Abstract

Investigations of two- and four-wave mixing in photorefractive materials are well known. However, these studies have mostly been carried out in volume holograms where diffraction phenomena are observed under Bragg conditions which impose strict limitations on possible combinations of interacting beams and, as a result, only interaction between the zero order of one beam and the first diffraction order of another beam is considered in most cases. This report discusses the studies of wave mixing in thin holograms where there are no Bragg limitations. In the experiments, thin plates of Bi₁₂TiO₂₀ and the adaptive interferometric technique involving phase modulation of one of incident beams were used. It was shown that not only two-wave, but also induced three-wave and even multiwave mixing can be detected in thin holograms in case of nonlinear holographic recording in spite of the fact that only two incident beams record the hologram. This occurs because different combinations of diffracted beams from various spatial, harmonics of an initial sinusoidal grating can propagate in the same direction and efficiently interfere with each other. As many as seven diffracted orders were observed. Thorough investigations of polarization have shown that they are associated with seven spatial harmonics of the recorded grating. Theoretical analysis of the observed phenomena has been performed.

© 1996 IEEE