Electromagnetically induced absorption in Rb atoms with circular polarization of laser beams: Effects of neighboring transitions

We have studied the effects of neighboring transitions on electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT) in the D2 transition line in Rb atoms with respect to the same circular polarization configurations (a+ - a+) of coupling and probe lasers. Spectra for the open Fg = 2-+ Fe = 2 transition of 87Rb and the Fg = 3-+ Fe = 2 and 3 transitions of 85Rb exhibit EIA, resulting from the neighboring effect of Fg = 2-+ Fe = 3 and Fg = 3-+ Fe = 4 transitions, respectively. In contrast, EIT is observed for the open Fg = 2-+ Fe = 1 transition of 87Rb, which indicates greater hyperfine energy splittings of 87Rb and weaker neighboring effects than those of 85Rb. Based on the theoretical results, we can confirm that EIT in the case of Fg > Fe for 87Rb for the same circular polarization configuration transforms into EIA due to the magnitude of the neighboring effects with a decrease in the hyperfine energy splittings.