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Effects of multiple crossed laser beams on stimulated Brillouin and Raman scattering (SBS and SRS) growth rates, as well as on the SBS and SRS competition, have been investigated in a preformed plasma using Thomson scattering of a short-wavelength probe beam. Reduction of the amplitude of ion acoustic waves (IAW) associated with SBS and amplification of the amplitude of electron plasma waves associated with SRS in the case of irradiation by two or three beams compared to a single beam are reported. Mechanisms by which crossed laser beams can reduce SBS by detuning the interaction or by nonlinearly enhancing the damping rate of the IAWs will be discussed. The same mechanisms could explain the enhancement of SRS backscatter through modified secondary decay processes of SRS. In a second experiment, nonlinear enhancement of extreme forward scattering of one laser beam going through a preformed plasma has been observed when a second interaction beam was present. The role of ion wave instabilities on forward scattering will be discussed, based on the spectral analysis of the forward scattered light.. [ABSTRACT FROM AUTHOR]

Presents a measurement of the Langmuir wave spectrum driven by stimulated Raman scattering using Thomson scattering. Comparison of the Langmuir waves' parallel and antiparallel to the incident's wave vector; Description of the relative amplitude of the two Langmuir waves.

Investigates the interplay between ion acoustic waves (IAW) and electron plasma waves (EPW) associated with stimulated Brillouin and Raman scattering. Growth of two types of waves over a limited region in the front part of the plasma; Observation of the inhibition of the EPW by the IAW.