV relies on making use of special equipment like a Blu ray player, 3D holographic technology makes use of images that are projected on the viewing area and then viewed from all angles by the viewer. It is clear that 3D TV will make the viewers wear special 3D glasses without which it is not possible to produce 3D effects on TV. Scientists are trying hard to obliterate the need of 3D glasses as they prove to be a stumbling block in the popularity of 3D TV. This is where holographic TV scores over 3D TV as it does not rely on special glasses at all. In fact, holographic TV is certain to revolutionize the way TV has been viewed so far as instead of mounting a TV on a wall, the beams can be projected even on the floor or on to any area which is suitable for viewing. The real stumbling block so far in the production of 3D holographic TV is the refresh rate as the present rates are not good enough to give the viewer a real sense of motion. But scientists are working on this problem of refresh rates and are certain that they can come up with refresh rates that will allow the user to view almost real life pictures. Another hurdle in the development of 3D technology is the actual dearth of 3D content as far as programs in 3D are concerned. No standards have been set as far as encoding of 3D content is concerned. This makes it confusing to differentiate between the features of different brands of 3D TV. Holographic TV promises to be a step farther than 3D as it allows the user to project the beam anywhere in the room thereby enhancing the real feeling of watching a sports program is concerned.

_______

3D holographic projector:

Holographic projectors use holograms rather than graphic images to produce projected pictures. They shine special white light or laser light onto or through holograms. The projected light produces bright two- or three-dimensional images. While plain daylight lets you see some simple holograms, true 3-D images require laser-based holographic projectors. You can view such images from different angles and see them in true perspective. Miniature versions of such projectors are in development. Using such a projector, a smartphone could create an image for the viewer in an empty space rather than on a small screen. By 2004, digital displays were able to create interference patterns and take the place of the hologram on film. This meant that companies could start work on projecting videos on holographic projectors. The projector shines lasers or pure white light through a digital display that is programmed with interference patterns corresponding to a series of images. The process creates an image in front of the projector by passing the light through the interference pattern. In traditional projectors, light passes through a graphical image that blocks some of the light to create shading, and lets only some colors through to color the projected picture. Holographic projectors generate the projected image by refraction through the interference pattern, losing hardly any light, and operating much more efficiently. They can be very small and generate very little heat. This makes them ideal for eventual applications in mobile electronic devices, for which power and space are limited. A hologram or a digital holographic interference pattern works only with one color, since the interference pattern comes from the interference from a single wavelength of light. To obtain color, holographic projectors have to use colored lasers that illuminate the corresponding interference patterns for their colors.

True 3-D holographic projector:

A simple holographic projector with a light source shining through a flat interference pattern can produce an image that has three-dimensional qualities, but it is still flat. To create a true 3-D image, a holographic projector can use a spinning mirror to reflect the image to the observer. The mirror sends an image corresponding to the angle from which the observer is viewing the subject. As the observer moves around the subject he views it in different perspectives, and sees a three-dimensional image floating in space.

Holographic projector patented by Google in 2010:

A projection device having a coherent light beam-generator that generates a light beam and a beam expander disposed to receive the light beam and to emit an expanded light beam. The projection device also includes a digital micro-mirror device disposed to receive a holographic transform of an original image and to display the holographic transform for illumination by the expanded light beam into a holographic light beam with a convergent or focusing lens disposed to receive and modulate the holographic light beam and a liquid crystal plate volumetric image reconstructor that receives the focused holographic light beam and emits a 3-dimensional holographic image of the original image.

_______

Holographic screen:

Holographic projection film is a clear window tint like material that has high performance projection technology embedded into the film itself, holographic projection film allows you to convert and transform standard glass or acrylic surfaces into holographic projection displays within minutes. The above image is a real-life example of a holographic screen, where a video projector shoots light at a specially-coated piece of glass to show you a translucent image on a screen. If we define “holographic” like this, then we already have the technology. This is holographic screen and not 3D holographic display.

_______

3D holographic display:

Holograms are 3D images of 3D objects on 2D surfaces, 3D holographic display adds time to it, and so it becomes real-time hologram. When we watch 2D TV, we see people talking and walking in 2 dimensions. In 3D holographic display, we see people talking and walking in 3 dimensions as if they are actually in front of you. Although 3D holographic display screen is 2 dimensional, light from it enters our eyes in such a way that we see objects in 3 dimensions and in real-time.

__

3D Holographic displays in your home are still years off:

So far, only few research groups are able to generate real holographic image with large enough size, wide viewing angle, colours and video rate. Large size means less than 100 mm in each dimension. Wide viewing angle means smaller than 10 degrees. Overall, holographic display is still in the lab stage, and very far away from the commercialization stage. People in this field normally say it will take another 20 years for it to come, if they are optimistic. For some pessimistic ones, it may take more than 50 years.

There are three big difficulties in 3D holographic display.

1) How we provide enough optical information

2) How we calculate holograms fast enough

3) How to deliver the massive amount of hologram data in real time

We are now still far away these issues from the commercialization level.

_

The problem with creating 3D holographic displays is that the amount of information a typical hologram contains is vast; light contains a lot of information! As an example, it is thought that the order of a million-trillion pixels are required in order to achieve a pure 3D holographic display, and with a typical refresh rate of, say, 30 fps, this is a staggering amount of data. Not only this, we also need technology that can record (in real-time) all of the complex information of the light field, communications technology capable of transmitting this huge amount of data, and then a computer in order to process this data. Considering we are just about entering the 4K TV era (which is a screen made of approximately 10 million pixels), we are some way off.

_

Researcher Xuewu Xu and some of his colleagues from Data Storage Institute in Singapore succeeded in developing a method to create “real” holograms.  This new method of generating high-resolution, full-color moving holograms in three dimensions shows life from a new angle.  A new way of streaming high-resolution, full-color full-parallax three-dimensional (3D) hologram videos may have applications in the entertainment and medical imaging industries. Three-dimensional (3D) movies, which require viewers to wear stereoscopic glasses, have become very popular in recent years. However, the 3D effect produced by the glasses cannot provide perfect depth cues. Furthermore, it is not possible to move one’s head and observe that objects appear different from different angles — a real-life effect known as motion parallax. Now researchers have developed a new way of generating high-resolution, full-color, 3D videos that uses holographic technology. Holograms are considered to be truly 3D, because they allow the viewer to see different perspectives of a reconstructed 3D object from different angles and locations. Like a photograph, a hologram contains information about the size, shape and color of an object. Where holograms differ from photographs is that they are created using lasers, which can produce the complex light interference patterns, including spatial data, required to re-create a complete 3D object. However, generating high-resolution, moving holograms to replace current 3D imaging technology has proved difficult. To enhance the resolution of their holographic videos, Xuewu Xu and colleagues at the Data Storage Institute in Singapore used an array of spatial light modulators (SLMs). “SLMs are devices used in current two-dimensional projectors to alter light waves and generate projections,” explains Xu. “In a 3D holographic display, SLMs are used to display hologram pixels and create 3D objects by light diffraction. Each SLM in our system can display up to 1.89 billion hologram pixels every second, but this resolution is not high enough for a seamless large video display.”

_

To address this challenge, Xu and his team divided every frame of their hologram video into 288 sub-holograms. They then streamed the sub-holograms through 24 high-speed SLMs stacked together in an array. This technique was combined with optical scan tiling, which uses a scanning mirror to combine the signals from the SLMs, thus filling in any gaps in the physical tiling array. Finally, the researchers sped up the full-color video playback using powerful graphics processing units. This combination of technologies produced one high-resolution, full-parallax moving hologram displaying 45 billion pixels per second. “We increased the resolution of the holographic display system by 24 times,” states Xu. “The full-color 3D holographic video plays at a rate of 60 frames per second, so it appears seamless to the human eye.” Potential applications of the new technique include 3D entertainment and medical imaging. However, new SLM devices with a smaller pixel size, higher resolution and faster frame rate are required before large-scale 3D holographic video displays can become reality.

_______

_______

Plasma laser hologram:

Sci-Fi Style Holograms may soon be a Reality:

Holograms have been a basic feature of science fiction books and movies for the majority of the last century. For optical engineers, the technology to create a true freestanding hologram has been considered to be nearly unattainable. Recent developments, however, may soon change that. Current consumer holograms are not “true” freestanding holograms. Essentially, what we have today is a photographic recording of a light field, instead of a lens-formed image. These holograms are capable of being produced in a 3D manner with both perspective and parallax, giving the images a realistic change with regards to the perspective of the observer. Recently, there have been a few major breakthroughs in holographic technologies to bring us one step closer to its sci-fi counterpart.

_

Plasma lasers used to create images in mid-air:

To create an aerial hologram, you need to have a medium to work with — something that will either reflect or emit light at precise locations throughout a given volume, creating a three dimensional image of an object. From a classical geometric optics standpoint, in order to create the illusion of an object there must be some sort of light-emitting or light-modulating surface along the line from your eye to the points on the simulated object. If we are determined that they appear as objects in three dimensional space rather than being purely in the eye of the beholder then we have to do something very clever with a couple of different ray sources. These excite the air molecules at their point of intersection to emit light in a given wavelength or to reflect light in a given wavelength. The researchers chose a very common medium, air, and did something less common with it: turning it to plasma. You’ve seen air emit light when lightning strikes — it requires ionizing the air — ripping some of the electrons off of air molecules (and often breaking molecular bonds) creating a plasma — a set of unbound charged particles, that overall is electrically neutral. As the electrons reattach themselves to the air particles and “fall” back to their lowest energy state, they emit electromagnetic radiation, much of which is not visible. Lightning occurs when electrons from ionized air molecules (air plasma) return back to their lowest energy states. The light that we can see from plasma created in air appears whitish-blue with hints of purple. By focusing a laser very precisely, the researchers managed to create a tiny, isolated volume of plasma. These voxels, as they’re called, are the 3D equivalent of pixels; just as “pixel” stands for “picture element”, a “voxel” is a “volume element” — the basic building block of a 3D display.

_

Aerial Burton has used a plasma laser to float a 3D image in mid-air. At the moment it’s very rudimentary stuff but it shows that light can be viewed without the need to bounce it off a surface. Until now any “hologram” examples have required glass, smoke or water to bounce light from. The Aerial Burton breakthrough creates light in the air. So how is this possible without light bouncing back towards our eyes? The technology uses a 1kW infrared pulse laser which is focused on direct points in the air via a 3D scanner. At this stage the molecules in the air are ionised to create plasma. Since these plasma bursts only last a short while the laser needs to pulse in order to keep the area lit. While this means basic single colour images right now it’s an important step in the right direction. Enhanced resolution could mean a future where TVs are replaced by hidden laser projectors that create an image on thin air. But for now Aerial Burton is focusing on using the holographic projector to create signs for emergency situations. The kit can be car mounted so could prove useful for setting up temporary signs. But what the future holds for this technology remains to be seen.

_

Femtosecond plasma laser hologram:

In the past, nanosecond (billionth of a second) laser pulses were used to create aerial plasma. While these worked, the energy associated with the lit voxels was large enough to burn tissue. This time researchers used laser pulses of the order of femtoseconds (a quadrillionth of a second), and were able to create short lived, light-emitting plasma voxels that would not burn skin when touched, but would burn softer tissue like eyeballs. (Luckily, the plasma voxels emit light in all directions, and a bit of the emitted light is enough to see the image; no need to go sticking your eye into a cloud of plasma.) Like lightning, the plasma holograms also emit ultraviolet radiation and infrared radiation that we do not see. An excess of these can damage eyes, so for the time being, the researchers are suggesting that glasses with infrared filters be worn as a precaution.  The location of the voxels is determined by using a computer-generated hologram, which is a method of digitally creating interference patterns that are printed on a mask or film. The mask or film is also called a spatial light modulator and its role is to alter the phase and location of the coherent light source illuminating it.

_

The maximum amount of energy that could be transferred to a voxel is equal to the energy of the laser pulse. Lasers are often defined by their power, the amount of energy they transfer per second measured in watts. A watt is defined as 1 joule of energy per 1 second. Imagine two pulse lasers, both able to transfer 1 watt or 1 joule per second. The nanosecond laser pulse lasts 40 billionths of a second, delivering 40 billionths of a joule of energy. This doesn’t sound like much, but it’s a lot of energy for such a small volume. The femtosecond laser pulse, on the other hand, lasts 40 quadrillionths of a second, delivering an equivalent amount of energy; one millionth of the nanosecond laser’s output. The researchers tested out the effects of the holograms they created for different pulse durations (between 30 fs and 100 fs), and for different exposure times (pulses occurred every millisecond over a duration between 50 ms and 6 seconds). They used pig leather rather than human tissue, and found that if the voxels were irradiated for longer than 2000 ms, the energy associated with the plasma would be enough to burn the leather. With the femtosecond laser, the researchers were able to create multiple plasma voxels with one pulse and create voxels at a faster rate, leading to a well defined, bright 3D holographic image safe enough to touch, and feel.

_

The reason one can feel this type of hologram is that when plasma interacts with material, a shock wave is produced that then impinges on the material touching the plasma, causing a haptic (relating to the sense of touch) sensation. Shock waves are generated by plasma when a user touches the plasma voxels. The user feels an impulse on the finger as if the light has physical substance. Plasma is a little noisy, and when you touch it, a sound is also produced. The researchers measured the sound level produced 20 mm from the hologram for various settings and found the maximum sound level without touching the plasma was 77.2 dB when using 40 fs pulses. This is on par with the kind of sounds we hear in everyday settings, and provides auditory as well as tactile feedback when the holograms are touched.

_____

_____

3D volumetric display:

Viewing imagery on volumetric displays, which generate true volumetric 3D images by actually illuminating points in 3D space, is akin to viewing physical objects in the real world. Viewers can use their inherent physiological mechanisms for depth perception to gain a richer, more accurate understanding of the virtual 3D scene. These displays typically have a 360° field of view, and the user does not have to wear hardware such as shutter glasses or head-trackers. As such, they are a promising alternative to traditional display systems for viewing in 3D. A volumetric display device is a graphic display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. One definition offered by pioneers in the field is that volumetric displays create 3D imagery via the emission, scattering, or relaying of illumination from well-defined regions in (x,y,z) space. Some volumetric displays use voxels to describe their resolution. For example, a display might be able to show 512×512×512 voxels.  A voxel represents a value on a regular grid in three-dimensional space. Though there is no consensus among researchers in the field, it may be reasonable to admit holographic and highly multiview displays to the volumetric display family if they do a reasonable job of projecting a three-dimensional light field within a volume.

Most, if not all, volumetric 3D displays are either autostereoscopic or automultiscopic; that is, they create 3D imagery visible to the unaided eye. Volumetric 3D displays embody just one family of 3D displays in general. Other types of 3D displays are: stereograms / stereoscopes, view-sequential displays, electro-holographic displays, parallax “two view” displays and parallax panoramagrams (which are typically spatially multiplexed systems such as lenticular-sheet displays and parallax barrier displays), re-imaging systems, and others.

_

Volumetric displays project image points to definite loci in a physical volume of space where they appear either on a real surface, or in translucent (aerial) images forming a stack of distinct depth planes. With the first type of system, a self-luminous or light reflecting medium is used which either occupies the volume permanently or sweeps it out periodically. Technical solutions range from the utilization of fluorescent gas (with external excitation through intersecting rays of infrared light) over rotating or linearly moved LED-panels to specially shaped rotating projection screens. Rotating screens have been implemented in the form of a disc, an Archimedian spiral or a helix, winding around the vertical axis. Among the displays with a real collecting surface, the helical design has reached maturity. The most elaborate equipment uses a double-helix filling an 91-cm-diameter by 46-cm-high volume at 10 revolutions per second with a maximum of 40,000 color pixels per frame (or 120,000 pixels in the color primaries) . Observers can walk around the display and see the imaged objects from different angles. The second type creates aerial images in free space which the observer perceives as cross sections of a scene lined-up one behind the other (multiplanar display). The images belonging to different depth layers are written time-sequentially to a stationary CRT. The observer looks at the screen via a spherical mirror with a varying focal length (varifocal mirror). Rendition of the depth layers is synchronized with changes of the mirror’s shape, so that slices of the 3-D volume are successively created in planes of varying distance. The oscillating process is repeated at 30 Hz (which is insufficient to avoid flickering). Due to phosphor persistence, only a limited number of planes can be displayed without visible image smear. Usually, the mirror is a circular flexing membrane with a metalized surface which is forced to oscillate by means of an acoustical woofer. The deformation of the mirror (maximum 4 mm) yields an optical leverage of approximately 70:1. Variations of optical magnification are compensated by reciprocal magnification of the CRT-images. A volumetric display with additional display of high-definition 2-D background images has been recently announced. In volumetric displays the portrayed objects appear transparent, since the light energy addressed to points in space cannot be absorbed by foreground pixels. Practical applications seem to be limited to fields where the objects of interest are easily iconized or represented by wireframe models.

_

From radar, sonar, and x-rays to lasers and multispectral technologies, new imaging systems are offering more options for war-fighters to gain a strategic advantage in situational awareness. And the next big advance could provide the most comprehensive view yet. 3D volumetric displays could give war-fighters a glasses-free, full color, high-resolution three-dimensional perspective of the battle-space — on, above, and even below it, depending on the environment. 3D volumetric displays will be key to the ongoing development and evolution of display technology. The latest research and development out of SCHOTT Defense’s joint development partner, 3DIcon, offers a glimpse of that future. Its volumetric displays create a 3D image by projecting precisely coordinated laser beams into a medium containing rare earth materials, exciting those materials to display a monochromatic image, though full-color images are planned for the future. 3DIcon’s CSpace technology is developing a unique clear host material doped with rare-earth ions to create a transparent 3D projection medium capable of fluorescence. This achievement means the CSpace 3D volumetric displays don’t require special eyeglasses or viewing aids, nor do they cause fatigue during prolonged use. CSpace allows the full display, manipulation, and exploitation of internal volume imaging as well, whereas other laser display systems, such as holographic displays, can only render surface volume, and are unable to show an interior view. Glass is the enabling and critical material acting as the host medium for the laser-excited rare earth materials. A new kind of laser glass could improve the quality of the image and the efficiency of the laser, while also facilitating the rapid scaling of 3D volumetric display systems so they can be deployed to war-fighters en masse. The glass’ laser properties, customizability to different compositions, and manufacturability all make it integral to the laser system used to project the 3D images. And like many defense technologies, 3D volumetric displays will eventually have applications far beyond the battlefield that could make the world safer, more aware, and better informed. Here are five ways 3D volumetric displays could eventually transform the wider world outside defense:

  1. Faster airport security checks and border crossings. By fully capturing the 3D capability of x-ray imagery, border and customs inspectors can more effectively scan and observe the interiors of vehicles, trucks, shipping containers, and packages. True 3D displays offer officials multiple perspectives to resolve ambiguity. TSA screeners would gain a clearer view of the objects in your suitcase, potentially reducing additional screenings of suspect luggage.
  2. Safer air traffic control. Several recent near-crashes between airplanes have raised scrutiny over air traffic control systems. Current systems display the position of airplanes as icons on a flat 2D display. With 3D volumetric displays, however, operators would have a more comprehensive overview of the airspace and planes’ location in relation to one another and better navigate them to and from runways.
  3. Better preparations for natural disasters and more. The federal government undertakes geospatial exploration in which it collects, maintains, and uses information linked to geographic locations to help in decision-making and to support national security, law enforcement, health care, environmental protection, and natural resources conservation, among other functions. 3D volumetric displays would offer more information for geospatial analysis that could improve road maintenance and natural disaster responses.
  4. More accurate oil and gas exploration. Seismic data is critical in assessing a particular area for potential oil and gas extraction. However, seismic data suffers because 3D data is still underutilized by 2D displays. 3D volumetric displays, by offering a detailed 3D depiction of where deposits might lie, how large they are, and how accessible they might be, can make the expensive process of oil and gas exploration more efficient, accurate, and productive.
  5. Greater visibility during medical operations. MRIs and CT scans are incredibly powerful diagnostic tools rich in 3D data. 3D volumetric displays can provide volume rendering of the surface and the interior of any human organ, increasing the effectiveness of real-time imaging systems for doctors and surgeons who need better awareness of what’s happening inside the human body.

