Chemical laser power spectral performance: a coupled fluid dynamic, kinetic, and physical optics model

Abstract

The simplified chemical fluid dynamic model employed by Sentman in his study of rotational nonequilibrium in cw chemical lasers has been coupled to a 1-D physical optics model of the cavity. Calculations have been performed for both rotational equilibrium and nonequilibrium cases for an unstable resonator with 50% geometric outcoupling. For the rotational equilibrium case, the solution resulted in most of the power being contained in one line (84% in J = 8, 10% in J = 9, and 6% in J = 4). For the rotational nonequilibrium case, 98% of the power is distributed over eleven lines, and the Fabry-Perot and unstable resonator power spectral distributions are almost identical, the major difference being that all lines whose saturated gain region does not extend into the central portion of the unstable resonator are cut off. Comparison of the results for the rotational equilibrium and nonequilibrium kinetic models shows that, for both resonators, the rotational nonequilibrium power is 30% less than the equilibrium case, whereas, for a given kinetic model, the unstable resonator produces only about 6% less power than the Fabry-Perot resonator. For the rotational nonequilibrium case, fluctuations in cw power are shown to occur on lines whose saturated gain zone does not fill the unstable resonator. The amplitude of the fluctuation is determined by the fraction of the resonator filled by the saturated gain zone of the oscillating line, and the frequency of the fluctuation is determined by the location of the intensity peak of the oscillating line.