Saturation of Brillouin Backscatter

Abstract

Saturation of Brillouin backscatter is observed from underdense plasma targets with C${\mathrm{O}}_2$ laser intensities as low as 2×${10}^{11}$ W/${\mathrm{cm}}^2$. Maximum reflectivity is about 5%, implying an ion-wave amplitude of 1%. The most likely limiting mechanism is found to be ion trapping, which is effective at our low $\frac{T_e}{T_i}$ ratio.