Modeling and demonstration of a saturated Ni-like Mo X-ray laser

Abstract

The technique of using a nsec pulse to preform and ionize the plasma followed by a psec pulse to heat the plasma has enabled us to achieve saturated laser output for low-Z neon-like and nickel-like ions driven by small lasers with less than ten joules of energy. In this work we present and model recent experiments done using the COMET laser at Lawrence Livermore National Laboratory to illuminate slab targets of Mo up to 1 cm long with a one joule, 600 ps prepulse followed 700 psec later by a five joule, one psec drive pulse. The experiments demonstrate saturated output on the Ni-like Mo 3d{sup 9} 4d {sup 1}S{sub 0} {yields} 3d{sup 9} 4p {sup 1}P{sub 1} laser line at 18.9 nm. The small signal gain and gain length product are estimated by measuring the laser output versus target length. Experiments are done using multilayer mirrors to obtain two-dimensional images of the output aperture of the laser and to measure the total laser energy as a function of various parameters such as the delay between the short and long pulses and the energy of the two pulses. To model the experiments the LASNEX code is used to calculate themore » hydrodynamic evolution of the plasma and provide the temperatures and densities to the XRASER code, which then does the kinetics calculations to determine the gain, The temporal and spatial evolution of the plasma is studied both with and without radiation transport included for the 4f and 4p {yields} 3d Ni-like Mo resonance lines. High gains are predicted for both the 3d{sup 9} 4d {sup 1}S{sub 0} {yields} 3d{sup 9} 4p {sup 1}P{sub 1} laser line at 18.9 nm and the 3d{sup 9} 4f {sup 1}P{sub 1} {yields} 3d{sup 9} 4d {sup 1}P{sub 1} photopumped line which is observed to lase at 22.6 nm.« less