Some characteristics of second harmonic generation under conditions of strong energy exchange between interacting waves

A theoretical analysis is made of the phase-matching curve of second harmonic generation for ultrahigh-power subnanosecond laser pulses. The conversion efficiency for a plane wave and the integrated conversion efficiency for a homocentric quasiplane beam are calculated as a function of the reduced mismatch and power density of the fundamental-frequency radiation over a wide range of introduced generalized parameters. It is shown that pulling of the zeros of the phase-matching curve toward the origin and an increase in the side maxima with increasing power density of the fundamental-frequency radiation results in an abrupt nonmonotonic dependence of the integrated conversion efficiency on this power density and possibly causes a shift of the optimal phase-matching direction. This should be distinguished from the self-interaction effects in media with a cubic nonlinearity.