Time evolution of the pulsed HF chemical laser system. I. Kinetic modeling - rotational nonequilibrium

A detailed model of a pulsed F + H₂ → HF + II laser is used to investigate the kinetic behaviour of the system and to provide input data for a thermodynamic analysis of its time evolution. The rate equations for all relevant vib-rotational level populations and photon densities are solved for various initial conditions without using the rotational equilibrium assumption. The results of the kinetic model are in good agreement with the experimental results of Berry in which high inert gas pressure was used to enhance rotational relaxation. The effects of specific kinetic processes on the time evolution of the molecular populations and the laser output are evaluated by varying the inert gas pressure and by “switching on and off” the influence of various kinetic factors. The laser efficiency ranges between ≈ 1 to 2 photons per molecule. The major rate process enhancing the efficiency is rotational relaxation. The reduction in laser efficiency due to vibrational relaxation is ≈ 20%.