TIME RESOLVED SPECTROSCOPY AND SMALL SIGNAL GAIN IN A FLASH INITIATED, PULSED HF LASER

An experimental and computer modeling investigation of a pulsed, flash photolysis initiated, H(,2) + F(,2) chemical laser was undertaken. Time resolved spectral (TRS) output, time history of small signal gain (SSG) and total pulse energy (TPE) were measured. Several experimental trends were noted.; For the TRS results, regular shifts of individual transition initiation, termination and peak intensity times with increasing rotational level are observed. Transition pulse duration increased with rotational level.; For the SSG results, regular shifts of positive gain initiation, termination and peak gain times with increasing rotational level were observed. Positive gain duration increased with rotational level.; The experimental TRS results were compared with those of other researchers and then with the results of computer simulations. Pulse duration in this work was longer than that reported elsewhere. This was most likely due to weak initiation of the H(,2) + F(,2) chain. No reportable rotational lasing was observed. This is in contrast to other work but in agreement with model calculations.; In addition to the experimental study, an existing computer model was modified by the substitution of a wavelength dependent threshold gain in place of the previous wavelength independent threshold gain and by the addition of a flash photolysis initiation option. The modified model and a second, simplified, model were used to simulate the TRS and SSG experiments. Two model rate coefficients were varied to investigate the effects of the hot reaction vibrational pumping distribution and of the vibrational deactivation mechanism rate coefficients on the simplified model TRS and SSF results.; The experimental TRS and SSG results were compared to the calculations resulting from the two models.; The results of the simplified model, assuming Vibrational-Translational energy transfer, more closely duplicated experiment than did the results of the modified model (assuming Vibrational-Rotational energy transfer). This is in contrast to the currently accepted understanding of kinetic mechanisms.; Conclusions reached in this study were: (1) The time scales of SSG and TRS are not the same, SSG having much longer durations. (2) The trends of initiation, termination and peak gain or intensity times are similar for SSG and TRS. (3) Computer models are capable of accurately predicting the time resolved characteristics of gain and emission. (4) Further work is necessary to determine the form of V-R,T energy transfer.