Demonstration of X-Ray Amplification in an X-Ray Laser Cavity Pumped by a Pulse-Train Yttrium Aluminium Garnet Laser

X-ray lasings of a Li-like Al transition line at 15.47 nm in the recombination scheme have been investigated using a tabletop pulse-train yttrium aluminium garnet (YAG) laser system. A cavity experiment has been carried out with a resonator consisting of a flat and a concave Mo/Si multilayer mirrors. Clear enhancement of the X-ray output from the cavity has been demonstrated. It was found that the cavity output beam has a divergence of about 3 mrad and an absolute intensity of about 1×108 photons/shot. The temporal feature of the observed cavity output can be reproduced by a simple ray-trace calculation with multiple times reflection and the presence of a lasing medium.