Electromagnetically Induced Transparency using six level atoms doped in   the crystalline medium
  Using the density matrix theory of interaction between light and matter, and relevant parameters of the relaxation rates for a six-level model, we have shown theoretically the possibility of realizing Electromagnetically Induced Transparency (EIT) and Slow Light effects in Pr(+3 ion) doped YSO crystal. In addition, we have presented a simplified method to analyse EIT effect in such a six level atomic system. Finally, we have demonstrated results of numerical calculation and have compared them with experimental measurements reported recently. 
Hassan Kaatuzian, Sina Mehrabadi, Ahmad Ajdarzadeh Oskouei