Prospects for resonant photoexcitation as a pumping mechanism for x-ray lasers

Using analytic estimates we compare the relative merits of resonant photoexcitation pumping with other excitation methods of x-ray lasers, specifically electron-collision and -recombination pumping. It is shown that the potential of line pumping to achieve high gain in the x-ray region (including the range 2.34.4 nm) is higher than that of the other methods using high-power lasers or Z-pinch plasmas as pump sources. In the second part of the paper, we investigate the conditions required to obtain an inversion if the pumping ion and the lasing ion are of the same kind. The analysis is performed for laser transitions of the type {Δ}n{≠}0 as well as for {Δ}n=0.