HISTORY OF HOLOGRAM

 

HISTORY OF HOLOGRAM

Hologram technology is a method of creating and displaying three-dimensional (3D) images that appear to be floating in space without the need for special glasses or equipment. Unlike traditional images displayed on screens, holograms have depth and can be viewed from different angles, making them look more realistic and immersive.

The basic principle of holograms involves recording and reproducing the interference patterns of light waves. This process captures both the intensity and phase of light, allowing the recreation of a complete 3D representation of an object. Holography was first invented by Hungarian-British physicist Dennis Gabor in 1947, but it wasn't until advancements in laser technology in the 1960s that holograms became more practical to produce.

Here's a simplified explanation of how holograms work:

1. Recording: A coherent light source, typically a laser, is split into two beams. One beam called the reference beam, is directed straight onto the recording medium (usually a photosensitive material like photographic film or a digital sensor). The other beam called the object beam, is directed at the object whose hologram we want to create. The light scattered off the object interacts with the reference beam on the recording medium, creating an interference pattern.
2. Reconstruction: To view the hologram, another coherent light source is used to illuminate the recorded interference pattern. When this light passes through the hologram, it diffracts and reconstructs the original light waves that were scattered off the object during the recording process. As a result, a 3D image of the object appears in space, seemingly floating in front of the hologram.

Hologram technology has numerous applications, such as:

1. Art and Entertainment: Holograms are used for artistic installations, holographic performances, and interactive exhibits in museums and entertainment venues.
2. Medical Imaging: Holography has potential applications in medical imaging and visualization, allowing for detailed 3D representations of anatomical structures.
3. Data Storage: Holographic data storage is a method that uses 3D holographic patterns to store large amounts of data in a compact space.
4. Holographic Displays: There have been ongoing efforts to develop holographic displays for consumer electronics, gaming, and other visual applications.

Despite these exciting applications, commercial holographic displays are still in the early stages of development, and many current implementations are limited to specialized and research settings. Nonetheless, as technology advances, hologram technology may become more prevalent in our daily lives, offering new and innovative ways to interact with information and content.

Holography

 

Not to be confused with Pepper's ghost.

"Hologram" redirects here. For other uses, see Hologram (disambiguation).

Two photographs of a single hologram taken from different viewpoints

Holography is a technique that enables a wavefront to be recorded and later reconstructed. Holography is best known as a method of generating real three-dimensional images, but it also has a wide range of other applications. In principle, it is possible to make a hologram for any type of wave.

A hologram is made by superimposing a second wavefront (normally called the reference beam) on the wavefront of interest, thereby generating an interference pattern that is recorded on a physical medium. When only the second wavefront illuminates the interference pattern, it is diffracted to recreate the original wavefront. Holograms can also be computer-generated by modeling the two wavefronts and adding them together digitally. The resulting digital image is then printed onto a suitable mask or film and illuminated by a suitable source to reconstruct the wavefront of interest.

Overview and history

The Hungarian-British physicist Dennis Gabor (in Hungarian: Gábor Dénes) was awarded the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method".

His work, done in the late 1940s, was built on pioneering work in the field of X-ray microscopy by other scientists including Mieczysław Wolfke in 1920 and William Lawrence Bragg in 1939. This discovery was an unexpected result of research into improving electron microscopes at the British Thomson-Houston Company (BTH) in Rugby, England, and the company filed a patent in December 1947 (patent GB685286). 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. The word holography comes from the Greek words ὅλος (holos; "whole") and γραφή (graphē; "writing" or "drawing").

A hologram is a recording of an interference pattern that can reproduce a 3D light field using diffraction. The reproduced light field can generate an image that still has the depth, parallax, and other properties of the original scene. A hologram is a photographic recording of a light field, rather than an image formed by a lens. The holographic medium, for example, the object produced by a holographic process (which may be referred to as a hologram) is usually unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of variations in the opacity, density, or surface profile of the photographic medium. When suitably lit, the interference pattern diffracts the light into an accurate reproduction of the original light field, and the objects that were in it exhibit visual depth cues such as parallax and perspective that change realistically with the different angles of viewing. That is, the view of the image from different angles represents the subject viewed from similar angles. In this sense, holograms do not have just the illusion of depth but are truly three-dimensional images.

