Transient laser gain: an alternative method for determination of rate constants for the relaxation of an anisotropic velocity distribution

Summary form only given. Collisions with cold unexcited and/or buffer gas relax the speed to a Maxwellian distribution and the angular distribution to an isotropic one. The corresponding relaxation rates give insight into the collisional dynamics and are typically measured using pump-probe techniques. If one of the products of the photolysis emerges in an excited state, it can provide optical gain and may be used as active laser medium. The thermalization process then manifests itself in a distinct time dependence of the gain. We demonstrate that the dynamic behavior of the laser pulse can be used to extract the information on the rate constants for the speed and anisotropy relaxation. As an. example we studied the photolysis of CF/sub 3/I excited by 20 ns pulse at 248 nm and the subsequent lasing of I* in the presence of various buffer gases.