Localização de Anderson da Luz: forte dependência com ângulo de incidência

Abstract

Anderson localization of light in 3D (true Anderson localization) is an open research frontier in science that shows prospects of completely new optical phenomena, which might one day result in important photonics devices. However, direct observation of localization has shown to be difficult and elusive. Instead, we propose a strategy of observing the phase transition to localization by means of a set of specifically designed experiments. We demonstrate that the outcome of these experiments is completely different than expected in the diffusive regime and can be explained by the onset of localization. This work 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 anomalous behavior 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.