Inverted population densities are measured in a laser-produced carbon plasma and interpreted in terms of absolute gain coefficients in the 1%/cm range for potential amplification in the XUV at 52-nm wavelength. Scaling to higher gain through increased ionization at higher pumping intensities is attempted, and a factor of 2 enhancement is indicated.
R. H. Dixon, J. F. Seely, and R. C. Elton, "Measured gain for XUV plasma lasers at varying pump intensities," Appl. Opt. 22, 1309-1312 (1983)