Guiding cold atoms in a hollow laser beam

Abstract

The theory of atom guiding in a far blue-detuned hollow laser beam ͑HLB͒ is developed for the dipole interaction scheme described by a three-level ⌳ model. The complete kinetic description of atomic motion based on the Fokker-Planck equation for the atomic distribution function is presented. The dipole gradient force, radiation pressure force, and momentum diffusion tensor are then derived. It is found that even for a far-detuned laser beam, the optical potential for a three-level ⌳ atom is not generally reduced to a sum of two independent potentials associated with the two two-level interactions in the ⌳ scheme. The theory developed here is also compared with the experimental guiding of cold 85 Rb atoms in the HLB. The experimental results are found to be in good agreement with the Monte Carlo simulations based on the three-level ⌳ model. We observe that the guiding efficiency depends strongly on the intensity and the detuning of the HLB and the initial temperature of atoms. In particular, the experimental results show that, at small detunings, the guiding efficiency is deteriorated strongly by the radiation pressure force. The Monte Carlo simulations also indicate that the efficiency of guiding versus detuning depends strongly on the direction of the HLB propagation with respect to that of atomic motion. Under optimal conditions, the guiding efficiency was found to be about 20%.

Optimized coupling of cold atoms into a fiber using a blue-detuned hollow-beam funnel

“…On the other hand, low-loss guidance of a LG 01 -like mode in a 19-m-long HC-PCF was recently demonstrated in [28]. Models of atom guiding in collimated blue-detuned hollow-beams in vacuum have also been developed and validated with experimental results [27,29,30], although to our knowledge no one has yet considered the cold atoms behavior in the diffracted field from the core of the fiber.…”

Physics with coherent matter waves

“…Optical waveguides based on a hollow blue detuned laser beam [261,262], creating a repulsive potential tube for were demonstrated for thermal atoms [263,264,265,266,267,268,269,270] and coherent matter waves [104]. In [104] a TEM 00 mode laser beam was transformed into a doughnut-shaped hollow TEM * 01 laser beam using a blazed-grating phase hologram.…”

Atom guiding along high order Laguerre–Gaussian light beams formed by spatial light modulation

“…Blue-detuned optical guiding, where the light frequency is tuned above resonance, has the advantage that the atoms are then restricted to regions of intensity minima, and perturbations induced by the light field are thus minimized. Blue-detuned guiding of a cold atomic beam along a hollow, low-order Laguerre-Gaussian light beam has already been reported [5,6], as has the guiding of cold atom clouds dropped from magneto-optical traps (MOTs) into hollow beams generated using axicon lenses [7] and hollow optical fibres [8]. These various schemes each have their merits, but these forms of beam generation are not true propagating modes and may show a significant change in transverse beam profile with propagation.…”

“…The frequency detuning is also a key parameter, and the near-resonant guiding of Song et al [7] is accompanied by significant radiation pressure, which can levitate or push the atomic cloud and which causes heating of up to 15 mK. When the detuning exceeds 10 GHz and the cloud is cooled in a molasses cycle, however, extended guiding can occur with relatively little heating [8].…”