Production, Excitation, and Laser Dynamics of Sulfur Monoxide

We have investigated the kinetics of excitation and lasing of the free radical SO by rotationally-resolved optical pumping near 250 nm with a continuously-tunable, narrow-line width KrF laser. Longitudinal photodissociation of SO[sub 2] by a 193-nm ArF excimer laser produced SO(X[sup 3][Sigma][sup [minus]]) concentrations close to 10[sup 16] cm[sup [minus]3] over a 50-cm length. Pumping of SO(B[sup 3][Sigma][sup [minus]]) by the KrF laser occurred from the v[double prime] = 2 ground state vibrational level which was preferentially produced by photodissociation. The fraction of ground state population that could be excited to SO(B) was determined by measuring the saturation fluence for excitation as a function of buffer gas pressure and comparing with a simple model. Addition of a buffer gas increased excitation by nearly 30 times due to increased rotational mixing in the ground electronic state. Lasing was demonstrated on six new vibrational bands of fully-allowed SO(B-X) band in the region 262-315 nm. A small-signal gain coefficient of 0.11 cm[sup [minus]1] and pulse energy of 11 [mu]J were achieved on the 270-nm SO(B,v[prime] = 2 [yields] X, v[double prime] = 5) laser transition. A full computational rate equation model of the excitation and lasing dynamics, including collisional rotational mixing, was developed. 58 refs., 20 figs.