Four-wave interaction phenomena contributing to holographic scattering in LiNbO3and LiTaO3

Experimental results are presented which indicate the importance of four-wave interactions for holographic scattering. In contrast to three-wave interactions there are no changes in the polarization of the scattered beams. But similar to three-wave interactions the rays are scattered in a cone emerging in the forward and backward directions from the sample. The cone angle is equal to the angle of reflection at the rear side of the sample. Reflected rays are necessary to initiate the scattering process. We present an explanation for the geometry of the pattern produced by the incident, reflected, and scattered beams. Furthermore, experimental results on the angular and time dependence of the scattered radiation are given for LiNbO3:Fe and LiTaO3:Fe crystals, demonstrating the predominance of four-wave interaction processes.