Broad-band coherent backscattering spectroscopy of the interplay between order and disorder in 3D opal photonic crystals

TL;DR

This study uses broad-band coherent backscattering spectroscopy to explore how order and disorder influence light transport in 3D photonic crystals, revealing detailed interactions near the stop gap.

Contribution

It introduces a broad-band measurement approach and a semi-empirical model to analyze backscattering in 3D photonic crystals, enhancing understanding of their optical properties.

Findings

Backscatter cones around the stop gap are well modeled by diffusion theory.

Significant variations in mean free path and cone enhancement are observed near the stop band.

The semi-empirical three-gap model accurately describes the experimental data.

Abstract

We present an investigation of coherent backscattering of light that is multiple scattered by a photonic crystal by using a broad-band technique. The results significantly extend on previous backscattering measurements on photonic crystals by simultaneously accessing a large frequency and angular range. Backscatter cones around the stop gap are successfully modelled with diffusion theory for a random medium. Strong variations of the apparent mean free path and the cone enhancement are observed around the stop band. The variations of the mean free path are described by a semi-empirical three-gap model including band structure effects on the internal reflection and penetration depth. A good match between theory and experiment is obtained without the need of additional contributions of group velocity or density of states. We argue that the cone enhancement reveals additional information on directional transport properties that are otherwise averaged out in diffuse multiple scattering.