Simulation assessment of 9.6 μm CO ₂ laser drive for Sn-LPP EUV generation

Conventional Sn laser-produced plasma extreme-ultraviolet sources are mainly driven by 10.6 μm CO ₂ lasers. In short-pulse CO ₂ laser amplification systems, the 9P band at 9.6 μm can serve as an additional gain channel for increasing the extracted laser energy. However, the impact of introducing a 9.6 μm CO ₂ laser drive on Sn-LPP plasma evolution and in-band EUV output remains to be assessed. In this work, we investigate pure 9.6 and 10.6 μm laser drives as the two reference endpoints of the dual-band output, and further examine mixed-wavelength CO ₂ laser drives with different 9.6 μm energy fractions using two-dimensional radiation-hydrodynamic simulations combined with detailed spectral post-processing. The 9.6 μm drive gives a higher laser absorption fraction and a larger radiation-energy partition, while producing plasma structures and emission spectra similar to those obtained with the 10.6 μm drive. At a peak intensity of 6 × 10 ⁹ W/cm ² , the laser absorption fraction increases from 29.5% to 33.0%, and the in-band conversion efficiency in 2π sr increases from 0.60% to 0.74%, with almost unchanged spectral purity. Mixed 10.6/9.6 μm laser drives further show a smooth increase in conversion efficiency with increasing 9.6 μm energy fraction. These results suggest that the 9P-band component can enhance in-band EUV output while preserving the spectral characteristics of conventional 10.6 μm CO ₂ laser-driven Sn plasmas.