Saturated x-ray lasers at 196 and 73 Å pumped by a picosecond traveling-wave excitation

Traveling-wave irradiation with a laser pulse of duration ~1 picosecond has been shown to achieve saturated operation of Ne- and Ni-like x-ray lasers. Gain at 196 {} was confirmed by observation of both forward and backward x-ray laser beams from a germanium plasma under ideal and nonideal traveling-wave conditions at a small signal gain of >40 cm^-1. Saturation was observed for targets $>4$ mm long consistent with a model of laser amplification along the plasma medium and with the output of a detailed ray-tracing post-processor coupled to a hydrodynamic and atomic physics code. Ni-like samarium targets, pumped under ideal traveling-wave conditions exhibited a small signal gain of ~19 cm^-1 at 73 {} with saturation observed for targets 8 mm long.