We present a simple gravito-optical atom trap consisting of a blue-detuned, conical doughnut-hollow beam and the gravity field. Cold atoms are loaded into the doughnut-hollow beam from a magnetic-optical trap and cooled by Sisyphus cooling and geometric cooling induced by the doughnut-hollow beam and a weak repumping beam. We calculate the light-shift potential for atoms confined in the doughnut-hollow beam, analyze the cooling and heating mechanisms in the trap and estimate the trap losses. Our study shows that an ultra-cold atomic sample with an equilibrium 3D rms momentum of about 2.5 (h) over bar k (a temperature of similar to 1 mu K) may be obtained in the trap. (C) 1998 Published by Elsevier Science B.V. [References: 21]
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