Diffusing-wave spectroscopy of nonergodic media - art. no. 061404

We introduce an elegant method that allows the application of diffusing-wav e spectroscopy (DWS) to nonergodic, solidlike samples. The method is based on the idea that light transmitted through a sandwich of two turbid cells c an be considered ergodic even though only the second cell is ergodic. If ab sorption and/or leakage of tight take place at the interface between the ce lls, we establish a so-called "multiplication rule," which relates the inte nsity 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 exp eriments using colloidal gels as model nonergodic media. Our experimental d ata are consistent with the theoretical predictions, allowing quantitative characterization of nonergodic media and demonstrating the validity of the proposed technique.