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'''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 [http://en.wikipedia.org/wiki/Three-dimensional_space three dimensional].

'''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 [https://en.wikipedia.org/wiki/Three-dimensional_space three dimensional].

The technique of holography can also be used to [[Optics|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.

The technique of holography can also be used to [[Optics|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.

==Overview==

==Overview==

Holography was [[discovered]] in 1947 by Hungarian physicist [http://en.wikipedia.org/wiki/Dennis_Gabor Dennis Gabor] (Hungarian name: Gábor Dénes) (1900–1979),[1] work for which he received the [[Nobel Prize]] in [[Physics]] in 1971. It was made possible by pioneering work in the field of physics by other [[scientists]] like Mieczysław Wolfke who resolved [[technical]] issues that previously made advancements impossible. The discovery was an unexpected result of [[research]] into improving [http://en.wikipedia.org/wiki/Electron_microscope 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.

Holography was [[discovered]] in 1947 by Hungarian physicist [https://en.wikipedia.org/wiki/Dennis_Gabor Dennis Gabor] (Hungarian name: Gábor Dénes) (1900–1979),[1] work for which he received the [[Nobel Prize]] in [[Physics]] in 1971. It was made possible by pioneering work in the field of physics by other [[scientists]] like Mieczysław Wolfke who resolved [[technical]] issues that previously made advancements impossible. The discovery was an unexpected result of [[research]] into improving [https://en.wikipedia.org/wiki/Electron_microscope 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.

The first holograms that recorded 3D objects were made in 1962 by [http://en.wikipedia.org/wiki/Yuri_Denisyuk Yuri Denisyuk] in the Soviet Union[2] and by Emmett Leith and Juris Upatnieks at University of Michigan, USA.[3] Advances in photochemical processing techniques to produce high-quality display holograms were achieved by Nicholas J. Phillips.[4]

The first holograms that recorded 3D objects were made in 1962 by [https://en.wikipedia.org/wiki/Yuri_Denisyuk Yuri Denisyuk] in the Soviet Union[2] and by Emmett Leith and Juris Upatnieks at University of Michigan, USA.[3] Advances in photochemical processing techniques to produce high-quality display holograms were achieved by Nicholas J. Phillips.[4]

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 "[http://en.wikipedia.org/wiki/Rainbow_hologram rainbow transmission]" hologram, allows more convenient [[illumination]] by white light or other monochromatic sources rather than by lasers. Rainbow holograms are commonly seen today on credit cards as a [[security]] feature and on product packaging. These versions of the rainbow transmission hologram are commonly formed as [[surface]] relief [[patterns]] in a plastic film, and they incorporate a [[reflective]] aluminium coating that provides the light from "behind" to reconstruct their imagery.

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 "[https://en.wikipedia.org/wiki/Rainbow_hologram rainbow transmission]" hologram, allows more convenient [[illumination]] by white light or other monochromatic sources rather than by lasers. Rainbow holograms are commonly seen today on credit cards as a [[security]] feature and on product packaging. These versions of the rainbow transmission hologram are commonly formed as [[surface]] relief [[patterns]] in a plastic film, and they incorporate a [[reflective]] aluminium coating that provides the light from "behind" to reconstruct their imagery.

Another kind of common hologram, the reflection or Denisyuk hologram, is capable of multicolour image reproduction using a white light illumination source on the same side of the hologram as the viewer.

Another kind of common hologram, the reflection or Denisyuk hologram, is capable of multicolour image reproduction using a white light illumination source on the same side of the hologram as the viewer.

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 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 [[researcher]]s, [[artists]] and dedicated hobbyists.

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 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 [[researcher]]s, [[artists]] and dedicated hobbyists.

==Theory==

==Theory==

Though holography is often referred to as 3D [[photography]], this is a misconception. A better [[analogy]] is [http://en.wikipedia.org/wiki/Sound_recording sound recording] where the sound field is encoded in such a way that it can later be reproduced. 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 an apparently [[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 it may no longer be present. There are a variety of recording materials which can be used, including photographic film.[http://en.wikipedia.org/wiki/Hologram]

Though holography is often referred to as 3D [[photography]], this is a misconception. A better [[analogy]] is [https://en.wikipedia.org/wiki/Sound_recording sound recording] where the sound field is encoded in such a way that it can later be reproduced. 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 an apparently [[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 it may no longer be present. There are a variety of recording materials which can be used, including photographic film.[https://en.wikipedia.org/wiki/Hologram]

== Further reading ==

== Further reading ==

== External links ==

== External links ==

* "''Wavefront reconstruction using a coherent reference beam''" — E. N. Leith et al.

* "''Wavefront reconstruction using a coherent reference beam''" — E. N. Leith et al.

* [http://nobelprize.org/physics/laureates/1971/gabor-autobio.html The nobel prize lecture of Denis Gabor]

* [https://nobelprize.org/physics/laureates/1971/gabor-autobio.html The nobel prize lecture of Denis Gabor]

* [http://www.media.mit.edu/spi/ MIT's Spatial Imaging Group with papers about holographic theory and Holographic video]

* [https://www.media.mit.edu/spi/ MIT's Spatial Imaging Group with papers about holographic theory and Holographic video]

* [http://www.holokits.com/a-holography_medical_applications.htm Medical Applications of Holograms]

* [https://www.holokits.com/a-holography_medical_applications.htm Medical Applications of Holograms]

* [http://science.howstuffworks.com/hologram.htm How Stuff Works - holograms]

* [https://science.howstuffworks.com/hologram.htm How Stuff Works - holograms]

* [http://holocenter.org Center for the Holographic Arts, New York - a non-profit organisation promoting holograpy]

* [https://holocenter.org Center for the Holographic Arts, New York - a non-profit organisation promoting holograpy]

* [http://news.bbc.co.uk/2/hi/technology/7230258.stm Faster way to produce holographic tiles]

* [https://news.bbc.co.uk/2/hi/technology/7230258.stm Faster way to produce holographic tiles]

* [http://www.newscientist.com/article/mg20126911.300-our-world-may-be-a-giant-hologram.html?page=3 Theory of reality as a hologram]  

* [https://www.newscientist.com/article/mg20126911.300-our-world-may-be-a-giant-hologram.html?page=3 Theory of reality as a hologram]  

[[Category: Physics]]

[[Category: Physics]]