Influence of CO2-laser pulse parameters on 13.5 nm extreme ultraviolet emission features from irradiated liquid tin target

Abstract

Abstract A laser-produced plasma excited by CO2 laser pulses with various durations and energies on liquid tin droplets with diameters of 150 μm and 180 μm is considered. A two-dimensional radiative-magnetohydrodynamic code is used for numerical simulations of multicharged ion plasma radiation and dynamics. The code permits to understand the plasma dynamics self-consistent with radiation transport in non-local equilibrium multicharged ion plasma. Results of simulations for various laser pulse durations and 75 ÷ 600 mJ pulse energies with both Gaussian and experimentally taken temporal profiles are discussed. It is found that if the mass of the target is big enough to provide the plasma flux required (the considered case) a kind of dynamic quasi-stationary plasma flux is formed. In this dynamic quasi-stationary plasma flux, an interlayer of relatively cold tin vapor with mass density of 1 ÷ 2 g cm−3 is formed between the liquid tin droplet and low density plasma of the critical layer. Expanding of the tin vapor from the droplet provides the plasma flux to the critical layer. In critical layer the plasma is heated up and expands faster. In the simulation results with spherical liquid tin target, the conversion efficiency into 2π is of 4% for 30 ns full width half maximum (FWHM) and just slightly lower—of 3.67% for 240 ns FWHM for equal laser intensities of 14 GW cm−2. This slight decay of the in-band extreme ultraviolet (EUV) yield with laser pulse duration is conditioned by an increasing of radiation re-absorption by expanding plasma from the target, as more cold plasma is produced with longer pulse. The calculated angular distributions of in-band EUV emission permit to optimize a collector configuration.