  We present a theoretical model, using density matrix approach, to study the
effect of weak as well as strong probe field on the optical properties of an
inhomogeneously broadened multilevel V-system of the $^{87}$Rb D2 line. We
consider the case of stationary as well as moving atoms and perform thermal
averaging at room temperature. The presence of multiple excited states results
in asymmetric absorption and dispersion profiles. In the weak probe regime, we
observe the partial transparency window due to the constructive interference
occurs between transition pathways at the line center. In a room temperature
vapour, we obtain an increased linewidth of the transparency window and steep
positive dispersion. For a strong probe regime, the transparency window with
normal dispersion switches to enhanced absorption with anomalous dispersion at
the line center. Here, we show how the electromagnetically induced transparency
(EIT) depends on the polarizations of the applied fields. We also discuss the
transient behaviour of our system which agrees well with the corresponding
absorption and dispersion profiles. This study may help to understand optical
switching and controllability of group velocity.
