Light transport through disordered media exhibits various behaviors depending on the disorder strength. Insight is gained on how light interacts with the medium by investigating the statistical properties of the scattering matrix. Historical results were obtained by considering non-resonant scattering systems. In this work, we present innovative numerical results using a microscopic description of systems entirely made out of point-like resonant scatterers. We access light transmission and energy storage in these systems. Their resonant behavior engenders strong frequency-dependent response to incident wavefronts which allows switching between transport regimes while fixing the scatterers density. We show that light can travel ballistically, diffusively or be localized, by only tuning the incident field frequency. The velocity of energy is affected by the resonant behavior of the scatterers, becoming dependent on the disorder strength. Our results suggest benefits in using fully resonant systems for applications aiming at maximal energy deposition within strongly scattering media.
When light passes through a disordered medium, its wavefront is scrambled, resulting in a seemingly random speckle pattern. In the multiple scattering regime, it is commonly assumed that this randomization removes any memory about the original wavefront, effectively destroying all its information content. But as linear elastic scattering is a purely deterministic process, information is not destroyed, but just hidden and redistributed within these patterns. We present an experimental observation of the correlations between reflected and transmitted speckle patterns, which indicate that information can survive even very strong scattering. We show that there are two distinct contributions to the correlation function - a narrow positive peak and a broad negative dip, which depend in a different way on the system parameters. We study the dependence of this correlation on the thickness of the scattering medium and the mean free path of the light in the sample, probing different regimes from ballistic to diffusive scattering. We propose an experimental procedure, based on the ghost imaging technique, that allows to use this correlation for imaging of the objects hidden behind the scattering media.
We study the fluctuations of light multiply scattered by particles under Brownian motion in a fluid. We focus
on the behavior of the time correlation function of the field in the non-diffusive regime, in both transmission
and reflection. In transmission through optically thin systems, an extended Diffusing-Wave Spectroscopy (DWS)
model based on the Radiative Transfer Equation (RTE) is described, which predicts substantial deviations from
the standard DWS theory. For backscattered light, experiments using unpolarized light show a clear dependence
on the anisotropy factor g. This behavior is not described by the standard DWS theory. A good agreement with
the data is obtained using the RTE model, and an approximate model in which the path-length distribution of
the standard DWS is corrected by a prefactor which depends on the level of anisotropy. These results should
have broad applications in diffuse-light biomedical imaging, and in the field of soft-materials and biomaterials
analysis.
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