Fig. I. Potential curves of the Br, molecule and the absorption coefficient. The photons corresponding to the shaded area cause dissociation. Those that cause the electron to be raised to the 3no+ level below AB create vibrational states and hence increase the temperature. The potential curves were taken from Ref. 3. of such a solar-pumped gas laser. The physical mechanisms assumed here are largely the same, but our analysis differs in several respects. First, extra nonlinear terms are included to take account of the depletion of the particles, otherwise at low pressures the above theory predicts more excited states than there were neutral particles in the first place. Second, the energy flow is discussed more fully, and estimates are shown of the temperatures of the medium at high concentrations of solar radiance. The temperature decides the density of the lower laser level. Third, solutions are obtained for the inversion density in terms of a wide range of parameters, including the gas composition and pressures. Fourth, an estimate of the efficiency is given. The physical mechanisms are discussed in Sec. 2, and estimates of densities of Br* and the upper laser level are obtained in Sec. 2.1. Section 2.2 considers the temperature rise of the laser medium and the population of the lower laser level. The inversion population is then displayed graphically as a function of gas composition. The efficiency estimates are presented in Sec. 3. Other combinations of halogen absorber-molecular lasants are then discussed in Sec. 4 and their overall efficiencies estimated. II. PHYSICAL MECHANISMS OF A Br2-CO2-He LASER The frequency of dissociations per bromine molecule is D = 4>AXo-, where <h is the solar flux (photons cm 2s ' per A), AX the absorption bandwidth, and a the cross section at the photodissociation peak. The cross section varies with wavelength X and also with the gas temperature T. The absorptivity of Br2 vs X and T has been studied by Passchier, Christian, and Gregory (2), who showed good agreement between theory and experiment. The theory showed that increasing the temperature
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