Broadband laser absorption study based on radiochromic film combined with fiber-optic probes at the low-coherence Kunwu laser facility

Abstract At the low-coherence Kunwu laser facility with a 0.6% bandwidth, we experimentally studied the laser absorption efficiency of laser–target coupling at intensities of (3–5) × 10 14 W cm –2 . To characterize side scattering across a wide angular range, we developed a novel radiochromic film-based diagnostic system, which enables continuous spatial mapping over approximately π steradians for the first time. The results indicate a substantial reduction in total loss rate (by more than three times) when compared to a monochromatic laser. We focused on analyzing the influence of laser bandwidth on stimulated Brillouin scattering and stimulated Raman scattering (SRS). Notably, we found that the broadband laser enhances SRS at high intensities, which is contrary to the results obtained at low intensities. These results highlight the role of bandwidth as a quantitative control parameter for improving laser–plasma coupling, which is of particular significance for advancing direct-drive inertial confinement fusion.