Broadband laser is considered the most promising way to suppress laser-plasma instabilities. Experimental results from the KunWu broadband laser facility are encouraging in suppressing stimulated Brillouin scattering (SBS). However, the experiments also revealed that the suppression of stimulated Raman scattering (SRS) weakened with increasing intensity. We performed PIC simulations to study the evolution of the BSRS driven by a broadband laser. These simulations demonstrate a correlation between the weakening of the suppression and the intensity fluctuations of the broadband laser. The bandwidth disrupts the temporal coherence of the laser, leading to significant intensity fluctuations and the generation of high-intensity localized pulses. These pulses trigger violent bursts in the nonlinear stage of BSRS, resulting in high reflectivity and the amount of hot electrons. A scheme for intensity-modulated broadband lasers is proposed based on the statistical properties of such lasers. This scheme can effectively suppress the burst by interrupting the amplification of back-scattered light during bursts. After using intensity modulation, the average reflectivity and hot electron yield decrease by an order of magnitude. Our work reveals the potential of broadband lasers to suppress high-frequency instabilities and contributes to understanding future direct-drive broadband laser ICF experiments.

broadband laser,laser plasma instabilities,Stimulated Raman scattering (SRS)