Chapter 6 - Recording Materials (Sample page excerpted from book) |
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Silver Halide Holographic Recording Materials
Photography has utilized silver halide recording materials for many decades. These silver halide emulsions are commonly coated onto films or glass plates for use in traditional cameras, in laboratories, and in factories. However, they were not designed for holographic applications. The important difference between photographic and holographic materials is resolving power, usually expressed in lines per millimeter. Whereas photographic films usually cannot resolve more than 50 - 100 lines per millimeter, holographic applications require between 1250 - 2500 lines per millimeter. Another difference is sensitivity, which is typically expressed as an ASA number. For example, popular photographic films are rated at ASA 120 - 400. Exposures are usually measured in hundreds of a second. Silver halide holographic recording materials are so
much less sensitive than standard films that their ASA
would only be rated as fractions. Therefore, their
sensitivities are usually expressed in micro-joules per
square centimeters (or ergs per centimeter squared).
Exposure times are typically measured in seconds, or even
minutes, depending on the amount of laser light
available. |
This
chapter discusses the major types of recording materials
used by holographers: silver halide, dichromate,
photoresist and photopolymer. Of special interest is the
updated information weve assembled from the three
main manufacturers of silver halide emulsions. ATTN: RECENTLY AGFA HAS STOPPED MANUFACTURING RED SENSITIVE SILVER-HALIDE EMULSIONS FOR HOLOGRAPHY. SEE LIST OF ALTERNATE SUPPLIERS IN HMP 6. Current Availability Unfortunately, the worldwide demand for these particular photosensitive materials has slowed, due in part to the increased use of electronic imaging, especially in the field of Non-Destructive Testing. Since the current combined needs of commercial holographers, educational facilities and hobbyists do not nearly compare to other industrial and mass market customers, the production of silver halide recording materials suitable for holography has decreased, while prices have generally increased. (To prevent potential supply problems, some commercial holographers have learned to utilize silver halide recording materials with characteristics similar to holographic films but which are intended for other industrial uses, such as micro-lithography.) Currently, the main suppliers of silver halide holographic recording materials are Agfa (Belgium) and Eastman Kodak (USA). Several distributors have begun to import previously hard-to-obtain emulsions by Slavich (Russia), but relevant product catalogs and associated technical specs....... |
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