INFLUENCE OF LONG WAVELENGTH ION ACOUSTIC WAVES ON THE GROWTH OF STIMULATED BRILLOUIN SCATTERING IN AN UNDERDENSE PREFORMED PLASMA

摘要

Our experiments show how ion acoustic waves produced by stimulated Brillouin scattering (SBS) can be perturbed by the growth of IAW associated with plasma-induced incoherence (PII) and the growth of secondary IAW arising from the unstable decay of the primary wave, known as two-ion decay. Each type of IAW was detected using a Thomson scattering diagnostic, set-up with the appropriate geometry, and providing us with time-resolved spectra at different locations along the laser axis. Results demonstrate that the two-ion decay instability does not appear to be an effective saturation mechanism for the SBS instability. The observation of transverse IAW, as they correlate well with other signatures of PII, strongly suggest that PII participates in the reduction of SBS activity in the rear part of the plasma.