Comparative evaluation of collisional relaxation mechanisms for gasdynamic lasers

Abstract

Three separate variations of a vibrational energy nonequilibrium flow of a supersonic expansion of a CO2-N2-H2O mixture through a gasdynamic laser nozzle are examined to demonstrate the relative importance of the error induced by neglecting various kinetic effects and anharmonicity. The significance of each important collisional relaxation mechanism is specifically demonstrated by comparing the error induced due to neglecting each effect, with the variation in the predicted inversion obtained by using three different sets of empirical relaxation time equations. Since the net effect of each relaxation mechanism is to drive the system towards equilibrium, thus decreasing the inversion, it is suggested that the application of the parallel mixture rule in a kinetic model to include different relaxation paths is incorrect. Two kinetic models are solved by first assuming the molecules to be harmonic oscillators and then using the Morse oscillator model to demonstrate the significance of anharmonicity. The influence of the reservoir temperature in establishing the significance of each kinetic effect on the inversion and small-signal gain is calculated.