Effect of gasdynamics on resonator stability in reactor-pumped lasers

A number of experiments involving reactor pumping of atomic xenon have been conducted on Sandia reactors, with lasing observed at 1.73 ..mu..m and 2.03 ..mu..m for a variety of conditions. In some of these experiments, lasing was observed to terminate well before the peak of the pumping pulse. Recent advances in gasdynamic modeling and laser resonator stability theory make it possible to discriminate between laser kinetics and gasdynamics issues to explain these terminations for some experiments. In the February/March ACRR experiment series, lasing termination and/or reinitiation that can be attributed to gasdynamically induced resonator stability transitions was observed for some conditions. A laser resonator stability theory based on the existence of a parabolic refractive index profile in the gain medium is developed in terms of an index gradient strength parameter ..gamma..*. The theoretically determined critical values of ..gamma..* for instability and restablization for the experimental configuration are in good agreement with gasdynamic computations of the ..gamma..* values at the experimentally observed termination and reinitiation times. Generic computations of the variations of ..gamma..* with the normalized pressure rise (the only important dynamic variable) are presented for most of the other ACRR experiments. In addition, laser intensity profile measurements made with pyroelectricmore » detector arrays for experiments on the ACRR and SPR III reactors provide additional information about higher-order laser mode behavior. 9 refs., 26 figs., 1 tab.« less