We present an investigation of an alternative mechanism for sub-Doppler cooling of atoms, based on a coherent population transfer in three-level Λ systems. The mechanism considered is that of a Λ atom interacting with two standing light waves with a mutual spatial phase shift cphi≠0. The spatial dependence of the level populations of the Λ atom for different values of cphi is presented. For cphi≠0, this clearly demonstrates coherent population transfer in an atom with transverse motion along the space-shifted nodes and antinodes of the two standing waves. We show that this allows translational temperatures well below the Doppler limit ${\mathit{T}}_{\mathit{D}}$=${\mathrm{ħ}}_{\gamma }$/${\mathit{k}}_{\mathit{B}}$ to be achieved.

• Received 21 March 1994

DOI:https://doi.org/10.1103/PhysRevA.50.1508