Light shift induced modification of electromagnetically induced resonances in atomic vapor

Abstract

We investigate the effects of a third laser on the electromagnetically induced transparency (EIT) spectrum obtained for the D2 line of 87Rb. The third laser converts a typical bi-chromatic laser-induced Λ type system into a four-level N type system. Our work considers two different configurations of N type system depending on whether the third laser is co-propagating or counter-propagating with respect to the other two. The effects of detuning on the EIT spectrum for both cases of N type systems have been experimentally studied. Our results demonstrate that for the counter-propagating case variation of detuning induces a switch from absorption to transmission. We interpret the experimental observations in terms of modification of light shifts by Doppler averaging within a dressed state formalism. Numerical results obtained using the density matrix formulation, which is in good agreement with the experimental results are also included to substantiate the experimental findings. We also find that in the presence of a magnetic field, due to the formation of certain subsystems that involves Zeeman sublevels, neither absorption nor transmission is observed in the probe transmission spectrum. We define these as the “missing resonance” peaks. We propose methods for recovering these peaks in the probe transmission spectrum.