Investigation of ion-acoustic-decay-instability thresholds in laser-plasma interactions

Abstract
The ion acoustic decay instability has been studied by monitoring the Stokes sideband of the second-harmonic emission from a laser-produced plasma. The intensity threshold decreased as the laser spot size increased. It reached homogeneous-plasma collisional values in planar plasmas produced using large laser spot sizes (D≳600 μm), for laser wavelengths of either 1.06 or 0.53 μm. These observations show that the ion acoustic decay instability may well play a more important role in laser fusion that had been generally believed.