Abstract

We have carried out experiments to determine the origin of broadband electromagnetic emission from laser-produced plasmas which has frequently been attributed to stimulated Raman scattering. Recent theory suggests an alternative explanation in terms of Thomson scattering, enhanced by the presence of a nonthermal electron distribution. The origin of this nonthermal distribution are streaming fast electrons produced by the two-plasmon decay (TPD) instability and/or resonance absorption occurring elsewhere in the plasma. The theory predicts two broad bands of scattered spectra, one with frequencies between the laser frequency and half of that frequency and the other one between the laser frequency and twice that frequency. The latter cannot be produced directly by instability. Thus observation of upscattered radiation is strong evidence for the enhanced Thomson scattering process.

© 1986 Optical Society of America