Soft x-ray population inversion by resonant photoexcitation in multicomponent laser plasmas

A scheme for population inversion in the soft x-ray (≳100 Å) region, where the upper laser level is photoexcited by resonant line radiation from an identical or different ion species, is proposed. Ion pairs that may be used in this scheme are presented. Applying the results obtained for a general case to the Mg XII ions pumped by C VI ions, it is shown that gains in excess of 100 cm−1 are possible for the 4→3 transition at ∼130 Å in typical laser-produced plasmas.