1. Introduction: mesoscopic physics 2. Wave equations in random media 3. Perturbation theory 4. Probability of quantum diffusion 5. Properties of the diffusion equation 6. Dephasing 7. Electronic transport 8. Coherent backscattering of light 9. Diffusing wave spectroscopy 10. Spectral properties of disordered metals 11. Universal conductance fluctuations 12. Correlations of speckle patterns 13. Interactions and diffusion 14. Orbital magnetism and persistent currents 15. Formulary Index.

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Mesoscopic Physics of Electrons and Photons

Photon Upmanship: Why Multiphoton Imaging Is More than a Gimmick

As one increases the concentration of a colloidal suspension, the system exhibits a dramatic increase in viscosity. Beyond a certain concentration, the system is said to be a colloidal glass; structurally, the system resembles a liquid, yet motions within the suspension are slow enough that it can be considered essentially frozen. For several decades, colloids have served as a valuable model system for understanding the glass transition in molecular systems. The spatial and temporal scales involved allow these systems to be studied by a wide variety of experimental techniques. The focus of this review is the current state of understanding of the colloidal glass transition, with an emphasis on experimental observations. A brief introduction is given to important experimental techniques used to study the glass transition in colloids. We describe features of colloidal systems near and in glassy states, including increases in viscosity and relaxation times, dynamical heterogeneity and ageing, among others. We also compare and contrast the glass transition in colloids to that in molecular liquids. Other glassy systems are briefly discussed, as well as recently developed synthesis techniques that will keep these systems rich with interesting physics for years to come.

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The Physics of the Colloidal Glass Transition

The diffusion of correlation is used to detect, localize, and characterize dynamical and optical spatial inhomogeneities in turbid media and is accurately modeled by a correlation diffusion equation. We demonstrate experimentally and with Monte Carlo simulations that the transport of correlation can be viewed as a correlation wave {analogous to a diffuse photon-density wave [Phys. Today48, 34 (1995)]} that propagates spherically outward from sources and scatters from macroscopic spatial variations in dynamical and/or optical properties. We demonstrate the utility of inverse scattering algorithms for reconstructing images of the spatially varying dynamical properties of turbid media. The biomedical applicability of this diffuse correlation probe is illustrated in studies of the depth of burned tissues.

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Spatially varying dynamical properties of turbid media probed with diffusing temporal light correlation

Concentrated colloidal suspensions are a well-tested model system which has a glass transition. Colloids are suspensions of small solid particles in a liquid, and exhibit glassy behavior when the particle concentration is high; the particles are roughly analogous to individual molecules in a traditional glass. Because the particle size can be large (100 nm - 1000 nm), these samples can be studied with a variety of optical techniques including microscopy and dynamic light scattering. Here we review the phenomena associated with the colloidal glass transition, and in particular discuss observations of spatial and temporally heterogeneous dynamics within colloidal samples near the glass transition. Although this Chapter focuses primarily on results from hard-sphere-like colloidal particles, we also discuss other colloidal systems with attractive or soft repulsive interactions.

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Glassy dynamics and dynamical heterogeneity in colloids

Dynamic light scattering is extended to optically thick (opaque) media which exhibit a very high degree of multiple scattering This new technique, called diffusing-wave spectroscopy (DWS), exploits the diffusive nature of the transport of light in strongly scattering media to relate the temporal fluctuations of the multiply scattered light to the motion of the scatterers A simple theory of DWS, based on the diffusion approximation for the transport of light, is developed to calculate the temporal electric field autocorrelation functions of the multiply scattered light Two important scattering geometries are treated : transmission and backscattering The theory is compared to experimental measurements of Brownian motion of submicron-diameter polystyrene spheres in aqueous suspension The agreement between theory and experiment is excellent The limitations of the photon diffusion approximation and the polarization dependence of the autocorrelation functions are discussed for the backscattering measurements The effects of absorption of light and particle polydispersity are also incorporated into the theory and verified experimentally It is also shown how DWS can be used to obtain information about the mean size of the particles which scatter light

https://hal.archives-ouvertes.fr/jpa-00212514/document

Diffusing-wave spectroscopy : dynamic light scattering in the multiple scattering limit

We discuss the entension of dynamic light scattering to very strongly scattering media, where the propagation of light is described by the diffusion approximation, allowing the distribution of the light paths to be determined. The temporal evolution of the length of each of these paths, due to the dynamics of the scattering medium, is calculated, and an expression for the temporal autocorrelation function of the intensity fluctuations of the scattered light is obtained. This relates the measured decay of the autocor-relation function to the dynamics of the medium. This technique is called diffusing wave spectroscopy (DWS). To extend its utility, we consider the consequences of interactions between the scattering particles on the light scattering. To illustrate its applications, we consider several examples of new physics that can be investigated using DWS. We study the transient nature of hydrodynamic interactions between a particle and the surrounding fluid. We are able to probe the decay of the velocity correlation function of the particles, and we demonstrate its algebraic decay, with a t−3/2 time dependence. We also show that the time-dependent self diffusion coefficient exhibits an unexpected scaling behavior, whereby all the data, from samples of different volume fractions, can be scaled onto a single curve. Finally, we discuss the applications of DWS to the study of the dynamics of foams, and show how it can be used to probe the rearrangement of the bubbles within the foam as they coarsen.

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J.X. Zhu

Papers

Diffusing-wave spectroscopy : dynamic light scattering in the multiple scattering limit

Diffusing-Wave Spectroscopy: The Technique and Some Applications