Third-order optical nonlinear properties of polymers.
Item
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Title
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Third-order optical nonlinear properties of polymers.
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Identifier
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AAI9119694
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identifier
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9119694
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Creator
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Yang, Lina.
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Contributor
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Co-Advisers: R. R. Alfano | R. Dorsinville
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Date
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1991
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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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Engineering, Electronics and Electrical | Engineering, Materials Science | Physics, Optics
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Abstract
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The development of polymers as nonlinear optical materials coincide with a renewed interest in the field of nonlinear optics, and its applications for the future photonic devices. Large nonresonant susceptibilities, fast electronic responses, and ease of processing make polymers one of the best candidates for the applications.;This thesis describes the study of the third order optical nonlinear properties in polymers. The studies have been focused on two classes of conjugated polymers: the {dollar}\pi{dollar}-electron system and the {dollar}\sigma{dollar}-electron system. Important parameters which fully characterize the nonlinearities of materials, such as magnitude, response time, and the sign of {dollar}\chi\sp{lcub}(3){rcub}{dollar} have been measured. Various mechanisms responsible for the observed nonlinearities have also been investigated.;The thesis consists of twelve chapters. The first two chapters provide an overview of the fundamental aspects of nonlinear optics, optical properties of polymers, and the experimental techniques, apparatus which can be used to investigate the third order optical nonlinearities of polymers, such as the degenerate four wave mixing and the single beam Z-scan technique.;The {dollar}\pi{dollar}-electron polymer systems are studied in Chapters III to VII. We have investigated the nonlinearities in polyacetylene, polydiacetylene, as well as in a relatively new material-polythiophenes. Most of the work has been concentrated on polythiophenes. For the first time, the spectrum of the nonlinear coefficient {dollar}\chi\sp3{dollar} covering the single photon transition band has been measured in polythiophene. The experimental results show that {dollar}\chi\sp3{dollar} is large ({dollar}>{dollar}10{dollar}\sp{lcub}-9{rcub}{dollar}esu) and fast ({dollar}<{dollar}15ps) above gap. The real part of {dollar}\chi\sp3{dollar} has also been found to be negative at both 532 and 1064 nm. The single photon resonance is responsible for the negative {dollar}\chi\sp3{dollar} at 532 nm, while two photon resonant absorption is responsible for the negative {dollar}\chi\sp3{dollar} at 1064 nm. For the first time, the enhancement of {dollar}\chi\sp{lcub}(3){rcub}{dollar} was observed about photoinduced polaronic bands in polythiophene thin films. Thus, in {dollar}\pi{dollar}-electron systems, {dollar}\chi\sp3{dollar} can be enhanced through electronic contributions ({dollar}\pi{dollar}-electron delocalization) as well as through photo(doping)-induced gap state transitions.;As a class of transparent nonlinear optical materials, {dollar}\sigma{dollar}-conjugated polysilane polymers (Chapter VIII to X) have shown to possess moderate large {dollar}\chi\sp{lcub}(3){rcub}{dollar}(10{dollar}\sp{lcub}-12{rcub}{dollar}esu), the upper limit of the time response has been determined to be {dollar}<{dollar}3ps. The sign of {dollar}\chi\sp{lcub}(3){rcub}{dollar} has been determined to be negative at 532nm and positive at 1064nm. Results implies that two photon absorption to the ultraviolent (UV) state plays an important role in nonlinear response in the visible.;The major conclusions of this thesis work are summarized in Chapter XI. Future research directions are presented in Chapter XII.
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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.
