Hidden Black: Coherent Enhancement of Absorption in Strongly-scattering Media

TL;DR

This paper demonstrates that by optimizing the input electromagnetic field, one can significantly enhance absorption in strongly scattering media, turning weakly absorbing materials into highly absorbing ones across their bandwidth.

Contribution

It introduces a method to optimize electromagnetic input fields to greatly increase absorption in strongly scattering media, supported by theoretical and numerical analysis.

Findings

Absorption can be increased from a few percent to over 99%.

Reflectivity can be suppressed by a factor related to scattering and absorption parameters.

Enhanced absorption is achievable even for buried weak absorbers in scattering media.

Abstract

We show that a weakly absorbing, strongly scattering (white) medium can be made very strongly absorbing at any frequency within its strong-scattering bandwidth by optimizing the input electromagnetic field. For uniform absorption, results from random matrix theory imply that the reflectivity of the medium can be suppressed by a factor ~(l_a/lN^2), where N is the number of incident channels and l,l_a are the elastic and absorption mean free paths respectively. It is thus possible to increase absorption from a few percent to > 99%. For a localized weak absorber buried in a non-absorbing scattering medium, we find a large but bounded enhancement.