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Though holography is the subject of intense research in commercial and university laboratories across the country, its practical use has been limited by two handicaps: holograms have displayed their pictures in only one color, the color of the original laser beam, and viewing the picture has also required laser light, which is not only expensive and difficult to handle but can cause serious eye injury as well. Holographer Stroke has apparently eliminated both these difficulties. At a meeting of the Optical Society of America in Washington this week, he reported that he and Student Antoine Labeyrie have produced holograms that can be seen with ordinary light and show their images in true colors. "The amazing thing," says Stroke, "is that no one had gone to work on eliminating these problems. It was widely assumed that it could not be done."
Multicolor Image. Stroke & Co. went to work on the problem last year, and in December decided to apply the principles of a photographic process that won Physicist Gabriel Lippmann a Nobel Prize in 1908. By changing the position of the holography mirror, Stroke directed the undisturbed laser light to the back, rather than the front, of a sheet of film. As the beam passed through the film, it met the scattered light reflected from the subject coming through in the opposite direction. The new arrangement had the effect of producing layers of interference patterns in the emulsion of the film. When a beam of ordinary white light was directed at the developed film, these layers filtered out all of its components except the color of the laser beam used to illuminate the subject. Thus only waves of this frequency were reflected back to the viewer as a single-color, three-dimensional image.
Last month, with the aid of scientists at the Bell Telephone Laboratories, Stroke began using overlapping red and blue laser beams to illuminate his holography subjects. The combined beams produced even more complex layers of interference patterns in the emulsion of the film and added a new facet to the hologram. In addition to carrying information about the intensity and phase of the light reflected from the subject, it now contained full color information—even though the hologram itself was made on black and white film. When ordinary white light was reflected from the new hologram, two colors—red and blue—reached the viewer's eyes in varying combinations that produced a multicolor image.
Movies in 3-D. Though there are many technical problems still to be solved before holograms come into widespread use, the University of Michigan development should speed the transition of holography from a laboratory curiosity to a valuable industrial and scientific tool. Stroke also sees it as a living-room entertainment medium. His new holograms can be framed and hung on the wall, where standard illumination will transform them into windows revealing . three-dimensional scenes Though movies and television present more difficult technical problems, holography may eventually be used to present them in three dimensions and in full color. "In our field," says Stroke, "this breakthrough is the equivalent of a successful Apollo shot. We asked for the moon and we got it."