STRONG-FIELD EFFECTS IN COHERENT SATURATION SPECTROSCOPY OF ATOMIC-BEAMS

We have investigated both theoretically and experimentally saturated absorption of a long-lifetime transition in a calcium atomic beam excited either by a standing wave or by two counterpropagating traveling waves. For standing-wave excitation the usual saturation dip is turned into a peak and then evolves into a triplet as the laser intensity is increased. A theoretical framework has been developed to account for the interaction of atoms with multiple-wave excitation based on a combination of free propagators and S matrices, also applicable to atomic interferometry. The shapes of the wave packets prepared by optical beam splitters are derived. The experimental size and shape of the absorption signal are reproduced by theory only when the actual laser profile is accurately represented and if the recoil physics is introduced because of multiple momentum exchanges between atoms and light in strong laser fields.