Horizontal symmetric text, by Dieter Jung

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, US. 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.

Optical holography needs a laser light to record the light field. In its early days, holography required high-power and expensive lasers, but currently, mass-produced low-cost laser diodes, such as those found on 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. A microscopic level of detail throughout the recorded scene can be reproduced. The 3D image can, however, be viewed with non-laser light. In common practice, however, major image quality compromises are made to remove the need for laser illumination to view the hologram, and in some cases, to make it. Holographic portraiture often resorts to a non-holographic intermediate imaging procedure, to avoid the dangerous high-powered pulsed lasers which would be needed to optically "freeze" moving subjects as perfectly as the extremely motion-intolerant holographic recording process requires. Holograms can now also be entirely computer-generated to show objects or scenes that never existed. Most holograms produced are of static objects but systems for displaying changing scenes on a holographic volumetric display are now being developed.

Holography is also used with many other types of waves.

Basics of holography

Recording a hologram

Reconstructing a hologram

 

This is a photograph of a small part of an unbleached transmission hologram viewed through a microscope. The hologram recorded an image of a toy van and car. It is no more possible to discern the subject of the hologram from this pattern than it is to identify what music has been recorded by looking at a CD surface. The holographic information is recorded by the speckle pattern.

Holography is a technique that enables a light field (which is generally the result 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. However, it is even more similar to Ambisonic sound recording in which any listening angle of a sound field can be reproduced in the reproduction.

Laser

In laser holography, the hologram is recorded using a source of laser light, which is very pure in 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 microscopic interference pattern that 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 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 that is 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.

Apparatus

A hologram can be made by shining part of the light beam directly into the recording medium, and the other part onto the object in such a way that some of the scattered light falls onto the recording medium. A more flexible arrangement for recording a hologram requires the laser beam to be aimed through a series of elements that change it in different ways. The first element is a beam splitter that divides the beam into two identical beams, each aimed in different directions:

• One beam (known as the 'illumination' or 'object beam') is spread using lenses and directed onto the scene using mirrors. Some of the light scattered (reflected) from the scene then falls onto the recording medium.
• The second beam (known as the 'reference beam') is also spread through the use of lenses, but is directed so that it does not come in contact with the scene, and instead travels directly onto the recording medium.

Several different materials can be used as the recording medium. One of the most common is a film very similar to photographic film (silver halide photographic emulsion), but with much smaller light-reactive grains (preferably with diameters less than 20 nm), 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.

Process

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.

Comparison with 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.
• 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. It can be thought of as viewing a street outside a house through a 120 cm × 120 cm (4 ft × 4 ft) window, then through a 60 cm × 120 cm (2 ft × 4 ft) window. One can see all of the same things through the smaller window (by moving the head to change the viewing angle), but the viewer can see more at once through the 120 cm (4 ft) window.
• A photographic stereogram is a two-dimensional representation that can produce a three-dimensional effect but only from one point of view, 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.

Physics of holography

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

For those unfamiliar with these concepts, it is worthwhile to read those articles before reading further in this article.

Plane wavefronts

A diffraction grating is a structure with a repeating pattern. A simple example is a metal plate with slits cut at regular intervals. A light wave that is incident on a grating is split into several waves; the direction of these diffracted waves is determined by the grating spacing and the wavelength of the light.

A simple hologram can be made by superimposing two plane waves from the same light source on a holographic recording medium. The two waves interfere, giving a straight-line fringe pattern whose intensity varies sinusoidally across the medium. The spacing of the fringe pattern is determined by the angle between the two waves, and by the wavelength of the light.

The recorded light pattern is a diffraction grating. When it is illuminated by only one of the waves used to create it, it can be shown that one of the diffracted waves emerges at the same angle at which the second wave was originally incident, so that the second wave has been 'reconstructed'. Thus, the recorded light pattern is a holographic recording as defined above.

Point sources

Sinusoidal zone plate

If the recording medium is illuminated with a point source and a normally incident plane wave, the resulting pattern is a sinusoidal zone plate, which acts as a negative Fresnel lens whose focal length is equal to the separation of the point source and the recording plane.

