Soft x-ray lasing in neonlike germanium and copper plasmas

Soft x-ray 3p\ensuremath{\rightarrow}3s lasing in neonlike germanium (${\mathrm{Ge}}^{22+}$) and copper (${\mathrm{Cu}}^{19+}$) in the wavelength interval of 195 to 285 A\r{} is observed for the first time, with gain coefficients ranging from 1.7 to 4.1 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, the higher gain with germanium. The lasing plasmas are produced by focusing a driving laser beam (\ensuremath{\lambda}=1.05 \ensuremath{\mu}m, 2-ns FWHM) into an 18-mm-long line onto thin films and slab targets. The measured J=0 to 1 gain coefficients are comparable to those of the J=2 to 1 transitions. The measured wavelengths of the six lasing lines compared favorably with recent calculations.