Fourth harmonic generation and pulse compression of a picosecond laser pulse

This paper describes harmonic generation and pulse compression of a picosecond laser pulse. By applying a time delay between the extraordinary and ordinary waves of the fundamental pulses, the group velocity mismatch and the nonlinear phase shift can be compensated by each other, resulting in pulse-width reduction at the fourth harmonic wavelength. It is shown that the reduction from 1 ps fundamental pulse to 0.25 ps fourth harmonic pulse with 45% energy conversion efficiency can be achieved at the incident intensity of 50 GW/cm(2).