Diffusing wave spectroscopy in dynamically heterogeneous random media

Abstract

We present a theoretical analysis of temporal autocorrelation functions of multiply scattered light in turbid dynamically heterogenous random media. Particular geometries of planar slab and cylindrical capillary inserted in an otherwise macroscopically homogeneous medium are considered. Analytical expressions for time autocorrelation functions of depolarized scattered electric field measured at the sample surface are derived assuming that scatterers dynamics inside dynamically heterogeneous region differs from that in surrounding medium. We show that space resolved measurements of the temporal autocorrelation function of multiply scattered light at the sample surface provide information on spatially heterogeneous particle dynamics inside the sample and allows one to image hidden dynamic inclusion under conditions of no static scattering contrast. Spatial contrast in this case is purely dynamic and can be provided by different particle sizes as well as by different types of particle dynamics inside the inclusion and in background medium. The limitations of presented theoretical approach are outlined. Finally, we estimate the performance of the imaging technique based on the considered theory.