Two-photon absorption resonance in the presence of transit effects

An analysis is made of the influence of transit effects on the profile of a two-absorption line of a gas interacting with a standing wave field. It is shown that in the case of a confined light beam the resonance width is governed by the transit times of atoms across the beam. When two light beams separated by a large distance are present, there is an additional resonance line of width which is the reciprocal of the transit time between the beams. This resonance is analyzed allowing for the relaxation of atomic levels.