While the current imperative is on improving the operational capabilities of the warfighter, the potential future applications are diverse and transformative, changing the way border patrol agents, air traffic controllers, seismologists, and doctors observe and understand the world around them.

______

Volumetric printing:

Volumetric printing is a three-dimensional digital-to-physical imaging technology developed in 2013 that uses ink or other pigments suspended in a volume to form a full-color volumetric scene in physical space. It is a static version of volumetric display. Volumetric prints are auto-stereoscopic, full parallax (in both horizontal and vertical viewing arrangements) and can be viewed by multiple viewers in regular room lighting. A volumetric print can be thought of as a reconstructed light field based on the scattering of light by distributed pigments in volume. Any three-dimensional scene can be volumetrically printed, although biological specimens and volumetrically X-rayed objects (i.e., CT scans) are thought to be particularly well suited to this type of imaging. There are several methods for producing a volumetric print, the most common being an index-matched stack of hundreds of sheets of thin clear material (most often PMMA, also known as Lucite or acrylic). Each sheet in the volumetric stack is printed with a color slice of a digital 3D model, placed in a vacuum chamber, and then injected with a fluid matching the index of refraction of the sheet material. Volumetric printing has been called “Hologram 2.0” by a company marketing the technology. Volumetric prints however are not produced in the same manner as holograms, in that there is no interference pattern generated or used in basic volumetric prints.

______

_______

Hologram and phone:

_

Holography in mobile phone:

Holographic projecting mobile phones will incorporate a powerful processor which will take a 2D image and then create 3D holograms by way of using “Fourier” algorithms to give them a third dimension without resolution loss.

Picture-

_

Virtual holographic projection imaging technique make use of interference and diffraction theory. It record and reproduce objects in real three- dimensional image. Haptic sensors are embedded along the device. If Holographic Projection is implemented successfully many touch screen such as one we seen in “Iron Man” movie can be implemented.

_______

RED surprises everyone with ‘hologram’ phone:

RED is introducing to the smartphone market, the world’s first holographic device, the Hydrogen one. RED is noted for making high quality-digital cinema cameras and is bringing all those awesome features into your pocket. The Hydrogen One promises to be the future of personal communication by offering 3D and 4D visuals on a 5.7’’ holographic display that allows you experience “look around depth” in the palm of your hand. Hydrogen One comes cased in either aluminium ($1,195) or titanium ($1,595).  But for that price, it’s promising a phone that can deliver a holographic view or ‘4-View’ without a wearable display and “multidimensional audio” powered by its H3O algorithm.  The device will also offer modular attachments for shooting video, stills, and holographic content. The phone also integrates with its cinema cameras as a user interface and monitor. It will be powered by Google’s Android operating system. Hydrogen One is a phone, sort of. It’s also a holographic playback device (plus 2D, 3D, AV/VR/MR). And, it looks like it will feature a modular design (like RED cameras) that will enable it to shoot high quality video footage handheld in a package not much bigger than a smartphone.  Essentially, RED Hydrogen One is an Android smartphone referred to as “holographic media machine” for viewing and capturing “multidimensional” imagery, and its special algorithms will be used to convert stereo sound into multi-dimensional audio to add to the immersive experience.

_

The idea is that the screen projects 3D objects that you can view from different angles based on your physical position. For example, a mapping application could theoretically look like a little model of a city with buildings poking out of the screen. You’d then be able to interact with the objects “above” the display through hover gestures. Light field displays makes use of numerous layers of LCDs with a directional backlight that would allow users to see two different views of the same object, generating a 3D effect.  The technology works through diffraction, producing a light field illumination with a layer of nanostructures added to a conventional LCD. This “diffractive light field backlighting” layer doesn’t significantly compromise the display’s quality, battery consumption, or thickness for non-holographic use. However, for photos, games and videos to be viewed in holographic form, they will have to be produced or shot in ‘.h4v’ format (holographic 4-View).

_____

Holoflex:

Researchers at Queen’s University Human Media Lab in Australia showed off Holoflex, a holographic, flexible phone with an OLED display that’s a breath of life into the future of smartphones. This means holograms without 3D glasses or any kind of equipment, that can be viewed at any angle. For the hologram to work, the phone’s display is covered by more than 16,000 fisheye lenses that bend the light from the screen, like projecting the image through a glass ball. The curvature of each lens shows a different portion of the image as the viewing angle changes, giving the impression of a hologram. While the underlying screen is 1920×1080 pixels, the final resolution (after being translated through all those fisheye lenses) is 160×104. That resolution won’t wow any consumers, but as the Human Media Lab’s video shows, it’s more than enough to be a proof of concept for tasks like video calling or playing simple 3D games. Plus, the phone still retains the standard Android phone specifications, with a 1.5 GHz Qualcomm Snapdragon 810 processor and 2 GB of memory, and it runs Android Lollipop. This technology certainly won’t be in smartphones in this decade, but in terms of promising future technology, this is near the top of the list. This holographic, flexible display could be used for 3D video conferences.

_____

_____

Applications of holograms:

Ever since its commercial usage in the 70’s, there is no looking back for holography and hologram products. The demand has only manifolded with each passing year. Holography has found its applications in almost all industrial sectors including commercial & residential applications. Holograms are big business. It is predicted that holographic technology in the display industry alone will earn a staggering $3.57 billion by 2020. There is no doubt about the fact that in few years from now, you will see a new world of holograms in every aspect. The use of holograms is the representation of a new visual language in communication, where we are moving into the age of light as the media of the future. Holography will soon be an integral part of the light age of information and communications. Holographic Technology has endless applications as far as the human mind can imagine. It will become a very integral part of human societies and civilizations in the future.  In future, holographic displays will be replacing all present displays in all sizes, from small phone screen to large projectors.

_

Holography – Current and Future Applications:

Holography is a very useful tool in many areas, such as in commerce, scientific research, medicine, and industry.

Some current applications that use holographic technology are:

  1. Holographic interferometry is used by researchers and industry designers to test and design many things, from tires and engines to prosthetic limbs and artificial bones and joints.
  2. Supermarket and department store scanners use a holographic lens system that directs laser light onto the bar codes of the merchandise.
  3. Holographic optical elements (HOE’s) are used for navigation by airplane pilots. A holographic image of the cockpit instruments appears to float in front of the windshield. This allows the pilot to keep his eyes on the runway or the sky while reading the instruments.  This feature is available on some models of automobiles.

_

  1. Medical doctors can use three-dimensional holographic CT scans to make measurements without invasive surgery. This technique is also used in medical education.
  2. Holograms are used in advertisements and consumer packaging of products to attract potential buyers.
  3. Holograms have been used on covers of magazine publications. One of the most memorable Sports Illustrated covers was the December 23, 1992 issue featuring Michael Jordan. Holograms have also been used on sports trading cards.
  4. The use of holograms on credit cards and debit cards provide added security to minimize counterfeiting.
  5. Holography has been used to make archival recordings of valuable and/or fragile museum artifacts.
  6. Sony Electronics uses holographic technology in their digital cameras. A holographic crystal is used to allow the camera to detect the edge of the subject and differentiate between it and the background. As a result, the camera is able to focus accurately in dark conditions.
  7. Holography has been use by artists to create pulsed holographic portraits as well as other works of art.

_

Future applications of holography include:

  1. Future colour liquid crystal displays (LCD’s) will be brighter and whiter as a result of holographic technology. Scientists at Polaroid Corp. have developed a holographic reflector that will reflect ambient light to produce a whiter background.
  2. Many researchers believe that holographic televisions will become available within 10 years at a cost of approximately $5000. Holographic motion picture technology has been previously attempted and was successful in the 1970s.The future of holographic motion pictures may become a reality within the next few years.
  3. Holographic memory is a new optical storage method that can store 1 terabyte (= 1000 GB) of data in a crystal approximately the size of a sugar cube.
  4. Optical computers:

An optical computer is a computer that performs its computation with photons as opposed to the more traditional electron-based computation. An optical computer (also called a photonic computer) is a device that uses the photons in visible light or infrared ( IR ) beams, rather than electric current, to perform digital computations. Optical or photonic computing uses photons produced by lasers or diodes for computation. For decades, photons have promised to allow a higher bandwidth than the electrons used in conventional computers. Electric energy flows slower than the speed of light in computers. This limits the rate at which data can be exchanged over long distances, and is one of the factors that led to the evolution of optical fiber. By applying some of the advantages of visible and/or IR networks at the device and component scale, a computer might someday be developed that can perform operations much faster than a conventional electronic computer. Visible-light and IR beams, unlike electric currents, pass through each other without interacting. Several (or many) laser beams can be shone so their paths intersect, but there is no interference among the beams, even when they are confined essentially to two dimensions. Electric currents must be guided around each other, and this makes three-dimensional wiring necessary. Thus, an optical computer, besides being much faster than an electronic one, might also be smaller. Optical computers will be capable of delivering trillions of bits of information faster than the latest computers. Holography is used in optical computers. Optical computers will use holograms as “circuit elements”. Parallel processing is made possible because when a Hologram is addressed, all the information comes out simultaneously. Indeed, as computing begins to be based on light (photons), rather than electricity (electrons), holographic storage could one day be the storage solution of choice.

_

Photonic devices:

Photonics is an emerging technology, comparable to semiconductor technology. Many functions in technical applications are currently realised by semiconductor products. The expectation is that photonic devices will partially replace existing semiconductor devices, but on top of that will also complement these in a qualitative way. Photonic devices are components for creating, manipulating or detecting light. This can include laser diodes, light-emitting diodes, solar and photovoltaic cells, displays and optical amplifiers. Other examples are devices for modulating a beam of light and for combining and separating beams of light of different wavelength. The unique characteristics of photonic devices create an additional dimension like enlarged bandwidth, energy saving and larger communication distances. In addition, photonic devices are less sensitive to interference and have unique physical characteristics. Future photonic devices such as electro-optical chips will undoubtedly incorporate micro-lasers and HOEs for optical computations, free-space interconnects, and massive analog and digital memory systems.

______

Hologram labels and stickers:

Hologram Labels:

Hologram labels are very widely demanded as they play a vital role for security in almost all conceivable sectors in the market from OEMs to distributors and retailers. Hologram labels are easy to use and are a very cost effective solution against duplication. These labels when affixed on the desired place provide a direct visual means for the final customer to verify the genuineness of the product. Today, it is seen that that the public universally accepts as proof of authenticity only those products with hologram labels depicting depth, color and movement in an imprint. The hologram is irreplaceable in the current battle against counterfeit merchandise. Many manufacturers supply hologram labels in sheets for manual application and in reels for automatic machine application.

_

Advantages of Hologram Labels:

Hologram labels have certain advantages which are not available in ordinary printed labels. These are as follows:

  • Hologram labels cannot be copied.
  • They cannot be altered.
  • They cannot be adapted or manufactured cheaply from scratch.
  • Hologram labels are also unique as they are able to provide covert (hidden) identity and overt (visual) identity embedded within the same area of the space printed.
  • From a purely branding and impact point of view, hologram labels affixed on any packaged product extends much more shelf-appeal and adds greatly to consumers’ perception of quality.

_

Applications of hologram labels:

Hologram labels are used in many products like as follows:

  • Company ID cards
  • Membership cards
  • Artwork
  • Coins
  • Autographed & licensed products
  • Gift certificates
  • Bank checks
  • Product Packaging for brand protection.
  • Parking Passes
  • Driver’s license
  • Pharmaceuticals
  • Cigarettes and alcohol
  • Clothing
  • Cosmetics etc.

_

Hologram Stickers:

Hologram stickers are widely used for various security and branded purpose. Hologram stickers are very popular and more demanded compared to other visual mediums that represent images on a two-dimensional surface because they are able to depict objects that are holographed with an added dimension of depth. Every detail on a hologram or hologram stickers from its depth to the textures is produced using coherent light sources like laser beams or electronic beams. Hologram stickers are today used to carry a variety of messages in a wide array of shapes, sizes and forms across a large spectrum of products and objects. Most hologram stickers are self-adhesive tamper-evident security hologram stickers providing authentication, security and protection against counterfeit.

_

Types of Hologram Stickers:

  • DOT-MATRIX Holographic Sticker

In Dot-Matrix Hologram, there are unlimited computer controlled and laser beam engraved dots. Each dot depicts a separate diffraction grating. They create a beautiful impact of variable images on a single sticker. Dot-matrix Hologram stickers can have lots zooming, moving, flipping effect etc. which add to their popularity.

  • True Color Holographic Sticker

True Color Holograms are those holograms that are made up of photographic quality artwork. These stickers are highly demanded because they are a very good way to achieve anti-counterfeit performance. This is because they cannot duplicate or copy hologram sticker close to original one if they do not get the original photo.

  • Flip-Flop Holographic Sticker

Flip-Flop hologram has the unique property of displaying two images from two different viewing angle. In other words, when the viewing angle changes left to right (horizontally) or upside and down (vertically), different images emerges through the hologram. One hologram image will be hidden and another hologram image will display when the view angle is changed.

  • Kinetic movement Sticker

Like flip flop hologram, Kinetic movement hologram stickers can also be seen from different viewing angle. These hologram stickers are made both by 2D/3D and dot-matrix type hologram.

  • Combination of Holograms

Combination holograms can be used to make stickers that create an impact that not only has extra-ordinary viewing effects but also security features. Usually, it is recommended to combine 2D/3D and dot-matrix types which can have the advantages of both the sharp kinetic movements of dot-matrix and the depth of 2D/3D holograms into the stickers.

  • 2D/3D Hologram Stickers

These hologram stickers are made up of multiple two dimension layers. The images are visually placed one over the other with visual depth which produce an effect of three-dimensional structure on the stickers. The stickers have very good visual depth between different layers and shininess on the first layer.

  • 2D Hologram Stickers

These stickers are made up of two dimension images. The images are given various colors and position in one layer. The sicker has one layer on hologram image without visual depth.

  • Micro text or image Sticker

These hologram stickers can be clearly seen by magnifier and difficult to be seen clearly by naked eye.

  • Transparent hologram sticker

These are see through type stickers, pasted onto documents. Then text under hologram image can be seen through transparent holographic sticker

_

Properties of Hologram Stickers

  • Pressure tamper evident holographic sticker:

These stickers are damaged when they are removed. The holographic image is easily destroyed under pressure when the sticker is teared off and then the sticker cannot be reused again.

  • Different Color or Thickness of Holographic Sticker:

Various color options are available like metalized film, silver, gold, blue, green etc. However, the most popular colors are usually silver color or golden metalized color. The stickers are also available in varied thicknesses. The thicker the material, the heavier is the sticker , and hence a little more expensive than the thinner sticker.

  • Hidden Text or Image

Hidden text or image feature on a hologram sticker means a unique encrypted image or text, which is invisible to the naked eye but is detected by means of a pocket laser reader.

  • Serial Number Hologram Sticker

Serial numbers on hologram stickers are extra security feature. They improve management of goods and provide anti-counterfeit ability by pasting each hologram sticker onto the package of goods.

  • Overprinting Release

Overprinting released hologram stickers leaves a black overpriting word ‘VOID’ after the sticker is peeled off. It can also be in other colors.

_

Applications of Hologram Stickers:

Hologram stickers are used to enhance brand image & security in various types of industries. Stickers are used as a very attractive and viable option in product packaging and security applications. Hologram stickers find application in industries & sectors as listed below.

The list of application of hologram stickers is growing day-by-day.

  • Chemicals / Detergents, Fertilizers, Seeds
  • Fine Jewellery / Watches
  • Building Material / Hardware
  • Aircraft/ Automotive & High Technology/Engineering Spares & Machine Parts
  • Sporting goods, Toys, Gifts/novelties
  • Electrical/ Electronic Appliances & Components
  • Recording Media
  • Clothing Hang-tags
  • Branded fashion wear & Accessories
  • Driving Licenses
  • Certificates
  • Confidential Documents & Envelopes
  • Security, Bonds, Financial & Share Certificates
  • Bank Cheques
  • Drafts & Guarantees
  • Loyalty / Vouchers/ Reward /Passes
  • Credit Cards/ Membership/ ID cards
  • Computer Peripherals
  • Stationery Products
  • Automotive Components
  • Passport
  • Excise Revenue Stamps etc.

_____

_____

Mapping:

Paper and such kind materials or plastic materials are used to produce maps. Conventional materials have some deficiencies to present the real geographic information such as terrain model and geographical features. Hologram as a map publishing material is at the point of covering these deficiencies.

__

Entertainment:

Holograms have also proven effective in the entertainment industry. Various Hollywood movies, specially the science fiction films, have used holographic special effects. Even movie posters are made holographic. Holograms are also used as promotional tools on records and CD covers.

_

Packaging(Consumer Goods Brand Protection):

This is one area where holograms have become popular. Hologram packaging includes flexible packaging, board packaging, rigid box, pack packaging etc. The holographic packaging provides eye catching visual impact, authentication, and added value. In reality, all products are subject to counterfeiting. Hence proper holographic packaging on consumer goods serve an important way for brand protection.  An example: Brach & Brock Candy Company projected a three-fold increase in sales using holographic packaging.

_

Promotional:

Holograms are widely used for promotional purpose. The use of hologram completes the packaging, the promotional activities associated with your product and add some attraction towards it. It is widely demanded because it enhances company’s image and some shelf appeal also.  An example: You open your favorite magazine and find a 3D image of the new BMW roadster driving right off the page and into your room. This is new age hologram.

_

Gifts:

Today holographic products have become important gift items for corporates as well as individuals. The holographic gifts serve as important way to enhance brand image. For many, holographic items are rare collectibles which they can treasure for a lifetime.

_

Point of Purchase Advertising:

An example: You walk into a shoe store and see a larger than life-size, complete-color image of the latest Nike shoe hovering before your eyes. It rotates so that you get a proper view from the front and side. That is the power of New Generation Hologram. It makes things look real.

_

Tax Stamp:

As a security devise, holograms are widely used on tax stamps of many countries. Tax stamps are issued by governments principally on alcohol and tobacco to ensure duty is paid and to distinguish genuine products from fakes. There are two varieties of holographic tax stamp—hologram tax stamp with security paper and only hologram with or without serial no.

_

Display:

Display holography use all types of holograms from decorative foils to display holograms to eye catching stereograms. Display holography is used in point of purchase, corporate display, trade show. They use various holograms , including large format holograms for their dramatic effect.  An example: A hologram was used in Continental Tire’s in-store display, which received highest ever dealer response.

_

Decoration:

Another main application of hologram is in decoration. With its glitter color changing effect, multi-channel visual enhancement, the packaging with hologram foil, holograms are sure to attract the customer and increase the visual value of products inside.  An example: Blanton Whiskey added a hologram to its bottle and this led to an instant and increased sale.

_

Art and Interactive Graphics

Art and Interactive Graphics is a very special area of holography, comprising is the most exciting area for printing. Holography is an art in itself as it deals with making some kind of visuals. By using holographic effects for the background of over printing lithography, some of the in-store lighting problems of holograms can be overcome. Color printing combined with holography form stunning interactive visual effects.

_

Engineering, Architecture & E-Commerce:

You can enhance design visualization by using a New Generation Hologram in computer-generated three-dimensional images, CAD/CAM designs. That is why holograms are widely preferred by professional users, such as architects, engineers, production companies.

_

Sports Events:

Holograms have become a common and a regular feature of the world’s premier sporting events. These are used to protect event tickets, event merchandise, and also accreditation programs.

_

Professional Photographers:

Professional photographers can also use holographic technique as add-ons or alternatives to regular two-dimensional portrait photography products.

