Anderson localization of light: Strong dependence with incident angle

TL;DR

This study investigates how the incident angle affects light transport and localization in a disordered medium of core-shell nanoparticles, revealing angle-dependent conductance, absorption, and non-reciprocal propagation phenomena.

Contribution

It introduces a novel analysis of angle-dependent localization effects and non-reciprocal light propagation in strongly disordered optical media.

Findings

Optical conductance decreases with increasing incident angle.

Absorption near the input border increases with incident angle.

Non-reciprocal propagation indicates mirror-symmetry breaking.

Abstract

This paper studies the transport of light for different incidence angles in a strongly disordered optical medium composed by core-shell nanoparticles (TiO2@Silica) suspended in ethanol solution. A decrease of optical conductance and an increase of absorption near the input border are reported when the incidence angle is increased. We associated this phenomenon to an increase of the density of localized states (localization increase) near the input border, which could be explained by a large increase of internal reflection with the incidence angle, which in turn would be a direct consequence of the enhancement of the effective refractive index near the input border by localization itself. The specular reflection, measured for the photons that enter the sample, is considerably lower than the effective internal reflection undergone by the coherently backscattered photons in the exact opposite direction, indicating a non-reciprocal propagation of light (mirror-symmetry breaking). This study represents a novel approach in order to understand the complex physics involved in a strongly disordered optical medium at the critical regime of approaching localization.