EFFECTIVE NONLINEARITY COEFFICIENTS FOR 3-WAVE INTERACTIONS IN BIAXIAL CRYSTALS OF MM2 POINT GROUP SYMMETRY

The effective nonlinearity coefficients for three-wave interactions in the orthorhombic biaxial crystals of mm2 point group symmetry for six different assignments between the crystallophysical (optical) and crystallographic (piezoelectric) coordinate systems have been obtained. In the former coordinate system the dielectric permeability tensor is the diagonal one, in the latter the square nonlinearity tensor is defined. The point group mm2 includes some new perspective nonlinear optical crystals such as KTP, LBO, mNA and others. For the particular case of light propagation in the principal planes of a biaxial crystal, possible types of phase matching between the interacting waves (types of interaction) and corresponding effective nonlinearity coefficients are given. The proposed method can be generalized to the nonlinear biaxial crystal of other point group symmetry.