Rotational nonequilibrium mechanisms in pulsed H_2 + F_2 chain reaction lasers 1: Effect on gross laser performance parameters

Abstract

A rate equation model of a pulsed H(2) + F(2) chemical laser is used to examine the relative importance of rotational nonequilibrium mechanisms on laser performance. This computer model yields the time history of the first thirteen rotational levels and the first twelve vibrational-rotational P-branch transitions for the first six vibrational bands of HF. With this model, the general effects of rotational nonequilibrium on the H(2) + F(2) laser were found (1) to increase the number of transitions that lase simultaneously, (2) to lower the intensity of each transition, and (3) to extend the duration of lasing on each transition; these trends are similar to those observed earlier for the F + H(2) laser. The major thrust of the present work is to isolate the relative importance of the various rotational nonequilibrium mechanisms. To this end, we have examined and compared several approaches to modeling R-T and V-R relaxation, nonequilibrium pumping distributions, and line-selected operation. The effects of these mechanisms (and their relative importance) on the laser output are clearly revealed by the model. The character of the spectra for the H(2) + F(2) model is significantly different from that observed for the F + H(2) model. The ability of the model to predict spectra observed in experiments is assessed, and the model is found to compare well with discharge-initiated lasers. Additional calculations demonstrate the effect of multiquanta V-T deactivation of HF by HF.