The reaction kinetics associated with microsecond laser pulses through an active medium have been described in Chapters 1 and 2, assuming that rotational relaxation is instantaneous, so that the rotational sublevels within each vibrational level are populated according to a Boltzmann distribution. Experimental measurements of Cheo and Abrams(51) indicate that the relaxation time, τR, corresponding to the time taken for the rotational sublevels to regain a Boltzmann distribution after one sublevel has been disturbed, is of the order τR ~ 0.1 nsec at atmospheric pressure. It is expected, therefore, that the assumption of equilibrium among the rotational levels will no longer be valid for pulses in the nanosecond regime.
KeywordsInput Pulse Population Inversion Coherence Time Small Signal Gain Rotational Relaxation
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