_

Holographic Interferometry [vide supra]:

Holographic interferometry is used in numerous laboratories for non-destructive testing (NDT). It visually reveals structural faults without damaging the sample. Holography offers a number of advantages, such as direct and overall visualization of defects, such as disbonding, formation of cracks, and inhomogeneities on large surfaces. This is done without interaction with the object under test and the surface to be studied. It is possible to detect deformations as small as a few microns. This kind of testing can be used to detect and observe cracking in fatigue tests; and it can be used for the visualization of the modes of vibration of mechanical structures. This technique is useful in industrial stress analysis, quality control etc.

_

Architecture:

Holographic technology will play a more prominent role in the creation of 3-D architectural models. Such architectural renderings would be able to show if a building design had any critical flaws, or if any of the dimensions were improperly calculated. Virtual holography provides an interactive 3-D model, which opens up considerable presentational opportunities, such as fully interactive virtual images. Architects can change the materials and interiors in real time with the help of a touchpad, tablet, or other device.

_

Display of artifacts:

Many museums have made holograms of valuable articles in their collections, both for insurance purposes and to check for deterioration. In the former Soviet Union exhibitions of holograms of national treasures were sent to remote areas, enabling people to see and appreciate their national heritage without the necessity of travelling to major museums in Moscow or St. Petersburg.

_

IT consumables:

Lots of the IT consumables use hologram on its package and opponent for security and logistic.

_

Optical Devices:

Holographic lenses, diffraction gratings are optical devices in which the “object” is a mirror or a lens. They can be used to perform more specialized functions like making the panel instruments of a car visible in the windshield for increased safety.

_

Hologram Mouse pad:

Hologram mouse pads are very popular category of mouse pad used for promotional purpose. Mouse pads of various types and materials are available in the market today. Lenticular and holographic mouse pads have seen a rising demand today because they serve both the purpose of fashion and functional. They provide that eye-popping promotion that will never be forgotten by any customer. Compared to a normal leather or a rubber mouse pad with graphic, there is no doubt about the fact that a holographic mouse pad will definitely catches everyone’s attention. Holographic mouse pads are ideal to make your clients mesmerized as any message or image comes to life through holographic processes increasing the impact of your promotional message.  Usually, holographic mouse pads are created using a thick polycarbonate clear plastic top or a polyester surface applied to a dense rubber base. The hologram image is then imprinted on the top. The image is then layered between a base material and the protective plastic surface creating a mouse pad of durability and style.

_

Holographic Wills:

Holographic wills tend to be wills that are in a testator’s own handwriting. Some states require that everything in the holographic will to be in writing in order to be valid. Other states only require that material provisions be in the testator’s handwriting.  And some states do not recognize these types of wills. A holographic will is written by the testator himself. Therefore, there is not usually much expense involved in comparison to an attested will that may be prepared by a lawyer. This also makes it easier for middle income and lower income individuals to have a will in existence.  Holographic wills can be drafted with a mere paper and pen. If a person knows that he or she is about to undergo surgery or an important medical procedure, he or she may quickly draft such a will without having to worry about the same formalities as attested wills, such as the requirement of having witnesses available.

_

Measurements:

Particle physicists make holographic records of bubble-chambers from which accurate measurements can be made.

______

______

Security [vide supra]:

One of the fastest and the most popular growing area for the use of holograms is the security and product authentication. The presence of holograms indicates the authenticity of these items. They provide a powerful obstacle to counterfeiting. The security holograms have proven to be unsurpassed when added to documents, anti-counterfeiting, tamper-proofing, customizing ticket protection, identification documents including credit and phone cards, drivers licenses etc. The trend that almost all credit cards carry a hologram is a good sign that security holography has proven to be very effective.  Security holograms are very difficult to forge, because they are replicated from a master hologram that requires expensive, specialized and technologically advanced equipment. They are used widely in many currencies, such as the Brazilian 20, 50, and 100-reais notes; British 5, 10, and 20-pound notes; South Korean 5000, 10,000, and 50,000-won notes; Japanese 5000 and 10,000 yen notes, India 50,100,500, and 1000 rupee notes; and all the currently-circulating banknotes of the Canadian dollar, Danish krone, and Euro. They can also be found in credit and bank cards as well as passports, ID cards, books, DVDs, and sports equipment.

_

Covertly storing information within a full colour image hologram was achieved in Canada, in 2008, at the UHR lab. The method used a fourth wavelength, aside from the RGB components of the object and reference beams, to record additional data, which could be retrieved only with the correct key combination of wavelength and angle. This technique remained in the prototype stage and was never developed for commercial applications.

_

Holographic scanners are in use in post offices, larger shipping firms, and automated conveyor systems to determine the three-dimensional size of a package. They are often used in tandem with checkweighers to allow automated pre-packing of given volumes, such as a truck or pallet for bulk shipment of goods. Holograms produced in elastomers can be used as stress-strain reporters due to its elasticity and compressibility, the pressure and force applied are correlated to the reflected wavelength, therefore its color.

____

____

Holographic Art:

Early on, artists saw the potential of holography as a medium and gained access to science laboratories to create their work. Holographic art is often the result of collaborations between scientists and artists, although some holographers would regard themselves as both an artist and a scientist. For over 30 years artists have been using holography as a technique to explore space, time, movement and light in artwork. Nevertheless, holographic art is still seen as more of a scientific subject than an artistic subject to the public eye, due mainly to the existence of old conceptions about what art is. The definition that Art is an open book means that “everything” can be art and “nothing” can be art. The artist can be a psychologist, philosopher, doctor, mathematician, politician, teacher, and scientist, whatever needs to be depicted in the subject within their art. Artists have a “motivation” that is close to them which makes them unique, special and an expert in their field. The use of Art as a vehicle to explore and illustrate the variety of a subject is a form that allows artists to express themselves giving the freedom for individual interpretation. Equally Holography has its own characteristics, which provide new opportunities for artists and artwork creating the possibility of presenting a subject in 3D space on a flat surface.  Artists became involved with holography almost as soon as it became a practical optical process.

_

Salvador Dalí claimed to have been the first to employ holography artistically. He was certainly the first and best-known surrealist to do so, but the 1972 New York exhibit of Dalí holograms had been preceded by the holographic art exhibition that was held at the Cranbrook Academy of Art in Michigan in 1968 and by the one at the Finch College gallery in New York in 1970, which attracted national media attention.  In Great Britain, Margaret Benyon began using holography as an artistic medium in the late 1960s and had a solo exhibition at the University of Nottingham art gallery in 1969.  This was followed in 1970 by a solo show at the Lisson Gallery in London, which was billed as the “first London expo of holograms and stereoscopic paintings”.  During the 1970s, a number of art studios and schools were established, each with their particular approach to holography. Notably, there was the San Francisco School of Holography established by Lloyd Cross, The Museum of Holography in New York founded by Rosemary (Posy) H. Jackson, the Royal College of Art in London and the Lake Forest College Symposiums organised by Tung Jeong. None of these studios still exist; however, there is the Center for the Holographic Arts in New York and the HOLOcenter in Seoul, which offers artists a place to create and exhibit work. During the 1980s, many artists who worked with holography helped the diffusion of this so-called “new medium” in the art world, such as Harriet Casdin-Silver of the United States, Dieter Jung of Germany, and Moysés Baumstein of Brazil, each one searching for a proper “language” to use with the three-dimensional work, avoiding the simple holographic reproduction of a sculpture or object. For instance, in Brazil, many concrete poets (Augusto de Campos, Décio Pignatari, Julio Plaza and José Wagner Garcia, associated with Moysés Baumstein) found in holography a way to express themselves and to renew Concrete Poetry. A small but active group of artists still integrate holographic elements into their work. Some are associated with novel holographic techniques; for example, artist Matt Brand employed computational mirror design to eliminate image distortion from specular holography. The MIT Museum and Jonathan Ross both have extensive collections of holography and on-line catalogues of art holograms.

_

Around the world, there are pioneering artists using the three-dimensional recording opportunities of holograms to bend and cut space; construct multiple, visually solid, objects in the same volume; combine collections of still images or video to produce animated 3D works, and to sculpt pure light. Holography can be used as a new artistic medium, as many artists use holograms to capture their subjects. Holograms also can be used to preserve art with a holographic copy, which can be made that is nearly as good as the original, without damaging the original.

_______

_______

Holography in Healthcare:

Holography could also revolutionise medicine, as a tool for visualising patient data while training students and surgeons. The medical sector is usually at the forefront of technological deployment. Any innovation that has the potential to drive discovery in research, improve medical operations and enhance patient care is likely to see some implementation. While some deployments have more wide-ranging and long-lasting effects than others, technology continues to spur understanding and progressive treatment in this essential field.  Digital holograms—whether of DNA, cells, full-sized organs, or even the life-sized human body itself—can be holographically printed for a range of 3-D analysis applications in the biomedical industry.  Many medical systems generate complex data using advanced imaging technology, such as Magnetic Resonance Imaging (MRI) and ultrasound scans. Normally, that electronic information is used to display a flat image on a computer screen, but it can also be used to produce full colour, computer-generated 3D holographic images.  3-D digital holograms can be created from almost any type of biomedical datasets from protein database files to medical scans, such as computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound scans. 3D holography, in particular, stands to enhance visual understanding of the human body. What 3D holographic technologies offer that other visual forms cannot is the ability to show parts of the human body in a real-life fashion. Furthermore, they are interactive, enabling medical practitioners to not only study images of the body, but to do so easily and from multiple perspectives. The capacity for enhanced visual engagement can benefit research, diagnostic efforts and treatments, as sophisticated 3D software, displays and holograms can be synthesized for a realistic, real-time look at patient conditions. One issue in medical training that previously seemed insurmountable was the lack of tools that allowed students to interact consistently with real human anatomy. If training is mostly confined to images seen in textbooks and on film, as well as occasional work with cadavers, many students have limited opportunities to engage directly with human anatomy. With 3D holograms, such as those Zebra Imaging produces, students can get better insight into the human form. The interactive, detailed human anatomy hologram lets students examine the actual 3D structure of the human body, rather than the 2D images that would be available in textbooks and computer-based learning tools. One study found that students who use medical holograms perform better than their textbook-informed counterparts, as they have a greater understanding of the myriad, minute spatial relationships in the human body.

_

Medical Applications of Holography Techniques:

Recent improvements in hologram recording techniques and the availability of tools for the interpretation of holographic interferograms and the success of holographic techniques in imaging through tissues, ophthalmology, dentistry, urology, otology, pathology, and orthopaedics shows a strong promise for holography to emerge as a powerful tool for medical applications. Holographic 3D images of eyes and interferometric testing of human teeth and chest motion during respiration were carried out quite early.

  • Mostly the holographic interferometric techniques have been used for biomedical applications. Holographic interferometric techniques have been widely applied with success for the study of different parts of human body including cornea, tooth mobility, tympanic membrane, basilar membrane, cochlea, temporal bone, incudo-mallar joint, chest, stull, and bones.
  • X-ray holography can be applied for real-time imaging of internal parts of the body and living biological specimens with very high resolution without the need for sample preparation.
  • Endoscopic holography has opened up the possibility of noncontact high resolution 3D imaging and nondestructive measurements inside the natural cavities of internal organs. Endoscopic holography is a powerful tool for non-contact high resolution imaging and nondestructive measurements inside the natural cavities of human internal organs.
  • Three dimensional images of biological specimens can be synthesised from a series of two dimensional radiological images using the techniques of holographic stereogram, holographic conical stereogram and multiplex hologram.
  • Holographic contour generation is useful for measurements for biomedical specimen.

_______

X-Ray Holography:

X-ray holography has the potential of examining the samples in aqueous solution with very high resolution without the need for sample preparation that often results in structural alternations. A X-ray hologram with a resolution better than that of a detector can be obtained by Fourier transform holography with a zone plate. The X-ray beam from a selenium X-ray laser (wavelength =20 nm, pulse length 200ps, output power 500 kW) falls on a narrow band X-ray mirror (bandwidth 10% and reflectivity 25% at 20nm wavelength) which reduces the broadband X-ray background produced by the Se laser. The mirror is a substrate with a flatness and roughness of better than 2nm to preserve the coherence of the X-ray laser beam, and is coated with alternate 20 layers each of silicon and molybdenum to provide high X-ray reflectivity. The sample on illumination with the X-ray beam scatters in the forward direction and forms the object beam. The object beam interferes with the portions of the X-ray beam that miss the sample. The recorded hologram can be reconstructed optically. The x-ray resist polymethyl methacrylate has high resolution but it requires development and reconstruction. If the source size is kept small to ensure spatial coherence and the diffraction pattern is enlarged by shadow projection, a moderate-resolution detector with a high quantum efficiency such as a backilluminated CCD camera can be used for recording the hologram, instead of polymethyl methacrylate. The reconstruction of such a hologram can be performed numerically. The system would permit the observation in real-time, which would be useful for biological samples. A resolution of 1.3 um has been obtained by taking d=1.0 um and N=23 lines/mm, and using a backilluminated CCD camera for hologram recording. The resolution obtained was limited by the resolution of the source size(1 um). These experiments show the promise of real-time observation of holograms of living biological specimens.

_______

Endoscopic Holography:

Endoscopic holography has potential of providing a powerful tool for non-contact high resolution 3D imaging and nondestructive measurements inside natural cavities of human body or in any difficult to access environment. It combines the features of holography and endoscopy. The ability to record a 3D large focal depth and high resolution image of internal organs and tissues greatly enhances the detection capability. The holographic endoscopy is of two types. In the one form the hologram is recorded inside the endoscope, while the other form uses an external recording device. Holographic endoscope can be attached to a salpingoscope for fallopian tube investigations or to otoscope for the inspection of outer and middle ear via an acoustic system to generate vibrations of the tympanic membrane. Holographic endoscope has been used with success for early recognition of cancerous indurations in the wall of urinary bladder.

______

Multiplexed Holography for Medical Tomography:

Multiplexed holography can be used for complete display of three-dimensional tomographic medical data. It uses photographically scaled images of the objects for making the hologram. The technique thus provides a way to make hologram whose images are of a different size from the original object. A series of photographic transparencies are made, all of which are used to make a multiple-exposure composit hologram. The reconstruction of the hologram produces the original object with a magnification equal to the scale factor of the transparencies. Holographic stereograms, known as Cross holograms uses multiangular views of the object. The method consists of three steps: data acquisition, image processing, and making of the stereogram. Since the holographic stereogram retains only the horizontal parallax of the object, it is limited to those applications in which surfaces are important such as prostheses and craniofacial surgery. Moreover, most biological data such as CT or MR scans are generally collected as serial scans rather than multiangular views, multiplexed holography that reconstructs the image with all the sections at correct depths (locations) and both horizontal and vertical parallaxes is more useful.

_

Multiplexed holograms which retains full parallax and physical depths cues are known as volumetric multiplexed holograms, or multiplane-multiplexed holograms or volumetric multiple exposure transmission holography (VMETH).  A volumetric multiplexed hologram is made from a stack of images such as a CT or MR scan. The first image in the stack is projected onto a screen placed in front of a holographic film. A hologram of this image is recorded by adding a reference beam. Next the screen is moved a few millimeters away from the holographic film and the second image in the stack is projected onto the screen, and a second exposure is made on the first one. All the images are similarly recorded, each at slightly greater distance than its predecessor. The film is then developed. When the hologram is reconstructed, it shows all the slices distributed in the three-dimensional space at different distances. Dispersion compensation techniques can be employed for making the multiplexed hologram so that the image can be viewed by a white light source. Since the volumetric multiplexed hologram uses serial sections at different Z coordinates in space, it can be termed as ‘zeta multiplexed hologram’ that is in contrast to a holographic stereogram which is known as ‘theta multiplexed hologram’ because it involves images at different angles. It may be pointed out that the volumetric multiplexed hologram faithfully reconstructs complete information including physical depth cues and all of the grey-scale tonality in every slice without geometric or photometric distortion. The complete system for producing and display of clinically useful multiplexed hologram can be automated. Stereography, or multiple exposure photography, involves the creation of a visual impression of depth by the superimposition of multiple positive images taken at a variety of angles. Unlike holography, however, stereography does not accurately reproduce depth or image intensity and renders only surface anatomic information (surface rendering). By contrast, VMETH imaging accurately reproduces both depth and intensity, including physical depth cues, such as accommodation, motion parallax, convergence, and stereo disparity.

_______

Exploring the potential use of holographic imaging in radiology:

Dynamic holography opens the door to three major potential uses of holography in radiology: teaching anatomy, PACS storage, and displaying more complex anatomic images that can be used to present more informative reports to treating physicians and their patients.  Digital holography is a two-step process. Step one involves recording the hologram where the radiographic image is transformed into a photographic record. Step two consists of reconstruction, in which the hologram is transformed into a virtual image. The digital hologram created contains a grid of holographic pixels, also known as holopixels or hogels. Holopixels are diminishing in scale, currently around 0.8 mm and now reducing to 0.5 mm or even 0.25 mm. Any type of 3D medical dataset, such as CT and MR images, can be converted to a digital hologram.  Such data can also be available in the form of a physical scan of an object, a mathematical description of the images, molecular data, or even a series of stills or video. For example, a 200 × 300 mm page-sized hologram with 0.8 mm hogel requires the creation of approximately 90,000 2D images. This target can be reached by using a combination of advanced computer modelling software with graphics rendering as well as specific proprietary algorithms, customized hardware engines can run a series of mathematical processes to generate the image data.

  1. Teaching anatomy:

The medical hologram, particularly in radiology, presents a performance boost over traditional textbook images. It brings in the “charm and has the potential to generate curiosity.” This can be achieved by using static holographic images of anatomical structures in textbooks, which can then easily display the relation of body structures with respect to each other in three dimensions. The 3D nature of the image generated provides superior visual capabilities. In a routine two-dimensional image many anatomical structures are difficult to conceptualize, such as the spatial relationships between various blood vessels. The normal and pathological structures can be easily understood by gauging such depth relationships. This can potentially be used in assessing mediastinal, vascular anatomy, the skull base, cranial nerves, and the renal, pelvic anatomy on CT or MRI images. The concept of optical composition suggests that the 3D concept relies on grouping visual subcomponents based on textures, color grade, and linking of structures.

  1. PACS storage:

A picture archiving and communication system (PACS) is a medical imaging technology which provides economical storage and convenient access to images from multiple modalities. There has been renewed interest in holography due to the recent propagation of 3D content and availability of 3D data from CT, MRI and ultrasound scanners, low-cost depth scanners, cinema/TV and 3D printing. Holographic storage and retrieval systems can be looked upon as a solution to calls for greater storage capacity, rapid retrieval, and smaller physical storage footprints. Current radiology study image sizes vary from 10 megabytes (MB) to 90 MB in size per test. By adopting PACS, there has been a turnaround in radiology productivity by channelling radiology workflow. Holographic media can be used specifically for data storage due to their unique ability to store information in three dimensions, in contrast to standard optical disks, which manage to store data only on the surface. Radiology units depend on PACS to achieve their goals of high-speed access to images, steadfastness and efficacy. Due to the unique ability of holograms to store data as a volumetric density and read it quickly, they are likely to become the storage medium of choice in the future. A DVD or optical disc player can read data at a rate which is exponentially slower compared to holography. Holographic recording and storage, therefore, can help significantly in intelligent PACS management. A rough estimate shows that high-resolution and specialized CT scans may occupy around 30 MB of data per scan. Over the last decade the quality of investigations has changed. Scans are now more focused, are of higher resolution and more detailed due to thinner sections and dynamic studies which are possible under both CT and MRI studies’ ability to create huge amounts of data. The current estimate suggests that for every 100,000 examinations performed, there will be a need to book approximately 3.1 terabytes of storage. The advantages of holography for data storage also include its ability to perform massive parallel recording and reading of data, unlike traditional optical disc, thus enabling significantly faster data transfer speeds in comparison to traditional optical discs. Another advantage is its ability to use the entire thickness of the recording media instead of just the surface. Holographic media are sensitive to light; using lasers, data can be recorded in 3-dimensional spaces. With holography, we can record 1 million bits of data with a single flash of light.

