Quasicontinuous atom laser in the presence of gravity

We analyze the extraction from a trapped Bose-Einstein condensate to a nont rapping state of a coherent atomic beam and its subsequent fall, at T = 0 K . Our treatment fully takes gravity into account but neglects the mean-fiel d potential exerted on the free falling beam by the trapped atoms. We deriv e analytical expressions for the output rate and the output mode of the qua sicontinuous "atom laser." Comparison with experimental data of Bloch rt al . [Phys. Rev. Lett. 82, 3008 (1999)] is satisfactory.