  We present a Maxwell-Bloch description of the dynamics of a light pulse
propagating through a spatially inhomogeneous system consisting of alternating
layers of EIT media and vacuum. We study the effect of a dynamical modulation
of the EIT control field on the shape of the wave packet: interesting effects
due to the presence of interfaces with group velocity mismatch are found. An
effective description based on a continuity equation is developed. Modulation
schemes that can be realized in ultracold atomic samples with standard
experimental techniques are proposed and discussed.
