Evidence of stimulated Brillouin backscattering from a plasma at short laser wavelengths

Abstract

Homogeneous plasmas are generated by irradiation of thin plastic foils with two laser beams delayed in time and focused on each side of the foil. We have studied the interaction of the second beam with the quasihomogeneous underdense plasma generated by the first beam. The intensity and the time-resolved spectra of the backscattered light are analyzed. We have measured the contribution of the stimulated Brillouin instability in the backreflected light. Its level is very low: (5--10)% at 0.53 \ensuremath{\mu}m and less than 0.1% at 0.26 \ensuremath{\mu}m at ${10}^{15}$ W/${\mathrm{cm}}^{2}$ for plasmas of L/\ensuremath{\lambda}\ensuremath{\sim}100--200, where L is the density-gradient scale length.