Modification of conditions for optimal focusing of high-power laser beams under frequency doubling conditions

An analysis is made of the conditions for optimal focusing of high-power pump laser radiation in second harmonic generation. It is shown that the radius of the pump beam should be reduced with increasing pump power if the maximum efficiency of frequency doubling is to be retained. Exact values of the optimal focusing parameter (in the case of focusing on the front face of a frequency-doubling crystal) are found as a function of the pump power by numerical integration of quasioptic frequency doubling equations.