Quasicontinuous Atom Laser in the Presence of Gravity

We analyze the extraction from a trapped Bose-Einstein condensate to a nontrapping state of a coherent atomic beam and its subsequent fall, at $T=0\mathrm{}\mathrm{K}$. Our treatment fully takes gravity into account but neglects the mean-field potential exerted on the free falling beam by the trapped atoms. We derive analytical expressions for the output rate and the output mode of the quasicontinuous “atom laser.” Comparison with experimental data of Bloch et al. [Phys. Rev. Lett. 82, 3008 (1999)] is satisfactory.