Mean field for a dilute Bose gas in the light field of an evanescent wave

The mean field for atoms undergoing ground-state collisions in a gravito-optical trap is determined in a fully self-consistent way. The atoms are confined by gravity and one atomic mirror formed by an evanescent laser wave. The vertical density distribution of the trapped Bose gas at zero temperature and the refractive modification of the electromagnetic field are obtained iteratively. In the regime of nearly total internal reflection, the sensitive variation of the evanescent wave with the index of the gas leads to large dipole-dipole shifts. In the limit of a steep evanescent wave and large detuning, ground-state interactions dominate.