Multiple Scattering of Classical Waves in Random Media.
This thesis is concerned with various aspects of the propagation of classical waves such as light in dense, multiple scattering media. Coherent backscattering of waves in uncorrelated media is studied using a photon Green's function technique. The vector nature of light allows for the study of the effects of broken time-reversal (T) and parity (P) symmetries on the coherent backscattering line shapes. These symmetries are broken by Faraday rotation and natural optical activity, which result in the suppression of the coherent peak in certain polarization channels. Faraday rotation suppresses the peak in the helicity-preserving channel, for which the incident and scattered waves are related by time-reversal. Optical activity suppresses the opposite-helicity channel, for which incident and reflected waves are related by parity. A transport theory of waves for the more general case of correlated scattering media is developed. The dependence of the multiply scattered intensity and field autocorrelation function on the structure factor of the medium is shown. Multiply scattered waves are characterized by diffusive propagation over sufficiently long length scales. Over shorter distances, however, the propagation becomes increasingly ballistic in nature. This leads to a remarkable persistence of the incident circular polarization of multiply scattered light. The transport theory developed here describes the crossover between ballistic and diffusive transport, and demonstrates that the non-diffusive modes of propagation depend sensitively on the structure of the scattering medium. This is explicitly demonstrated for the case of a medium composed of hard spheres. Moreover, it is shown that the multiply scattered light can be used to completely characterize the structure factor of the scattering medium.
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- Physics: Condensed Matter; Physics: General; Physics: Optics