We report what is to our knowledge the first observation of a recombination pumped soft-x-ray laser with He-like ions. Amplification was observed for the 3<sup>1</sup><i>D</i>–2<sup>1</sup><i>P</i> transition of He-like <i>N</i> at 185.2 Å in a laser-produced boron nitride plasma. From time-resolved experiments, a small-signal gain between 3 and 4 cm<sup>−1</sup> and a maximum gain–length product of 3.0 at 2.25 ns after the pump pulse were observed in a region of the plasma 200 μm from the target surface.
© 1995 Optical Society of America
Tsuneyuki Ozaki and Hiroto Kuroda, "Observation of gain on the 31D–21P soft-x-ray transition of heliumlike nitrogen," J. Opt. Soc. Am. B 12, 1338-1342 (1995)