  1. Image display:

The use of holographic displays in radiology is still in research, but they can soon find their way into commercial use and become economically viable.  A holographic screen can be created using a specially coated glass media for the projection surface of a video projector, therefore creating a free-space display, as the image bearer appears very transparent. In addition, by controlling the beam with special lenses, the image can be made to appear to be floating in front of or behind the glass, rather than directly on it. These views can be particularly advantageous in radiology, as computers will send the 3D CT data to a projector, which will beam it to a computer screen. The radiologist, by touching the screen, will create a series of electrical impulses which will be sent to the computer. The computer will interpret the signal and modulate the projected image according to the information, thereby eliminating the use of the mouse. Furthermore, 3D reconstruction of 2D images from sectional imaging can lead to detailed 3D models of body structures, which can then be holographically displayed. This approach may be especially useful to surgeons, who are not used to viewing the body in sectional images, thus helping them in planning different approaches to, and guiding interventions during, surgery.

_____

Holograms will let Doctors see 3-D Views of our insides:

Most biomedical imaging techniques require doctors to create 3-D visualizations out of a dataset of 2-D images gathered by a CT scanner, MRI, ultrasound, or other devices. It can be a tedious and time-consuming process. But more importantly, this imperfect system can’t always represent patient tissue and organs with enough accuracy or precision, creating holes in the pictures—more literal than figurative—that make it difficult for doctors to decide how to best diagnose and treat patients.

Holography tries to fix those problems by providing doctors with a full, 3-D image of a body part or organ that they can move around, zoom in on, and manipulate. Current systems like GE’s Vivid E9 with XDclear already take datasets from CT and MRI scans and turn them into 3-D visualizations, but they’re still relegated to flat, 2-D screens. Holography goes a step further and creates a virtual object in actual 3-D space. It’s important to clarify that many of these new technologies aren’t real holograms, which perfectly recreate the patterns of light that reflect off an object in real life. What EchoPixel (which prefers to call their technology 3-D imaging) and others are doing is closer to stereoscopic vision, like what you see in 3-D movies or gadgets like the Nintendo 3DS. Other companies, like Zebra Imaging and RealView Imaging, create true holograms. No matter the term, though, the goal remains the same: to give doctors and patients alike a much clearer sense of the physical size and shape of the human anatomy. This might not necessarily lead to vastly improved insights in diagnosing and treating patients, but there are some areas with potential. Holograms could allow doctors to conduct more detailed colonoscopies in virtual space, supplanting the uncomfortable physical procedure. Medical holograms could also be a great asset for identifying problems with very complex organs, like the heart or brain, where abnormalities might be subtle.

_

EchoPixel’s 3-D software:

It takes data from CT and MRI scans and transforms it into 3-D holographic images so doctor can view and interact with patient tissues and organs as if they were real physical objects. Medical 3-D imaging is not new, but the way organs appear to pop out of the screen and the ease at which the anatomy can be manipulated has never been seen before in medicine.  Basically it is actually a virtual reality system, just without the VR headset. Instead, the user wears 3-D glasses paired with a HP Zvr display. A stylus allows the physician to effortlessly grab and manipulate the anatomy.

Using a stylus, physicians can manipulate organs and tissue. EchoPixel’s 3-D is already in use in hospitals. The Cleveland Clinic is using the technology to plan and prepare for liver surgery; paediatric surgeons at Stanford University use it to plan heart surgeries on babies missing pulmonary arteries; the technology has also enabled surgeons to detect more congenial heart defects in 40 percent less time. And one of the most promising uses of the technology is in colorectal cancer detection. Colon cancer is the third most common type of cancer in the U.S. according to the National Cancer Institute and 50 percent of the U.S. population never goes in for screening because they fear colonoscopies.

_______

Holography in Ophthalmology:

Recording of a three dimensional image of the eye was one of the earliest applications of holography in the field of ophthalmology. Any retinal detachment or intraocular foreign body can be detected. Holography can also be applied for the measurement of corneal topography and crystalline lens changes and for the study of surface characteristics of both the nerve head and the cornea. Current methods of determining the shape of the central surface miss the central part and its periphery. The major advantage of holographic technique is the ultra-high precision (sub-um range) with which such measurements are possible. The elastic expansion of the cornea can also be measured by holographic interferometry. This information is vital for corneal surgery. The expansion of the cornea of fresh enucleated bovine eyes has been examined as a result of a small increase in intraocular pressure using double exposure holographic interferometry. Their first investigations have revealed that each bovine cornea has its own typical expansion. The studies made so far show that holography has potential to investigate corneal endothermal morphology, changes on the cornea, crystalline lens changes, and surface characteristics of both the nerve head and the retina.

_

Sight Restoration:

Holographic imaging systems designed for safe and efficient activation of photovoltaic retinal prosthesis enable the projection of contour images with high efficiency, high irradiance and much lower total power than traditional LCD or DMD-based displays. Integration of light over the photosensitive elements reduces speckling noise to acceptable levels for diodes as small as 20 μm. Very compact design of video goggles is based on defocusing of the zero diffraction order, and refocusing the image using Fresnel lens added to the hologram of the encoded image. As a proof of concept, the system was successfully tested in-vivo by measuring cortical responses to alternating gratings, thus demonstrating feasibility of the holographic approach to near the eye display.  Using this technique, researchers demonstrated cortical response to motion in rats.

_______

Holography in Dentistry:

Both continuous wave and pulse laser holography have been used for applications of holography in dentistry.

  • The holograms offer a convenient way of storing toothprints, i.e. dental records of the casts of upper and lower dentitions for legal and forensic purpose.
  • Holograms can be used for storing orthodontic study models that can be retrieved by a laser beam or a white light source for accurate 3D measurements. This saves a lot of storage space.
  • The holographic images are clinically reliable and random errors are not clinically significant. By studying the old and new records, orthodontists can watch the progress of their patients.
  • Holograms can be employed as training aids in the disciplines of dental anatomy and operative dentistry.
  • Holographic interferometry has been used for the contactless measurement of in-vivo tooth mobility and its movement in three dimensions, and measurement of dimensional changes of the tissue bearing surfaces of maxillary full dentures due to deformation of dentures material by oral fluids.
  • Holographic contouring technique can reveal the topography of teeth.

______

Holography in Otology:

  • Double exposure and time-average holographic interferometric techniques are powerful for studying different parts of the human peripheral hearing organ.
  • The vibration behaviour of models of the inner ear parts such as unrolled cochlea and coiled basilar membrane have been studied by time-average holography.
  • Time-average holographic interferometry has also been used for the study of vibration analysis of incudo-mallar joint with forces applied to the middle ear muscles has demonstrated that the incus and malleus move like a lever around a frequency dependent axis. The holographic time-average interferometry is particularly suitable in studying the modes of vibration of the eardrum of living human as the modes of vibration are observed simultaneously over the whole area. Hearing impairments occur when micro-fractures of petrous pyramids in the human skull base are created by accidents. Double-exposure holographic interferometry has been applied for the study of deformation of the human skull under different load conditions to investigate petrous pyramids.

______

Holography in Orthopaedics:

Holography offers an excellent tool for the contactless study of orthopaedic structures, specifically external fixtures to reveal and measure strains on fixation pins and rods. Such studies are important in osteosynthesis with external fixture used for long bone fractures, to prevent dislocations of both fractured ends that are mainly caused by decrease in strength of the fixation pins. Dry bone-in cantilever bending mode has also been studied by heterodyne holographic interferometry to determine the piezoelectric coefficients of bone.

______

3D Cell Explorer from NanoLive:

Other companies are focusing on creating floating virtual prints of organs and body parts. Not NanoLive—their 3D Cell Explorer is a superpowered laboratory microscope that uses holographic algorithms to create detailed stereoscopic visualizations of microbial and cellular life. You can pull up the images on a tablet or other touchscreen and play around with them as you see fit. The 3D Cell Explorer hasn’t made its way into many medical settings, but the NanoLive hopes its device can help researchers, doctors, and patients alike get a better grasp of how diseases and disorders at the microscopic level manifest and operate.

____

Hologram House Calls:

To open the 9th annual USC Body Computing Conference, Dr. Leslie Saxon, a cardiologist and the conference’s founder, screened a short video for a mixed crowd of technologists and medical specialists. In the video, she stands front of a camera while her image is beamed in real time as a hologram to her patient in Dubai. Saxon asks her patient about her symptoms, diagnoses the problem, and walks her through her treatment options, face-to-face, without ever leaving her office. This is what Saxon calls hologram house calls, and it’s part of the University of Southern California’s recently announced Virtual Care Clinic that will use technology like virtual reality, artificial intelligence, mobile apps and wearables to make health care both more personalized and more accessible. The clinic is founded on the belief that in the same way we’ve seen a revolutionary change in the way culture and society use technology, we’ll soon see the same in the medical industry. The mobile app would ask users to enter their specifics–age, medical condition, the diseases that run in their family–and would then provide information about various treatments specifically tailored to them. For this, the center is working with Dr. Evidence, a software platform that pulls data from published clinical studies, FDA drug labels, and epidemiological databases to provide drug companies and specialists with the most up-to-date medical evidence on new drugs and treatments. The goal is to make this information available to patients as well. Still, as Saxon is quick to point out, it’s not a complete health care system. For surgeries and other consultations that require hands-on care, people will still need to visit doctors’ offices and hospitals. But by using technology like virtual reality and artificial intelligence, physicians will be able to greatly increase the number of patients they can see each day. And perhaps most importantly, patients would have unprecedented access to medical data and the latest discoveries.

_____

_____

Holography in Education:

This technology has been used in the entertainment, healthcare, and retail industries, but the venture into education is new terrain. On the education front, holographic technology will add vibrancy to the learning process and just might entice students to look further into topics they are passionate about.

  1. Physics simulation – Holograms could mimic real life scenarios that may be either too dangerous, expensive or difficult to perform in the classroom.
  2. Remote collaboration – Students could work with students, teachers or professionals located all over the world in a near face-to-face engagement. This takes the concept of video conferencing to a whole new physical level.
  3. Gaming – A 3-Dimensional, interactive hologram makes for a more immersive gaming experience, meaning students will be more engaged and mentally involved with the system. This could lead the way for a whole generation of 3D educational games.
  4. Motor skill development – This type of interface can be used to test and assess a child’s ability to use small muscles, specifically their hands and fingers. Results can be used to configure software to focus on skill development and problem areas for children with muscular and co-ordination difficulties.
  5. Experience history – Students could tour historical sites in 3D and have their questions answered by a hologram. Virtual field trips would allow entire classrooms to see and hear a Tudor castle or a national park or a museum.
  6. 3D designing- Students in classrooms or makerspaces could complete a design project in three dimensions and then print it on a 3D printer.
  7. Teach employment skills- Taking career tech education into the 21st century, holograms could train students how to do job-related tasks in vocational fields of interest.

___

“Holographic Telepresence” can be a part of the instructional process:

Advancements in technology continue to change educator’s teaching approaches. Many of the chalkboards that once adorned our school walls have been replaced with projection screens or interactive white boards. In some classrooms, tools like these are being used to bring remote students, teachers, or guests into the classroom as virtual guests. On the horizon is the next step forward in this evolution – the use of holographic telepresence to bring digital participants and remote location into the class in 3D!

How can this advanced technology benefit the instructional process?

  1. Have experts illustrate processes live, in person, in 3D: Imagine a surgeon demonstrating a surgical procedure to medical students in person, without having to actually be there (or expose the operating room to all those germs). How about automotive engineers demonstrating engine features, or fluid dynamics engineers conducting an experiment in 3D? The possibilities for enhanced, interactive demonstrations via holographic telepresence are endless!
  2. Connect geographically remote classrooms: How cool would it be connect a room full of Spanish speaking students with a room full of English speaking students, so they can engage in real conversations and 3D show-and-tell as an immersive Foreign Language course experience, without having to fly across the ocean! Bringing students from across the globe together is increasingly common in today’s classrooms thanks to Internet technologies, and it is only natural to envision holographic telepresence adding a new dimension (pun intended!) to this powerful teaching and learning technique.
  3. Deliver lectures to multiple classrooms, anywhere, at the same time: Holographic technology could allow an in-demand lecturer to present to multiple lecture halls full of students at the same time. Highly sought-after experts and ‘edutainers’ could provide their expertise to a much wider audience, breaking down time and distance barriers.
  4. ‘Remote attendance’: Taking the above idea a step further, if and when the technology becomes affordable enough, small ‘personal’ holographic projectors could enable students at home to participate in a lecture with a teacher projected into their living room in 3D. One can envision some sort of interface so that a teacher could take questions and engage in dialogue with outlying students through chats or voice systems, since having dozens of student projected for the instructor to see would be impractical.
  1. Remote access – ‘be there’ in 3D: As holographic technologies continue to evolve, one could envision the day when teachers and students will be able to feel like they are actually in a remote location. Imagine studying the Coliseum by taking a virtual, live trip there.
  2. A whole new dimension to instructional content: The content developed for holographic teaching is only limited by our imaginations. Educational creators will have the ability to literally bring their works to life. Sites and sounds could be brought to a classroom to enhance a lecture.
  3. Could simulations be done to create a 3D immersion in a recreated situation? Children could be immersed underwater and experience the aquatic life-forms without being endangered. Field trips would take on a whole new meaning.

As holographic telepresence technology becomes more commonplace and finds its way into our education institutions, it could bring a previously unimagined level of engagement and excitement to the learning process and attract students and encourage further studies. The possibilities are truly exciting!

_____

_____

Military use of holography:

_

Military mapping and Better view of battlefield:

Geographic intelligence is an essential part of military strategy and fully dimensional holographic images are being used to improve reconnaissance. One American company has delivered over 13,000 3D holographic maps of “battle-spaces” for the US army. This allows soldiers to view three-dimensional terrain, look “around” corners and helps with mission training.  The company does this by taking complex computerised image data, which they make into a holographic sheet. Not only can users “look into” the high quality 3D image of the terrain stored in the hologram sheet, but the technology is simple to use and can be rolled up for easy storage and transportation. These maps are also useful in disaster evacuation and rescue scenarios. Being able to “unroll” an accurate 3D holographic image of new terrain clearly offers strategic advantages, but such technologies also generally filter down to wider society. Perhaps we can expect flexible 3D Google Maps at some point.

_

There’s no arguing that some critical battlefield information would be better understood when viewed in three dimensions rather than two. The desire to enable the U.S. military to view such information via holograms is the driving force behind a number of research projects under way at some of the nation’s top universities and imaging companies. The military is already using heads-up displays (HUD) on holographic windshields installed in combat aircraft.  While holographic weapons are not yet under development, researchers are developing capabilities that will enable the military to use holograms for battlefield intelligence, military planning and explosives disposal purposes.

_

Holographic night vision goggles:

The military has developed holographic night vision goggles with 3-D vision perception and sensor fusion. They have been especially developed for the advanced future needs of individual soldiers, drivers, Special Forces, and helicopter crews.

For the soldier of the 21st century, they offer a distinctive concept of image mixture with total depth perception and day/night awareness of the battlefield situation. Due to the holographic optical elements, a see-through image is possible with a large field of view during unforeseen changes in the level of light. Reports, such as digitized battlefield information, are continuously available in the field of view and can be viewed by the soldier at any time without disturbing the observation of the battlefield.

_

Holographic soldiers:

The United States Army is pursuing a quantum physics project that will allow commanders to put holographic soldiers on the field to confuse or intimidate enemies. They’re attempting to do it by harnessing a highly technical phenomenon called “quantum ghost imaging,” which allows images to be created by using photons that don’t bounce off objects, but instead bounce off other photons, which have themselves bounced off objects.  The effect is a “ghost” image of the object reflecting the second set of photons. Harnessing ghost imaging would allow the army to gin up images of people or vehicles on clouds of ambient smoke from a removed distance. The Army’s science and technology office is also working on developing interactive holograms of soldiers with low-level human intelligence, realistic dialogue and emotional expressiveness — essentially making possible entire working units of faux personnel and equipment that look, move and even sound like the real thing.

_____

_____

Holographic People:

Holographic people can improve theme park experiences, greet hotel guests, and provide information in an airport. They’re programmed workers that don’t require a regular salary, and are becoming the future workforce. Here are some examples of these workers:

  1. Holographic Speakers:

In 2008 Prince Charles gave a keynote speech at an energy summit in Abu Dhabi in the form of a hologram. Though this pre-recorded appearance received mixed feedback, it gained global attention and sparked an interest among developers such as Musion in improving this method for travel-free presentations. Since then, entertainers have used this methodology in their performances, including Tupac, Madonna, and Psy.

  1. Holography Used in Meetings:

Since Prince Charles’ presentation, holography has come a long way in the development of live virtual meetings. You’ve probably participated in some form of digital conferencing, as these have been around for quite some time. Web cameras and Skype technologies have made long-distant meetings possible. However, they often come with many limitations. Holographic conferences are personal, engaging, and they cut the need for travel. Innovators such as AV Concepts now advertise these services claiming that “Holograms will make the attendees of any corporate gathering sit up, pay attention, and truly enjoy the experience.” Cisco has already managed to use holographic telepresence successfully via many presentations and conferences and have gathered much attention in the media.

  1. Holographic Fashion Shows:

It didn’t take long for the fashion industry to catch up. In 2011, designer Tim Jockel created the first completely holographic fashion show for German haute couture fashion label Stefan Eckert. Soon after, other designers joined in the trend. Burberry hosted an impressive holographic runway show in Beijing attracting global attention. That same year, Forever 21 presented their fall collection via the same strategy, boasting models walking on the ceilings and on invisible stairs. Even Lady Gaga is messaging Artpop – the integration or art, music and technology. Not only are designers incorporating holography into their shows, but also in clothing. In recent news, Lady Gaga attracted attention for sporting her holographic shades as she strutted through London’s Heathrow airport. The Spring 2013 fashion show displayed many clothing items with holographic prints, patterns, and fabrics. These standout pieces make a statement and have been a stylish hit this year

  1. Holograms at Work:

Will holograms replace jobs? Possibly- here are some examples.

Receptionist:

Perhaps gaining the most attention is Shanice, the holographic receptionist who greets visitors at London’s Brent Town Hall. The concern is that she would replace British local government jobs. Though she is only programmed to answer a limited number of questions, and doesn’t provide a genuine human experience, she comes with many qualities of an ideal worker. Her demeanour is always pleasant, she can speak many languages, and doesn’t require an annual salary.

Hotel Concierge Hologram:

When checking into a hotel, there’s a chance that you might be greeted by a holographic concierge. These programmed agents can assist you with a reservation, give you directions, and provide you with details about the hotel’s amenities. They’ll catch your attention and are available 24/7. In 2011, Marketing Ad Group worked with Aloft Hotel to implement a holographic concierge that could provide guests with information about local deals and discounts. With a computer memory, this kind of worker is quick, efficient, and saves travellers and workers time from having to look up this information on their own.

Airport Hologram:

In 2011, France began to experiment with utilizing holographic workers in airports to provide travellers with information. Now you can find these workers in New York City airports. Whether or not you’re in a rush to catch your flight, they will stop you in your tracks. These workers have gained mixed feedback, and the negative ones are typically in regards to their robot-like behavior. However, they only cost about two years worth of a salary, are more patient than real agents, and will work overtime without complaining or requesting additional pay.

London deploys a Hologram to enforce New Escalator Rules as seen in the figure below:

London’s Tube Network has a new weapon in its bid to get people to stand on both sides of the escalator: a singing hologram. Try to exit the city’s Holborn Station during morning rush hour and you’re now greeted by a blond woman projected onto a human-shaped cutout. This smiling Stepford Train Guard urges you to stand on both sides of the escalator rather than reserve one side for walking only. As if the hologram’s grating cheerfulness wasn’t enough, she has now apparently started singing. According to recent commuter reports, the ghost guard has started blurting slogans and breaking into a somewhat tuneless renditions of Elton John’s “I’m Still Standing,” among other songs. The approach isn’t just novel, it’s completely ineffective. Visiting Holborn during rush hour this morning, not a single person was standing on the escalator’s left side.

