Lower-level decay kinetics in discharge-excited Sr+ recombination lasers

A pulsed strontium recombination laser operating at 430 nm is described for which mean output powers of up to 2 W have been obtained at pulse repetition frequencies of several kilohertz. The experimental setup and procedure are described. The results for unsaturated conditions of the λ = 430-nm transition show that the metastable state population decays exponentially in two distinct phases. In the early afterglow (t ≤ 3 μs) the decay rate is typically 10⁶s^-1 in optimum conditions for λ = 430-nm laser output and is an order of magnitude larger than the rate at later times. This early rate is certainly consistent with superelastic electron collisional clearing to the Sr⁺ ground state. However, an estimation of the feed rate from the lower laser level (and thus the clearing rate of the lower laser level) can be obtained from experiments in which the population of the lower laser level is itself perturbed.