Speckle-visibility spectroscopy: A tool to study time-varying dynamics

TL;DR

Speckle-visibility spectroscopy is a novel dynamic light scattering method that uses speckle pattern variance to study time-varying motion of scattering sites, especially useful for non-stationary samples.

Contribution

This paper introduces a simplified multispeckle technique based on speckle visibility, enabling analysis of non-stationary dynamics in scattering samples.

Findings

Effective for samples with changing dynamics

Applicable to soft-glassy materials and biological tissues

Validated with colloidal suspension and foam

Abstract

We describe a multispeckle dynamic light scattering technique capable of resolving the motion of scattering sites in cases that this motion changes systematically with time. The method is based on the visibility of the speckle pattern formed by the scattered light as detected by a single exposure of a digital camera. Whereas previous multispeckle methods rely on correlations between images, here the connection with scattering site dynamics is made more simply in terms of the variance of intensity among the pixels of the camera for the specified exposure duration. The essence is that the speckle pattern is more visible, i.e. the variance of detected intensity levels is greater, when the dynamics of the scattering site motion is slow compared to the exposure time of the camera. The theory for analyzing the moments of the spatial intensity distribution in terms of the electric field autocorrelation is presented. It is demonstrated for two well-understood samples, a colloidal suspension of Brownian particles and a coarsening foam, where the dynamics can be treated as stationary. However, the method is particularly appropriate for samples in which the dynamics vary with time, either slowly or rapidly, limited only by the exposure time fidelity of the camera. Potential applications range from soft-glassy materials, to granular avalanches, to flowmetry of living tissue.