Graduation date: 1994

This thesis describes the fabrication and characterization of waveguides in the nonlinear, Raman-active optical crystal potassium gadolinium tungstate (KGW). Ion implantation and femtosecond laser writing techniques are used for the first time to fabricate waveguides in this material. The light ion implanted waveguides using hydrogen ions showed unexpected refractive index increases in the damage regions of approximately 0.3% of the nominal refractive index values for three of the four polarization orientations, with only the highest refractive index polarization exhibiting a refractive index decrease of approximately 0.2%. Waveguides fabricated using high-energy carbon, oxygen and fluorine ion irradiations resulted in strongly confining waveguides with wide amorphous damage regions. Carbon ion irradiation of KGW showed the most promise, with sharp step-like waveguides with a maximum refractive index change of delta-n=0.2 with excellent preservation of the Raman properties in the waveguide core. Microreflectivity measurements on the carbon ion irradiated sample revealed unexpected intermittent refractive index changes in the core region, a feature not detected using standard characterization techniques found in the literature. The oxygen ion irradiation of KGW also generated strongly confining waveguides with a maximum refractive index change of delta-n=0.17, however the Raman performance was shown to be reduced to less than 50% in the waveguide cores. Fluorine ion irradiations of KGW resulted in amorphous regions fabricated in the surface regions, offering promise for masking techniques for creating two-dimensional structures. The waveguides written using femtosecond laser writing processes were used to write buried channel waveguides using compressive stresses to form the waveguide. These waveguides exhibited low-losses down to to 2.0 dB/cm in the telecommunications spectrum, with high coupling efficiency to SMF fiber, and excellent Raman properties in the waveguide core. These channel waveguides also successfully showed SRS generation into the 1.8-1.9 \mu m infrared region using a high power picosecond pump source in the telecommunications band. The use of the microreflectivity and micro-Raman spectroscopy measurement techniques were demonstrated to be valuable characterization tools for each of the fabrication methods.

The present thesis describes a novel photonic crystal platform dubbed the photonic nose, a color-based analogue of the human olfactory system. The platform is founded on a one dimensional photonic crystal architecture known as Bragg stacks, which are fabricated using bottom-up self-assembly approaches. Structural and compositional aspects of this novel class of photonic crystals are established that provide them with functionality and utility. Silicon dioxide, titanium dioxide, tin oxide, clays and zeolites are among the materials incorporated into one-dimensional photonic structures. Retention of materials functionality is demonstrated by vapor and liquid sensing experiments. This class of Bragg stacks displays well defined optical properties that have been thoroughly investigated by use of spectroscopic ellipsometry, as we demonstrate in a chapter dedicated to the technique. Utilizing conventional building blocks comprised of nanostructured silicon and titanium dioxide we discuss various aspects of technique pertaining single layered as well as multilayered films. In terms of practical applications these kinds of Bragg stacks show significant potential in areas such as display and sensors that exploit their vibrant and tunable colors. These colors are an important attribute of photonic crystals with bandgaps in the visible range and in this thesis work we present new approaches for characterizing photonic crystal color using well established methods from the field of color imagery. With this knowhow we have been able to assemble a pixilated array of chemically functionalized Bragg stacks in which each pixel responds differently to vapor phase analytes. The combinatorial response of the entire array enables a unique diagnostic fingerprint of a given analyte vapor as determined from color imagery and multivariate statistical methods of analysis. It was possible to discriminate between ethanol, butanol, hexanol, hexane, octane and decane. We also demonstrate the power of the photonic nose platform by distinguishing different bacteria from a photonic nose color analysis of the complex mixture of vapors in the bacteria culture headspace. Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa could be discriminated based on this technique.

Deuterium (2H) and Nitrogen 14 (14N) NMR spectroscopy were used to investigate the molecular dynamics in one thermotropic and one lyotropic liquid crystal. Quantitative analyses of deuterium spectral densities of motion for three deuteron sites (ring and C-alpha) at two different Larmor frequencies (46 and 61.4MHz) are reported in the smectic A and C* phases of (S)-[4-(2-methylbutyl)phenyl]-4’-octylbiphenyl carboxylate (8BEF5-d15), a partially deuterated smectogen. 2H spectral densities for two deuteron sites on the chain (C1 and C2/C3) at Larmor frequency 61.4MHz and 14N spectral densities for the head group (NH4+) of the molecule decylammonium chloride (DACl) at 28.9MHz are reported in the lamellar phase of a partially deuterated sample, DACl-d11/H2O binary system. The motional model is the small step rotational diffusion for reorientations plus internal rotations in the strong collision limit. In the chiral C* phase of the first molecule, 8BEF5-d15, the helical axes are aligned along the external magnetic field and the deuteron spins appear to relax in a macroscopically uniaxial environment. After including the molecular tilt, the reorientation processes in the SmC* phase are found to have higher activation energies than those in the smectic A phase. Applying the same motional models to the lyotropic molecule DACl-d11, the tumbling motion of the long axis of the molecule in the aggregates is more rigorous in comparison to the molecular spinning motion. The similarity of deuterium spectral densities from the C1 and C2/C3 sites may indicate a relatively rigid unit of C1-C2-C3-C4 in the backbone. / February 2005

This dissertation reports a study of three kinds of liquid crystals using modern solid state NMR techniques: chiral rod-like liquid crystals, bent-core mesogens and disc-like liquid crystals. The properties and structures of liquid crystals are first introduced in Chapter 1. To understand the principles of different NMR phenomena, quantum mechanical theory is adopted to study different nuclear spin interactions and NMR techniques in Chapter 2. In the next part of this dissertation (Chapter 3-6), deuterium NMR methods are used to investigate the dynamics and structures of some liquid crystal phases. This is first done using the spin relaxation study. The parameters obtained from the model simulation can describe the molecular motion and internal dynamics in the fast motion region. Secondly, we investigate the dynamic process of discotic mesophases and unwound smectic C* phase using the line shape simulation study. 2D deuterium NMR exchange experiments are then performed to study the jump process in TGBA* phase and SmC* phase. The above investigation has demonstrated some powerful NMR methods for the dynamic study of liquid crystals. The third part of the dissertation (Chapter 7-9) is concerned with C-13 NMR techniques. After we introduce the quantum theory of different pulse sequences, theoretical models are presented to fit observations such as chemical shifts and dipolar splittings. Moreover high resolution liquid C-13 NMR experiments are introduced to study some bent-core molecules. They are useful to assist the carbon peak assignments of these molecules. The structure and ordering information of liquid crystals can be determined in their mesophases. Finally, a brief summary of the dissertation is given in the last chapter. / October 2007

Includes bibliographical references (p. 155-159).

Thesis (Ph.D.)--Kent State University, 2008. / Title from PDF t.p. (viewed Jan 5, 2010). Advisor: Philip J. Bos. Keywords: liquid crystal, smectic, display, ferroelectric. Includes bibliographical references (p. 190-194).

Thesis (Ph. D.)--Drexel University, 2003. / Includes abstract and vita. Includes bibliographical references (leaves 145-152).

Thesis (M.S.) in Physics--University of Maine, 2002. / Includes vita. Bibliography: leaves 74-77.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 57-58).