A multilevel pulsed chemical laser model

Short-pulsed chemical lasers are analyzed with regard to establishing diagnostic relations and determining limits on laser performance. Time-dependent population inversions incorporating the effects of collisional deactivation, stimulated emission, and chemical source variation are determined using a rigorous matrix procedure. These inversions are combined with a radiative rate equation, and the resulting output intensity profiles and total energy density are evaluated for three types of source variations: 1) constant source strength, 2) exponentially varying source strength, and 3) chain reaction source. The effect of chemical branching on laser performance is investigated by using a positive exponential. A negative exponential is used to determine the effect of a declining free radical population (incomplete chain reaction) on laser performance. Both collisional deactivation and free radical decline are shown to have deleterious effects on laser output and chemical efficiency, as compared to earlier more optimistic estimates. A chain reaction source with three body volumetric termination processes is used to describe an HF laser. At low pressures the laser output is a linear combination of the constant source and exponentially declining source solutions. At high pressure either an enhanced "reactive recombination" mechanism or formation of HF dimers causes a nonmonotonic laser output pressure dependence similar to experimental observations.