Electromagnetically induced transparency in multi-level cascade scheme   of cold rubidium atoms
  We report an experimental investigation of electromagnetically induced transparency in a multi-level cascade system of cold atoms. The absorption spectral profiles of the probe light in the multi-level cascade system were observed in cold Rb-85 atoms confined in a magneto-optical trap, and the dependence of the spectral profile on the intensity of the coupling laser was investigated. The experimental measurements agree with the theoretical calculations based on the density matrix equations of the rubidium cascade system. 
J. Wang, L. B. Kong, K. J. Jiang, K. Li, X. H. Tu, H. W. Xiong, Yifu   Zhu, M. S. Zhan