Current Search: Cirloganu, Claudiu (x)
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Title
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EXPERIMENTAL AND THEORETICAL APPROACHES TO CHARACTERIZATION OF ELECTRONIC NONLINEARITIES IN DIRECT-GAP SEMICONDUCTORS.
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Creator
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Cirloganu, Claudiu, Van Stryland, Eric, University of Central Florida
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Abstract / Description
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The general goal of this dissertation is to provide a comprehensive description of the limitations of established theories on bound electronic nonlinearities in direct-gap semiconductors by performing various experiments on wide and narrow bandgap semiconductors along with developing theoretical models. Nondegenerate two-photon absorption (2PA) is studied in several semiconductors showing orders of magnitude enhancement over the degenerate counterpart. In addition, three-photon absorption ...
Show moreThe general goal of this dissertation is to provide a comprehensive description of the limitations of established theories on bound electronic nonlinearities in direct-gap semiconductors by performing various experiments on wide and narrow bandgap semiconductors along with developing theoretical models. Nondegenerate two-photon absorption (2PA) is studied in several semiconductors showing orders of magnitude enhancement over the degenerate counterpart. In addition, three-photon absorption (3PA) is studied in ZnSe and other semiconductors and a new theory using a Kane 4-band model is developed which fits new data well. Finally, the narrow gap semiconductor InSb is studied with regard to multiphoton absorption, free-carrier nonlinearities and decay mechanisms. The non-degenerate two-photon absorption was investigated in several direct-gap semiconductors with picosecond and femtosecond pulses. Large enhancements in 2PA were demonstrated when employing highly non-degenerate photon pairs and the results were shown to be consistent to a simple 2-parabolic band theory based on a ÂÂ"dressedÂÂ" state approach. The nonlinear refractive index induced in such configurations was also calculated and possible implications of such extreme behavior are discussed. A large number of measurements of 3PA were taken at multiple wavelengths and in several semiconductors. The subsequent analysis has shown that simple 2-band model calculations (based on either perturbative or tunneling approaches) do not adequately describe the experimental trends. A more comprehensive model, based on KaneÂÂ's 4-band theory was developed and we calculate three-photon spectra for zincblende structures within the perturbative framework. We have confirmed the results of our calculations performing a series of Z-scans in semiconductors ZnSe and ZnS, yielding complete experimental three-photon spectra. A systematic approach based on using a large variety of pulse durations was needed to quantify the wealth of nonlinear optical processes in InSb, accessible in the mid-infrared range. Femtosecond pulses provided a lower limit to measurements of the instantaneous effects (absorptive and refractive), while picosecond pulses allowed further characterization of the free-carrier effects, including population dynamics in the high density regime (Auger effects). The model developed permitted us to verify the temperature dependence of free-carrier absorption recently predicted, and to successfully model optical limiting data with longer, nanosecond pulses.
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Date Issued
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2010
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Identifier
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CFE0003401, ucf:48417
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003401
