Observation of the critical regime near Anderson localization of light

TL;DR

This paper reports experimental evidence of the critical transition from diffusive transport to Anderson localization of light in strongly scattering media, demonstrating deviations from classical diffusion consistent with a phase transition.

Contribution

It provides the first experimental observation of the critical regime near Anderson localization of light in disordered media.

Findings

Deviations from classical diffusion increase as the mean free path decreases.

The results show signatures of a phase transition to localization.

The measurements are not explained by absorption or geometry effects.

Abstract

Diffusive transport is among the most common phenomena in nature [1]. However, as predicted by Anderson [2], diffusion may break down due to interference. This transition from diffusive transport to localization of waves should occur for any type of classical or quantum wave in any media as long as the wavelength becomes comparable to the transport mean free path $\ell^*$ [3]. The signatures of localization and those of absorption, or bound states, can however be similar, such that an unequivocal proof of the existence of wave localization in disordered bulk materials is still lacking. Here we present measurements of time resolved non-classical diffusion of visible light in strongly scattering samples, which cannot be explained by absorption, sample geometry or reduction in transport velocity. Deviations from classical diffusion increase strongly with decreasing $\ell^*$ as expected for a phase transition. This constitutes an experimental realization of the critical regime in the approach to Anderson localization.