EDITORIAL & OPINION — NEW HORIZONS — Holograms indebted to silver

To the eye, the color image is almost indistinguishable from the original object.

Essential to the quality of the color holograms is the fine-grain, silver-halide film required to record the laser light reflected from an object illuminated by three differently colored lasers. The requirements for this ultra-fine-grain silver halide are more stringent than even the fine grain found in films for microscopic images. This precise photographic record on silver-halide film becomes the master copy from which copies can be made.

When holography was first invented, lasers were only available in a single color. Now that lasers have been developed to provide the three basic colors of red, blue and green, holograms can be developed in living color. The results are images so perfect to the eye that the holographic image appears to be the object itself.

A three-dimensional hologram is simply developed. Light from red, green and blue lasers is combined into one beam. The beam is widened with a lens and directed through a silver-halide-coated glass plate. On the other side of the plate is the object to be recorded. The light that is scattered off the object and back toward the plate interferes with the direct light coming through, and forms microscopic patterns of the two waves of light. The plate is developed and bleached so that the patterns appear on a transparent background.

To reproduce the image, a point source of incandescent light is directed at the finished transparency from the same direction as the original lasers. The patterns on the film defract the incoming white light, recreating an image indistinguishable from the original object.

— The preceding is an excerpt from Silver News, a publication of The Silver Institute, based in Washington, D.C.