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Pulse propagation of CO2 laser amplifiers

Numerical predictions of pulse amplification in atmospheric CO2 laser amplifiers are discussed. A conventional four-temperature kinetic model is first used to establish the kinetic temperatures of relevant CO2 vibrational levels in a pumped amplifier or arbitrary gas composition and pressure. The power amplification of a (single-line) pulse or arbitrary duration propagating through this amplifier is then examined in the simplifying approximation that N2-CO2 relaxation can be neglected. The treatment includes multi-level (rotational and vibrational) energy exchange, and Fermi coupling between the (100) and (020) levels. Coherent effects, of importance for sub-nanosecond propagation, are handled with terms including the dipole-dephasing time tau 2. Asymptotic pulse shapes are observed.