Driver wavelength and intensity dependence of extreme ultraviolet emission from laser-produced tin microdroplet plasmas

Extreme ultraviolet (EUV) lithography sources driven by laser-produced tin (Sn) plasmas require optimal matching of driver laser parameters to maximize in-band conversion efficiency (CE) and spectral purity (SP). In this work, we systematically investigate the driver wavelength (1.064-10.6 µm) and intensity dependence of EUV emission from Sn microdroplets using the two-dimensional radiation-hydrodynamics code RHDLPP and its three-dimensional spectral post-processing module SpeIma3D. Our simulations reveal a fundamental physical trade-off governing source performance. Short-wavelength drivers (e.g., 1.064 µm) efficiently couple energy into dense plasma regions but suffer from severe in-band radiation trapping and opacity broadening, limiting maximum CE and SP. Conversely, long-wavelength drivers (e.g., 10.6 µm) produce highly transparent coronas that yield excellent SP (up to ∼29.4%) but suffer from significantly reduced absolute emission measures, thereby capping the overall CE. By mapping the wavelength-resolved escape factor and spatial emission distributions, we identify the mid-infrared range (4.0-5.0 µm) as an optimal operating window. In this regime, a favorable balance between sufficient intrinsic emissivity and mitigated optical depth is achieved, yielding a maximum predicted CE of ∼3.41%. These findings provide a comprehensive physical scaling and valuable guidelines for the development of alternative mid-infrared solid-state laser drivers for next-generation EUV lithography sources.