The rate equations governing the temporal evolution of photon densities and level populations in pulsed F+H2→HF+H chemical lasers are solved for different initial conditions. The rate equations are solved simultaneously for all relevant vibrational–rotational levels and vibrational–rotational P-branch transitions. Rotational equilibrium is not assumed. Approximate expressions for the detailed state-to-state rate constants corresponding to the various energy transfer processes (V–V, V–R,T, R–R,T) coupling the vib–rotational levels are formulated on the basis of experimental data, approximate theories, and qualitative considerations. The main findings are as follows: At low pressures, R–T transfer cannot compete with the stimulated emission, and the laser output largely reflects the nonequilibrium energy distribution in the pumping reaction. The various transitions reach threshold and decay almost independently and simultaneous lasing on several lines takes place. When a buffer gas is added in excess to the reacting mixture, the enhanced rotational relaxation leads to nearly single-line operation and to the J shift in lasing. Laser efficiency is higher at high inert gas pressures owing to a better extraction of the internal energy from partially inverted populations. V–V exchange enhances lasing from upper vibrational levels but reduces the total pulse intensity. V–R,T processes reduce the efficiency but do not substantially modify the spectral output distribution. The photon yield ranges between 0.4 and 1.4 photons/HF molecule depending on the initial conditions. Comparison with experimental data, when available, is fair.
The conditions for effective pumping of non-resonant, highly excited vibrational levels are outlined. Hydrogen fluoride is chosen as a model system and examined under various aspects. Its absorption behaviour is taken as a diagnostic for collisional processes; fast temperature measurements serve as an indicator for dissociation. The results can be generalised.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.