Angle-dependence of the frequency correlation in random photonic media: the diffusive regime and its breakdown near localization

TL;DR

This paper investigates how the frequency correlation of light in complex media depends on angle, revealing effects of coherent backscattering and signaling the breakdown of diffusion near localization.

Contribution

It demonstrates the angle dependence of frequency correlations in transmission and reflection, and links coherent backscattering to the breakdown of diffusion near localization.

Findings

Frequency correlation shows pronounced angle dependence.

Coherent backscattering contribution varies with scattering strength.

Breakdown of diffusion theory near localization is indicated.

Abstract

The frequency correlations of light in complex photonic media are of interest as a tool for characterizing the dynamical aspects of light diffusion. We demonstrate here that the frequency correlation shows a pronounced angle dependence both in transmission and in reflection geometries. Using a broadband white light supercontinuum, this angle dependence is characterized and explained theoretically by a combination of propagation effects outside the medium and coherent backscattering. We report a strong dependence of the coherent backscattering contribution on the scattering strength which cannot be explained by the diffusion theory. Our results indicate that coherent backscattering of the frequency correlation forms a sensitive probe for the breakdown of the diffusive regime near localization.