_

Will Holographic workers displace Jobs?

Although there’s much interest in holographic workers for their consistency, cost efficiency, and programmable memory, there’s also much that a holographic worker is not able to do. For example, they cannot engage in meaningful conversation, exchange new ideas, or share opinions. Therefore, there’s still a long way to go with technology before holographic workers displace jobs.

_________

_________

Limitations and challenges of holography:

Right now, holograms exist. There are companies experimenting with it and many R&D departments trying to make it work for consumers. Currently, there are very few easy ways of making this happen, often resulting in costs that are too high for most consumers to undergo for a novelty no one is really producing images for. For now, holograms are used to render still images rather than recorded video or three-dimensional animations. Aside from the cost of adding in holographic capabilities to an otherwise healthy and entertaining 4K display, there’s also the standing danger of getting retinas damaged from a possible laser burn. We’re not talking about high-powered lasers, but that doesn’t mean that prolonged exposure to them doesn’t carry consequences. The researchers noted that no one should view the laser beam directly, only the image it projects, and they advise that users still wear infrared glasses until the technology has fully matured. Making the technology work would require some sort of other medium that doesn’t need an intricate series of plates and lasers to operate.

_

The current limitations of holography are fairly significant. Holography requires relatively complicated methods to record holographic images, making them costly and less accessible. Further, displaying holographic images requires elaborate machinery. Currently, holographic display technology lies far behind commercially available 2D and 3D displays. The most advanced holographic displays currently have very poor spatial resolution, and can display images at only about two frames per second. Significant research is required to improve these displays to make them truly useful to the practicing doctor rather than the novel technological preview which they are currently. Holographic images are also inherently poor at visualizing subtle tissue contrast differences. They are thus more useful at showing areas of interest to people unfamiliar with radiological sectional images than for actual radiological diagnosis.

_

Storage solutions based on holography are facing significant challenges at bringing the technology into the market. A significant problem in holographic recording is destructive readout. In the process of accessing the holographic data, the reading laser disturbs the recording in a way that leads to its gradual erasure. Another challenge is growing crystals with the required optical quality at sufficient speeds to enable widespread application of the technology. Such challenges have limited the adoption of holographic storage, despite significant research into the field.

______

______

Pros and cons of holography:

_

Benefits of Hologram:

Holograms and holographic products are today widely used in any and every industry to enhance the image of their brands as a genuine and authenticated brand in the market. Since holograms are almost impossible to counterfeit, they are widely used for security applications. They are also used in attractive product packaging, fancy gifts, 3-D art, registration of artifacts, new technology aircraft, automobiles, etc. Because of its applicability in various applications, holograms are widely demanded. The reasons for using Hologram and holographic products are as follows:

  1. Pass Around Value: Since holograms have impressive appearance, it is likely that people will bring them to top notice of colleagues and associates.
  2. Impact: It is a known fact that holograms are looked at significantly and longer than other graphic mediums because they are eye-catching. Any name or logo or slogan on the hologram has greater impact and the message is enforced.
  3. Security: Holograms are widely used for security purpose. It is not possible to duplicate holograms and hence they have become an essential part of many government and commercial security programs. Holograms are applied to documents, ID cards, currency, and product labels.
  4. Retention: Holograms are certain objects which can be treasured for a long time which is not the case with another object, be it a pen or a calendar or a diary.
  5. Commercial Purpose: Commercially holographic products comprise a very unique market in themselves. They are sold as retail products in the market. Various products like greeting cards, direct-mail literature, trading cards, collectibles, packaging and displays etc. have holographic images.
  6. Promotional Purpose: Holographic products have great promotional effects as they diffract the seven colors of the spectrum when the light falls on them and create an unique three-dimensional image. Once applied to the product, the apparent value of the product is automatically enhanced no matter which way you look at it.

___

Advantages of holograms:

  1. Holograms combat counterfeiting.
  2. They cannot be reproduced.
  3. They provide product authentication.
  4. They minimizes document tampering
  5. Holograms are quick and easy optical validation.
  6. They enhance packaging appeal and increase brand sales.
  7. They are cost effective
  8. They have higher storage capacity
  9. They increase feasibility of objects (depth)
  10. They enable achievement of multiple images on a single plate
  11. They have ability to combine with other technologies
  12. They are easily applied on products
  13. They are difficult to alter or transpose
  14. They are verifiable by its specific manufacture
  15. They are available in various forms, shapes and sizes
  16. They can be tailor made as per the customer’s requirement
  17. They impart a very hi-fi look to the product
  18. They retain the confidence of the end consumer
  19. They are seen without wearing any eyewear/headwear

____

Disadvantages of hologram:

  1. Provide static images
  2. Do not produce images of complex movement
  3. Require complicated precise machinery to produce and view an image
  4. Low axial resolution of inline holography
  5. High production costs, production cost is much higher than 2D
  6. Still developing technology
  7. Lack of studies of its impact on human being.
  8. Reference illumination beams are collinear
  9. Not easily seen under Florescent Lighting
  10. Requires above lighting
  11. Application to products is costly
  12. Time consuming when it comes to constructing images

______

______

Dangerous outcomes of holograms:

Not only do holograms have the ability to provide medical professionals with long distance medical consulting so that they do not have to put themselves in danger by visiting places of highly concentrated communicable disease, but they also have the potential to flip the industry of communications technology upside-down. Holograms possess the ability to change the way we communicate as much as the invention of telephones did, and many companies are heading toward the development of it. Holograms have to potential not only to control the spread of communicable diseases, but to develop a real-time method of face-to-face communication for the future as well.

_

Because Holographic medical consultation has such a safer way of doing their job (helping the poor and sick across the world), Doctors without Borders is afraid that more doctors will leave their organization for the safety of consulting via hologram. In their statement, the organizations claimed that the primary intentions of Holographic medical consultation, to make a safer way to stop the spread of disease, were ridiculous, and that they would never work. Doctors without Borders claimed that possible holographic medical consultation was a mockery of their work, and that it would never be a prevalent way of handling the stopping of the spread of disease. They asserted that the mere thought of not having doctors physically visit areas of densely populated disease is unethical, that implementing holograms in the medical consulting would hurt many more people than it would help.

_

Also the development of holograms used for everyday communication will not only socially cripple the world in the future, but also provide the world with a wealth of terrifying issues. Once holograms are attainable for everyday use, people will cease to participate in human-to-human interaction and only communicate through the media of holograms. Such holograms would make people even lazier than they are today and more dependent on their technology than they are today, slowly shifting the world from its real, alive state, to a virtual, completely online state. The holographic communication will give people no reason to go out into the world to see others or do work, that holograms will change the world as we know it, and not for the best.

_____

_____

Counterfeit hologram:

_

If you have a credit card or just bought a copy of Microsoft Windows, you’re familiar with security holograms – those sparkly bits of film that vouch for the validity of everything from driver’s licenses to software and sports league items. But as the goods they certify become more valuable, the profit incentive to add counterfeit holograms to counterfeit goods has grown.  It turns out, they’re aren’t as secure as they are sparkly. Experts say the number of counterfeit holograms affixed to equally counterfeit merchandise has tripled in the past three years, as the technology to make them has spread. Today, crafting a convincing duplicate of a security hologram has never been easier or more profitable.

_

The simplest method for duplicating an embossed hologram is to use the hologram itself as a mold for producing an embossing die. This is accomplished by removing any adhesive or other coatings from the embossed surface of the hologram, silvering the clean embossed surface, and electroforming a metal such as nickel onto the silver. The electroform is then directly usable as a die for embossing into aluminized polyester or PVC. Counterfeits made this way can be so perfect that no expert will be able to distinguish them from the original hologram. Almost as simple as mechanical copying is the method of contact printing. In this case, a copy hologram is made by laying a photoresist coated plate in close contact to the original hologram and illuminating the original hologram through the photoresist plate. Diffracted and undiffracted light is reflected from the original hologram and a nearly identical copy is formed on the photoresist plate. The photoresist plate is then silvered and electroplated with nickel; and the nickel plate is used as an embossing die. Counterfeits made by contact printing are similar enough to the original to pass even a close inspection, though with the right tools an expert may be able to detect them. Holograms can also go out the back door of the hologram printer — saving counterfeiters the trouble of making them. The International Hologram Manufacturers Association began a program to register holograms for their clients in 2003. About 70 manufacturers, mostly European, have signed up for the program – a fraction of the manufacturers worldwide. The industry tries to police itself, but with limited success. Now that there are machines everywhere, so there are lots of counterfeit holograms – either going out the back door of the legitimate manufacturer or just copied.

_

Countermeasures against hologram counterfeiting:

The holographic identification card is highly resistant to counterfeiting. In particular, it will inhibit the use of all of the counterfeiting methods that have been discussed here. This card uses a hologram which is hot stamped in a pattern consisting of an array of very small dots. Over the hot stamping is applied a coating which bonds to the substrate between the dots. Before the hologram is applied, the substrate is printed with variable information. The hologram itself is a stereogram of a well-known human face. Mechanical copying is effectively prevented because if an attempt is made to delaminate the coating from the substrate, the hologram is left as a large number of isolated dots which are useless as the basis for making an embossing die. Differential adhesion between the hologram dots and the coating to the substrate will make it extremely difficult to remove the coating and the dots together as a single unit, for example to transfer to another card. Contact copying is effectively prevented because the information printed on the substrate will be recorded in the contact copy. If an attempt is made to make a two-step copy of the hologram, the same problem arises: the variable printed information is recorded at the same time. A photograph cannot be mistaken for a stereogram because the photograph lacks three dimensionality. As is well known in the security printing industry, a human face is very difficult to counterfeit without detection, so re-mastering the stereogram using a look-alike will be risky. Any good look-alike of a famous person would be rather easy for the authorities to trace. Re-mastering is made considerably more difficult by the fact that the hologram itself is a stereogram. Aside from the greater complexity of producing stereograms, the use of a well-known human subject will greatly complicate the counterfeiter’s task. Re-mastering and simulation are unlikely to be effective because human beings are exceptionally good at recognizing human faces and noticing small differences between them.

_

What really defeats the idea that holograms provide security is simply that few people have expertise and equipment to study them closely, and most consumers can’t tell the difference between a reasonable counterfeit and the authentic item. Shiny does not a hologram make. For a trained eye, it used to be easy to tell a counterfeit, but the counterfeits are getting far better than they used to be. The covert features aren’t detectable by the human eye, so unless people are carrying equipment when they buy league clothing, they have to trust their eyes.

_

Note:

Fake (false) holograms need to be differentiated from counterfeit holograms. Fake holograms create illusion of three dimensional images by not employing technology of real holograms and by not offering many visual depth cues, but are perfectly legal e.g. Tupac, 3D TV etc.  Counterfeit holograms are illegal replica of original hologram in such a way that most consumers can’t tell the difference between counterfeit and the authentic item.

______

______

Is our universe a hologram?

Points to ponder:

  1. The fundamental laws of physics are incapable of explaining how the universe as we know it, with all its contents, could’ve fit in a small package that exponentially expanded.
  2. Enter the holographic model of the universe – a model that suggests that the laws of physics can apply to the universe as a two-dimensional plane.

For decades now, scientists have been investigating the possibility that our Universe is, or once was, a giant hologram, where the laws of physics require just two dimensions, but everything appears three-dimensional to us. It sounds far-fetched, but if true, it would actually solve some pretty hefty questions in physics.

_

The Holographic Principle:

The ‘holographic principle,’ the idea that a universe with gravity can be described by a quantum field theory in fewer dimensions, has been used for years as a mathematical tool in strange curved spaces. New results suggest that the holographic principle also holds in flat spaces. Our own universe could in fact be two dimensional and only appear three dimensional — just like a hologram.  At first glance, there is not the slightest doubt to us, the universe looks three dimensional. But one of the most fruitful theories of theoretical physics in the last two decades is challenging this assumption. The “holographic principle” asserts that a mathematical description of the universe actually requires one fewer dimension than it seems. What we perceive as three dimensional may just be the image of two dimensional processes on a huge cosmic horizon. Up until now, this principle has only been studied in exotic spaces with negative curvature. This is interesting from a theoretical point of view, but such spaces are quite different from the space in our own universe. Results obtained by scientists at TU Wien (Vienna) now suggest that the holographic principle even holds in a flat spacetime.

_

Everybody knows holograms from credit cards or banknotes. They are two dimensional, but to us they appear three dimensional. Our universe could behave quite similarly. The theory suggests that the volume of space appears three-dimensional, but is actually encoded on a two-dimensional boundary or an observer-dependent horizon that requires one less dimension than it appears. In short, we see it as three-dimensional, but it is projected from a two-dimensional source, similar to how a hologram screen works.  In 1997, the physicist Juan Maldacena proposed the idea that there is a correspondence between gravitational theories in curved anti-de-sitter spaces on the one hand and quantum field theories in spaces with one fewer dimension on the other. Gravitational phenomena are described in a theory with three spatial dimensions, the behaviour of quantum particles is calculated in a theory with just two spatial dimensions — and the results of both calculations can be mapped onto each other. Such a correspondence is quite surprising. It is like finding out that equations from astronomy textbook can also be used to repair a CD-player. But this method has proven to be very successful. More than ten thousand scientific papers about Maldacena’s “AdS-CFT-correspondence” have been published to date.

Correspondence Even in Flat Spaces:

For theoretical physics, this is extremely important, but it does not seem to have much to do with our own universe. Apparently, we do not live in such an anti-de-sitter-space. These spaces have quite peculiar properties. They are negatively curved, any object thrown away on a straight line will eventually return. “Our universe, in contrast, is quite flat — and on astronomic distances, it has positive curvature,” says Daniel Grumiller. However, Grumiller has suspected for quite some time that a correspondence principle could also hold true for our real universe. To test this hypothesis, gravitational theories have to be constructed, which do not require exotic anti-de-sitter spaces, but live in a flat space. For three years, he and his team at TU Wien (Vienna) have been working on that, in cooperation with the University of Edinburgh, Harvard, IISER Pune, the MIT and the University of Kyoto. Now Grumiller and colleagues from India and Japan have published an article in the journal Physical Review Letters, confirming the validity of the correspondence principle in a flat universe. “If quantum gravity in a flat space allows for a holographic description by a standard quantum theory, then there must be physical quantities, which can be calculated in both theories — and the results must agree,” says Grumiller. Especially one key feature of quantum mechanics -quantum entanglement — has to appear in the gravitational theory.

_

When quantum particles are entangled, they cannot be described individually. They form a single quantum object, even if they are located far apart. There is a measure for the amount of entanglement in a quantum system, called “entropy of entanglement.” Together with Arjun Bagchi, Rudranil Basu and Max Riegler, Daniel Grumiller managed to show that this entropy of entanglement takes the same value in flat quantum gravity and in a low dimension quantum field theory. “This calculation affirms our assumption that the holographic principle can also be realized in flat spaces. It is evidence for the validity of this correspondence in our universe,” says Max Riegler (TU Wien). “The fact that we can even talk about quantum information and entropy of entanglement in a theory of gravity is astounding in itself, and would hardly have been imaginable only a few years back. That we are now able to use this as a tool to test the validity of the holographic principle, and that this test works out, is quite remarkable,” says Daniel Grumiller. This however, does not yet prove that we are indeed living in a hologram — but apparently there is growing evidence for the validity of the correspondence principle in our own universe.

_

The holographic principle was inspired by black hole thermodynamics, which conjectures that the maximal entropy in any region scales with the radius squared, and not cubed as might be expected. In the case of a black hole, the insight was that the informational content of all the objects that have fallen into the hole might be entirely contained in surface fluctuations of the event horizon. The concept of the universe as a hologram arises from the mathematical study of black holes. When an object – say a red rubber ball – gets sucked into a black hole, it passes the event horizon and is lost. The distinctions that make that object unique, however, do not disappear. Instead, information about the ball’s redness and spherical shape spreads over the surface of the event horizon, forming a two-dimensional shell of information. Theoretically, a computer could even use that shell to reconstruct a duplicate of the original ball. The math that describes the black hole’s information shell matches the math describing the universe as a hologram. The holographic principle resolves the black hole information paradox within the framework of string theory. However, there exist classical solutions to the Einstein equations that allow values of the entropy larger than those allowed by an area law, hence in principle larger than those of a black hole. These are the so-called “Wheeler’s bags of gold”. The existence of such solutions conflicts with the holographic interpretation, and their effects in a quantum theory of gravity including the holographic principle are not yet fully understood.

_

Making sense of Cosmic Inflation:

The researchers arrived at this conclusion after observing irregularities in the cosmic microwave background — the Big Bang’s remnant. The team used a model with one time and two space dimensions. Actual data from the universe, including cosmic microwave background observations, were then plugged into the model. The researchers saw that the two fit perfectly, but only if the universe is no more than 10 degrees wide.

_

Space-time is usually understood to describe space existing in three dimensions, with time playing the role of a fourth dimension and all four coming together to form a continuum, or a state in which the four elements can’t be distinguished from each other. Flat space-time and negative space-time describe an environment in which the Universe is non-compact, with space extending infinitely, forever in time, in any direction. The gravitational forces, such as the ones produced by a star, are best described by flat-space time. Negatively curved space-time describes a Universe filled with negative vacuum energy. The mathematics of holography is best understood for negatively curved space-times. According to holography, at a fundamental level the universe has one less dimension than we perceive in everyday life and is governed by laws similar to electromagnetism. The idea is similar to that of ordinary holograms where a three-dimensional image is encoded in a two-dimensional surface, such as in the hologram on a credit card, but now it is the entire Universe that is encoded in such a fashion.

_

Holography is a huge leap forward in the way we think about the structure and creation of the universe. Einstein’s theory of general relativity explains almost everything large scale in the universe very well, but starts to unravel when examining its origins and mechanisms at quantum level. Scientists have been working for decades to combine Einstein’s theory of gravity and quantum theory. Some believe the concept of a holographic universe has the potential to reconcile the two.

_

Experiment shows that the universe is not a hologram:

A team of researchers at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, have performed an experiment that they say rules out the hologram theory once and for all, reports Science. Fermilab theorist Craig Hogan had an idea. He reasoned that if the universe was a hologram, then something called “holographic noise” should make it extremely problematic to measure directions — forward-backwards, up-down, left-right — with the same precision. This is because in a holographic universe, there are only really two dimensions. Using a device called an interferometer, which is essentially a system of lasers and mirrors, Hogan checked to see if precise measurements of lasers pointed in different directions were difficult to come by. If the universe was a hologram, then the lasers should “jiggle” ever-so-slightly. It turns out, no jiggle. Hogan therefore declared that the holographic principle was falsified, but his results have stirred up controversy. Not all theorists are convinced that the holographic principle entails the existence of noise that would cause a measurable jiggle, meaning that Hogan’s experiment might not make for an adequate test.

_

My view:

In my theory of duality of existence, I have shown that there is a dual existence of everything in universe and therefore a single frame of logic/rationale/laws cannot explain all phenomena associated with it. So we don’t have to go overboard to reconcile Einstein’s theory of gravity with quantum theory. In my view holographic universe is going overboard. In my photon weaving theory, I have shown that the weaving of photons into mass by photons moving in circle is multidimensional and it is the multi-dimensionality of encircled photon that gives other properties of matter like charge, color, flavor etc. The universe both at the micro-level and macro-level cannot exist without multi-dimensionality. Black hole thermodynamics and irregularities in the cosmic microwave background need to be explained but holographic principle is not the best way.

