nth-order photon correlation spectroscopy: From theory and instrumentation to intermittency in granular flows

This dissertation proceeds in two steps. It first extends traditional dynamic light scattering techniques by introducing intensity correlation of higher-order. It then investigates the intermittency transition in granular flow using this newly developed formalism.; The intermittency transition occurs when a granular system relaxes intermittently despite being driven continuously. It is of practical importance as granular materials play a crucial role in geophysical phenomena and industry. It is of theoretical importance as similar behavior has been observed other systems such as colloidal glasses and foams near the onset of jamming. In order to study such flows we need to simultaneously capture the fast single-grain dynamics and the much slower collective intermittency. For this, we turn to dynamic light scattering techniques. In these techniques, the dynamic properties of the medium are extracted from a second-order quantity, the intensity auto-correlation g(2). This approach is limited to systems where the scattered electric field is a Gaussian random variable, and breaks down when the scattering sites are few or correlated.; We first demonstrate that intensity correlations functions g (n) of higher-order can be used to both detect non-Gaussian scattering processes, and extract information not available in g (2) alone. The g(n) are experimentally measured by a combination of a commercial correlator and a custom-designed digital delay line. This approach is first tested in prototypical experimental situations, then specialized to the study of intermittent dynamics.; We then introduce a model system for the study of granular flows near the intermittency transition, in the form of a granular heap by the steady addition of grains at its top. Using the higher-order light intensity framework we obtain the first continuous picture of granular dynamics across the intermittency transition. We find that microscopic gain dynamics during an avalanche are similar to those in the continuous flow just above the transition. We also find that there is a minimum jamming time, even arbitrarily close to the transition.