Absorption-dispersion in a three-level electromagnetically induced transparency medium including near dipole-dipole interaction effects

Dynamical evolution and electromagnetically induced transparency (EIT) is investigated here in a three-level $\lambda$-type atomic system including near-dipole-dipole interaction among atoms. The system is driven by the probe and coupling fields. Exact numerical solutions under steady-state condition are given for the density operator equation to get information about population in various levels and the linear susceptibility of probe-transition. Also, obtained are the closed form expressions for linear and third order non-linear susceptibilities for the probe transition under perturbation approximation.