_____

_____

Holonomic brain theory:

The holonomic brain theory, developed by neuroscientist Karl Pribram initially in collaboration with physicist David Bohm, is a model of human cognition that describes the brain as a holographic storage network. Pribram suggests these processes involve electric oscillations in the brain’s fine-fibered dendritic webs, which are different from the more commonly known action potentials involving axons and synapses. These oscillations are waves and create wave interference patterns in which memory is encoded naturally, and the waves may be analyzed by a Fourier transform. Gabor, Pribram and others noted the similarities between these brain processes and the storage of information in a hologram, which can also be analyzed with a Fourier transform. The Fourier Transform is a tool that breaks a waveform (a function or signal) into an alternate representation, characterized by sine and cosines. The Fourier Transform shows that any waveform can be re-written as the sum of sinusoidal functions.  In a hologram, any part of the hologram with sufficient size contains the whole of the stored information. In this theory, a piece of a long-term memory is similarly distributed over a dendritic arbor so that each part of the dendritic network contains all the information stored over the entire network. This model allows for important aspects of human consciousness, including the fast associative memory that allows for connections between different pieces of stored information and the non-locality of memory storage (a specific memory is not stored in a specific location, i.e. a certain neuron).

_

According to the holonomic brain theory, memories are stored within certain general regions, but stored non-locally within those regions. This allows the brain to maintain function and memory even when it is damaged. It is only when there exist no parts big enough to contain the whole that the memory is lost. This can also explain why some children retain normal intelligence when large portions of their brain—in some cases, half—are removed. It can also explain why memory is not lost when the brain is sliced in different cross-sections. A single hologram can store 3D information in a 2D way. Such properties may explain some of the brain’s abilities, including the ability to recognize objects at different angles and sizes than in the original stored memory. Pribram proposed that neural holograms were formed by the diffraction patterns of oscillating electric waves within the cortex. It is important to note the difference between the idea of a holonomic brain and a holographic one. Pribram does not suggest that the brain functions as a single hologram. Rather, the waves within smaller neural networks create localized holograms within the larger workings of the brain. This patch holography is called holonomy or windowed Fourier transformations. A holographic model can also account for other features of memory that more traditional models cannot. The Hopfield memory model has an early memory saturation point before which memory retrieval drastically slows and becomes unreliable.  On the other hand, holographic memory models have much larger theoretical storage capacities. Holographic models can also demonstrate associative memory, store complex connections between different concepts, and resemble forgetting through “lossy storage.”

_

Holographic models of memory and consciousness may be related to several brain disorders involving disunity of sensory input within a unified consciousness, including Charles Bonnet Syndrome, Disjunctive Agnosia, and Schizophrenia. Charles Bonnet Syndrome patients experience two vastly different worlds within one consciousness. They see the world that psychologically normal people perceive, but also a simplified world riddled with Pseudohallucination. These patients can differentiate these two worlds easily. Since dynamic core and global workspace theories insist that a distinct area of the brain is responsible for consciousness, the only way a patient would perceive two worlds was if this dynamic core and global workspace were split. But such does not explain how different content can be perceived within one single consciousness since these theories assume that each dynamic core or global workspace creates a single coherent reality. The primary symptom of Disjunctive Agnosia is an inconsistency of sensory information within a unified consciousness. They may see one thing, but hear something entirely incompatible with that image. Schizophrenics often report experiencing thoughts that do not seem to originate from themselves, as if the idea was inserted exogenously. The individual feels no control over certain thoughts existing within their consciousness. Holographic models of memory and consciousness explains such disorders.

______

______

Non-optical holography:

_

In principle, it is possible to make a hologram for any wave.

  1. Electron holography:

Electron holography is the application of holography techniques to electron waves rather than light waves. Electron holography was invented by Dennis Gabor to improve the resolution and avoid the aberrations of the transmission electron microscope.

Today it is commonly used to study electric and magnetic fields in thin films, as magnetic and electric fields can shift the phase of the interfering wave passing through the sample. Electron imaging is a technique in which, by observing the phase shift of electron interference (due to electric and material field) as they pass through thin film materials, it is possible to determine the composition of materials. The principle of electron holography can also be applied to interference lithography.

_

  1. Acoustic holography:

Acoustic holography is a method used to estimate the sound field near a source by measuring acoustic parameters away from the source via an array of pressure and/or particle velocity transducers. Measuring techniques included within acoustic holography are becoming increasingly popular in various fields, most notably those of transportation, vehicle and aircraft design, and NVH. Noise, vibration, and harshness (NVH) is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. The general idea of acoustic holography has led to different versions such as near-field acoustic holography (NAH) and statistically optimal near-field acoustic holography (SONAH). One dimensional sound frequencies’ holographic recording is done in acoustic hologram. For audio rendition, the wave field synthesis is the most related procedure. Acoustical holography applications include engineering inspection, underwater viewing, and medical diagnosis.

_

Scientists made Beautiful Holograms using Sound:

We’re all familiar with holograms, the projected 3D images created by manipulating light.

But can you create a hologram with sound?

Actually, yes.

Scientists at the Max Planck Institute in Germany used tiny silicone beads assemble into patterns on the surface of water, holding that shape for as long as the sound persisted. In effect, they created acoustic holograms. Fischer and his colleagues made pretty water rings in the shape of dove, levitated a water drop, and propelled little paper boats across the surface. They did it using acoustic levitation, a technique often used to study bubbles and foams, among other applications, suspending them in mid-air to keep gravity from causing them to coarsen. Technically, all you need to build an acoustic levitation system is a transducer (a vibrating surface) to produce the sound; a reflector; and sound waves with just the right combination frequencies (usually in the ultrasound regime). When those reflected waves interact with each other in just the right way, the troughs and crests cancel each other out, and you can levitate various small objects, like insects or fish. In this case, the German team built a system that reflected sound waves of different amplitudes and frequencies off an object from many different angles. They put a speaker underwater to serve as the transducer, and projected sound waves up toward the surface. Other academic institutes are also currently working to make 3D holograms cheaper and safer. For instance Brigham Young University and MIT have found a way to make video holograms possible, using acoustic waves that divide colour frequencies safely.

_

  1. Atomic holography:

Atomic holography has evolved out of the development of the basic elements of atom optics. With the Fresnel diffraction lens and atomic mirrors, atomic holography follows a natural step in the development of the physics (and applications) of atomic beams. Recent developments including atomic mirrors and especially ridged mirrors have provided the tools necessary for the creation of atomic holograms, although such holograms have not yet been commercialized.

_

  1. Neuron holography:

An optical hologram contains far more information about an object’s appearance than a simple photo does, though they don’t generally tell us much about its hidden interior. Hidden interiors, however, are just what neutron scientists explore. Neutrons are great at penetrating metals and many other solid things, making neutron beams useful for scientists who create a new substance and want to investigate its properties. But neutrons have limitations, too. They aren’t very good for creating visual images; neutron experiment data is usually expressed as graphs.

New neutron holography technique opens a window for obtaining clear 3-D atomic images: a 2017 study:

Neutron beam holography has been used to see the inside of solid objects. Nagoya Institute of Technology at particle accelerator facilities shows that neutron holograms can reveal the precise atomic structure of doped materials, offering a new characterization technique for materials scientists. People usually associate holograms with futuristic 3D display technologies, but in reality, holographic technologies are now being used to help study materials at the atomic level. X-rays, a high energy form of light, are often used to study atomic structure. However, X-rays are only sensitive to the number of electrons associated with an atom. This limits the use of X-rays for studying materials made up of lighter elements. Neutron measurements can often fill in the gaps in structures when X-ray measurements fail, but neutron beams are harder to make and have lower intensities than X-ray beams, which limits their versatility. Now, a collaboration among Japanese researchers working at national particle accelerator facilities across Japan has developed a new multiple-wavelength neutron holography technique that can give insights into previously unknown structures. They demonstrated a new neutron holographic method using a Eu-doped CaF2 single crystal and obtained clear three-dimensional atomic images around trivalent Eu substituted divalent Ca, revealing never-before-seen intensity features of the local structure that allows it to maintain charge neutrality. The new holographic method works by firing neutrons with controlled speed at a sample, which in this case is the europium-doped calcium fluoride crystals. Neutrons are normally thought of as particles, but also have wave-like properties similar to light, depending on their speed. When the neutrons hit europium atoms, gamma rays are produced in a pattern controlled by the local structure. The gamma ray patterns, or holograms, measured from neutrons travelling at different speeds are combined to produce a three-dimensional representation of the europium atoms in the crystal.

______

______

Recent advances and research in holography:

_

Stretchy Metamaterials allow for Shape-Changing Holograms:

Almost all of our holograms are just recordings of a single picture, though some are capable of switching between a few images. However, that could be changing very soon. In another recent hologram research publication, researchers have been able to create holographic images that are capable of changing form, a potentially ground breaking discovery that could lead to further research and development of moving 3D holograms. A team of scientists, led by Ritesh Agarwal from the University of Pennsylvania, have created a hologram that produces different images when stretched. The new lens was built upon from research that produced a metasurface lens from a stretchy material composed of polydimethylsiloxane that had been embedded with gold nanorods. This research showed that by stretching the metamaterial surface from the corners, that they could effectively change the focal length of the lens, allowing magnification. Using the prior research, Agarwal thought it possible to create a hologram from the same material he had used to create the lens. Using various simulations and computer programs, the researchers were able to create hologram designs. The team precisely aligned gold nanorods onto a silicon wafer in specific patterns that would produce different images when stretched, then layered it in polydimethylsiloxane. There have already been 3D polarized holograms that could produce up to two different images. Unfortunately, this technology can only house two images and requires sizeable optical equipment to make adjustments. Meanwhile, the new stretch hologram is sized on a micrometer scale, is capable of storing three holographic images (which increases drastically with device size), and has the ability to encode data. It is also possible to create a much larger version of their stretchy hologram that could contain thousands of different images which, in turn, opens the door to creating animated holograms.

_____

_____

Make holograms by copying butterflies’ wings:

High-quality holograms require a laser and special equipment are needed to project them. Indeed, if the hologram is in colour, three lasers are needed, one for each primary: red, green and blue. The result is not always persuasive. Getting the primary holograms to overlap perfectly is hard. And to see the picture usually requires a darkened room. All this led Rajesh Menon, an engineer at the University of Utah, to start eyeing up butterflies—notably the bright blue morphos found in Central and South America. The striking colour of a morpho’s wing is the product not of pigment, but of the structure and arrangement of the scales on those wings. These scales refract light, splitting it into its component wavelengths, and also diffract it, causing those various wavelengths to interfere with one another. As a result, blue wavelengths are intensified and reflected back to the onlooker while those of other colours either cancel each other out or are scattered, and thus minimised. Moreover, unlike today’s holograms, the colour and appearance of a morpho’s wings remain the same, regardless of the angle they are viewed from. Dr Menon and his team thought mimicking the way morphos refract and diffract light might thus let them create more realistic and usable holograms than today’s. In a paper just published in Scientific Reports, they describe how they have done this.

_

A conventional hologram is made by splitting a laser beam in two, scanning one of the half beams over the object to be holographed, recombining the half beams and then capturing an image created by the recombined beams on a photographic film. The result is an interference pattern imprinted on the film by the interaction between the out-of-kilter half beams. Shine light (ideally of the same frequency as the original laser) on this pattern and the process is, in essence, reversed. That produces a 3D representation of the original object. Dr Menon’s approach differs from this established method in several ways. First, it dispenses with the laser. Second, the film on which the hologram is captured is not a smooth one but, rather, a sheet of transparent plastic with microscopic bumps and grooves in it. Third, the pattern of those bumps and grooves is created not photographically but as the product of calculations by a computer.

_

Instead of the laser, Dr Menon starts with multiple images, taken from different directions, of the object to be holographed. These can come either from a special, stereoscopic camera or, more prosaically, from a single camera moved around to different vantage points. These images are then fed into a computer. Here, a special algorithm calculates how to shape the topography of the plastic sheet so that it will manipulate the light eventually used to illuminate that sheet in a way which creates the desired 3D image. In essence, the sheet’s bumps and grooves act like the scales of a morpho’s wings, refracting and diffracting the incident light to produce the desired effect. Once the computer has calculated the topography needed to do this, that topography (or, rather, it’s inverse) is inscribed onto a master version using photolithography—a technique also employed to make computer chips. This master may then be used to stamp multiple copies of the hologram, in a similar fashion to that employed to make vinyl records.

_

Crucially, the result—having been created using ordinary light rather than special laser beams—does not require lasers to recreate the image. A beam of white light will do the trick. Even a torch will work. Using one, Dr Menon can generate holograms with a full spectrum of colours and with a richness which he estimates is up to ten times that of today’s most sophisticated holograms. The new holograms may also be viewed from all angles without distortion. And they cost a fraction of those produced by existing techniques. For now, Dr Menon and his colleagues are focusing on the kind of holograms used as security features, although they have also created holographic images of 3D objects in free space. Eventually, they hope to make holographic movies, using devices called phase spatial light modulators controlled directly by the output from the hologram-generating algorithm. Such modulators deploy liquid crystals instead of bumps on a surface to manipulate light. If that idea can be made to work, then fantasies such as holographic television might indeed be brought into being. A more immediate market, though, is replacing existing security holograms with ones that are clearer, harder to forge and viewable from any angle. Perhaps, if Dr Menon has his way, the portraits of heads of state and other worthies on banknotes will soon pop up to greet the user as they are pulled from his wallet.

________

_______

Touch hologram:

Sensation of touch is felt when you touch hologram and various technologies allow it to happen:

Tactile holographic with haptic display feedback:

Haptics is the science of applying touch (tactile) sensation and control to interaction with computer applications. Haptics offers an additional dimension to a virtual reality or 3-D environment and is essential to the immersiveness of those environments. By using special input/output devices (joysticks, data gloves or other devices), users can receive feedback from computer applications in the form of felt sensations in the hand or other parts of the body.  Haptic technology allows the user to interact with a hologram and receive tactile responses. The research uses ultrasound waves to create acoustic radiation pressure, which provides tactile feedback as users interact with the holographic object. The haptic technology does not affect the hologram, or the interaction with it.

_

Hololens with Ultrahaptics:

This demonstration presents a surprising human-computer experience combining a pair of mixed reality smart glasses and a haptic device. This one involves existing technologies: the HoloLens from Microsoft and the touch development kit from Ultrahaptics. By mixing a holographic display and an array of ultrasonic transducers, Immersion gives tangible feedback to a hologram. This colocation of feedbacks drastically enhances the presence of the object. This also gives a spatial reference in order to interact with the virtual environment.

__

Japanese scientists have created a new type of hologram that you can actually feel:

Researchers have built a machine that renders holograms touchable, adding to a growing body of “telehaptic” prototypes released in 2015. The holographic machine is called Haptoclone and was developed by researchers at the University of Tokyo. It consists of two boxes, one containing an object and the other displaying a hologram of that object. If a user puts her hand into the second box to interact with the hologram, she’ll feel it—thanks to ultrasonic radiation pressure emitted onto her hand. The tactile sensation is pretty realistic. The technology is limited for now. It can only emit a “safe” level of ultrasound radiation, meaning that the degree of tactile feedback it can simulate is confined to things like lightly stroking an object. It can’t yet emulate a handshake or a bear-hug, as Motherboard noted.

_

Femtosecond plasma laser holograms [discussed vide supra] also allows sensation of touch. Shock waves are generated by plasma when a user touches the plasma voxels. The user feels an impulse on the finger as if the light has physical substance.

_

HoloTouch® human-machine interface (“HMI”) technology:

HMIs using HoloTouch technology allow people to intuitively enter commands and data into a wide range of electronic equipment by simply passing a finger through holographic images of what would otherwise be buttons or keys of keypads, keyboards and other controls, floating in the air at a convenient location – intuitive, touchless controls. An infrared sensor detects intrusion of a finger into those images, identifies which command has been selected and transmits that selection to the device’s internal software, in much the same way as pressing a button on any ordinary device. Interfaces customized with HoloTouch technology provide output to USB, serial and other PC ports as well as relay output to other devices such as PLCs.  Increasingly sophisticated sensors, some capable of mapping multiple points on planes in space, combined with more creative hologram recording techniques, provide the simple and inexpensive basis for multiple “button” touchless, holographic HMIs such as the functional equivalents of keypads or touch screens but with no moving parts and nothing to actually touch in using them, providing “wow” and no contamination transfer.

_

There are a multitude of possible applications for tactile holograms, from informational displays to interactive communication devices. For example, a holographic keyboard projected by a future smartphone could allow you to type up a paper. In the classroom, an educator could use this technology to draw and manipulate vectors in three dimensions for their students.

_______

_______

3D Holographic Images on wearables using graphene:

The research efforts in nanotechnology have significantly advanced development of display devices. Graphene, an atomic layer of carbon material that won scientists Andre Geim and Konstantin Novoselov the 2010 Nobel Prize in Physics, has emerged as a key component for flexible and wearable displaying devices. Owing to its fascinating electronic and optical properties, and high mechanical strength, graphene has been mainly used as touch screens in wearable devices such as mobiles. Wearable technology with displays have advanced a lot with screen technology – but they’re still display only 2D images. This technical advance has enabled devices such as smart watches, fitness bands and smart headsets to transition from science fiction into reality, even though the display is still 2D flat. In a paper, published in Nature Communications, authors show how our technology realises wide viewing-angle and full-color floating 3D display in graphene based materials. Ultimately this will help to transform wearable displaying devices into floating 3D displays. The 3D hologram are only 1cm in size at the moment – but it’s a start. The physical realisation of high definition and wide viewing angle holographic 3D displays relies on the generation of a digital holographic screen which is composed of many small pixels. These pixels are used to bend light carrying the information for display. The angle of bending is measured by the refractive index of the screen material – according to the holographic correlation. The smaller the refractive index pixels, the larger the bending angle once the beam passes through the hologram. This nanometer size of pixels is of great significance for the reconstructed 3D object to be vividly viewed in a wide angle. The process is complex but the key physical step is to control the heating of photoreduction of graphene oxides, derivatives of graphene with analogous physical structures but presence of additional oxygen groups. Through a photoreduction process, without involving any temperature increment, graphene oxides can be reduced toward graphene by absorbing a single femtosecond pulsed laser beam. During the photoreduction, a change in the refractive index can be created. Through such a photoreduction authors are able to create holographically-correlated refractive index pixel at the nanometer scale. This technique enables the reconstructed floating 3D object to be vividly and naturally viewed in a wide angle up to 52 degrees. This result corresponds to an improvement in viewing angles by one-order-of-magnitude compared with the current available 3D holographic displays based on liquid crystal phase modulators, limited to a few degrees. In addition, the constant refractive index change over the visible spectra in reduced graphene oxides enables full-colour 3D display.

_______

_______

Researchers develop projection-type see-through holographic 3-D display technology:

National Institute of Information and Communications Technology (NICT) has developed a new projection-type see-through holographic 3-D display technology combining an optical screen of a digitally designed holographic optical element (DDHOE) and a digital holographic projection technique. Holographic 3-D image reconstruction was successfully demonstrated via the see-through screen to a target observation area as seen in the figure above. Basically, dynamic holographic 3-D display technology faces the severe limitation of the spatial-temporal resolution of the spatial light modulator (SLM) to realize a practical display size and visual angle. Moreover, the general system design of holographic 3-D displays requires a large optical setup behind the display window.  In this work, a holographic 3-D image was largely projected to a see-through screen of DDHOE by using the digital holographic projection technique. The screen was fabricated using a hologram printer, which was developed by NICT. The light of the enlarged holographic 3-D image was then concentrated to a target observation area by an appropriately designed reflection function to increase the visual angle. The technology offers a high degree of freedom of both the display size and the visual angle independently, and also the high usability of the see-through display system. It should therefore accelerate the adoption of holographic three-dimensional displays in industrial applications such as digital signage, in-car head-up displays, smart-glasses and head-mounted displays.

