Purely optical dark lattice.

We study a new type of optical lattice in which the localized atoms experience a much reduced optical pumping and fluorescence rate. An optical standing wave is tuned to the blue of the F = 2 ? F = 2 transition of the (87)Rb D(2) line and induces periodic optical potentials by coupling the F = 2 ground state to both the F = 2 and F = 3 excited states. A Sisyphus mechanism efficiently cools the atoms into the lattice sites. We adiabatically release the atoms from the optical lattice and measure their momentum distribution with a resolution of one third of a single photon recoil. This allows us to determine the population of the two lowest energy bands in the optical lattice (44% and 20%).