A technique for projecting holographic images to make both still and moving three-dimensional displays is undergoing development. Unlike older techniques based on stereoscopy to give the appearance of three-dimensionality, the developmental technique would not involve the use of polarizing goggles, goggles equipped with miniature video cameras, or other visual aids. Unlike in holographic display as practiced until now, visibility of the image would not be restricted to a narrow range of directions about a specified line of sight to a holographic projection plate. Instead, the image would be visible from any side or from the top; that is, from any position with a clear line of sight to the projection apparatus. In other words, the display could be viewed as though it were an ordinary three-dimensional object. The technique has obvious potential value for the entertainment industry, and for military uses like displaying battlefield scenes overlaid on three-dimensional terrain maps.
An essential element of the technique is the use of block of silica aerogel as the display medium. Silica aerogel is an open-cell glass foam with a chemical composition similar to that of quartz and a density as low as about one-tenth that of quartz. The sizes of cell features are of the order of 100 Å. Silica aerogel is a suitable display medium because it is nearly completely transparent, with just enough scattering and reflection to enable the generation of a real image.
The figure illustrates a conceptual application in which a three-dimensional topographical map would be displayed by fusing images projected into a block of silica aerogel from four separate holograms. One could use static holograms to project still images, either alone or in combination with computer-generated holograms to project moving or still images. A computer-generated hologram would be downloaded into a large liquid-crystal, which would be illuminated by a laser projection apparatus to display the holographic image in the aerogel block. For example, the terrain image could be projected from static holograms, while a computer-generated hologram would be used to depict a vehicle moving on the terrain.
This work was done by Frederick Mintz, Tien-Hsin Chao, Peter Tsou, and Nevin Bryant of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Physical Sciences category.A Three-Dimensional Topographical Map, projected from holograms for display in a block of aerogel, would be visible from any position above the projection table. One of the holograms could be generated by a computer to depict a vehicle moving on the terrain.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, NASA Management Office–JPL (818)354-2240. Refer to NPO-20101.
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