Probing 85Rb MOT in 5P3/2(F = 4) → 5D5/2(F′) transitions. In search for effective Rabi frequency

The aim of this work was to provide a simple justification and applicability limits for the concept of effective Rabi frequency being related to an average atom–field interaction in MOT. We sampled 85Rb MOT with a weak probe beam tuned across the 5P3/2 (F′ = 4) → 5D5/2(F″ = 3, 4, 5) hyperfine transitions, while the 5S1/2(F = 3) → 5P3/2(F′ = 4) transition was driven by the red-detuned trapping beam. The probe absorption spectra were registered for a number of detunings Δ and intensities P of the trapping beam. The Autler–Townes splitting δ of the clearly dominating F′ = 4 → F″ = 5 line was the subject of analysis. The character of the space-dependent interactions of atoms with MOT fields is of a complex nature, which brings the notion of the effective Rabi frequency for MOT into challenge. However, we argue that for the range of the typical values of P and Δ, it is justified to characterize MOT with an effective Rabi frequency Ω0eff, by using the intuitive formula Ω0eff=BP, where B is a mean scaling factor experimentally determined, basing on predictions of a straightforward 3-level model. We postulate that our simple procedure, providing both the B value and the applicability limits of the approach, should be repeated with each new implementation of MOT (e.g., with trap beams realignment), which may change conditions experienced by cold atoms.

Research Highlights
► The MOT atoms are in complex interaction with MOT fields.
► An averaging over MOT inhomogeneities is still possible under controlled conditions.
► Effective Rabi frequency can be approximately assigned to an ensemble of MOT atoms.
► Applicability limits of the applied approach are given.