OPTICAL-DIPOLE-FORCE FIBER GUIDING AND HEATING OF ATOMS

We present an experimental and theoretical investigation characterizin g the flux of laser-guided atoms through hollow-core optical fibers an d show how it depends on laser detuning from resonance, laser intensit y, and fiber curvature. The guiding employs dipole forces arising from the interaction of the atoms with the optical field. Laser light is f ocused into the hollow region of 40-mu m-inner-diam capillary fiber an d guided through the fiber by grazing incidence reflection from the gl ass walls. The lowest-order mode is azimuthally symmetric with maximum intensity on the fiber axis and nearly zero intensity at the walls. R ubidium atoms are attracted to the high-intensity region along the axi s when the laser is detuned to the red of resonance and consequently g uided through the fiber. Of particular interest is the evolution of th e atom-flux versus laser-detuning profile of increasing intensity. At low intensities the dipole guiding potential is purely conservative an d the flux profile is roughly dispersion shaped. At high intensity, vi scous dipole forces heat the atoms and ''burn a hole'' in the flux-det uning curve. We find that transverse heating of the atoms and the expo nential attenuation of optical mode intensity limit the distance atoms may be guided to about 20 cm in a 40-mu m-diam fiber. Bending the fib er can reduce the effects of heating on atom flux.