Guiding cold atoms in a hollow laser beam

The theory of atom guiding in a far blue-detuned hollow laser beam (HLB) is developed for the dipole interaction scheme described by a three-lever Lam bda model. The complete kinetic description of atomic motion based on the F okker-Planck equation for the atomic distribution function is presented. Th e dipole gradient force, radiation pressure force, and momentum diffusion t ensor are then derived. It is found that even for a far-detuned laser beam, the optical potential for a three-level Lambda atom is not generally reduc ed to a sum of two independent potentials associated with the two two-level interactions in the Lambda scheme. The theory developed here is also compa red with the experimental guiding of cold Rb-85 atoms in the HLB. The exper imental results are found to be in good agreement with the Monte Carlo simu lations based on the three-level Lambda model. We observe that the guiding efficiency depends strongly on the intensity and the detuning of the HLB an d the initial temperature of atoms. In particular, the experimental results show that, at small detunings, the guiding efficiency is deteriorated stro ngly by the radiation pressure force. The Monte Carlo simulations also indi cate that the efficiency of guiding versus detuning depends strongly on the direction of the HLB propagation with respect to that of atomic motion. Un der optimal conditions, the guiding efficiency was found to be about 20%. [ S1050-2947(99)09112-X].