  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.
