1. Overview and history
2.1 Holographic recording process
2.2 Interference and diffraction
2.3 Plane wavefronts
2.4 Holographic reconstruction process
3. Mathematical model
4. Viewing the hologram
5. Holographic recording media
6. Comparision of holography with photography
7.1 Data storage
7.3 Interferometric microscopy
7.4 Hobbyist use
1.OVERVIEW AND HISTORY
Holography (from the Greek, ὅλος hólos whole + γραφή grafē writing, drawing) is a technique that allows the light scattered from an object to be recorded and later reconstructed so that it appears as if the object is in the same position relative to the recording medium as it was when recorded. The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the recorded image (hologram) appear three dimensional.
The technique of holography can also be used to optically store, retrieve, and process information. While holography is commonly used to display static 3-D pictures, it is not yet possible to generate arbitrary scenes by a holographic volumetric display.
Holography was invented in 1947 by the Hungarian-British physicist Dennis Gabor ,work for which he received the Nobel Prize in Physics in 1971. Pioneering work in the field of physics by other scientists including Mieczysław Wolfke resolved technical issues which previously had prevented advancement. The discovery was an unexpected result of research into improving electron microscopes at the British Thomson-Houston Company 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 holography as a light-optical technique did not really advance until the development of the laser in 1960.
One of the most promising recent advances in the short history of holography has been the mass production of low-cost solid-state lasers, such as those found in millions of DVD recorders and used in other common applications, which are sometimes also useful for holography. These cheap, compact, solid-state lasers can, under some circumstances, compete well with the large, expensive gas lasers previously required to make holograms, and are already helping to make holography much more accessible to low-budget researchers, artists and dedicated hobbyists.
2.1 Holographic recording process
In holography, some of the light scattered from an object or a set of objects falls on the recording medium. A second light beam, known as the reference beam, also illuminates the recording medium, so that interference occurs between the two beams. The resulting light field is a seemingly random pattern of varying intensity which is the hologram. It can be shown that if the hologram is illuminated by the original reference beam, a light field is diffracted by the reference beam which is identical to the light field which was scattered by the object or objects. Thus, someone looking into the hologram "sees" the objects even though they are no longer present. There are a variety of recording materials which can be used, including photographic film.
A portion of the light from the laser, the "illumination beam," is aimed at the scene where it bounces off the objects in the scene directly onto the film--the window--with no pinhole or lens interposed. Another portion of the laser light, the "reference beam," instead of striking the object first, is split off from the original laser beam and directed straight onto the film. To "play back" the scene , one resupplies the reference...
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