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Inhomogeneous broadening effects in multimode cw chemical lasers
Abstract:
Analytic solutions are presented for inhomogeneous broadening effects in multimode cw chemical lasers. A Fabry-Perot (F.P.) resonator and a saturated amplifier are considered in the limits Deltanu(h) << Deltanu(d) and Deltanu(c) << Deltanu(h), where Deltanu(h), Deltanu(d), and Deltanu(c) are homogeneous, Doppler, and longitudinal mode separation widths, respectively. The former inequality requires p(Torr) = 0(10). The results are believed valid for Deltanu(c)/Deltanu(h) = 0(1) and apply for resonator mirror separation lengths and amplifier lengths of the order of 10 m or more. The normalized frequency difference from line center is denoted X, and the value of X corresponding to the largest longitudinal mode frequency is denoted X(f). The quantity X(f) is a measure of laser frequency band-width and the number of active longitudinal modes. For the case of an F.P. resonator, X(f) varies with streamwise distance. The local value of X(f) is independent of upstream conditions for the case of a saturated F.P. resonator. The variation of lasing intensity with X at each streamwise station is found to be a truncated Gaussian. The slope of the curve of eta - 1 (anomalous index of refraction) vs X is positive in the lasing region |X| < X(f). The magnitude of eta - 1 is proportional to the threshold gain. For a typical saturated cw chemical laser oscillator, the anomalous index of refraction is shown to be small, compared with the regular index, for medium pressures in the range p(Torr) >/= 0(1). The present analytic results are in good agreement with the numerical results of Bullock and Lipkis.
