Broadband lasers have recently attracted significant attention as novel driving light sources and promising tools for mitigating laser-plasma instabilities (LPI). Under different plasma conditions, different dominant mechanisms govern the nonlinear evolution of plasma waves, thereby influencing the behavior of broadband LPI. This study investigates the nonlinear evolution of stimulated Raman scattering (SRS) near 1/4 n_c driven by a broadband laser. We demonstrate that broadband laser induces strong fluctuations in the intensity of primary electron plasma waves (EPWs) via SRS, effectively suppressing subsequent Langmuir decay instability (LDI) and mode-coupling processes associated with ion-acoustic waves (IAWs). For moderate laser bandwidths, intensity fluctuations are efficiently transferred to primary EPWs with high phase velocities, leading to intermittent bursts that generate an increased number of super-hot electrons (>50 keV). These fluctuations inhibit the formation of IAWs via LDI and reduce plasma density perturbations, which, in turn, suppress the growth of coupled EPWs with lower phase velocities. Consequently, the number of hot electrons trapped by coupled EPWs in the [10 keV, 50 keV] range decreases, limiting the rise in background plasma temperature. As the laser bandwidth increases (Δω ≥ 3%), both primary SRS and LDI are significantly suppressed, resulting in a reduction in the number of hot electrons across all energy ranges. These findings provide insight into the evolution of electrostatic waves and energy transfer processes driven by broadband lasers.

laser-plasma instabilities,stimulated Raman scattering,broadband laser,nonlinear evolution