In the field of Inertial Confinement Fusion (ICF), the suppression of Laser-Plasma Instabilities (LPI) is paramount. Increasing the spectral bandwidth of ultraviolet (UV) drivers is a primary strategy for achieving effective beam smoothing and enhancing energy coupling. However, achieving high energy and broad bandwidth simultaneously in the UV regime remains a significant technical challenge for next-generation laser facilities.
This study investigates the physical mechanisms of UV broadband light generation through active signal injection. By employing a seed signal to selectively excite Stimulated Rotational Raman Scattering (SRRS) within the final-stage gas medium, we demonstrate a deterministic approach to spectral broadening. Experimental results show that this method yields a high-power UV output with a maximum energy exceeding 6 kJ and a fractional bandwidth of 1%.
Our research identifies a critical synergistic effect between the SRRS and Four-Wave Mixing (FWM) processes during the spectral evolution. We found that the FWM process plays a vital role in redistributing energy across the vibrational and rotational manifolds, significantly enhancing the broadening efficiency beyond the traditional Raman limit. To characterize these complex nonlinear dynamics, a preliminary numerical model was developed, which shows good agreement with experimental observations.
These results provide a robust pathway for the development of megajoule-class broadband laser drivers. Future research will focus on refining the theoretical models to optimize the injection pulse shapes and gas medium parameters. Such advancements are expected to further improve the uniformity of focal spots and provide a more flexible platform for studying high-energy-density physics and fusion ignition.

Ultraviolet broadband generation, Stimulated Rotational Raman Scattering (SRRS), Four-Wave Mixing (FWM), Signal injection, Beam smoothing