Peak Intensity Enhancement and Pulse Compression of a Picosecond Laser Pulse by Frequency Doubling with a Predelay

Abstract

Theoretical investigation of frequency doubling of a short-duration, high-intensity laser pulse in a potassium dihydrogen phosphate (KDP) crystal is given. The coupled nonlinear equations for the parametric process, including the third-order nonlinear susceptibility, have been solved. By applying a time delay between the extraordinary and ordinary waves for the fundamental pulse in type-II phase matching, the group velocity mismatch and the nonlinear phase shift can be made to compensate each other, resulting in peak intensity enhancement and pulse width compression. The optimum conditions for the incident intensity, the crystal thickness and the predelay time have been derived. It is shown that intensity conversion efficiency of 440% accompanied by pulse width reduction from 1 ps fundamental pulse to 100 fs second-harmonic pulse is achieved for incident intensity of 50 GW/cm 2 .