Electromagnetically Induced Transparency in a Four-LevelAtomic System

In this paper, we analyze and discuss theabsorption properties of the probebeam in a four-level atomic system with a nearly hyper-fine doubletstructure of two higher-lying excited levels based on electromagneticallyinduced transparency (EIT) for the two cases of transient process andsteady-state process. The main gain of this work is to investigatetheoretically the influence of the nearly hyper-fine levels on the probeabsorption. For the transient process, using the numerical calculations by asimple Mathematica code we find that the magnitude of the probe absorptionat the line center is small compared to the typical three-level atomicsystem in the context of electromagnetically induced transparency. For thecase of the steady state, our results show that the probe absorption can becompletely eliminated at the line center of the probe transition just as theusual three-level EIT scheme.