Dark-hollow-beam gravito-optical atom trap above an apex of a hollow optical fibre

We propose a novel gravito-optical atom trap composed of a blue-detuned plug beam and a blue-detuned dark hollow beam generated from the output beam of a LP,, mode in a micrometer-sized hollow optical fibre. Cold atoms from a magneto-optical trap are loaded into the dark hollow beam and trapped above an end (apex) of the hollow fibre, As the cold atoms bounce inside the dark hollow beam, they experience transverse Sisyphus cooling induced by the dark hollow beam, longitudinal Sisyphus cooling induced by the plug beam and longitudinal geometric cooling induced by a weak repumping beam propagating downwards. We analyze the cooling: and heating mechanisms and estimate the final 3D equilibrium temperature in the trap. Our results show that an ultracold, dense atomic sample with a 3D equilibrium temperature of similar to 3 mu K and an atomic density above the point of Bose-Einstein condensation may be obtained in this dark optical trap. (C) 1998 Elsevier Science B.V. All rights reserved.