We characterize the properties of extreme ultraviolet (EUV) light source plasmas driven by laser wavelengths in the λ_laser = 1.064 − 10.6 μm range and laser intensities of I_laser = 0.5 − 5 × 10^11 W cm^−2 for λ_laser = 1.064 μm. Detailed numerical simulations of laser-irradiated spherical tin microdroplet targets reveal a strong laser-wavelength dependence on laser absorptivity and the conversion efficiency of generating in-band EUV radiation. For λ_laser = 1.064 μm irradiation, the increase in in-band radiation with increasing laser intensity is offset by only a minor reduction in conversion efficiency. Radiative losses are found to dominate the power balance for all laser wavelengths and intensities, and a clear shift from kinetic to in-band radiative losses with increasing laser wavelength is identified. Yet, with increasing laser intensity, such a shift is absent. We find that the existence of a maximum conversion efficiency, near λ_laser = 4 μm, originates from the interplay between the optical depths of the laser light and the in-band EUV photons for this specific droplet-target geometry.

AIP Publishing
Phys. Plasmas
EUV Plasma Processes

Hemminga, D., Versolato, O., & Sheil, J. (2023). Simulations of plasmas driven by laser wavelengths in the 1.064—10.6 μm range for their characterization as future extreme ultraviolet light sources. Phys. Plasmas, 30(3), 033301: 1–9. doi:10.1063/5.0125936