Role of multistage collisions of the second kind in the mechanism of pumping of a helium–strontium recombination laser

A study was made of multistage charge transfer and of a multistage Penning process in the pumping of levels of an ionic He–Sr laser (λ = 430.5 nm). An analysis was made of the results of an experimental study of the kinetics of the populations of metastable strontium and helium levels, and of electrical and optical filling (emptying) of these states, and also of the results of a mathematical modeling of an He–Sr laser. These results demonstrated that multistage charge transfer played a minor role and that recombination pumping predominated. The Penning process could make a significant contribution (up to 30%) to the formation of doubly charged strontium ions recombining in the late afterglow.