Spectroscopy of x-ray lasers

Two promising methods of pumping plasma X-ray lasers, namely, matched-line photoexcitation and electron-collisional excitation, are reviewed from a spectroscopic viewpoint. For the former, numerous possible elements are listed, and a recently obtained experimental spectrum for a most promising sodium-neon test case is presented. For the second, progress in electron-collisional excitation pumping of Delta n = 0 laser transitions is reviewed along with electron-recombination pumping of Delta n = 1 laser transitions, and a novel synergistic system is proposed for enhanced recombination pumping in 1s2 2s2 2pq sequence ions. The accumulation of consistent data and the availability of the necessary supporting atomic and spectroscopic information result in continued optimism that, with a truly dedicated effort, useful gain can be achieved on a reasonable time scale.