Abstract
High‐intensity laser‐plasma experiments conducted on targets consisting of carbon and magnesium indicate population inversion in Mg+10 and Mg+11 ions at wavelengths of ∼100 Å. The results indicate that soft x‐ray population inversion has been achieved, for the first time, by resonant photoexcitation. By this process, intensity inversions of the hydrogenic resonance lines from n=3 and n=4 are observed at electron densities as high as 1020 cm−3.