Sub-Doppler cooling in reduced-period optical lattice geometries

It is shown that sub-Doppler cooling occurs in an atom-field geometry that can lead to reduced-period optical lattices. Four optical fields are combined to produce a “standing wave” Raman field that drives transitions between two ground state sublevels. In contrast to conventional Sisyphus cooling, sub-Doppler cooling to zero velocity occurs when all fields are polarized in the same direction. Solutions are obtained using both semiclassical and quantum Monte Carlo methods in the case of exact two-photon resonance. The connection of the results with conventional Sisyphus cooling is established using a dressed state basis.