Holography
However, in common practice, major image quality compromises are made to remove the need for laser illumination to view the hologram.
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[11] and by Emmett Leith and Juris Upatnieks at the University of Michigan, US.
[13][14][15] A major advance in the field of holography was made by Stephen Benton, who invented a way to create holograms that can be viewed with natural light instead of lasers.
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 which a plate, film, or other medium photographically records.
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.
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 rarely done outside of scientific and industrial laboratory settings.
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 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.
Each point source wave interferes with the reference beam, giving rise to its own sinusoidal zone plate in the recording medium.
[18] 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.
[21] None of these studios still exist; however, there is the Center for the Holographic Arts in New York[22] and the HOLOcenter in Seoul, which offers artists a place to create and exhibit work.
[23] Some are associated with novel holographic techniques; for example, artist Matt Brand[24] employed computational mirror design to eliminate image distortion from specular holography.
The ability to store large amounts of information in some kind of medium is of great importance, as many electronic products incorporate storage devices.
In 1971, Lloyd Cross opened the San Francisco School of Holography and taught amateurs how to make holograms using only a small (typically 5 mW) helium-neon laser and inexpensive home-made equipment.
Holography had been supposed to require a very expensive metal optical table set-up to lock all the involved elements down in place and damp any vibrations that could blur the interference fringes and ruin the hologram.
Cross's home-brew alternative was a sandbox made of a cinder block retaining wall on a plywood base, supported on stacks of old tires to isolate it from ground vibrations, and filled with sand that had been washed to remove dust.
The mirrors and simple lenses needed for directing, splitting and expanding the laser beam were affixed to short lengths of PVC pipe, which were stuck into the sand at the desired locations.
This was a very important development for amateurs, as the price of red laser diodes had dropped from hundreds of dollars in the early 1980s to about $5 after they entered the mass market as a component pulled from CD, or later, DVD players from the mid 1980s onwards.
These kits enabled students, teachers, and hobbyists to make several kinds of holograms without specialized equipment, and became popular gift items by 2005.
[31] In 2006, a large number of surplus holography-quality green lasers (Coherent C315) became available and put dichromated gelatin (DCG) holography within the reach of the amateur holographer.
[38] The 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.
Such holograms come in a variety of forms, from adhesive strips that are laminated on packaging for fast-moving consumer goods to holographic tags on electronic products.
Holographic scanners are in use in post offices, larger shipping firms, and automated conveyor systems to determine the three-dimensional size of a package.
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.
As of April 2019, holographic license plates are required on vehicles in parts of India to aid in identification and security, especially in cases of car theft.
Due to the shorter wavelength of x-rays compared to visible light, this approach allows imaging objects with higher spatial resolution.
Although widely called a "hologram protest" in news reports,[70] no actual holography was involved – it was yet another technologically updated variant of the Pepper's ghost illusion.
[72] Science fiction writers absorbed the urban legends surrounding holography that had been spread by overly-enthusiastic scientists and entrepreneurs trying to market the idea.
[72] 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.
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.
