Anisotropic diffraction from photorefractive gratings and Pockels tensor of Sn2P2S6

The first observation of anisotropic diffraction and anisotropic self diffraction in low symmetry photorefractive crystal Sn(2)P(2)S(6) is reported. From comparison of the diffraction efficiency of isotropic and anisotropic diffraction the ratios of the Pockels tensor components are deduced, including some nondiagonal components that have never been evaluated until now. The particular orientation of the optical indicatrix in Sn(2)P(2)S(6) (roughly at 45 degrees to z- and x-axes at ambient temperature) has a paradoxical consequence: The efficiency of anisotropic diffraction depends solely on diagonal components of the Pockels tensor, while the efficiency of the isotropic diffraction is considerably affected by nondiagonal components. With already known results and data presented in this article we can state that all 10 nonvanishing Pockels tensor components of the m-symmetry class crystal like Sn(2)P(2)S(6) do manifest themselves in various types of nonlinear wave mixing.