Theoretical evaluation of the effects of absorption of a laser beam at 10.6 μ has been investigated using the techniques of geometric optics. The interaction is nonlinear because the refractive index depends, through the mechanism of absorption, upon the irradiance distribution in the propagating wave. Atmospheric absorption at 10.6 μ is caused by CO2 and H2O in the atmosphere. Associated with absorption by CO2 and transverse flow caused by atmospheric winds or beam motion are vibrational relaxation effects, which can either heat or cool the atmosphere. If the atmosphere is cooled, the beam is self-focused. The velocity-altitude dependences of the heating and cooling regimes are defined. The amount of cooling increases with increasing altitude and decreasing relative humidity. Numerical results for the irradiance distribution in each regime are presented. At low altitudes the initially circular contours of the constant irradiance have been deformed into crescent-shaped contours and the beam has deflected into the wind. At high altitudes where significant cooling has occurred, the contours of constant irradiance are oval shaped with significant enhancement of the peak irradiance.
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