Transverse mode of an atom laser

The transverse mode of an atom laser beam that is outcoupled from a Bose–Einstein condensate is investigated and is found to be strongly determined by the mean-field interaction of the laser beam with the condensate. For repulsive interactions, the condensate acts as a diverging lens for the outcoupled atoms, and transverse interference fringes in the atomic beam are predicted due to the coherent addition of amplitudes for atoms emitted from different regions in the condensate. This effect can be used to investigate the transverse coherence of an atom laser beam.