Energy bands and Bloch states in 1D laser cooling and their effects on the velocity distribution

We describe calculations that predict and analyze distinctive features in the velocity distribution in 1D laser cooling for light shift potential well depths only a few times the recoil energy. These features can be interpreted in terms of populations of energy bands or even Bloch states in the periodic potential. They occur with a σ+ standing wave, with and without a small B field, and for linlin laser cooling. We have observed these features experimentally in a beam of metastable helium atoms cooled on the 23S123P2 transition, with velocity resolution ∼0.3 recoil.