High densities of cold atoms in adarkspontaneous-force optical trap

A new magneto-optical trap is demonstrated which confines atoms predominantly in a ‘‘dark’’ hyperfine level, that does not interact with the trapping light. This leads to much higher atomic densities as repulsive forces between atoms due to rescattered radiation are reduced and trap loss due to excited-state collisions is diminished. In such a trap, more than ${10}^{10}$ sodium atoms have been confined to densities approaching ${10}^{12}$ atoms ${\mathrm{cm}}^{\mathrm{-}3}$.