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Electromagnetic induced transparency in the Doppler broadened cascade transition with multiple excited levels

A theoretical model using the density matrix approach has been presented to show the influence of multiple excited states on electromagnetically induced transparency (EIT) in a cascade-type Doppler broadened medium. A five-level system has been considered that is a simple case of the 87Rb atom. In a room temperature vapour, when the Doppler broadening is comparable with hyperfine splitting in the middle states, there is a strong reduction in EIT. By performing the thermal averaging in the five-level Doppler broadened system, we observe an asymmetric transparency that has already been shown in most of the experimental work.