Non-stationary space-time correlations in multiply scattered light

Light interacting with disordered media is pervasive, and understanding its specific manifestations is critical for many applications. Here, we reveal a feature in multiple scattering from materials bounded by realistic interfaces. We demonstrate that variations of the statistically non-stationary temporal responses measured in reflection at two different points across the interface are not always independent. Their correlation depends on the spatial separation distance, and it evolves in time in a manner that allows discriminating statistically between bulk and interfacial contributions. These space-time correlations permit a comprehensive characterization of both surface and bulk phenomena in highly scattering media.