_____

_____

3D Printing using Holograms is actually printing in 3D:

Daqri’s holographic 3D printing technology:

Daqri’s process is akin to SLA (stereolithography). In SLA, a laser beam is shone onto a pool of resin, hardening the resin at the beam’s point. The laser scans across the resin’s surface, drawing one layer. More resin is added and then the next layer is drawn.  Daqri’s process however, uses a holographic chip of their own making to project the laser for all the layers at the same time into the material, a light-activated monomer. In a demo, Daqri prints a small paperclip. But if it’s scaled up then heating may become an issue. The “hardening” that goes on, called polymerization, involves the formation of long, tangled polymers from monomers and is exothermic, meaning it gives off heat. If you’ve worked with resin before then you’ve probably noticed how hardening a large volume of resin produces more heat than hardening a small volume. That heating can be enough to melt and deform the object itself. There’s no word on when this process will escape the lab and appear in our workshops.

_____

_____

Quantum hologram:

Until quite recently, creating a hologram of a single photon was believed to be impossible due to fundamental laws of physics. However, scientists at the Faculty of Physics, University of Warsaw, have successfully applied concepts of classical holography to the world of quantum phenomena. A new measurement technique has enabled them to register the first-ever hologram of a single light particle, thereby shedding new light on the foundations of quantum mechanics.  Scientists at the Faculty of Physics, University of Warsaw, have created the first ever hologram of a single light particle. The spectacular experiment was reported in the prestigious journal Nature Photonics. The successful registering of the hologram of a single photon heralds a new era of quantum holography, which offers a whole new perspective on quantum phenomena. “We performed a relatively simple experiment to measure and view something incredibly difficult to observe: the shape of wavefronts of a single photon,” says Dr. Radoslaw Chrapkiewicz.

_

In standard photography, individual points of an image register light intensity only. In classical holography, the interference phenomenon also registers the phase of the light waves—it is the phase that carries information about the depth of the image. When a hologram is created, a well-described, undisturbed light wave—the reference wave—is superimposed on another wave of the same wavelength but reflected from a three-dimensional object. The peaks and troughs of the two waves are shifted to varying degrees at different points of the image. This results in interference and the phase differences between the two waves create a complex pattern of lines. Such a hologram is then illuminated with a beam of reference light to recreate the spatial structure of wavefronts of the light reflected from the object, and as such, its 3D shape.

_

One might think that a similar mechanism would be observed when the number of photons creating the two waves were reduced to a minimum—that is, to a single reference photon and a single photon reflected by the object. But that is not the case. The phase of individual photons continues to fluctuate, which makes classical interference with other photons impossible. Since the Warsaw physicists faced a seemingly impossible task, they attempted to tackle the issue differently: Rather than using classical interference of electromagnetic waves, they tried to register quantum interference in which the wave functions of photons interact. Wave function is a fundamental concept in quantum mechanics and the core of its most important principles, the Schrödinger equation. In the hands of a skilled physicist, the function could be compared to putty in the hands of a sculptor. When expertly shaped, it can be used to ‘mould’ a model of a quantum particle system. Physicists are always trying to learn about the wave function of a particle in a given system, since the square of its modulus represents the distribution of the probability of finding the particle in a particular state, which is highly useful

_

“All this may sound rather complicated, but in practice, our experiment is simple at its core. Instead of looking at changing light intensity, we look at the changing probability of registering pairs of photons after the quantum interference,” explains doctoral student Jachura. Why pairs of photons? A year ago, Chrapkiewicz and Jachura used an innovative camera built at the University of Warsaw to film the behaviour of pairs of distinguishable and non-distinguishable photons entering a beam splitter. When the photons are distinguishable, their behaviour at the beam splitter is random—one or both photons can be transmitted or reflected. Non-distinguishable photons exhibit quantum interference, which alters their behaviour. They join into pairs and are always transmitted or reflected together. This is known as two-photon interference or the Hong-Ou-Mandel effect. “Following this experiment, we were inspired to ask whether two-photon quantum interference could be used similarly to classical interference in holography in order to use known-state photons to gain further information about unknown-state photons. Our analysis led us to a surprising conclusion: it turned out that when two photons exhibit quantum interference, the course of this interference depends on the shape of their wavefronts,” says Dr. Chrapkiewicz.

_

Quantum interference can be observed by registering pairs of photons. The experiment needs to be repeated several times, always with two photons with identical properties. To meet these conditions, each experiment started with a pair of photons with flat wavefronts and perpendicular polarisations; this means that the electrical field of each photon vibrated in a single plane only, and these planes were perpendicular for the two photons. The different polarisation made it possible to separate the photons in a crystal and make one of them ‘unknown’ by curving their wavefronts using a cylindrical lens.  Once the photons were reflected by mirrors, they were directed toward the beam splitter (a calcite crystal). The splitter didn’t change the direction of vertically-polarised photons, but it did deviate horizontally polarised photons. In order to make each direction equally probable and to make sure the crystal acted as a beam splitter, the planes of photon polarisation were bent by 45 degrees before the photons entered the splitter. The photons were registered using the state-of-the-art camera designed for the previous experiments. By repeating the measurements several times, the researchers obtained an interference image corresponding to the hologram of the unknown photon viewed from a single point in space. The image was used to fully reconstruct the amplitude and phase of the wave function of the unknown photon.

_

The experiment conducted by the Warsaw physicists is a major step toward improving understanding of the fundamental principles of quantum mechanics. Until now, there has not been a simple experimental method of gaining information about the phase of a photon’s wave function. Although quantum mechanics has many applications, and it has been verified many times with a great degree of accuracy over the last century, we are still unable to explain the nature of wave functions—are they simply a handy mathematical tool, or are they something real? “Our experiment is one of the first allowing us to directly observe one of the fundamental parameters of photon’s wave function—its phase—bringing us a step closer to understanding what the wave function really is,” explains researcher Michal Jachura. The Warsaw physicists used quantum holography to reconstruct wave function of an individual photon. Researchers hope that in the future, they will be able to use a similar method to recreate wave functions of more complex quantum objects, such as certain atoms. Will quantum holography find applications beyond the lab to a similar extent as classical holography? Such existing practical applications include security (holograms are difficult to counterfeit), entertainment, transport (in scanners measuring the dimensions of cargo), microscopic imaging and optical data storing and processing technologies. “It’s difficult to answer this question today. All of us—I mean physicists—must first get our heads around this new tool. It’s likely that real applications of quantum holography won’t appear for a few decades yet, but if there’s one thing we can be sure of it’s that they will be surprising,” summarises Prof. Konrad Banaszek.

______

______

Ultra-thin metasurface nano hologram:

  1. The world’s first ‘nano hologram’ could bring 3D technology to your smartphone:

Researchers created the first ‘nano hologram’ and now want to bring it to your phone.  A team of scientists from RMIT University and the Beijing Institute of Technology have designed the ‘world’s thinnest’ hologram. It is said the hologram is capable of being integrated into everyday products such as smartphones. The work was led by RMIT’s Min Gu led the project and claims the holographic technology can be seen without 3D goggles and is 1,000 times thinner than human hair. The academics dubbed the technology a ‘nano hologram’. At present, the constraints that hold back holographic technology lie in the limits of optical thickness. Regular holograms modulate light to project the illusion of a three-dimensional shape. But this needs to be within the parameters of the optimal thickness limit – computer-generated holograms are too large to fit atop smartphones and therefore have limited practical application.

Traditional holograms are created by the modulation of light phases to produce the illusion of depth. These holograms are facilitated by the principle of interference. In our conventional holographic device, we will have a reference beam that is concentrated on a recording surface and another beam of light concentrated on an object. When the two beams cross each other, an interference pattern in created. But, in order to produce these illusions, the holograms must be as thick as the optical wavelengths to create enough phase shifts. Gu’s research team was able to find a way to overcome the traditional limitations of thickness by using metamaterials to create a thin film of antimony telluride to create optical resonant cavities. These cavities cause light that enters to reflect enough times to produce waves in different phases, which creates a 3D illusion. Min and the team behind the work has developed a 25 nanometer hologram using topological insulator material. It has a lower refractive index on the surface layer, but an ultrahigh refractive index in bulk. This thin insular film can enhance the holographic image without sacrificing its compact design. Min says that the nano hologram is “fabricated using a simple and fast direct laser writing system, which makes our design suitable for large-scale uses and mass manufacture.” Theoretically, the technology may be able to fit inside smartphones and other devices but there is still work to be done. The next step is to shrink this technology even further, so that it can become suitable for integration upon LCD and smartphone screens, effectively producing a holographic device in your pocket. What makes the research even more interesting is that these holograms aren’t like your traditional freestanding holograms in that there isn’t actually any distinct light being projected above the screen. The new hologram works by producing flat holograms that trick your eyes but in a much higher resolution, making the images appear to be larger and more detailed. The possibilities for portable holograms are appealing for a wide range of industries. Integrating holography into everyday electronics would make screen size irrelevant – a pop-up 3D hologram can display a wealth of data that doesn’t neatly fit on a phone or watch. From medical diagnostics to education, data storage, defence and cyber security, 3D holography has the potential to transform a range of industries and this research brings that revolution one critical step closer.

_

  1. Researchers create 3-D full-color holographic images with nanomaterials:

Researchers at Missouri University of Science and Technology are creating a new approach to reconstruct 3-D full-color holographic images by using just one layer of nanoscale metallic film. This work has a huge potential to change our daily lives by equipping our cell phones with 3-D floating displays and printing 3-D security marking onto credit cards. Dr. Xiaodong Yang, an assistant professor in mechanical and aerospace engineering at Missouri S&T, and Dr. Jie Gao, an assistant professor of mechanical and aerospace engineering at Missouri S&T, describe their ultrathin full-color holograms in “ACS Nano.” And they illustrate their approach by reproducing several full-color holographic images with nanometer-scale aluminum thin films. A nanometer is one billionth of a meter, and some nanomaterials are only a few atoms in size. The method described in the “ACS Nano” article “Full-Color Plasmonic Metasurface Holograms” involves the use of ultrathin nanometer-scale metallic films with metasurfaces that can manipulate the wavefront of light. The researchers’ metasurface hologram is one 35-nanometer thick aluminum film punctured with tiny rectangular holes of 160 nanometers by 80 nanometers with different orientation angles created by a microfabrication process known as focused ion beam milling. Experimenting with the interplay of red, green and blue laser light on metasurface structures, the researchers demonstrated “clean and vivid full-color holographic images with high resolution and low noise.” The three primary colors — red, green and blue — were produced, and the secondary colors of cyan, magenta, yellow and white also were produced. To illustrate their reconstructed holographic images, they made “CMYW” letters, an apple and a Rubik’ cube. They believe the metasurface hologram holds promise for future applications, such as credit card security marking, biomedical imaging, 3-D floating displays and big-data storage. “By adjusting the orientation angle of the nanoscale slits, we are able to fully tune the phase delay through the slit for realizing the phase modulation within the entire visible color range,” says Yang. “In addition, the amplitude modulation is achieved by simply including or not including the slit. Our holograms contain both amplitude and phase modulations at nanometer scale so that high resolution and low noise holographic images can be reconstructed.” The researchers created the metasurface hologram by drilling out tiny rectangular slits with various orientation angles through the aluminum thin layer. Under a scanning electron microscope, the hologram looks like a needlepoint pattern. “Different from the currently existing metasurface holograms which are mostly designed for limited colors, our wavelength-multiplexed method — by encoding additional phase shifts into the holograms and introducing tilted incident angle illumination of laser light — results in the successful reconstruction of almost all visible colors,” says Gao, co-author of the paper.

_

  1. Silicon pillar hologram:

Scientists have developed a nano-material device that they say creates the highest-quality holographic images ever produced. Unlike previous attempts at hologram technology, the researchers’ system is made possible by a new nano-material that manipulates light with extreme fidelity. And because the device is so tiny, it means hologram technology could even be a feature in small personal gadgets, like smartphones.  The nano-material used in the researchers’ new device lets them control light-based projections in three dimensions in infrared. The nano-material is composed from millions of tiny silicon pillars, each up to 500 times thinner than a human hair. By manipulating this surface layer of nano-pillars – each of which acts kind of like a pixel projector on a conventional display – the system is capable of generating grayscale (monochromatic) 3D holograms. This new material is transparent, which means it loses minimal energy from the light, and it also does complex manipulations with light. In testing with the new device, the researchers created holograms ranging in size from 0.75 mm to 5 mm in width – so these won’t be replacing your wall-hugging flat-screen any time soon. But the researchers say the output represents the highest-efficiency holograms created to date, and if the system can be refined, it could introduce a whole new range of hologram technologies. It’s still early days, but in the long run, this kind of technology could find a home in the gadgets we use every day – potentially enabling cameras that record light in three dimensions, as well as advancing optical systems used in scientific equipment. This ability to structure materials at the nanoscale allows the device to achieve new optical properties that go beyond the properties of natural materials.

_

  1. New hologram technology created with tiny nanoantennas:

Researchers have created tiny holograms using a “metasurface” capable of the ultra-efficient control of light, representing a potential new technology for advanced sensors, high-resolution displays and information processing. The metasurface, thousands of V-shaped nanoantennas formed into an ultrathin gold foil, could make possible “planar photonics” devices and optical switches small enough to be integrated into computer chips for information processing, sensing and telecommunications, said Alexander Kildishev, associate research professor of electrical and computer engineering at Purdue University. Laser light shines through the nanoantennas, creating the hologram 10 microns above the metasurface. To demonstrate the technology, researchers created a hologram of the word PURDUE smaller than 100 microns wide, or roughly the width of a human hair. “If we can shape characters, we can shape different types of light beams for sensing or recording, or for example pixels for 3-D displays. Another potential application is the transmission and processing of data inside chips for information technology,” Kildishev said. “The smallest features—the strokes of the letters—displayed in our experiment are only 1 micron wide. This is a quite remarkable spatial resolution.”

_

Metasurfaces could make it possible to use single photons—the particles that make up light—for switching and routing in future computers. While using photons would dramatically speed up computers and telecommunications, conventional photonic devices cannot be miniaturized because the wavelength of light is too large to fit in tiny components needed for integrated circuits. Nanostructured metamaterials, however, are making it possible to reduce the wavelength of light, allowing the creation of new types of nanophotonic devices, said Vladimir M. Shalaev, scientific director of nanophotonics at Purdue’s Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering. “The most important thing is that we can do this with a very thin layer, only 30 nanometers, and this is unprecedented,” Shalaev said. “This means you can start to embed it in electronics, to marry it with electronics.” The layer is about 1/23rd the width of the wavelength of light used to create the holograms.

_

Under development for about 15 years, metamaterials owe their unusual potential to precision design on the scale of nanometers. Optical nanophotonic circuits might harness clouds of electrons called “surface plasmons” to manipulate and control the routing of light in devices too tiny for conventional lasers. The researchers have shown how to control the intensity and phase – or timing – of laser light as it passes through the nanoantennas. Each antenna has its own “phase delay”—how much light is slowed as it passes through the structure. Controlling the intensity and phase is essential for creating working devices and can be achieved by altering the V-shaped antennas.

_______

_______

Researchers claim they’ve built the first real 3D color hologram:

Korean researchers are laying claim to the world’s first 360-degree color hologram — a floating Rubik’s cube. A 16-company consortium called ETRI, led by LG Display division, has created “tabletop holographic display” that can be viewed from all angles. The research is the fruit of a 2013 Korean government project to develop hologram tech. The effect is produced by powerful, rapid lasers that create the 3D object using diffraction, and produce color via interference between multi-hued lasers. There are significant limitations — the holograph is only 3-inches in size, and uses a complex system of lasers. However, ETRI plans to commercialize a 10-inch Holo TV by 2021, which should be just about the right size to fit into your flying car.

______

______

7D Hologram:

A 7D hologram is a method for capturing a high quality hologram using 7 parameters.

The universe exists in 3D space with time often considered a fourth dimension. The reason that a 7D hologram has so many dimensions is that the hologram is captured from a large number of positions that surround the scene or subject of the hologram. Each position is described in 3D space. Each position captures a variety of viewing directions in 2D space. Two additional parameters are captured for each direction: image intensity and time. A 7D hologram is like having a bunch of photographers surrounding a subject. The position of each photographer is described in 3D. The angle each photographer is pointing the camera is described in 2D. Each camera records light properties and time.

The resulting parameters are: 3D position + 2D angle + time + light properties = 7D.

7D hologram is also known as 5D Plenoptic Function. The five dimensions that describe position and angle are known as a 5D Plenoptic Function. Currently, holograms based on 5D plenoptic functions are prohibitively large. A number of competing technologies exist for recording and projecting holograms. Many approaches involve creating 3D models by scanning a physical subject with lasers. 7D Holography is the science of making holograms for displaying high resolution, seven dimensional, life-like images that are truly magnificent. The 7D Holographic Technology is expected to enhance the movie going experience.

_

Overview: 7D Hologram:

Type Hologram

Augmented Reality

Definition (1) A method for capturing a high quality hologram using 7 dimensions.
Definition (2) A method for recording a light field with the 7 parameters (Vx, Vy, Vz, θ, φ, t, λ) that describe a 5D Plenoptic Function with time and light intensity or chromacity.
Current State Future / Experimental
Also Known As 5D Plenoptic Function
Related Concepts Augmented Reality

Holograms

Light Field

_____

Is this real 7D hologram?

The above-displayed video was originally created by a company called Magic Leap in order to demonstrate the potential capabilities of its technology. While the Magic Leap device is still shrouded in mystery, several articles written about the device explain that it’s a wearable that deals in “mixed reality,” which layers unreal, virtual objects over real, tangible ones. Users will be required to wear something over their eyes (similar to Google Glass or Microsoft’s HoloLens) in order to see three-dimensional virtual imagery, but as the children in the video are not wearing any sort of special headgear, we can assume that they did not actually witness a hologram whale splashing through their gym floor. Even if they were actually seeing it, the whale would appear in the usual three dimensions, not seven.

____

____

Synopsis of hologram is depicted in the figure below:

 

____

____

Moral of the story:

_

  1. The separation of our eyes means that each eye sees the world from a slightly different perspective. This is called “binocular disparity” and is the basis of depth perception. Our powerful brains take these two slightly-different 2D images of the world and do all the necessary calculations using parallax to gain depth perception so that we see the world in three dimensions. If you keep one eye closed you will notice how much harder it is to gauge distance. The binocular vision and our brain work together to see world in three dimensions. Our retina is just a 2D screen i.e. see 3D world in 2D only i.e. record wavelength and amplitude of light waves and not phase of light waves. It is the brain that construct 3D image. There are several different types of 3D technology in use today, but they basically do the same thing. 3D movies and 3D glasses work together to send each of your eyes different perspectives of the same image and your brain constructs 3D image.

_

  1. Although the term “3D” is ubiquitously used, it is important to note that the presentation of dual 2D images is distinctly different from displaying an image in three full dimensions. The most notable difference to real 3D displays is that the observer’s head and eyes movements slightly will not increase information about the 3 dimensional objects being displayed. Holographic and volumetric displays are real 3D displays where observer’s head and eyes movements slightly will increase information about the 3 dimensional objects being displayed as opposed to presentation of dual 2D images in 3D movies. The hologram records an infinite number of views of the object, whereas a photograph records only one view and 3D movie records dual images of one view with different perspectives. When viewing a hologram, the left eye sees a different set of information than the right eye so that the image appears three dimensional with depth perception, and as head and eyes of the observer moves slightly, another 3D view of object is seen. 3D movies seen with 3D glasses are stereoscopic displays but not real 3D displays. Like a photograph, a hologram is a permanent record of the light reflected off an object. But a hologram also looks real, three-dimensional and moves as you look around it, just like a real object. This is because photograph records wave length (color) and amplitude (intensity) of light waves while hologram records wave length (color), amplitude (intensity) and phase (timing) of light waves. Holograms perform the most complex manipulations of light by storing and reproduction of all information carried by light in 3D. In contrast, standard photographs and computer monitors capture and display only a portion of 2D information.

