Chapter 6 - Recording Materials

(Sample page excerpted from book)

Silver Halide Holographic Recording Materials

Photographic Verses Holographic 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.

ATTN: RECENTLY AGFA HAS STOPPED MANUFACTURING RED SENSITIVE SILVER-HALIDE EMULSIONS FOR HOLOGRAPHY. SEE LIST OF ALTERNATE SUPPLIERS IN HMP 6.

Current Availability
In response to an anticipated demand, several major manufacturers of silver halide emulsions adapted their existing production techniques and formulations to provide affordable recording materials for holographic applications. This spurred the growth of the holography industry, which needed a reliable supply of basic materials. These silver halide emulsions were high quality, ready to use, and had a reasonably long shelf life.

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.......