PhD, University of Cincinnati, 2014, Arts and Sciences: Physics

The intensity dependent diffraction efficiency of a phase coherent photorefractive (PCP) ZnSe quantum well (QW) is investigated at 80 K in a two-beam four-wave mixing (FWM) configuration using 100 fs laser pulses with a repetition rate of 80 MHz. The observed diffraction efficiencies of the first- and second-order diffracted beam are on the order of 10-3 and 10-5, respectively, revealing nearly no intensity dependence. The first-order diffraction is caused by the PCP effect where the probe-pulse is diffracted due to a long-living incoherent electron density grating in the QW. The second-order diffraction is created by a combination of diffraction processes. For negative probe-pulse delay, the exciton polarization is diffracted at the electron grating twice by a cascade effect. For positive delay, the diffracted signal is modified by the destructive interference with a χ(5) generated signal due to a dynamical screening effect. Model calculations of the signal traces based on the optical Bloch equations considering inhomogeneous broadening of exciton energies are in good agreement with the experimental data. To study the carrier dynamics responsible for the occurrence of the PCP effect, three-beam FWM experiments are carried out. The non-collinear wave-vectors k1, k2 and k3 at central wavelength of 441 nm (~2.81 eV) were resonantly tuned to the heavy-hole exciton transition energy at 20 K. In the FWM experiment the time coincident strong pump pulses k1 and k2 create both an exciton density grating in the QW and an electron-hole pair grating in the GaAs while the delayed weak pulse k3 simultaneously probes the exciton lifetime as well as the electron grating capture time. The model calculations are in good agreement with the experimental results also providing information about the transfer delay of electrons arriving from the substrate to the QW. For negative probe-pulse delay we still observe a diffracted signal due to the long living electron density grating in (open full item for complete abstract)

Committee: Hans Peter Wagner Ph.D. (Committee Chair); Howard Everett Jackson Ph.D. (Committee Member); Rostislav Serota Ph.D. (Committee Member); L.C.R. Wijewardhana Ph.D. (Committee Member) Subjects: Physics

PhD, University of Cincinnati, 2007, Arts and Sciences : Physics

We study the dynamics of excitons in bimodal CdSe quantum dots. The effect of exciton localization is investigated by identifying transfer mechanisms due to thermalization and redistribution of excitons. We observe an exciton emission from low energy (QDs1) and weaker emission from high energy (QDs2) at low excitation levels at 10 K. Temperature-dependent photoluminescence (PL) studies reveal a thermally activated exciton transfer from QDs1 to QDs2. Time-resolved PL estimate the characteristic radiative and nonradiative decay rates as well as the trapping rate from the QD-precursor layer. The observed PL is reasonably reproduced using a coupled rate equation model. We investigate 10 nm Zn0.94Mg0.06Se/ZnSe quantum well (QW) with two-beam four-wave mixing (FWM) using 90 fs pulses. At high intensity the signal is dominated by χ(3) FWM processes and at low intensity it reveals an exciton resonant phase coherent photorefractive (PCP) effect that is attributed to the formation of an electron grating within the QW by the interference of coherent QW excitons. The observed traces and spectra are reproduced by the model based on a 15-level system and a phenomenological PCP model. The dynamical properties of the electron grating responsible for the PCP is further studied reducing the pulse repetition at 45, 55 and 65 K. The PCP diffraction reveals a nearly constant efficiency up to 1 μs that implies a constant average equilibrium electron density. With increasing temperature, the efficiency decreases due to QW electron escape back to the substrate reducing the grating lifetime. The observed PCP efficiency is studied with a model that considers the equilibrium density dynamics in the QW. We further report on PCP effect in Zn0.9Mg0.1Se/ZnSe QW by performing intensity dependent and polarization dependent two-beam FWM experiments using 30 fs pulses at 2.79 and 2.84 eV. The PCP effect is attributed to the formation of an electron grating within the QW by the interference of exc (open full item for complete abstract)

Committee: Hans-Peter Wagner (Advisor) Subjects: Physics, Condensed Matter

Doctor of Philosophy, The Ohio State University, 2011, Electrical and Computer Engineering

