Electromagnetically induced absorption and transparency in a closed lambda-shaped four-level system

A quasi-lambda four-level system shows both electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT). In addition to an optical coupling field and a probing field, there is a radio field which interacts with two excited state hyperfine levels of the quasi-lambda four-level system consisting of two excited state hyperfine levels and two ground state hyperfine levels. If a driving field which interacts with two ground state hyperfine levels is introduced, the quasi-lambda four-level system is modified to a closed-lambda four-level system. The behaviors of the driving field and radio field are studied in this paper and it is seen that the occurence of EIA or EIT and the whole probing properties are controlled by the Rabi frequencies of both driving field and radio field.