Abstract Laser-produced plasma (LPP) from nozzle-based gas target is considered a promising option as extreme ultraviolet (EUV) sources due to its debris free, long time stable fuel supply and easy operation. However, a low EUV emission of the conventional gas target comparing to solid target has been an obstacle to hinder its implementation in practical application. In this study, we propose to improve the EUV emission around 11nm from Xe target LPP source through the reduction of self-absorption at the operating wavelength of Ru/Sr multilayer mirror. The opacity calculation of Xe plasma reveals that Xe9+-Xe12+, corresponding to EUV emission around 11 nm, shows a large self-absorption around the wavelength. Accordingly, we mix Xe with various gases (Ar, N2 and He) to diminish the self-absorption in the LPP experiment. Spectral measurement results demonstrate that the in-band radiation intensity of the EUV source around 11nm is enhanced by a factor of approximately 7.0 with the Xe-Ar gas mixtures at the ratio of 1:4 comparing to pure Xe target. The significant enhancement of the in-band EUV emission with the Xe-Ar mixture target can be attributed to the compromise of the self-absorption around 11 nm and laser energy absorption in the Xe-Ar mixture. Additionally, it is found that EUV radiation intensity with Xe-Ar gas mixtures exhibits a reduced dependence of laser focus position relative to the nozzle, enabling strong EUV emission at lower laser energies and relatively larger nozzle-to-focus point distances, thereby mitigating effect of nozzle erosion and improving source stability. Our results suggest that a gas mixture Xe target is an effective strategy to enhance EUV emission and improve the performances of Xe-based LPP sources.
Wang et al. (Mon,) studied this question.