The ideal recording material for holography should have a spectral sensitivity well matched to available laser wavelengths, a linear transfer characteristic, high resolution, and low noise. In addition, it should either be indefinitely recyclable or relatively inexpensive.

While several materials have been studied [Smith, 1977; Hariharan, 1980b], none has been found so far that meets all these requirements. However, a few have significant advantages for particular applications. This chapter reviews the properties of some of these materials in the light of the general considerations discussed in Chapter 6 (see Table 7.1 for a summary of their principal characteristics).

Silver halide photographic emulsions

Silver halide photographic emulsions are widely used for holography because of their high sensitivity and their commercial availability. In addition, they can be dye sensitized so that their spectral sensitivity matches the most commonly used laser wavelengths.

An apparent drawback of photographic materials is that they need wet processing and drying; however, development is actually a process, with a gain of the order of 106, which amplifies the latent image formed during the exposure to yield high sensitivity as well as a stable hologram. Another advantage of the formation of a latent image is that the optical properties of the recording medium do not change during the exposure, unlike materials in which the image is formed in real time.