The OH and OD laser: Collision-induced energy transfer pumping

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Detailed studies of the relative intensities of pure rotational lasing in the v=0, 1, 2, 3 states of OH(2Π1/2) and the v=0, 1, 2, states of OD(2Π1/2) are presented. Differences in the laser patterns of these two molecules, such as variation in intensity maxima for specific J levels and double pulsed lasing phenomena, are explained on the basis of a computer simulation model incorporating R→T and V→R energy transfer mechanisms. The probability of collisionally induced R→T transitions is assumed to be given by exponential gap model in which the rotational parameter is evaluated by information theory (sum rule) approximations. The V →R relaxation is described in a two step process: first, the change of oscillator vibrational energy directly into oscillator rotational energy, and second, the absorption or removal of the energy defect (mismatch) by collisional R→T processes. The appropriate parameters for this transfer mechanism are also calculated with sum rule assumptions for the two molecules. The temporal evolution of nascent populations relaxing by the mechanisms lead directly to population inversions which corroborate in specific detail the lasing patterns observed experimentally.