Chalcogenide glasses are amorphous, glassy, semiconducting materials containing S, Se, or Te as the primary components, with network modifiers such as Ge, As, Sb and Bi. They are of interest in photonics because of their low-loss transmission in the infrared, their large third order susceptibility, low two photon absorption at telecommunications wavelengths, and variety of bond rearrangement effects such as photoexpansion, photodarkening, electron beam induced deformation, and electron beam induced second harmonic generation. The large Kerr nonlinearities and large refractive indices of chalcogenide glasses enable compact integrated optical circuits capable of all-optical switching. In this thesis, electron beam induced deformations are explored as a way of fabricating optical waveguides in Ge0.2Se0.8 chalcogenide glasses because this is an etchless technique that potentially allows writing waveguides whose surface roughness is limited only by the roughness of the as-deposited film, allowing for a minimum of surface roughness scattering loss. Thin films (100 nm to several microns thick) of Ge0.2Se0.8 glass are deposited using pulsed laser deposition (PLD). Another option for depositing films, which has the advantage of being lower cost, is explored: spin coating. A process to deposit thin amorphous Ge-Se films using spin coating from amine-based solutions is developed. Mixing in an alcohol such as methanol in relatively small proportions (< 10 mol %) allows for the production of thicker films while maintaining stoichiometry. Films thicker than 1 μm and with surface roughness less than 1 nm RMS can be obtained in a single layer. Exposure to focused electron beams (generated in an electron beam lithography system) is investigated as a way to directly write waveguides into thin PLD Ge0.2Se0.8 films. These waveguides are mound-shaped and similar to rib waveguides. Electron beam parameter sweeps are run demonstrating a transition from mound formation to trench formati (open full item for complete abstract)

Committee: Ronald Reano PhD (Advisor); Betty Lise Anderson PhD (Committee Member); Fernando Teixeira PhD (Committee Member); Roberto Rojas-Teran PhD (Committee Member); Stewart Shapiro PhD (Committee Member) Subjects: Optics

Master of Science, University of Akron, 2011, Physics

The temperature dependence of thermo-optic coefficient in silica-based fibers containing fiber Bragg gratings (FBGs) includes thermal instability of chemical composition gratings, non-linear temperature dependence of FBGs written in different fibers, quadratic behavior of FBGs, and long-term stability of silica-based FBGs. Experimental measurements of the thermo-optic coefficient for the temperature interval 50 – 780°C in fused silica fiber containing FBGs were conducted while the temperature shift of the Bragg's peak was monitored between 1300 and 1311 nm with sub-Angstrom precision. Numerical computations were focused on the FBG's diffraction efficiency calculations accounting for the temperature drift of the gratings and found to be in excellent agreement with obtained experimental data. It has been found that the thermo-optic coefficient changes between 0.79*10-5 and 1.45*10-5 K-1 and undergoes a minimum in the vicinity of 440°C. Additional observation indicates a negative sign of the second-order thermo-optic coefficient. The experiments reveal that the grating reflectivity decays at temperatures higher than 660°C which correlates with calculated decay of the refractive index modulation. It suggests that an FBG is erased at high temperatures. Based on the energy dispersive spectroscopy it has been determined that thermal erasing of the FBGs at a temperature around 780°C correlates well with germanium sublimation (apparently in the form of germanium monoxide) out of silica-based fiber cores.

Committee: Sergei F. Lyuksyutov Dr. (Advisor); David S. Perry Dr. (Committee Member); Robert R. Mallik Dr. (Committee Chair) Subjects: Optics

PHD, Kent State University, 2024, College of Arts and Sciences / Materials Science Graduate Program

