Effect of spontaneously generated coherence on absorption in a V-type system: Investigation in dressed states

We investigate the spectrum of a four-level V-type system. We show that spontaneously generated coherence between the two closely spaced excited levels produces interference effects in the absorption. As a result, more transparency windows appear comparing to the normal three-level V system. We can also control the number of the transparency windows to be two or three just by tuning the Rabi frequency of the coupling field. We present an equivalent system without the rigorous requirement of close-lying levels to observe the phenomena. We also experimentally demonstrate the corresponding features in a rubidium atomic beam.