Fundamental absorption bandwidth to thickness limit for transparent homogeneous layers

TL;DR

This paper establishes a universal fundamental limit on the absorption bandwidth to thickness ratio for transparent homogeneous layers, extending previous metal-backed layer results using Kramers-Kronig relations and validating with simulations.

Contribution

It introduces a new fundamental relationship for non metal-backed layers based on Kramers-Kronig relations, broadening the understanding of absorption limits.

Findings

Derived a universal bandwidth-thickness limit for transparent layers

Validated the theory with transfer matrix calculations

Confirmed results with electromagnetic metamaterial simulations

Abstract

Past work has considered the analytic properties of the reflection coefficient for a metal-backed slab. The primary result established a fundamental relationship for the minimal layer thickness to bandwidth ratio achievable for an absorber. There has yet to be establishment of a similar relationship for non metal-backed layers, and here we present the universal result based on the Kramers-Kronig relations. Our theory is validated with transfer matrix calculations of homogeneous materials, and full-wave numerical simulations of electromagnetic metamaterials. Our results place more general fundamental limits on absorbers and thus will be important for both fundamental and applied studies.