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 Δ_d 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 Δ_d. Two different domains of laser cooling are identified. For small Δ_d, atoms are cooled due to a well-known mechanism that also occurs in standard optical lattices. For large Δ_d, atoms are cooled based on Raman transitions. We study the transition between the two domains of laser cooling in detail.