Kinetic modeling of rotational nonequilibrium in chemical lasers. a comparison of three models applied to the Cl₂/HI/He system

In this study three theoretical models which yield the temporal evolution of photon densities and population levels for a pulsed chemical laser are compared. The models are applied to the Cl₂/HI/He chemical laser system. The simplest one is the well-known Boltzmann equilibrium model (BEQM) which assumes instantaneous rotational equilibrium throughout the lasing period. This assumption is removed in the detailed rotational nonequilibrium model (DRNM) which follows the time development of each vib-rotational population level separately. A third model, recently introduced by Baer, Top, and Alfassi, is an approximate rotational relaxation model (ARRM) which represents the rotational distribution in each vibrational level as a linear combination of three known functions with time-dependent coefficients. The main conclusions are as follows: (1) The BEQM is inadequate for providing the properties of a laser operating under low and intermediate inert-gas pressures. It can serve at most to derive an upper bound for the actual laser performance. (2) The ARRM provides very good estimates of total laser energy and efficiency as well as of more detailed properties, such as band intensities and the temporal behavior of the vibrational populations, for a wide range of pressures. (3) The use of the DRNM cannot be avoided if fine details, such as spectral distribution of output energy or rotational energy profiles, are required.