PEAK INTENSITY ENHANCEMENT AND PULSE-COMPRESSION OF A PICOSECOND LASER-PULSE BY FREQUENCY-DOUBLING WITH A PREDELAY

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