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 phot odissociation of SO2 by a 193-nm ArF excimer laser produced SO(X(3) Si gma(-)) concentrations close to 10(16) cm(-3) over a 50-cm length. Pum ping of SO(B-3 Sigma(-)) by the KrF laser occurred from the v''=2 grou nd state cm vibrational level which was preferentially produced by pho todissociation. The fraction of ground state population that could be excited to SO(B) was determined by measuring the saturation fluence fo r 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-a llowed SO(B-X) band in the region 262-315 nm. A small-signal gain coef ficient of 0.11 cm(-1) and pulse energy of 11 mu J were achieved on th e 270-nm SO-(B,v'=2-->X,v''=5) laser transition. A full computational rate equation model of the excitation and lasing dynamics, including c ollisional rotational mixing, was developed. The A(3) Pi electronic st ate of SO was also investigated as a possible ultraviolet energy stora ge laser medium. Excitation of SO(A(3) Pi,v'=5,6) near 250 nm was achi eved after a time delay from photodissociation to allow for vibrationa l relaxation into SO(X,v''=0). Measurements of the radiative lifetime, deactivation rate, and saturation fluence, along with computation mod eling, indicate that a storage laser based on the weak SO(A,v'=0-->X,v ''=4) transition is not feasible with our production and excitation ca pabilities. Lasing on a direct-pumped single rotational transition of the SO(A,v'=5-->X,v''=1) band may be possible, but with very limited c apacity to store energy.