Demonstration of amplification of a polarized soft-x-ray laser beam in a neonlike germanium plasma

We report results of polarization experiments on the collisionally excited Ne-like Ge soft-x-ray laser where we have used an injector-amplifier multistage geometry. The polarization state of the x-ray beam was analyzed by two crossed 45{degree} angle of incidence multilayer mirrors which act as linear polarizers. Results were evaluated by comparing intensities of time-integrated beam patterns behind each polarizer. The polarization state of the amplified spontaneous emission (ASE) output at 23.2 and 23.6 nm from the injector plasma alone was systematically studied and, as expected, revealed no macroscopic degree of polarization observable within the precision of the experiment. When the injector output beam was linearly polarized by using a third 45{degree} angle of incidence multilayer mirror and coupled into the amplifier plasma, the degree of polarization of the amplifier output was {similar_to}0.98, the total gain-length product attained for the polarized beam was {approx}12, and the final beam energy was {approx}20 nJ. The results obtained are discussed with relevance to processes determining the polarization properties of unsaturated ASE systems.