Correlations between reflected and transmitted intensity patterns emerging from opaque disordered media

TL;DR

This paper demonstrates experimentally that reflected and transmitted speckle patterns from opaque scattering media are correlated, revealing that information persists through multiple scattering and can be used for non-invasive light control.

Contribution

It provides the first experimental evidence of correlations between reflection and transmission in thick disordered media, enabling new control methods without feedback.

Findings

Reflected and transmitted speckle patterns are correlated even in thick media.

Information about transmitted light can be inferred from reflected speckle.

Correlations enable non-invasive control of transmitted light.

Abstract

The propagation of monochromatic light through a scattering medium produces speckle patterns in reflection and transmission, and the apparent randomness of these patterns prevents direct imaging through thick turbid media. Yet, since elastic multiple scattering is fundamentally a linear and deterministic process, information is not lost but distributed among many degrees of freedom that can be resolved and manipulated. Here we demonstrate experimentally that the reflected and transmitted speckle patterns are correlated, even for opaque media with thickness much larger than the transport mean free path, proving that information survives the multiple scattering process and can be recovered. The existence of mutual information between the two sides of a scattering medium opens up new possibilities for the control of transmitted light without any feedback from the target side, but using only information gathered from the reflected speckle.