Stimuli-responsive functional soft materials have been the focus of attention and been widely applied in advanced devices. Chiral nematic liquid crystals (also called cholesteric liquid crystals, CLCs), which possess intrinsic self-organized helical superstructures, are good candidates to create diffraction gratings (DGs) for optical devices, due to the characteristics of adjustable pitch under external stimuli like light, temperature, electric field, and so forth. Here, we develop two novel photoresponsive CLCs, which are enabled by adding two novel axially chiral molecular switches into the nematic LC host, respectively. Those chiral molecular switches exhibit superior compatibility, high helical twisting power (HTP), and a big HTP change under photoisomerization. Accordingly, electro- and photo-driven orthogonal switching of CLC diffraction gratings, and visible light, temperature, and electric field-driven in-plane rotation of CLC diffraction gratings are demonstrated, which exhibit great potential application in beam steering, spectrum scanning, and beyond. Like CLCs, twist-bend nematic liquid crystals (NTB LCs) also possess an intrinsic heliconical structure although the constituent molecules are achiral, but the molecular director is tilted with a cone angle around the conic helical axis and the heliconical pitch is very small. We study the structure and optical properties of NTB LCs when the chiral dopant is introduced. We show that adding chiral dopant does not induce a twisting of the heliconical axis, but increases the cone angle. Then, based on this fundamental study, we develop a novel thermally switchable smart window enabled by phase transition from NTB phase to chiral nematic phase. Such smart window is energy-saving and exhibits great potential in applications for buildings, vehicles, and beyond. Moreover, we develop a novel switching mechanism between planar and focal conic states in bistable reflective display. The CLC is switched from the foca (open full item for complete abstract)

Committee: Deng-Ke Yang (Advisor); Quan Li (Advisor); Barry Dunietz (Committee Member); Xiaoyu Zheng (Committee Member); Philip J. Bos (Committee Member) Subjects: Chemistry; Materials Science; Physical Chemistry; Physics

PHD, Kent State University, 2023, College of Arts and Sciences / Materials Science Graduate Program

Waveguide liquid crystal display (WLCD) is a newly developed transparent display technology. Since polarizers and color filters are not necessary for the WLCD, high transparency is easily reached. A light-emitting diode (LED) is installed on the edge of the display and the produced light is coupled into the display. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light propagates through the display in waveguide mode due to the total internal reflection at the interface between the substrate and air, and no light comes out of the viewing side of the display. The display appears transparent. When a voltage is applied, the liquid crystal is switched to a micrometer-sized polydomain state and becomes scattering. The incident light is scattered out of the waveguide mode and comes out of the viewing side of the display. We developed a few methods to improve the performance of the waveguide display. First, by using patterned photo-polymerization or patterned ITO electrode, the scattering efficiency of the liquid crystal in the voltage-on state is significantly enhanced. Second, the spatial uniformity of the light intensity of the display is significantly improved by the light waveguide plate. Third, we achieved 8 inch full color transparent light waveguide LCD prototype that utilizes field sequential color (FSC) scheme to display full color images. Fourth, we developed a light waveguide LCD based on the flexoelectric effect using dimer, which exhibits high contrast ratio. Lastly, based on the flexoelectric effect we developed a reconfigurable liquid crystal diffraction grating whose diffraction angle and efficiency can be controlled by the applied voltage. The light waveguide liquid crystal transparent display has the merits of high contrast ratio, suitable driving voltage, and a sub-milli second ultrafast response time. It does not use polarizers and color filter as in conventional LCDs. It also has an ultrahigh tra (open full item for complete abstract)

Committee: Dengke Yang (Advisor); Philip J. Bos (Committee Member); Songping Huang (Committee Member); Sam Sprunt (Committee Member); Hiroshi Yokoyama (Committee Member) Subjects: Materials Science; Optics; Physics

