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The evaluation of conventional light-scattering experiments in turbid media is often highly complicated because of the presence of multiple scattering contributions. The three-dimensional (3-D) cross-correlation method presented provides an effective and handy method to suppress the influence of multiply scattered light. As the time dependence of the 3-D cross-correlation function is determined solely by the singly scattered light, the evaluation of the decay constant yields reliable values for the effective diffusion coefficient and the hydrodynamic particle size of the suspended particles. Furthermore, analysis of the amplitude of the 3-D cross-correlation function permits the determination of the differential scattering cross section even for highly turbid suspensions.

The space-time correlation function of the intensity of light scattered off a medium with a constant velocity gradient has been calculated. One property, in particular, of this correlation function, which may be referred to as speckle motion or speckle flow, enables an experimental determination of the tensor components of the velocity gradient. Influence of Brownian motion and finite scattering volume are estimated. Experimental results, obtained at a tube flow, are shown to be in accordance with the theory.