Soft x-ray lasing in neonlike germanium and copper plasmas

Soft x-ray 3p{→}3s lasing in neonlike germanium (Ge²²⁺) and copper (Cu¹⁹⁺) in the wavelength interval of 195 to 285 A{} is observed for the first time, with gain coefficients ranging from 1.7 to 4.1 cm^-1, the higher gain with germanium. The lasing plasmas are produced by focusing a driving laser beam ({λ}=1.05 {μ}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.