Interfacial scattering and microparticle resonances in random media.
Item
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Title
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Interfacial scattering and microparticle resonances in random media.
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Identifier
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AAI9405548
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identifier
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9405548
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Creator
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Li, Jiang Hong.
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Contributor
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Adviser: Azriel Z. Genack
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Date
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1993
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter | Physics, Optics
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Abstract
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A quantitative description of wave propagation in random media is presented in this thesis. It provides a diffusion model for both static and dynamic transport and makes connection between them. In order to achieve this, we must incorporate interfacial scattering into diffusion model and understand the influence of microparticle resonances. A diffusion model utilizing a minimum number of parameters is established to give a self-consistent description of transport. The model incorporates internal reflection and randomization processes at the sample interfaces. The model is in excellent agreement with a variety of independent optical measurements, including total transmission, surface intensity profiles and transit time distribution. Internal reflection and surface penetration depth are varied independently in these measurements. The transition from ballistic to diffusive transport is found in measurements of transmission. We find that the diffusion model does not adequately describe measurements of the intensity profiles in reflection. We also apply the diffusion model to describe the underlying wave nature of propagation. We demonstrate experimentally a Fourier transform relationship between the angular correlation functions and the spatial intensity distributions. Measurements of the angular correlation functions are in excellent agreement with diffusion model without adjustable parameters. The correlation function within laser speckle and the "memory effect" are treated on the same footing and obtained from a single relationship.;We study microwave propagation in a system of randomly positioned nearly spherical dielectric particles of uniform size. At low filling fraction, resonances in the transport mean free path {dollar}\ell,{dollar} diffusion coefficient D and absorption time are found due to the Mie scattering from individual spheres in this system. We find that the resonances persist up to filling fraction as high as f = 0.4. Resonances structure in transport parameters is 'washed out' at f = 0.56 where the scatterers are closely packed. Utilizing the diffusion model, we determine the transport mean free path {dollar}\ell{dollar} and diffusion coefficient D as a function of frequency and filling fraction of the scatterers. The transport velocity {dollar}\nu\sb{lcub}t{rcub}{dollar} inferred from the relation {dollar}\nu\sb{lcub}t{rcub} = 3D/\ell{dollar} is found to be substantially lower than the phase velocity {dollar}\nu\sb{lcub}p{rcub},{dollar} but resonances in {dollar}\nu\sb{lcub}t{rcub}{dollar} is not convincingly observed.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
