Effects of continuous phase plate on plasma corona homogeneity and laser-plasma instabilities in experiments with three target materials

Abstract

Corona homogeneity and spectra of scattered light and hot electrons produced by laser-plasma instabilities inside laser-produced plastic, aluminum, and gold plasmas were investigated with and without the use of continuous phase plate (CPP) to the laser beam. Improvement of the corona homogeneity was observed for all three materials after applying CPP, while the inhibition of the intensity of backward-scattered light and the amount of emitted hot electrons was not always synchronous for different materials, which is interpreted as a result of the changes in thresholds of the stimulated Raman scattering (SRS) and the two-plasmon decay (TPD) instability before and after the application of CPP. By comparing the changes of SRS scattered light intensity with the amount of hot electrons in different kinetic energy ranges for all three target materials in our experiments, we conclude that SRS is more responsible for the diagnosed hot electrons between 50-150 keV, and those above 150 keV should be generated by TPD, which could be explained by the difference in phase velocity of electron plasma waves between SRS and TPD calculated from measured and simulated parameters of corona and laser-plasma instabilities.