Enhanced extreme ultraviolet conversion efficiency of a 2 μ m laser-driven preformed tin-droplet target using short picosecond pre-pulses

Abstract

In this study, an extreme ultraviolet (EUV) conversion efficiency (CE) of 6.9% was obtained in simulation by controlling the delay between a picosecond pre-pulse and a main-pulse with a wavelength of 2 μm; this value is about 7.5% higher than the ns pre-pulse scheme of the EUV emission produced by a 2 μm laser-driven tin-droplet target. In the simulation, the tin droplet expanded into hollow spherical structures after irradiation with a picosecond pre-pulse laser. Notably, compared with a nanosecond pre-pulse, in this case, the density of the tin plasma was lower, and the expansion range was wider for the same delay. Therefore, ps pre-pulse can make the tin plasma reach the optimal state of EUV emission in a shorter delay. In both pre-pulse schemes, the CE value maintains a high value (>5.7%) within a certain delay range (800 ns) between pre-pulse and main-pulse. In this study, the FLASH radiation hydrodynamic code and FLYCHK atomic code were used to investigate the energy conversion and spectra. The results obtained can be potentially useful for EUV lithography under a two-pulse scheme.

Production of 13.5 nm light with 5% conversion efficiency from 2 μ m laser-driven tin microdroplet plasma

“…9,[11][12][13][14] Combined with the low wall-plug efficiencies of 10 lm gas lasers, this has motivated research into plasmas driven by shorter wavelength, highly efficient solid-state lasers to strongly accelerate in recent years. [15][16][17][18][19][20][21] Radiationhydrodynamic simulations have shown promise of high CE plasma sources driven by 2-5 lm lasers 13 without the need for complex target shaping. Given the maturity of 1.064 lm solid-state laser technology, and the strong progress in 1.88 lm laser development, 20,21 studies have focused on tin plasmas generated by 1-and 2 lm laser light.…”

“…Given the maturity of 1.064 lm solid-state laser technology, and the strong progress in 1.88 lm laser development, 20,21 studies have focused on tin plasmas generated by 1-and 2 lm laser light. 15,19,[22][23][24] Relatively low CEs have been recorded for 1 lm plasmas due to re-absorption losses in dense plasma media, 16,18 given the relation n $ k À2 between drive laser wavelength k and n, the critical plasma density. 3 Consistently, twofold higher CEs have been found using 2 lm laser light, under otherwise comparable conditions.…”