Abstract

The time-resolved and integrated spectra of the backscattering second harmonic emission were presented in previous papers.¹,² Reported here are the time-resolved spectrum of both high temporal resolution (~10 ps) and spectral resolution (~6 Å) 2ω₀ harmonic taken at 90° to the laser axis. It has been found that the intensity of the primary and the secondary peaks of the second harmonic emission is not a continuous distribution but composed of many fine and bright fringes with the interval ~1.5–3 Å in relation to atomic weight. On the basis of this observation we considered theoretically the influence of the standing electromagnetic wave and the ponderomotive force on the plasma dispersion relation and gave a unified description of the ion-acoustic frequency ω_i, for the linear conversion and the parametric decay. The results we obtained are basically consistent with the experiments. Another important point is that the second harmonic emission for P polarization lasts for a longer time than that for S polarization, which means that a certain threshold exists to produce the linear conversion by the laser self-focusing filamentation.

© 1986 Optical Society of America