Time Resolved Correlation measurements of temporally heterogeneous dynamics

摘要

Time Resolved Correlation (TRC) is a recently introduced light scatteringtechnique that allows to detect and quantify dynamic heterogeneities. Thetechnique is based on the analysis of the temporal evolution of the specklepattern generated by the light scattered by a sample, which is quantified by$c\_I(t,\tau)$, the degree of correlation between speckle images recorded attime $t$ and $t+\tau$. Heterogeneous dynamics results in significantfluctuations of $c\_I(t,\tau)$ with time $t$. We describe how to optimize TRCmeasurements and how to detect and avoid possible artifacts. The statisticalproperties of the fluctuations of $c\_I$ are analyzed by studying theirvariance, probability distribution function, and time autocorrelation function.We show that these quantities are affected by a noise contribution due to thefinite number $N$ of detected speckles. We propose and demonstrate a method tocorrect for the noise contribution, based on a $N\to \infty$ extrapolationscheme. Examples from both homogeneous and heterogeneous dynamics are provided.Connections with recent numerical and analytical works on heterogeneous glassydynamics are briefly discussed.