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(-1) 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 mu s 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(-13) cm(3) s(-1). 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.