Kinetics of an optically pumped metastable Ar laser

In recent studies, an optically pumped Ar*/He laser has been demonstrated using the Ar 4p[1/2]1→4s[3/2]2 transition at 912.55 nm. Time-resolved data for this system, recorded using CW laser excitation and pulsed discharge production of Ar* 4p[3/2]2, yielded laser output pulses that were of unexpectedly short duration. It was speculated that radiative relaxation from the upper laser level to the 4s[3/2]1 state (607 cm above 4s[3/2]2) caused termination of the laser pulse. In the present study this hypothesis has been tested by observing the energy transfer kinetics of the 4s[3/2]2 and 4s[3/2]1 states in Ar/He gas mixtures. Following pulsed laser excitation out of 4s[3/2]2, population recovery was observed on a μs time scale. Energy transfer from 4s[3/2]1 to 4s[3/2]2, induced by collisions with He, was characterized. The rate constant was found to be (1.0±0.5)x10 cm s. These observations confirmed that radiative transfer to 4s[3/2]1 was responsible for the short duration laser pulses. Modeling of a fully CW optically pumped Ar* laser shows that radiative transfer to 4s[3/2]1 reduces the number density of the Ar* atoms involved in lasing, but is otherwise benign.