Helium-like recombination pumped soft x-ray lasers

Experimental studies on recombination pumped soft x-ray lasers with helium-like ions are presented. The four-beam multi-TW neodymium-doped phosphate glass laser system at the Institute for Solid State Physics of the University of Tokyo was used in this work, From simultaneous time- and space-resolved spectra of the resonance lines of helium-like aluminium ions, population inversions between the n = 3 and 2 levels were observed. Details on the first observation of amplification in a recombination-pumped helium-like soft x-ray laser, exhibiting a time-resolved small-signal gain of 3.3 +/- 0.5 cm(-1) for the 3 D-1-2 P-1 transition of helium-like nitrogen, are also given.