Modeling and optimization of third-harmonic generation with dual-wavelength injection

The spectral broadening scheme based on stimulated rotational Raman scattering (SRRS) with signal-beam injection has demonstrated kilojoule-level ultraviolet output with bandwidths exceeding 1%, showing potential for further suppression of laser-plasma instabilities. In this scheme, signal-beam injection into third-harmonic generation (THG) promotes additional sum-frequency mixing, thereby generating multiple spectral components. To further enhance spectral broadening, THG under dual-wavelength injection is investigated, enabling precise control of the input spectrum for SRRS. A coupled-wave dynamical model of THG under dual-wavelength injection is developed, revealing the synergistic effects of energy ratio and crystal detuning angle on the spectral distribution and conversion efficiency. Numerical simulations show that, by optimizing the dual-wavelength energy ratio and the detuning angle of the third-harmonic crystal, a balance between conversion efficiency and spectral broadening can be achieved. This work provides a theoretical framework for harmonic generation under dual-wavelength injection, with potential to further improve SRRS spectral broadening and inspire advances in multi-line frequency generation.