Transition of laser cooling between standard and Raman optical lattices

Reduced-period optical lattices based on Raman transitions allow for sub-Doppler laser cooling. An important parameter of this Raman optical lattice is the frequency difference Δd between two virtual energy levels involved in the atom-field interaction scheme. In this work, we use experimental time-of-flight data and quantum simulations to characterize laser cooling in the Raman lattice as a function of Δd. Two different domains of laser cooling are identified. For small Δd, atoms are cooled due to a well-known mechanism that also occurs in standard optical lattices. For large Δd, atoms are cooled based on Raman transitions. We study the transition between the two domains of laser cooling in detail