Investigation of a strontium vapor laser

An experimental investigation was made of the time dependence of the intensity of spontaneous lines of strontium atoms and ions in an He–Sr plasma formed in 5- and 10-cm diameter discharge tubes. The intensity of the intercombination atomic line (λ = 689.3 nm) fell on reaching the maximum current. An absorption method was employed to measure the time dependence of the population of the 4d²D_5/2Sr⁺ metastable level which is the lower active level for the λ = 1033 nm self-terminating transition. Three decay time constants were discovered, depending on the helium pressure p_He. It was found that the decay of the population of the metastable level mainly resulted from collisions with electrons, the most rapid decay of the population with τ₁ = 1 – 10 μsec being due to relaxation of the electron temperature and the slowest decay (with τ₂ = 10–80 μsec) due to plasma recombination. At low values of p_He < 1.5 kPa, ambipolar diffusion made the principal contribution to the process of decay of the population of the 4d²D_5/2Sr⁺ level. The minimum time delay after which λ = 1033 nm lasing appeared following the second excitation pulse was equal to the time needed for the completion of the decay of the 4d²D_5/2Sr⁺ level population, while the influence of the first excitation pulse on the second vanished after a time τ₂.