3-D Holographic Display Using Strontium Barium Niobate (1998 Army Research Laboratory Doc)

in #technology3 years ago (edited)

The following is a few excerpts from an interesting Army Research Laboratory document that was published in February 1998, which is titled, 3-D Holographic Display Using Strontium Barium Niobate.

Abstract - An innovative technique for generating a three-dimensional holographic display using strontium barium niobate is discussed. The resultant image is a hologram that can be viewed in real time over a wide perspective or field of view. The holographic image is free from system-induced aberrations and has a uniform, high quality over the entire field of view. The enhanced image quality results from using a phase-conjugate read beam generated from a second photorefractive crystal acting as a double-pumped phase-conjugate mirror. Multiple three-dimensional images have been stored in the crystal via wavelength multiplexing.

Introduction - Present holographic displays, such as those generated by computers or emulsion films, usually require intermediate preprocessing or postprocessing and are, therefore, not capable of real-time production and viewing and have limited information storage capacity. The use of photorefractive crystals, such as strontium barium niobate, as a holographic storage medium eliminates these and other limiting factors. For example, when a photorefractive storage medium is used, holograms may be recorded and projected without time-consuming processing and with greater storage capacity through various forms of multiplexing. Additionally, the photorefractive recording medium is sensitive to low level intensity and is reusable. Therefore, previously stored holograms may be erased, and the crystal can be reused to store other holograms. Until recently, however, research in photorefractive holography has been limited to the production of two-dimensional holograms and very limited field-of-view 3-D holograms. The proposed method employs a volume hologram recorded and read in real time in a photorefractive crystal to produce a 3-D image. This innovative technique is simple, and it differs from previous attempts at 3-D displays. We used a photorefractive material, Strontium Barium Niobate, to record a hologram, and a phase-conjugate read beam, which is generated from a double-pumped phase-conjugate mirror, to accurately reproduce the holographic image in space over a large perspective. The resultant holographic image is free from system-induced aberrations, may be viewed over a wide range of angles that can be expanded by the use of a mosaic of crystals, and has uniform high quality over the entire field of view

Conclusions - A simple method for recording a real-time, 3-D hologram using Strontium Barium Niobate has been demonstrated. The 3-D hologram is a realistic image that can be viewed over a large field of view. A double-pumped phase-conjugate mirror was used to produce a phase conjugate read beam in order to view the hologram over the maximum perspective. We further increased the field of view of the hologram by storing the hologram in a mosaic of two Strontium Barium Niobate crystals. Multiple 3-D images have been stored and read out of the crystal via wavelength multiplexing. The holograms were also noted to persist without any external fixing mechanisms. During readout, the holograms persisted for hours. When the photorefractive storage crystal was kept in a dark environment, the holograms persisted for days.

If your interested in learning more, you can read the entire "Holographic Display Using Strontium Barium Niobate" document from the Defense Technical Information Center .mil site, at the link below.
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA338490 (downloadable pdf)

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