Calculation of the gain for transitions in helium-like ions in the range λ < 50 nm

A calculation is made of the gain experienced by far ultraviolet radiation in a plasma containing multiply charged helium-like ions. The populations of ionic levels are found by solving a system of rate equations, which allow for radiative decay processes and electron-ion collisions. The solutions are obtained for two cases of optically thin and optically thick plasmas. It is shown that, under steady-state conditions, the inversion density for intercombination transitions reaches 10¹³–10¹⁵ cm^–3. The use of stimulated Raman scattering of optical radiation by a plasma of this kind should result in single-pass generation of far ultraviolet radiation (λ~19–40 nm) in an active medium ~0.1–1 cm long.