SPECIFIC FEATURES OF 2ND-HARMONIC GENERATION IN BIAXIAL NONLINEAR-OPTICAL CRYSTALS

The main specific features of second-harmonic generation in biaxial cr ystals (the presence of birefringence angles for all waves, the replac ement of the terms ordinary and extraordinary waves by the terms fast and slow waves, the presence of two phase-matching angles, the necessi ty to specify the nonlinear tensor and field components in the same sy stem of coordinates, and the difference of the crystal-physical system from the crystal-optical system) are considered. It is demonstrated t hat, in calculating the efficiency of second-harmonic generation, one should precisely define the order of smallness for the accompanying ef fects of approximately the same magnitude. We discuss the procedure fo r choosing the optimal form of the differential operator in equations for slowly varying amplitudes by means of the estimation of the dimens ionless effective lengths of the relevant accompanying processes.