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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.

An all-optical approach to edge-enhanced proton radiography is realized by using a relativistic vortex laser irradiating on nanometer-thick foil. In the proof-of-principle experiments, the hollow proton beam was successfully produced by the transparent target normal electric field sheath in the break-out after-burner acceleration mechanism, using a superintense Laguerre–Gauss laser with the highest intensity of the laser exceeded 1020 W/cm2. An insect was imaged with the proton beam; the leg structures on the edge were clearly captured. By contrast, the dot proton source produced by a Gaussian laser was almost completely blocked by the insect's body, losing most edge information. Hollow-structured proton beams driven by vortex lasers conquer the dot imaging limit for high-energy proton beams, which may benefit imaging of capsule implosions in inertial confined fusion, instability research on expanding plasma, and precise positioning in medical therapy.