Investigation of Electromagnetically Induced Transparency in Open V, $\Lambda$ and Cascade Doppler-Broadened Molecular Systems

We have demonstrated electromagnetically induced transparency (EIT) for two-color transitions in inhomogeneously broadened lithium and sodium dimer vapors. EIT has been observed via fluorescence detection in three systems of different energy level configurations (V, $\Lambda $, $\Xi )$ by employing two continuous-wave single frequency lasers. The dependence of the transparency profile on the beam geometry (V-system), coupling laser intensity ($\Lambda $-system) and wavelength ratio of the applied fields (cascade system) has been investigated. The openness of the molecular V-type system is accountable for rendering the medium transparent even for residual Doppler line widths greater than the induced Autler-Townes splitting. Our findings have been complemented by theoretical studies that trace the presence of EIT at the density matrix level. These theoretical predictions agree well with the experimental results.