Characteristics of two-layer phase holograms

Theoretical and experimental investigations were made of thin two-layer phase holograms. It was found that their properties were intermediate between thin and volume holograms. The diffraction efficiency of such two-layer holograms was considerably higher than the theoretical limit for a thin phase hologram and could reach 67%. Moreover, they were found to have a high angular selectivity, which differs qualitatively from the selectivity of volume holograms. The characteristics of two-layer holograms were studied as a function of the angle between the recording waves and as a function of the exposure. A good agreement was observed between the experimental and theoretical data.