Theoretical evaluation of the effects of absorption at 10.6 μm on the diffracted field has been investigated. The physical model of the nonlinear interaction process includes the effects of absorption by CO2 and H2O, transverse flow and vibrational relaxation effects associated with atmospheric absorption by CO2. The analysis is based upon the scalar wave equation in the Fresnel limit and the governing equation is integrated numerically using a stable, finite difference method. Diffraction patterns in the far field for an unfocused beam and at the focal point for a focused beam are presented. The atmosphere acts as a nonlinear lens with aberrations and the irradiance distributions exhibit a complicated filamentary pattern at the focal point.