Characterization of charge state distributions in Near-Infrared Laser-Driven tin plasmas for efficient EUV generation

Abstract

In this paper, the charge state distributions of extreme ultraviolet (EUV) light source plasmas produced by near-infrared-wavelength lasers are systematically characterized. The spatiotemporal properties of laser-irradiated planar tin targets are examined using radiation-hydrodynamic simulations and non-local thermodynamic equilibrium calculations. Focusing on the distributions of Sn11+–Sn14+ ions, which are primarily responsible for “in-band” EUV emissions, a mean charge state of 12.5 is identified as the optimal ionization level for efficient EUV generation. This prediction is consistent with the experimental observation by Behnke et al. (2021) of short-wavelength spectra in the 7–10 nm range, where the contributions of the Sn11+–Sn14+ ions are well identified. Simulations further reveal that spatially and temporally uniform pulses more efficiently achieve the optimal mean charge state, producing up to 45 % more Sn11+–Sn14+ ions than Gaussian pulses of the same energy. These findings provide foundational insights for advancing laser-driven EUV light sources for industrial applications. © 2025 Elsevier B.V., All rights reserved.