HIGHLY EFFICIENT FREQUENCY TRIPLING OF LASER-RADIATION IN A LOW-TEMPERATURE LASER-PRODUCED GASEOUS PLASMA

Relatively efficient (up to 3%) third-harmonic generation of picosecond Nd:YAG laser pulses for wavelength lambda = 1.06-mu-m in a low-density laser plasma is reported for a coherent (i.e., collinear) geometry. The third-harmonic beam produced is nearly diffraction limited and coherent and can be used in other nonlinear-optical experiments. A simple theoretical model is proposed in order to explain this result. In the model, third-harmonic generation is considered to be a process that arises from the scattering of electrons by ions in the presence of the strong laser field.