Recombination lasers utilizing vapors of chemical elements. II. Laser action due to transitions in metal ions

General requirements specifying the distribution of energy levels and discharge conditions are used as the basis of a discussion of the stimulated emission mechanisms in ionic recombination lasers utilizing strontium, calcium, beryllium, aluminum, tin, and lead vapors. The attention is concentrated on the strontium vapor laser. The population inversion which results in the emission of λ=430.5 nm radiation from Sr II is calculated allowing for radiative and collisional transitions between the levels. The role of deexciting collisions with slow electrons in the depopulation of the lower laser level is demonstrated. The results are given of theoretical and experimental determination of the electron temperature in the afterglow of gas discharges in mixtures of metal vapors with inert gases. The electron temperature is found to rise with the metal vapor pressure and this effect is explained. Average powers of 0.5 W at λ=373.7 nm from Ca II and 1 W at λ=430.5 nm from Sr II at the pulse repetition frequency 5 kHz and efficiencies of 0.1–0.14% are reported. The distributions of the active levels of new recombination laser transitions are considered briefly for beryllium, aluminum, tin, and lead ions.