Diffusing-wave spectroscopy of nonergodic media

Abstract

We introduce an elegant method which allows the application of diffusing-wave spectroscopy (DWS) to nonergodic, solidlike samples. The method is based on the idea that light transmitted through a sandwich of two turbid cells can be considered ergodic even though only the second cell is ergodic. If absorption and/or leakage of light take place at the interface between the cells, we establish a so-called "multiplication rule", which relates the intensity autocorrelation function of light transmitted through the double-cell sandwich to the autocorrelation functions of individual cells by a simple multiplication. To test the proposed method, we perform a series of DWS experiments using colloidal gels as model nonergodic media. Our experimental data are consistent with the theoretical predictions, allowing quantitative characterization of nonergodic media and demonstrating the validity of the proposed technique.

Rheology and structural arrest of casein suspensions

“…Since a photon traversing the sample is now scattered from many particles, very small displacements of the many particles along the scattering path give rise to an appreciable phase shift of the detected electric field; DWS thus typically probes the short-time dynamics of a system. We used a commercial DWS apparatus (Rheolab, LS Instruments [28]), in which the two-cell method is implemented to ensure a proper ensemble average of the intensity auto-correlation function [29][30][31]. The measurements were performed at a laser wavelength of 632:8 nm.…”

Measuring Dynamics Of Scattering Centers In The Ocular Fundus

“…Qualitatively, we can associate the long delay times information with the short trajectories of photons. In fact, photons with long trajectories are completely decorrelated at long delay times, thus their contribution to the field autocorrelation function is not significant [4]. Photons with short trajectories consist of the few photons travelling into the retinal layer without reaching the choroidal capillaries.…”

“…Moreover, contribution of different layers can be recovered. According to Scheffold et al [4], long delay time information can be associated with the short trajectories of photons, i.e. superficial layers.…”

Temporal fluctuations of waves in weakly nonlinear disordered media

“…[50][51][52] Recently, the DWS approach has been extended to nonergodic turbid media. 53,54 The above-mentioned, extensive studies of temporal fluctuations of multiple-scattered waves, as well as the numerous application of DWS, are all restricted to linear disordered media. In general, little information is available on the subject of multiple scattering in nonlinear disordered media.…”