Coupled wave analysis of anisotropic conical diffraction in doped (K_0.5Na_0.5)_0.2(Sr_0.61Ba _0.39)_0.9Nb₂O₆ crystals

Three anisotropic diffraction cones in doped (K_0.5Na_0.5)_0.2(Sr_0.61Ba _0.39)_0.9Nb₂O₆ crystals with two extraordinary polarized incident beams can be observed for the experimental configuration where the c axis is parallel or perpendicular to the incident plane. These cones are attributed to anisotropic conical self-diffraction and cross-diffraction process, respectively. Photorefractive multiwave interaction caused by the incident beams and forward scattered beams satisfying the phase matching condition is proposed to explain the experimental results. The coupled wave equations and its numerical solution including anisotropic self-diffraction and cross diffraction are also presented. Theoretical analysis and experimental results show that anisotropic conical cross-diffracted light arising from the contribution of both incident beams.