Absorption profile of a three- Ievel ladder atomic system with incoherent PumPing

Abstract

We have studied the effects of adding an incoherent populationpumping on the absorption and dispersion profile of a driven three- levelladder system. Two coherent fields are assumed to drive our system, acoupling field on the upper transition and a probe field on the lowertransition. The absorption profile of such a system with no incoherentpumping is well known. It consists of two symmetric (asymmetric)Autler- Townes peaks for resonant (off- resonant) coupling field' Wehave found that applying an additional incoherent pumping field wouldwork first to merge the two peaks into a central weak absorption line andthen to drive the system to a state of electromagnetically inducedtransparency (EIT). We have found differences in the details of this effectwhen the pumping field is applied to the upper or to the lower atomictransition, in the latter case the transition of the system to the (EIT) statetakes place very rapidly as compared to the former case. In the secondcase ancl for an off - resonant coupling field and fast upper transitionrelaxation, we have noticed an interesting effect manifested in the factthat the incoherent pumping field would shift the absorbed energy fromthe larger to the smaller absorption peak resulting in a non - central weakabsorption line befbre reaching the ultimate (ElT) state.