Diamond-like semiconductors are interesting materials to study due to the wide variety of technologically useful properties that these materials possess. These normal valence compounds have structures that are based on that of diamond, either the cubic or hexagonal polymorph. Though there are a finite number of possible compounds, due to isovalent and isoelectronic principles, the total number of potential compounds is quite extensive. Quaternary diamond-like semiconductors provide a unique opportunity, because much of the previous research has focused on binary and ternary systems leaving quaternary systems, relatively unexplored. Additionally, quaternary diamond-like semiconductors possess a greater degree of compositional flexibility compared to binary and ternary materials, which could result in the ability to more carefully tune desired physical properties. <br>In order to prepare the new materials, Li2ZnGeS4, Li2ZnSnS4, Li2CdGeS4, Li2CdSnS4 and Ag2MnSnS4, several synthetic methods have been employed, including high-temperature solid-state synthesis, polychalcogenide flux synthesis and solid-state microwave synthesis. The solid-state microwave synthetic method was itself studied using a number of target systems such as the ternary diamond-like semiconductor, AgInSe2. Additionally, several intermetallic compounds, such as Ag3In, AuIn2 and Bi2Pd were prepared using this procedure. Solid-state microwave synthesis is not as well known as some of the other synthetic methods that were employed in this work possibly due to a lack of understanding of the method, training and equipment. Despite these problems, the method has the potential to save time, energy and cost due to the unique nature of microwave heating. In an attempt to gain a better understanding of this synthetic method and its capabilities, the solid-state microwave synthetic method was used to prepare diamond-like semiconductors and intermetallic compounds. / Bayer School of Natural and Environmental Sciences / Chemistry and Biochemistry / PhD / Dissertation

Conventional step-index silica fibers do not possess a second-order optical nonlinearity due to symmetry concerns. However, through the process of poling, the generation of a frozen-in DC field $E^{DC}$, and in turn, a non-zero second-order nonlinearity $\chi^{(2)} = 3\chi^{(3)}E^{DC}$, can be created in optical fibers. In this thesis, I measure the individual $\chi^{(2)}$ tensor elements of birefringent periodically poled fiber via second-harmonic generation and sum-frequency generation experiments. The symmetry of the $\chi^{(2)}$ tensor is consistent with that of the $\chi^{(3)}$ for isotropic media. This is the first study that characterizes all the $\chi^{(2)}$ tensor elements in birefringent poled fiber. Furthermore, I investigate the intermix of the $\chi^{(2)}$ tensor elements by twisting the fiber, which results in the generation of new second-harmonic signals not observed in untwisted fiber. The conversion efficiencies and spectral positions of these new signals can be varied by twisting the fiber.

The three wave mixing process was modeled in GaAs:AlGaAs superlattices using two new modeling tools that were developed in the course of this work: A 2D beam propagation tool for optimizing quasi-phase matching gratings, and a 1D iterative beam propagation tool for determining the output powers and threshold of optical parametric oscillators of arbitrary geometries. The 2D tool predicts close to 80% enhancement of conversion e ciency by phase matching near 800 nm compared to 775 nm, which was the originally designed operation wavelength. The model also predicts resonant behaviour for an abrupt grating pro le. The 1D tool was used to determine the threshold conditions for para- metric oscillation for di erent geometries. The performances of di erent phase matching approaches in AlGaAs were quantitatively compared. The model also indicated the need for pulsed operation to achieve reasonably low threshold powers in AlGaAs waveguides.

Conventional step-index silica fibers do not possess a second-order optical nonlinearity due to symmetry concerns. However, through the process of poling, the generation of a frozen-in DC field $E^{DC}$, and in turn, a non-zero second-order nonlinearity $\chi^{(2)} = 3\chi^{(3)}E^{DC}$, can be created in optical fibers. In this thesis, I measure the individual $\chi^{(2)}$ tensor elements of birefringent periodically poled fiber via second-harmonic generation and sum-frequency generation experiments. The symmetry of the $\chi^{(2)}$ tensor is consistent with that of the $\chi^{(3)}$ for isotropic media. This is the first study that characterizes all the $\chi^{(2)}$ tensor elements in birefringent poled fiber. Furthermore, I investigate the intermix of the $\chi^{(2)}$ tensor elements by twisting the fiber, which results in the generation of new second-harmonic signals not observed in untwisted fiber. The conversion efficiencies and spectral positions of these new signals can be varied by twisting the fiber.

The three wave mixing process was modeled in GaAs:AlGaAs superlattices using two new modeling tools that were developed in the course of this work: A 2D beam propagation tool for optimizing quasi-phase matching gratings, and a 1D iterative beam propagation tool for determining the output powers and threshold of optical parametric oscillators of arbitrary geometries. The 2D tool predicts close to 80% enhancement of conversion e ciency by phase matching near 800 nm compared to 775 nm, which was the originally designed operation wavelength. The model also predicts resonant behaviour for an abrupt grating pro le. The 1D tool was used to determine the threshold conditions for para- metric oscillation for di erent geometries. The performances of di erent phase matching approaches in AlGaAs were quantitatively compared. The model also indicated the need for pulsed operation to achieve reasonably low threshold powers in AlGaAs waveguides.

Collagen is an important structural protein in living organisms and plays an indispensable role in connecting cells and tissues, such as in musculature, bone, and ligament. The stability and conformation of collagen are, however, strongly influenced by ambient temperature and constitutes an interesting subject of study. Thermally induced conformation change of collagen has been investigated by techniques such as differential scanning calorimetry (DSC) and second harmonic generation. DSC is a powerful method in uncovered important thermal dynamics properties including phase change, enthalpy, and thermal stability of the collagen. However, due to its collective nature, no localized information can be found. For comparison, second harmonic generation, which reflects structural symmetry, can be combined with laser scanning microscopy to investigate localized variation. It has been shown in previous studies that the thermal stability of collagen is strongly influenced by the water content within collagen. For comparison, we are investigating the conformational change of collagen under a vacuum stat with second harmonic microscopy so as to isolate environmental effects, particularly those from water and oxygen. In this way, we have found the conformational change of collagen takes place at a much higher temperature and activation energy. Additionally, the high spatial resolution achieved also allows many further possibilities.

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Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 72-82). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2010. / Committee Chair: Rick Trebino; Committee Member: Ahmet Erbil; Committee Member: John Buck; Committee Member: Stephen Ralph; Committee Member: Zhigang Jiang. Part of the SMARTech Electronic Thesis and Dissertation Collection.