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 t...