Research progress of broadband laser-plasma interaction experiments on Kunwu laser facility

Laser-plasma instabilities (LPI) in direct-drive inertial confinement fusion (DD-ICF) give rise to laser scattering and hot-electron generation. These detrimental effects induce laser energy dissipation, target preheat, degraded irradiation uniformity and impaired implosion performance, posing a fundamental bottleneck for the advancement of fusion ignition performance. As a promising candidate for mitigating LPI-related parametric processes, broadband low-coherence laser technology has attracted intensive research efforts over recent years. This paper reviews the recent progress of plasma physics experiments implemented on the Kunwu low-coherence broadband laser facility at the Shanghai Institute of Laser Plasma, China Academy of Engineering Physics. Experimental observations demonstrate that broadband lasers deliver remarkable suppression on backward stimulated Brillouin scattering (SBS) in comparison with conventional narrowband lasers. Effective mitigation of backward stimulated Raman scattering (SRS) is also achieved at low laser power densities. Nevertheless, an evident enhancement of hot-electron emission is detected under high-power-density irradiation. The distinct physical behaviors between broadband and narrowband laser drivers are clearly identified. Although the capability of broadband lasers to improve laser-target coupling efficiency has been experimentally validated, two critical issues associated with moderate bandwidth, namely the amplification of side-scattered SRS and excessive hot-electron production, remain unresolved. Consequently, synergistic research combining experimental characterization with theoretical and numerical modeling is essential to fully uncover the underlying physics of broadband lasers and promote their practical deployment in ICF facilities.