Perfect interference-less absorption at infrared frequencies by a van der Waal's crystal

TL;DR

This paper demonstrates that perfect infrared absorption can be achieved using naturally anisotropic materials like hexagonal boron nitride without interference effects, simplifying design for optical applications.

Contribution

It introduces a novel approach to perfect absorption utilizing intrinsic material properties, eliminating the need for complex metamaterials or interference-based methods.

Findings

Achieved perfect absorption with hBN in the mid-infrared range

Demonstrated theoretical and experimental validation

Applicable to various crystal structures beyond hBN

Abstract

Traditionally, efforts to achieve perfect absorption have required the use of complicated metamaterial-based structures as well as relying on destructive interference to eliminate back reflections. Here, we have demonstrated both theoretically and experimentally that such perfect absorption can be achieved using a naturally occurring material, hexagonal boron nitride (hBN) due to its high optical anisotropy without the requirement of interference effects to absorb the incident field. This effect was observed for p-polarized light within the mid-infrared spectral range, and we provide the full theory describing the origin of the perfect absorption as well as the methodology for achieving this effect with other materials. Furthermore, while this is reported for the uniaxial crystal hBN, this is equally applicable to biaxial crystals and more complicated crystal structures. Interference-less absorption is of fundamental interest to the field of optics; moreover, such materials may provide additional layers of flexibility in the design of frequency selective surfaces, absorbing coatings and sensing devices operating in the infrared.