Shock waves in gas-jet target of a laser-produced-plasma short-wave-radiation source with two-pulse plasma excitation

Previous investigations of the laser plasma at two-pulse mode of its generation revealed long-living perturbations of the gas-jet target by the first pulse, leading to significant modulations of the plasma radiation. In the present paper, results of a numerical hydrodynamic simulation of the gas-jet target are reported which provide explanation of the observed phenomena. An impact of the first pulse (prepulse) upon the target results in formation of a dense quasi-spherical layer in it, with a low-density area inside. This layer expands with the time and drifts downstream with the gas flow. Depending on the time interval between pulses, the second laser pulse can either intersect the dense layer or pass through the low-density gas, whereby the observed modulations of the plasma emission can be explained.