Spatial coherence of light inside three dimensional media

TL;DR

This paper presents the first direct measurements of light intensity correlations inside disordered media, revealing deviations from theory due to near-field effects and polarization correlations, advancing understanding of bulk speckle phenomena.

Contribution

It introduces a novel method for in situ measurement of bulk speckle properties inside random media using embedded emitters, providing new insights into speckle size and polarization.

Findings

Measured intensity correlations inside disordered media.

Observed deviations from theoretical predictions.

Attributed deviations to near-field and polarization effects.

Abstract

Speckle is maybe the most fundamental interference effect of light in disordered media, giving rise to fascinating physical phenomena and enabling applications in imaging, spectroscopy or cryptography, to name a few. While speckle formed outside a sample is easily measured and analysed, true bulk speckle, as formed inside random media, is difficult to investigate directly due to the obvious issue of physical access. Furthermore, its proper theoretical description poses enormous challenges. Here we report on the first direct measurements of intensity correlations of light inside a disordered medium, using embedded DNA strings decorated with emitters separated by a controlled nanometric distance. Our method provides in situ access to fundamental properties of bulk speckles as their size and polarization degrees of freedom, both of which are found to deviate significantly from theoretical predictions. The deviations are explained, by comparison with rigorous numerical calculations, in terms of correlations among polarization components and non-universal near-field contributions at the nanoscale.