Effects of spontaneously generated coherence on resonance fluorescence in a microwave-driven four-level atomic system

We investigate the spectrum of the resonance fluorescence from a coherent driven four-level atomic system. We observe interesting features such as controllable triple narrow peaks. The number, widths and heights of the emission peaks can be controlled by tuning the Rabi frequencies of the laser fields and the microwave field. We attribute these features to the effects of Spontaneously Generated Coherence between the close-lying levels in the dressed state picture. We also explain the observed spectrum with the transition properties of the dressed states generated by the coupling of the two laser fields and the microwave field.