Dynamic light scattering on agitated granular media

Light scattering is an established measuring technique for colloidal and molecular systems to measure the translational and rotational dynamics 1. For granular media, the situation is more difficult because the scattering mechanisms are more system-specific, and the short wavelength is more sensitive to shorter length scales than the investigated grain sizes. We discuss the possibility of using diffusing wave spectroscopy to extract particle velocities and inter-particle distances to obtain diffusion coefficients, as well as the limitations of this technique. The paper compares the analysis of a dense model system of 130 μm polystyrene spheres excited by a voice coil 2 and a piezo agitation 3, 4 setup, and discusses the experimental differences. These experiments have been conducted both on Earth and on board the International Space Station.