Simulation of an X-ray laser in the transient gain-saturation regime

By using the TRANS code, we performed three-dimensional calculations of amplified spontaneous emission (ASE) in X-ray lasers on the 3p?3s transition in Ne-like Ge (? = 19.6 nm) and Ti (? = 2.6 nm) operating in the transient regime upon irradiation of a flat target by a high-power picosecond laser pulse focused into a line with one or two nanosecond prepulses. The hydrodynamics and population kinetics of the active medium of X-ray lasers were calculated by using the SS-9M code. The pulse duration, the gain, the spatial structure of the laser beam and the type of influence of a 'travelling' pump wave on the ASE brightness obtained in calculations are in agreement with the experimental data. The use of the 'travelling pump wave' leads not only to the increase in the ASE brightness but also considerably reduces its angular divergence.