Time-resolved measurements of population densities in a Sr+recombination laser

Time-resolved Sr I and Sr II population densities have been measured in an Sr+ recombination laser. The results indicate that the Sr vapor is fully ionized during the longitudinal discharge pulse and that 3 percent of this ionization persists until the start of the next pulse some 265 μs later. A lower limit of 1.3-2.6 \times 10^{20} m -3 was placed on the electron density during the 180 A current pulse. The steady-state Sr I ground state population showed strong radial gradients, and the estimated population of 1.3 \times 10^{20} m -3 was lower than that anticipated from vapor pressure considerations. The data were used to discriminate between two proposed mechanisms for laser emission from Sr+ and confirm the dominance of the recombination mechanism.