Asymmetry of saturation resonances due to lens and aperture effects during propagation of off-axial Gaussian beams in a nonlinear medium

A new modification of the generalized method of moments is applied to off-axial Gaussian beams in nonlinear inhomogeneous media. Numerical estimates of the induced astigmatism, deformation of the spot, and bending of the beam are obtained for a traditional saturation spectroscopy scheme with a probe counterpropagating beam tilted slightly from the axis of a saturating beam. It is shown that this tilt results in an asymmetry of the radial dependence of the frequency shift of a saturation resonance, which is in good qualitative agreement with the experimental results.