Suppression of absorption of resonance fluorescence in a folded three-level atom

In recent years there has been a lot of interest in using the Λ-system atom to reach a very cold temperature through velocity-selective coherent population trapping (VSCPT). However, since VSCPT takes a long time, the system is bright initially. To determine what kind of density can be achieved in such a system, it is therefore necessary to look at the density-limiting effects during the initial stage when significant VSCPT has not yet taken place. The most important effect is due to the heating caused by absorption of the emission of neighboring atoms. In this paper we find that this absorption is strongly suppressed in the Λ system under a very general set of conditions. Tabosa et al. considered various schemes that also experience such suppressions. However, the system we are considering is of great practical interest since a trap employing Λ-system atoms may be cooled to a temperature substantially below the recoil limit. In addition, this result bodes well for the density achievable in a rectified force trap of Λ atoms.