Effect of H2pressure on pulsed H2+F2laser, experiments, and theory

Predictions and measurements of stimulated emission for this laser are compared for H2pressures from threshold to stoichiometric, a range of several orders of magnitude. Slowly flowing helium-diluted 50-torr mixtures were initiated photolytically. Two dilution ratios and two output couplers are studied. Good agreement is found for time-to-threshold and pulse duration versus H2and for threshold H2pressure. Spiking and possibly mode beating, features not modeled, are observable in some pulses. Mostly, however, predicted intensity versus time agrees in pulse shape with laser output. Observed and predicted peak intensities nearly match for low H2pressure. The predicted increase of peak intensity with low H2is fairly well followed. For2in the vicinity of one-tenth stoichiometric the data show an abrupt leveling off of peak intensity while the calculations predict a continuing increase. This behavior seemingly cannot be attributed to uncertainties iu the kinetic model. All rate modifications considered prove to be incapable of prodating a large or abrupt enough change to explain the data. Experimental results are presented supporting the notion that parasitic oscillations cause this change in laser output. Future comparisons providing fuller tests of the theory are identified as are experiments to test parasitic oscillation suppression schemes.