Electromagnetically induced absorption

A large increase in atomic absorption due to coherent interaction with resonant radiation is predicted for a closed transition between two degenerate atomic levels verifying $0<\mathrm{}{F}_g<F_e{(F}_g$ and $F_e$ are the total angular momentum of the ground and the excited levels, respectively). In good agreement with the theoretical prediction, a total absorption enhancement by a factor 1.7 was obtained on the $D_2$ line of ${}^{85}\mathrm{Rb}\mathrm{}$ in a vapor cell experiment.