Geometric constraints for the design of diffusing-wave spectroscopy experiments.

Diffusing-wave spectroscopy (DWS) experiments require the choice of suitable sample geometry. We study sample geometries for transmission experiments by performing DWS measurements on a variable thickness cell. The data reveal that DWS works well, giving consistent answers to within 5% when the cell is more than 10 random walk step lengths thick, and that the input geometry is less significant when sample cells are immersed in water than when they are surrounded by air. Further, we see that the applicability of the diffusion approximation depends on the anisotropy of individual scattering events.