Simultaneous observations of electromagnetically induced transparency (EIT) and absorption (EIA) in a multi-level...

We report here simultaneous experimental observation of Electromagnetically Induced Transparency (EIT) and Electromagnetically Induced Absorption (EIA) in a multi-level V-type system in D₂ transition of Rb87, i.e., F=2→F^' with a strong pump and a weak probe beam. We studied the probe spectrum by locking the probe beam to the transition F=2→F^'=2 while the pump is scanned from F=2→F^'. EIA is observed for the open transition (F=2→F^'=2) whereas EIT is observed in the closed transition (F=2→F^'=3). Sub natural line-width is observed for the EIA. To simulate the observed spectra theoretically, Liouville equation for the three-level V-type system is solved analytically with a multi-mode approach for the density matrix elements. We assumed both the pump and the probe beams can couple the excited states. A multi-mode approach for the coherence terms facilitates the study of all the frequency contributions due to the pump and the probe fields. Since the terms contain higher harmonics of the pump and the probe frequencies, we expressed them in Fourier transformed forms. To simulate the probe spectrum, we have solved inhomogeneous difference equations for the coherence terms using the Green's function technique and continued fraction theory. The experimental line-widths of the EIT and the EIA are compared with our theoretical model. Our system can be useful in optical switching applications as it can be precisely tuned to render the medium opaque and transparent simultaneously.