Measurements of the stability of bleached photographic phase holograms

Although efficient high quality, bleached holograms have been made using photographic film, the tendency of the bleach products to darken upon exposure to light seriously limits their usefulness in many practical situations. Nevertheless, the great sensitivity of photographic emulsions makes their use in holography highly desirable. To shed light on the problem of stability, relative measurements of light induced darkening were made on heavily exposed plates bleached to yield one of the reaction products: silver chloride, silver bromide, silver iodide, and silver ferricyanide. We have found that the resistance of the emulsion to darkening increases significantly as the molecular weight of the halide ion is increased. Efficient, high quality, silver iodide holographic gratings usable over the wavelength range from 450 nm to 1200 nm, have been made which exhibit complete immunity to darkening when exposed to white light. Representative measurements of holograms made on Agfa 8E70 plates using the more stable emulsions are presented.