STIMULATED COMPTON-SCATTERING FROM PREFORMED UNDERDENSE PLASMAS

The electron-density-fluctuation spectra induced by stimulated Compton scattering (SCS) are directly observed for the first time. A CO2 laser is focused into plasmas with densities n(e) spanning (0.4-6) x 10(16) cm-3. The fluctuations corresponding to backscatter are probed using Thomson scattering. At low n(e), the scattered spectrum peaks at a frequency shift DELTA-omega = k-upsilon-e and appears to be in a linear convectively saturated regime. At the highest n(e), a nonlinear saturation of the SCS instability is observed possibly due to a self-induced perturbation of the electron distribution function.