  On the basis of general theoretical results developed previously in JETP 112,
246 (2011) we analyze the atomic polarization created by weak monochromatic
light in an optically thick, dense and cold atomic ensemble. We show that the
amplitude of the polarization averaged over a uniform random atomic
distribution decreases exponentially beyond the boundary regions. The phase of
this polarization increases linearly with increasing penetration into the
medium. On these grounds, we determine numerically the wavelength of the light
in the dense atomic medium, its extinction coefficient, and the complex
refractive index and dielectric constant of the medium. The dispersion of the
permittivity is investigated for different atomic densities. It is shown that
for dense clouds, the real part of the permittivity is negative in some
spectral domains.
