Study on tabletop x-ray lasers pumped by a YAG laser

A pulse-train YAG laser beam was line focused on an Al slab target by a focusing lens system consisted of a segmented prism array, a beam expander and a cyclindrical lens. The intensity distribution was uniform along the focal line including micro dots. Amplification of Li-like Al soft x-ray transitions was observed in recombining Al plasmas produced by irradiation of the pulse-train YAG laser with the input energy of 1.5-2 J. The gain coefficient measured for 15.47 nm line was 3.2 cm(-1) and the duration of gain was longer than 1 ns. Two types of cavities, an unstable cavity and a cavity with a soft x-ray beam-splitter, were tried. Clear output signals from the unstable cavity were observed for the first lime for Al XI 3p-4d (15.06 nm) and Al XI 3d-4f(15.47 nm) transition lines. Experiments on the cavity with a soft x-ray beam-splitter also showed that clear evidences of enhancement in the two Li-like Al ion lines.