  In this article, we demonstrate experimentally and verified numerically the
excitation of Berreman modes that propagate in a dielectric film of uniaxial
anisotropic nanoporous alumina grown on an aluminium substrate. It is an
air-dielectric-metal asymmetric polaritonic system with a real part of the
effective permittivity having a value near zero. The modes are excited at a
wavelength lower than the epsilon near zero wavelength region. Minimum
reflection is observed for the mid-infrared p-polarized light, while maximum
reflection is observed for the s-polarized light. The experimental results are
numerically reproduced for both p- and s-polarized light and confirm the
Berreman modes excitation in the system. At the exciting wavelength, the field
is confined in the dielectric region near the air-dielectric interface. The
reported system is straightforward and could be easily fabricated over a large
scale and is helpful in a variety of mid-infrared applications such as thermal
management systems, sensors, passive radiative cooling devices, non-linear
applications, and terahertz frequency generation.
