Peculiarities of self-action in second harmonic generation of laser radiation in nonlinear crystals

By using the generalized method of strong interaction of nonlinear waves an d computer simulation, an analysis of the influence of self-action effects on second harmonic generation of an intense diverging pico-second pulse is performed. Using the approximation of strong wave interaction, an analytic solution is obtained for frequency conversion of the laser radiation taking into account the pump intensity depletion, the influence of the angular di spersion effect (ADE), and the higher nonlinearities. It is shown that the self-action effects, the ADE, and the linear phase mismatch can compensate for each other, increasing the efficiency of second harmonic generation. Op timum conditions for second harmonic generation in converging and diverging laser beams were found. An asymmetry of the angular dependence of the seco nd harmonic intensity was experimentally observed and theoretically explain ed. The asymmetry is caused by the reverse energy conversion of the second harmonic into the pump by the influence of the ADE and Kerr nonlinearities. (C) 2000 MAIK "Nauka/Interperiodica".