Broadband laser driven near-forward scattering light of planar film target

Abstract

Laser-plasma instability (LPI) is one of the key problems in the ignition process of inertial confinement fusion (ICF), and has been extensively studied in theory, simulation, and experiment for many years. Broadband laser, due to its low temporal coherence, can reduce the effective electric field strength when interacting with plasma and disrupt the phase-matching conditions of LPI, thus an effective approach to solving LPI issues is considered. Current extensive simulation studies indicate that broadband laser can suppress the generation of phenomena such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), and two-plasmon decay (TPD) to some extent. There are also a few backward scattering experimental studies, but more experimental researches, such as side-scattering, are still needed. Therefore, based on the broadband second harmonic laser facility “Kunwu”, the experiments are designed for studying the lateral scattering of critical density plasma driven by broadband laser and traditional narrowband laser, and the production of hot electrons as well in this work. The experimental results show that the side SBS spectra and side SRS spectra and portions at different angles excited by broadband lasers with a power density of 1×10<sup>15</sup> W/cm<sup>2</sup> are significantly different from those by narrowband lasers. Further analysis reveals that the overall portion of transverse hot electrons in broadband laser cases is higher than that in narrowband laser case. However, for broadband laser, the portion of SRS at small forward angle and backward angle are significantly lower than that for narrowband laser. Preliminary qualitative analysis suggests that SRS may not be the main mechanism for hot electron generation in this case, and that PDI might play a dominant role in generating hot electrons.