Shift and asymmetry of the saturated absorption resonance in the field of counterpropagating elliptically polarized waves

The saturated absorption resonance in an atomic gas in the field of counterpropagating light waves with an arbitrary elliptical polarization is investigated. A conclusion about the peculiarities of the resonance shape is drawn from a general analysis of the symmetry of the problem. In particular, a new effect has been found: the polarization parameters of the light waves can lead to an asymmetry and shift of the resonance. These conclusions are corroborated by an approximate analytical solution for the F g = 1 → F e = 2 transition and by numerical calculations. Apart from their fundamental importance, the results obtained can have important applications in metrology (frequency and time standards).