Plasma Density Fluctuations in the Presence of Optical Mixing of Light Beams

Abstract

The density-fluctuation spectrum and wave-vector distribution are calculated for a plasma subjected to the influence of two intense laser beams. The influences of the plasma ions, a possible external uniform magnetic field, the spectral intensity distribution of the mixed laser beams, and their finite diameter are taken into account. The spectrum is shown to consist of two contributions, of which one is recognized as the thermal-fluctuation spectrum while the other is induced by a force generated by the mixed laser beams. Both contributions simply add as a result of the incoherent nature of the thermal fluctuations. It is shown that the theoretical results are in agreement with recent experimental observations. Special attention is also directed to the case in which two beams, generated by the same laser, are mixed in a plasma, and it is shown that enhancement of the ion feature in the spectrum of more than two orders of magnitude against the thermal case can be produced by employing common $Q$- switched ruby lasers.