Electromagnetically induced transparency and Autler-Townes effect in a generalized Λ-system: A five-level model

We calculate electric susceptibility of a laser-dressed atomic medium. The model adopted in this work refers to the experiment with cold Rb-85 atoms, where the states F' = 1, 2, 3 of the hyperfine manifold 5P(3/2) (F') are strongly coupled with the ground state 5S(1/2) (F = 2), and the coupling is probed by a weak probing field from the other ground-state component 5S(1/2) (F = 3). We present a five-level model in which the states F = 2, 3 and F' = 1, 2, 3 are taken into account, while the non-coupled state F' = 4 is neglected. The model is used as a starting point to reproduce spectral features observed in the absorption of probe light passing through a cold sample of Rb-85 atoms in a magneto-optical trap. Basing on numerical solutions of this model, we have also studied in detail the impact on the probe spectra from the presence of the state F' = 1 to which probing is forbidden by electric-dipole transition, but coupling is allowed [see, e.g., Proc. of SPIE 8770 (2013) 87700Q].