Mechanisms for formation of a population inversion in the levels of metal atoms and ions in a plasma jet

The mechanisms for formation of population inversions in plasma jets of lithium, sodium, cadmium, and strontium vapor are studied. The primary contribution to forming a population inversion over the transitions of the alkali atoms is found to be three-body electron-ion recombination, and for transitions between the ion levels of strontium and cadmium, inelastic collisions with the buffer gas play an important role. Using helium instead of argon as a buffer leads to a substantial increase in the magnitude of the inversion. Zh. Tekh. Fiz. 68, 134–135 (June 1998)