INHOMOGENEOUS BROADENING EFFECTS IN CW CHEMICAL-LASERS

The effects of inhomogeneous broadening on the performance of cw chemical lasers are investigated. A simple two-level vibrationai model and a Fabry-Perot resonator are assumed. Laser performance is found to depend on the parameters Δvh/Δvd and R, where Δvh is the homogeneous linewidth, kvd is the Doppler line width, and R is the ratio of molecular collision rate to the excited molecule deactivation rate. Typical values are in the range R = O(100) and Δvh/Δvd = 0(0.01-0.1). Analytic solutions are obtained for [I/(1 + R)]2 ≪ 1, where I is a normalized lasing intensity. Numerical results are presented for a cw chemical laser with laminar diffusion and with a single longitudinal optical mode. The variation of differential number density Δ/N and local lasing intensity I with stream wise distance and the variation of net laser output power with tuning frequency are presented. The latter exhibits a Lamb dip near line center, which is in agreement with experimental observations. Inhomogeneous broadening effects are found to become negligible for (Δvh/Δvd)R ≥ O(10). The latter parameter is approximated by the expression (Δvh/Δvd)R = O[p(Torr)] where p is the static pressure in the lasing region in Torr. Thus, in typical devices, inhomogeneous broadening effects become negligible for p ≥ O(10) Torr. These effects become important in single longitudinal mode lasers operating in the regime p (Torr) ≤ O(1) and in lasers wherein the streamwise length of the resonator is short compared with the streamwise length of the positive gain region. © 1979 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.