An atom laser based on dark-state cooling: a detailed description

It was proposed by two of us (Wiseman H M and Collett M J 1995 Phys. Lett. A 202 246) that a device producing a coherent atomic wave (that is, an atom laser) could be built using dark-state cooling of atoms in a trap. Here we present a more complete analysis of this system, including the effects of atomic interactions through dipole-dipole coupling and hard-core collisions . We show that for reasonable physical parameters the dipole interactions h ave little contribution to the atomic dynamics. In contrast, the hard-core collisions are likely to dominate the laser linewidth. In fact, it would ap pear necessary to select (or produce) a species with a hard-core scattering radius of much less than one nm in order for the output of the device to b e phase coherent.