_

  1. To create a hologram, a laser beam (coherent light) is split in two: one beam that stays undisturbed, called the reference beam, strikes a photographic plate. The second beam, called the object beam, strikes the subject and then bounces onto the plate. The subject’s interfering with the second beam causes the two beams to become out of phase. This difference—called phase interference—is what is recorded on the photographic plate. These two beams interfere with each other, causing a specific pattern of bright and dark spots where there has been constructive and destructive interference, spots where the waves added and subtracted. This creates areas of high amplitude and low amplitude, or bright and dark bands. Interference fringe means a bright or dark band caused by beams of light (laser) that are in phase or out of phase with one another. Note that phase information is converted into intensity pattern. These bands are recorded on the holographic surface, and preserved through the developing process. These bright and dark bands act as an extremely sophisticated diffraction grating, so that when a hologram is later illuminated with coherent light of the same frequency that created it, a three-dimensional image of the subject appears. This is due to production of light field identical to the one originally produced by the scene and scattered onto the hologram. In a transmission hologram, monochromatic light shines through the hologram to make an image. In a reflection hologram, monochromatic or white light reflects off of the surface of the hologram to make an image. The reflected or transmitted light is scattered by the interference patterns into your eye. At this point, the eye-brain system interprets the light rays and reconstructs the image of the original object. It is able to do this because all the space-time information has been captured by the interference patterns on the hologram. Hence, the eye-brain mechanism cannot distinguish any difference between the light scattering off the original object and the light being redirected (via the diffraction pattern) by the hologram. In either case the “image” is the same.

_

  1. Most photosensitive materials respond to variations in the intensity of the incident light only and therefore only record the distribution of the amplitude (or intensity), and cannot directly record the phase distribution. The phase information of an object can be converted to variations in intensity by creating an interference pattern between the light scattered from the object (i.e. the object beam) and a second reference beam which originates from the same coherent light source. The intensity at any point in this interference pattern depends on the phase of the object wave; therefore, the intensity variation recorded in the photosensitive medium (i.e. the hologram) contains both the phase and amplitude information of the object. The photography records only the intensity of dispersed light, i.e. its amplitude characteristics. So information about the phase difference of the beams, i.e. about the distances between various points of the object characterising its three-dimensionality, vanishes. Remember it is the phase that carries information about the depth of the image. Holography means recording of the three-dimensional structure of the light wave dispersed by the object. This record is obtained by the interference image that keeps the amplitude ratio of the dispersed light, i.e. relative intensities on which the rate of blackening of dark areas in the interference image depends, as well as its phase ratio defining the mutual distribution of dark and bright areas. If the hologram is then illuminated with the same reference beam, the original object wave will be reconstructed and can be viewed by an observer looking through the hologram. When suitably lit, the interference pattern diffracts the light into a reproduction of the original light field and the objects that were in it appear to still be there, exhibiting visual depth cues such as parallax and perspective that change realistically with any change in the relative position of the observer.

_

  1. To replicate the original object beam exactly, the reconstructing reference beam must be identical to the original reference beam and the recording medium must be able to fully resolve the interference pattern formed between the object and reference beams. Any change in the shape, orientation or wavelength of the reconstruction beam gives rise to aberrations in the reconstructed image. For instance, the reconstructed image is magnified if the laser used to reconstruct the hologram has a shorter wavelength than the original laser. Nonetheless, good reconstruction is obtained using a laser of a different wavelength, quasi-monochromatic light or white light, in the right circumstances.

_

  1. The basis of holography is 3D storage of the phase and amplitude profile of the desired wavefront in a manner that allows that wavefront to be reconstructed by interference when the hologram is illuminated with a suitable coherent source. Holography in its most basic sense, is recording then reconstruction of all the light-field information such that when viewed, the observer is unable to tell the difference from the original scene because the hologram is giving the observer all of the original information. Holography is a real 3D display technique that involves using interference and diffraction to record and reconstruct optical wavefronts. Holography is visual recording and playback process that can record our 3 dimensional worlds on a 2 dimensional recording medium, playback the original object or scene to the unaided eyes as a 3 dimensional image. The image demonstrates complete parallax and depth of field and floats in space either behind, in front of, or straddling the recording medium. A hologram is the imprint on a recording medium (holographic media) that is created during holographic recording. The hologram itself is not an image (it doesn’t look anything like the recorded objects), and it is not three-dimensional, either. A holographic image is the three-dimensional image that is reconstructed by shining (coherent) light onto a hologram. Most people refer to the holographic images as “holograms” somewhat confusingly. Based on the strict definition, the hologram is not the floaty 3D thing, but the flat transparent plate behind it (or in front of it). There is a popular misconception that holographic images are free-standing but without holographic plate/screen, no image will be visible. Holograph and hologram are synonymous. Holographic display has the ability to provide all four eye mechanism: binocular disparity, motion parallax, accommodation and convergence. The 3D objects can be viewed without wearing any special glasses and no visual fatigue will be caused to human eyes.

_

  1. Holography is a much broader field than most people have perceived. Recording and displaying truly three-dimensional images are only small parts of it. Holographic optical elements (HOE) can perform the functions of mirrors, lenses, gratings, or combinations of them, and they are used in myriad technical devices. Holographic interferometry measures microscopic displacements on the surface of an object and small changes in index of refraction of transparent objects like plasma and heat waves. Optical computer is a computer that performs its computation with photons (light) as opposed to the more traditional electron based computation. Optical computer is faster and smaller than electronic computer. Optical computers will use holograms as “circuit elements”. Future photonic devices such as electro-optical chips will undoubtedly incorporate micro-lasers and HOEs for optical computations, free-space interconnects, and massive analog and digital memory systems.

_

  1. Holograms are classified in many ways—transmission and reflection holograms, laser light and white light reconstruction holograms, static and dynamic (real time) holograms, thin and thick (volume) holograms, amplitude and phase modulation holograms, optically processed and electronically processed holograms, light wave holograms and non-light wave holograms like X-rays, sound waves, electrons and neutrons. Holography is based on most fundamental properties of waves i.e. interference and diffraction. Holography is therefore applicable to all kinds of waves besides visible light waves. So we have optical holography (with or without use of computer) and non-optical holography. Non-optical holography includes X-ray holography, electron holography, acoustic holography, atomic holography and neutron holography.

_

  1. If an image appears to be on the other side of the hologram, like looking through a window, it is called virtual. If an image jumps right out of the hologram and appears in front of the film, it is called real, since it has left the “virtual” world inside the film and entered the “real” world. It is possible to photograph the reconstituted real image, by ordinary photographic means, at a selected depth, in exact focus. Most real image holograms are holograms of holograms. The real image from a hologram—that is, the one that can be photographed—appears pseudoscopic, i.e. inside out with a reversed curvature. This reversal can be eliminated by making a double hologram, first by preparing the single hologram and then by using it as an object in the creation of a second hologram. With a double reversal the image becomes normal again.

_

  1. Typical characteristics of hologram include three dimensionality, divisibility, scaling, jumping mediums and multiple images can be recorded on the same holographic plate and each of them can be reconstructed without any failures of the other records or different color of same object can be recorded separately and reconstruction give rise to an image in its natural colour of the object.

_

  1. Real Holograms cannot be copied by any known printing technique. All printing is done with ink whereas hologram is an inkless optical process that cannot be scanned, photocopied, or electronically transmitted. A properly specified and executed hologram is very difficult to duplicate. Security holograms are labels with a hologram printed onto it for security reasons. Security holograms are an essential method of protection against forgery. Security holograms are very difficult to forge, because they are replicated from a master hologram that requires expensive, specialized and technologically advanced equipment. They cannot be copied by standard printing techniques or replicated by colour copiers or computer scanning equipment. They are used widely in several banknotes around the world, in particular those that are of high denominations. They are also used in passports, credit and bank cards as well as quality products. Although it is commonly believed that holograms cannot be counterfeited, as a matter of fact, it is rather easy to counterfeit the holograms that are commonly used today in security applications. This is not news to the holographic industry, but it may be a revelation to some of the users and potential users of security holograms. Counterfeit holograms are either going out through the back door of the legitimate manufacturer or just copied. And most consumers can’t tell the difference between a reasonable counterfeit and the authentic item. Many of the so called ‘security holograms’ are just 2D/3D holograms i.e. multilayer images and not real holograms. So crafting a convincing duplicate of a security hologram is not difficult. The good news is that there are countermeasures against hologram counterfeiting which can be extremely effective.

_

  1. Smart Holograms involve the field of “portable” diagnostics and hologram sensors wherein a hologram is made with a modified material that interacts with certain molecules generating a change in the fringe periodicity or refractive index, therefore, the color of the holographic reflection. So holographic gratings can be fabricated that respond to humidity, water, solvents, dissolved gases, ions, metabolites, drugs, antibiotics, sugars or enzymes, and these substances can be monitored in real time. Smart Holograms’ novel sensors can monitor almost anything, from glucose to bacteria.

_

  1. Augmented reality is an enhanced version of reality created through technology by incorporating more information into the physical world to enhance one’s current perception of reality. Some experts label hologram as an augmented reality device because it adds something into reality that wasn’t otherwise there. In my view, real hologram is three dimensional depiction of reality but it does not add anything to reality. Holographic projection system like the Hololens, Meta and ODG headsets are augmented reality platforms that superimpose data onto reality using a headset impacting human perception, but they are not real holograms.

_

  1. We have true holograms (real holograms), lookalike holograms (e.g. volumetric display, hololens) and fake holograms (e.g. Tupac) depending on technology and visual depth cues offered by them to create illusion of three dimensional images. Real holographic viewing system (laser generated hologram plus proper illumination) covers all depth cues for any number of viewers without any headset or eyewear. True holograms need laser to record interference pattern on media but its lookalike has nothing to do with lasers and interference patterns; yet create the experience of apparently solid three-dimensional objects floating in thin air by giving major depth cues to eye-brain system that help us perceive three dimensions. In other words, most remarkable thing about lookalike holograms is not how they’re made, but the illusion they create. There are important differences between 3D displays of lookalike holograms and real holographic displays. Most currently existing 3D displays of lookalike holograms (except volumetric display) don’t provide for proper accommodation, leading to accommodation/ vergence conflict and decoupling; only work for a single viewer, and require some headgear. Fake hologram makes 3D effects through 2D images. Fake holograms (3D TV and 3D movie) may lead to eye fatigue or even headaches, or one simply cannot fuse the two views and sees double images.

_

  1. Fake (false) holograms need to be differentiated from counterfeit holograms. Fake holograms create illusion of three dimensional images by not employing technology of real holograms and by not offering many visual depth cues, but they are perfectly legal e.g. 2D/3D security hologram, Tupac, 3D TV etc. Counterfeit holograms are illegal replica of original hologram in such a way that most consumers can’t tell the difference between counterfeit and the authentic item.

_

  1. Computer generated holography is any process chain of either completely synthetically preparing holographic light wavefronts or digitally recording and processing of optically generated holographic data of existing objects (digital holography); and then displayed on a spatial light modulator (SLM) or digitally printed on holographic media; and then illuminated with a reference beam to view 3D image.

_

  1. Analog holography (optical recording and reconstruction of wavefronts) is slow but gives image with high resolution and full parallax while digital holography (digital recording and processing) is faster and can be performed at video rates; but gives image with low resolution without full parallax. However digitalisation of hologram allows application of whole range of powerful numerical techniques in the computer, and makes holographic interferometry possible without aberrations.

_

  1. Computer generated holography (CGH) including digital holography (DH) can be used to record and displayed singly as 3D displays, printed as fixed images, or recorded and projected in sequence to produce holographic videos, movies, or telepresence. Other applications of CGH/DH include holographic optical elements (HOE), Holographic interferometry, digital holographic microscopy, and optical data processing and data storage.

_

  1. Digital holographic microscopy distinguishes itself from other microscopy methods by not recording the projected image of the object. Instead, the light wave front information originating from the object is digitally recorded as a hologram, from which a computer calculates the object image by using a numerical reconstruction algorithm. Digital holographic microscopes can display 3D images of living cells in real time on computers.

_

  1. Digital Holographic Interferometry can be applied successfully to any situation to study distortion/deformation of any object surface by superimposing the two wave fronts on the hologram, reflected before and after distortion/deformation effect has been introduced. When reconstructed, the hologram provides a clear picture of the object, crossed by interference fringes to detect distortion/ deformations as small as a few microns. Digital Holographic Interferometry is used in numerous laboratories for non-destructive testing (NDT). From laser vibrometry to laser Doppler imaging, from spectroscopy to remote sensing, from mechanical and optical metrology to oceanography and seismology, from quantum mechanics to nuclear and plasma physics, the range of digital holographic interferometry applications is extremely broad.

_

  1. Holographic data storage is a technique that can store information in form of holographic image at high density inside crystals or photopolymers. Unlike CDs and DVDs, which store their data on the disc’s surface, holograms store data in three dimensions and those pages can overlap in the storage space. Holographic Versatile Disc (HVD) is an optical disc technology still in the research stage which would hold up to 3.9 terabyte (TB) of information which is approximately 6000 times the capacity of a CD-ROM, 830 times the capacity of a DVD, 160 times the capacity of single-layer Blu-ray-Discs, and about 8 times the capacity of standard computer hard drives. The HVD has a data transfer rate of 1gigabyte/s. Even if HVD is damaged or broken, all information can still be obtained from other parts. A difficulty with the HVD technology had been the destructive readout. The re-illuminated reference beam used to retrieve the recorded information, also excites the donor electrons and disturbs the equilibrium of the space charge field in a manner that produces a gradual erasure of the recording.

_

  1. In movies, holograms can appear to move and recreate entire animated scenes in mid-air, but today’s holograms can only mimic movement. You can get the illusion of movement by exposing one holographic emulsion multiple times at different angles using objects in different positions. The hologram only creates each image when light strikes it from the right angle. When you view this hologram from different angles, your brain interprets the differences in the images as movement. Holograms are 3D images of 3D objects on 2D surfaces, 3D holographic display adds time to it, and so it becomes real-time hologram i.e. hologram in motion. When we watch 2D TV, we see people talking and walking in 2 dimensions. In 3D holographic display, we see people talking and walking in 3 dimensions as if they are actually in front of you. Although 3D holographic display screen is 2 dimensional, light from it enters our eyes in such a way that our brain construct image in 3 dimensions and in real-time having motion. Both holographic TV and holographic telepresence involves 3D holographic display. The problem with creating 3D holographic displays is that the amount of information a typical hologram contains is vast! As an example, it is thought that the order of a million-trillion pixels are required in order to achieve a pure 3D holographic display, and with a typical refresh rate of 30 fps, this is a staggering amount of data. Not only this, we also need technology that can record (in real-time) all of the complex information of the light field, communications technology capable of transmitting this huge amount of data, and then a computer in order to process this data. Considering we are just about entering the 4K TV era (which is a screen made of approximately 10 million pixels), we are some way off.

_

  1. Holographic telepresence is an evolving technology for full-motion, three-dimensional (3D) video conferencing. Holographic telepresence systems can project realistic, full-motion, real-time 3D images of distant people and objects into a room, along with real-time audio communication, with a level of realism rivalling physical presence. The idea is to record digital holograms at a video-like frame rate, transmit them, then display them in their full three-dimensional glory at the same frame rate. So far, the most impressive “holographic” demonstrations have not involved any real holograms. CNN hologram was not real hologram but tomograms, which are images that are captured from all sides, reconstructed by computers, and then displayed on screen. French presidential candidate Jean-Luc Mélenchon and Indian Prime Minister Narendra Modi have used “Pepper’s Ghost” technology to allow them to be “transported” to plenty of locations simultaneously for campaigning but it is not holographic telepresence.

_

  1. 3D volumetric display is a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. 3D volumetric display offers all depth cues for any number of viewers, but in small display volume. Laser based volumetric display allows full display, manipulation, and exploitation of internal volume imaging whereas laser based holographic display can only render surface volume and are unable to show an interior view. Volumetric display is real 3D display similar to holography but not 3D holographic display. 3D holographic display means digital holography in real time i.e. holographic TV, video and telepresence. Though there is no consensus among researchers in the field, it may be reasonable to admit holographic and highly multiview displays to the volumetric display family if they do a reasonable job of projecting a three-dimensional light field within a volume.

_

  1. Pixel stands for picture element. Most 2D display screens produce pixels that are points emitting light of a particular color and brightness. They never take on a different brightness or color hue no matter how or from where they are viewed. This omnidirectional emission behavior prevents 2D display screens from producing a true 3D sensation. Picture components that form 3D display images are called voxels (volumetric picture elements) or hogels (holographic picture elements) and they are directional emitters—they appear to emit directionally varying light. A Voxel is a volumetric pixel: it says that this volume of space is this colour (or whatever). A hogel (hoxel) is different from a voxel in that it contains information that is specific to displaying it in a hologram; in particular diffraction patterns that holograms are composed of.

_

  1. In conventional hologram, when the two beams cross each other, an interference pattern in created. But in order to produce 3D image, the holograms must be as thick as the optical wavelengths to create enough phase shifts. So current hologram technology is somewhat limiting, given that the material on which the light is recorded, has to have the same thickness as the light’s wavelength. As a result, it is too thick to incorporate into personal devices. Nano-holograms are 25 to 35 nanometer thick metasurface holograms which can be integrated into everyday electronic devices including smartphones. Integrating holography into everyday electronics would make screen size irrelevant – a pop-up 3D hologram can display a wealth of data that doesn’t neatly fit on a phone or watch. Metasurfaces could also make it possible to use single photons for switching and routing in future optical computers. While using photons would dramatically speed up computers and telecommunications, conventional photonic devices cannot be miniaturized because the wavelength of light is too large to fit in tiny components needed for integrated circuits. Nanostructured metamaterials, however, are making it possible to reduce the wavelength of light, allowing the creation of new types of nanophotonic devices. The metasurface can make possible “planar photonics” devices and optical switches small enough to be integrated into computer chips for information processing, sensing and telecommunications.

_

  1. Holographic art is a new artistic medium as many artists use holograms to capture their subjects. Holograms also can be used to preserve art with a holographic copy and make archival recordings of valuable and/or fragile museum artifacts.

_

  1. Applications of holography include security, advertisements, promotional, consumer packaging, merchandise, automotive design, navigation, music, entertainment, theme parks, commerce, industry, scientific research, medicine, art, architecture, education, military and as holographic workers. It is predicted that holographic technology in the display industry alone will earn a staggering $3.57 billion by 2020.

_

  1. 3D digital holograms can be created from almost any type of biomedical datasets from protein database files to medical scans, such as computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound scans. 3D holography stands to enhance visual understanding of the human body with potential uses of teaching anatomy and better surgical management. Holographic interferometric techniques have been widely applied with success for the study of different parts of human body including cornea, tooth mobility, tympanic membrane, basilar membrane, cochlea, temporal bone, incudo-mallar joint, chest, stull, and bones. Endoscopic holography is a powerful tool for non-contact high resolution imaging and nondestructive measurements inside the natural cavities of human internal organs. X-ray holography has shown the promise of real-time observation of living biological specimens.

_

  1. Military use of holography include military mapping and better view of battlefield, holographic night vision goggles, battlefield intelligence, military planning, explosives disposal and as holographic soldiers.

_

  1. Biggest limitations of holography are cost, accessibility and a standing danger of getting retinas damaged from a possible laser burn. Researchers noted that no one should view the laser beam directly, only the image it projects, and they advise that users still wear infrared glasses until the technology has fully matured. Aside from its uses in digital holographic microscopy and digital holographic interferometry, holography is therefore applied only when other methods have failed or are not precise enough.

_

  1. We are moving into the age of light where hologram is a representation of a new visual language in information and communication technology. Holographic technology has endless applications and it will become a very integral part of human societies and civilizations in future. However, there is a danger that holograms would make people even lazier than they are today and more dependent on their technology than they are today, slowly shifting the world from its real, alive state, to a virtual, completely online state.

______

Dr. Rajiv Desai. MD.

September 17, 2017

______

Postscript:

I have learnt a lot about hologram while writing article on hologram. Education is at its best when educator gets educated.

______

 

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

4 comments on “HOLOGRAM”

Leave a Reply

Your email address will not be published. Required fields are marked *

Designed by @fraz699.