Experimental observation of Berreman modes in uniaxial anisotropic nanoporous alumina film on aluminium substrate

TL;DR

This study experimentally and numerically demonstrates the excitation of Berreman modes in a uniaxial nanoporous alumina film on aluminum, revealing potential for mid-infrared applications like sensors and thermal management.

Contribution

First experimental observation and numerical verification of Berreman modes in nanoporous alumina on aluminum, highlighting a scalable system for mid-infrared applications.

Findings

Minimum reflection for p-polarized light at specific wavelengths

Maximum reflection for s-polarized light observed

Field confinement near the air-dielectric interface

Abstract

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.