CALCULATION AND CLASSIFICATION OF THE DIRECTION LOCI FOR COLLINEAR TYPE-I, TYPE-II AND TYPE-III PHASE-MATCHING OF 3-WAVE NONLINEAR-OPTICAL PARAMETRIC INTERACTIONS IN UNIAXIAL AND BIAXIAL ACENTRIC CRYSTALS

Phase-matching for sum and difference quadratic frequency mixing of ty pes I, II and III in positive and negative uniaxial and biaxial crysta ls has been detailed. The principal refractive indices and their dispe rsion in frequency determine 72 classes for the loci of the phase-matc hing directions: we find 48 classes in the usual case of birefringence previously considered by Hobden and Stepanov et al.; we also examine the unusual situation providing 24 new classes. The complete classific ation is made in tables which constitute a usefull guide for the study of collinear phasematching.