Band Population Measurements in a Purely Optical Dark Lattice

Abstract

We create a dark optical lattice structure using a blue detuned laser field coupling an atomic ground state of total angular momentum F simultaneously to two excited states with angular momenta F and F-1, or F and F+1. The atoms are trapped at locations of purely circular polarization. The cooling process efficiently accumulates almost half of the atomic population in the lowest energy band which is only weakly coupled to the light field. The populations of the two lowest energy bands reaches 70%. Kinetic energies on the order of the recoil energy are obtained by adiabatically reducing the optical potential. The band populations are directly mapped on free particle momentum intervals by this adiabatic release. In an experiment with subrecoil momentum resolution we measure the band populations and find good absolute agreement with the theoretically calculated steady state band populations.