Large-Amplitude Ion Acoustic Waves in a Laser-Produced Plasma

The frequency and wave number of ion acoustic waves (IAWs), with wave numbers corresponding to stimulated Brillouin scattering (SBS), have been measured as a function of the laser intensity, with time-resolved collective Thomson scattering. At high intensities $(I>\mathrm{}{10}^{13}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2)$, the scattered light contains a novel component with a large frequency shift, in addition to light frequency shifted by the amount anticipated $\left({2k}_0{c}_s\right)$ for SBS-driven ion waves. This is the first observation of large IAWs driven by the interaction laser and not necessarily associated with a parametric instability.