Bright light dots caused by interference of parametric scattering processes in LiNbO_3 crystals

Propagation of two extraordinarily polarized pump beams in LiNbO3:Cu crystals leads to a complicated pattern of photoinduced scattering on a viewing screen behind the sample. This pattern includes a considerable number of light rings and unclosed lines, and at some of the intersections bright light dots appear. For a scattering distance of a few millimeters the dots can contain most of the transmitted light intensity. Our theoretical study indicates that the light dots are caused by constructive interference of four different processes of parametric scattering. We show within the photovoltaic transport model that such an interference may increase the rate of exponential growth of the seed waves by a factor of 1.5–2. Good agreement between theory and experiment is demonstrated.