Master of Science, The Ohio State University, 2019, Mechanical Engineering

Structural health monitoring (SHM) is a rapidly growing field focused on detecting damage in complex systems before catastrophic failure occurs. SHM systems provide the potential to improve safety and significantly reduced costs. Advanced sensor technologies are necessary to fully harness SHM in applications involving harsh or remote environments, life-critical systems, mass production vehicles, robotic systems, and others. Fiber Bragg grating (FBG) sensors are an attractive solution for in-situ health monitoring due to their low weight, resistance to electromagnetic noise, ability to be multiplexed, and accuracy for real-time measurements. However, effective embedment of FBG sensors into metal has proved challenging. Ultrasonic additive manufacturing (UAM) has been demonstrated for solid-state fabrication of 3D structures with embedded FBG sensors. In this thesis, UAM embedded FBG sensors for SHM applications are investigated. Embedment of a fiber using UAM was shown to have little effect on the tensile and fatigue properties of aluminum coupons. Furthermore, the ability of UAM embedded FBG sensors to detect and monitor crack growth in Compact Tension (CT) specimens is demonstrated. UAM embedded FBG sensors 3 mm from the initiation site were able to accurately detect cracks of length 0.286 ± 0.033 mm. UAM embedded FBG sensors are shown to accurately track crack growth until near failure. Furthermore, UAM embedded FBG sensors 3 mm, 6 mm, and 9 mm from the initiation site detected a crack that initiated to 0.350 mm. Finally, the potential for high temperature applications is also examined through elevated temperature testing. Fiber optics embedded into aluminum using UAM are shown to be more resilient to degradation at elevated temperatures than exposed fibers. UAM embedded FBG sensors are therefore shown to be an effective type of sensor for SHM applications.

Committee: Marcelo Dapino Dr. (Advisor); David Hoelzle Dr. (Committee Member) Subjects: Mechanical Engineering

PHD, Kent State University, 2018, College of Arts and Sciences / Chemical Physics

Commending topological defects of liquid crystals (LCs) facilitates many configurational simulations and experimental manipulations of active soft matter for electro-optical (EO), optical and photonic applications. In this dissertation, investigation of topological defects in cholesteric liquid crystals (CLCs) enables better visualizing and control unique self-assembly, dielectric and optical properties of CLCs and leads to the development of a fast switching active retarder film based on a CLC with uniform lying helix (ULH) texture, a bistable light diffractive CLC films based on metastable bubble domain (BD) texture, and an in-plane-switching (IPS) LC device based on two-dimensional graphene electrode. We first demonstrate a giant flexoelectro-optic effect (FOE) in a CLC with ULH texture. The electric-field-induced helical axis (HA) rotation of a ULH structure due to flexoelectric coupling is accomplished by the surface-localized polymer network stabilization. A 40 times enhancement in flexoelastic coefficient compared to a conventional CLC materials is achieved by using the CLC based on CB7CB bimesogen. The giant FOE of a polymer-stabilized ULH (PS-ULH) enables the development of an active retarder having high optical contrast and sub-millisecond response time. The second part of dissertation is to investigate topology-mediated optical and electro-optical properties of CLCs with BD texture (CLC-BD) providing unique bistability between the light transmission and light scattering states. The CLC-BD device requires electric field only during switching between transparent and opaque states creating great potential applications as active diffusers and smart windows. An opto-mechanical modulation is demonstrated with a light-sensitive chiral azo-benzene dye doping in a CLC-BD device. To close, the augmentation of EO behavior in a nematic IPS device with graphene transparent electrode is demonstrated. We command the EO switching on photo-lithographically-pat (open full item for complete abstract)

Committee: Liang-Chy Chien Dr. (Advisor) Subjects: Engineering; Optics; Physics

Doctor of Philosophy, University of Akron, 2017, Integrated Bioscience

Understanding the color production mechanisms is important to the advancement of understanding color evolution, ecology, adaptation, and functions. Therefore, investigating how spiders produce colors is a critical piece of the puzzle to fully understand spider biology. In this dissertation, I investigated how spiders produce colors through pigments and biogenic photonic structures using varies techniques. We discovered the presence of eumelanin and carotenoids in spiders, which are both common in nature but were previously thought to be absent in spiders. I also discovered melanosomes – a melanin-containing cellular organelle previously assumed to be a synapomorphy for vertebrates – in spiders. Pigments aside, I described many novel and unique biogenic photonic structures in spiders. The blue color for many tarantulas is produced via specialized setae with diverse photonic structures within. A phylogenic analysis on the blue traits iii showed that despite being a very specific (narrow band) blue color, the blue traits evolved independently at least 8 times. In other words, diverse photonic structures evolved convergently to produce a very specific blue color in tarantulas, suggesting an important visual function for yet to be determined receivers. Among these structures, a flower-shaped multilayer structure is of particular interests due to its ability to attenuate iridescence. This particular structure may inspire the design and fabrication of vibrant, durable colorants in the future. On the other hand, two particular species of peacock spiders showcase extremely angle sensitive iridescence, which produces all the colors within the human visible spectrum with the slightest movement. We determined that this rainbow-iridescent optical effect was produced by unique airfoil-shaped setae with surface nanogratings. These setae also possess an unusual high wavelength resolving capability that may contribute to the design and fabrication of miniature optical components (open full item for complete abstract)

