The effects of Feshbach resonance on spectral shifts in photoassociation of Cs atoms.

We study the effects of magnetic Feshbach resonance on the shifts in photoassociation (PA) spectra of ultracold Cs atoms. A series of atom loss spectra show a linear variation of the frequency shift with the PA laser intensity at different magnetic fields near the d-wave Feshbach resonance of optically trapped Cs atoms. The magnetic field-dependence of the slope of the shift on the PA laser intensity exhibits a dispersive change near the Feshbach resonance. The theoretical formula derived from a model based on Fano resonance fits well with the experimental data. Using a model rectangular potential with tunable well depth and applying the Franck-Condon principle, we obtain numerical results, which are found to be largely in disagreement with the experimental findings.