When a plane wavefront illuminates a negative lens, it is expanded into a wave that appears to diverge from the focal point of the lens. Thus, when the recorded pattern is illuminated with the original plane wave, some of the light is diffracted into a diverging beam equivalent to the original spherical wave; a holographic recording of the point source has been created.

When the plane wave is incident at a non-normal angle at the time of recording, the pattern formed is more complex but still acts as a negative lens if it is illuminated at the original angle.

Complex objects

To record a hologram of a complex object, a laser beam is first split into two beams of light. One beam illuminates the object, which then scatters light onto the recording medium. According to diffraction theory, each point in the object acts as a point source of light so the recording medium can be considered to be illuminated by a set of point sources located at varying distances from the medium.

The second (reference) beam illuminates the recording medium directly. Each point source wave interferes with the reference beam, giving rise to its own sinusoidal zone plate in the recording medium. The resulting pattern is the sum of all these 'zone plates', which combine to produce a random (speckle) pattern as in the photograph above.

When the hologram is illuminated by the original reference beam, each of the individual zone plates reconstructs the object wave that produced it, and these individual wavefronts are combined to reconstruct the whole of the object beam. The viewer perceives a wavefront that is identical to the wavefront scattered from the object onto the recording medium so that it appears that the object is still in place even if it has been removed.

Holography using other types of waves

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

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. The principle of electron holography can also be applied to interference lithography.

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.

Neutron beam holography has been used to see the inside of solid objects.

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 mediums. The reconstruction is then retrieved via computation. Due to the shorter wavelength of x-rays compared to visible light, this approach allows imaging 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.

False holograms

A Pepper's ghost illusion made from a clear plastic frustumShows making using of projected images are erroneously marketed as "holographic"

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. Such illusions have been called "fauxlography".

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". 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 at the 2005 MTV Europe Music Awards and the 48th Grammy Awards; and Tupac Shakur's virtual performance at Coachella Valley Music and Arts Festival in 2012, rapping alongside Snoop Dogg during his set with Dr. Dre.

Swedish supergroup ABBA returned to the stage in May 2022, as digital avatars performing much-loved hits using technology which is an updated version of Pepper’s Ghost.

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.

In 2011, in Beijing, apparel company Burberry produced the "Burberry Prorsum Autumn/Winter 2011 Hologram Runway Show", which included life-size 2-D projections of models. The company's own video shows several centered and off-center shots of the main 2-dimensional projection screen, the latter revealing the flatness of the virtual models. The claim that holography was used was reported as fact in the trade media.

In Madrid, on 10 April 2015, a public visual presentation called "Hologramas por la Libertad" (Holograms for Liberty), featuring a ghostly virtual crowd of demonstrators, was used to protest a new Spanish law that prohibits citizens from demonstrating in public places. Although widely called a "hologram protest" in news reports, no actual holography was involved – it was yet another technologically updated variant of the Pepper's Ghost illusion.

Holography is distinct from specular holography which is a 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, not by using interference and diffraction.

In fiction

Holography has been widely referred to in movies, novels, and TV, usually in science fiction, starting in the late 1970s. Science fiction writers absorbed the urban legends surrounding holography that had been spread by overly-enthusiastic scientists and entrepreneurs trying to market the idea. This had the effect of giving the public overly high expectations of the capability of holography, due to the unrealistic depictions of it in most fiction, where they are fully three-dimensional computer projections that are sometimes tactile through the use of force fields. Examples of this type of depiction include the hologram of Princess Leia in Star Wars, Arnold Rimmer from Red Dwarf, who was later converted to "hard light" to make him solid, and the Holodeck and Emergency Medical Hologram from Star Trek.

Holography served as an inspiration for many video games with science fiction elements. In many titles, fictional holographic technology has been used to reflect real-life misrepresentations of potential military use of holograms, such as the "mirage tanks" in Command & Conquer: Red Alert 2 that can disguise themselves as trees. Player characters are able to use holographic decoys in games such as Halo: Reach and Crysis 2 to confuse and distract the enemy. Starcraft ghost agent Nova has access to "holo decoy" as one of her three primary abilities in Heroes of the Storm.

Fictional depictions of holograms have, however, inspired technological advances in other fields, such as augmented reality, that promise to fulfill the fictional depictions of holograms by other means.