Committee: Todd Blackledge (Advisor); Matthew Shawkey (Advisor); Peter Niewiarowski (Committee Member); Abraham Joy (Committee Member); Morgan Sibbald (Committee Member) Subjects: Animal Sciences; Animals; Biology; Biophysics; Evolution and Development; Experiments; Morphology; Optics

Master of Science, The Ohio State University, 2017, Mechanical Engineering

Fiber Bragg Grating (FBG) sensorsare optical fibers that detect in-situ strain through deviation of a reflected wavelength of light to detect in-situ strain. These sensors are immune to electromagnetic interference, and the inclusion of multiple FBGs on the same fiber allows for a seamlessly integrated sensing network. FBGs are attractive for embedded sensing in aerospace applications due to their small noninvasive size and prospect of constant, real-time nondestructive evaluation. FBGs are typically used in composite laminate type applications due to difficulties in building them into metallic structures. Additive manufacturing, also referred to as 3D printing, can allow for the inclusion of sensors inside of structural entities by the building of material around the sensor to be embedded. In this study, FBG sensors are embedded into aluminum 6061 via ultrasonic additive manufacturing (UAM), a rapid prototyping process that uses high power ultrasonic vibrations to weld similar and dissimilar metal foils together. UAM was chosen due to the desire to embed FBG sensors at low temperatures, a requirement that excludes other additive processes such as selective laser sintering or fusion deposition modeling. This study demonstrated the feasibility of embedding FBGs in aluminum 6061 via UAM. Further, the sensors were characterized in terms of birefringence losses, post embedding strain shifts, consolidation quality, and strain sensing performance. Sensors embedded into an ASTM test piece were compared against an exterior surface mounted foil strain gage at both room and elevated temperatures using cyclic tensile tests. The effects of metal embedment at temperatures above the melting point of the protective coating (160 degrees Celsius) of the FBG sensors were explored, and the hermetic sealing of the fiber within the metal matrix was used to eplain the coating survival. In-situ FBG sensors were also used to monitor the UAM process itself. Lastly, an example app (open full item for complete abstract)

Committee: Marcelo Dapino (Advisor); Mo-How Shen (Committee Member) Subjects: Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2016, Electro-Optics

A distributed feedback laser (DFB) is a type of semiconductor laser where the cavity is periodically structured as a diffraction grating. This allows the same grating region to act as a resonator, out-coupler and the gain region simultaneously. While conventional DFB lasers emit light along its edges, by modifying the grating structure, it is possible to make the output appear from the top surface. This is known as the surface-emitting DFB laser. This thesis will discuss the case in which a two-dimensional grating (which consists of a 2D grid of holes or pillars) etched into the top cladding surface of the waveguide. The thesis consists of four main parts. For the first part, we give the background principles and the coupled wave equations with radiation modes. In the second part, we derive the equations for a waveguide that utilizes a grating strip for guidance. The effective index of this guide is then used in the 2D DFB crossed grating structure. The third part begins with calculations of a particular GaAs:GaAlAs waveguide geometry with a grating. We present the fundamental resonant modes by utilizing the numerical shooting method. Then, the matrix solution method is applied in the calculation of the higher order guided and radiation modes. In the last part, we solve the transcendental equations for the eigenvalues to get the threshold gain and near field radiation pattern from the DFB surface.

Committee: Sarangan Andrew (Committee Chair); Banerjee Partha (Committee Member); Qiwen Zhan (Committee Member) Subjects: Engineering; Optics

Doctor of Philosophy, The Ohio State University, 2016, Physics

In controlling interacting nano- and micro-particles as well as biomolecules, one gains access to a broad range of applications spanning from self-assembly and nanofabrication to creating useful soft matter constructs. This dissertation investigates interacting superparamagnetic particles residing on two different patterned micro-magnetic thin-film platforms: zigzag CoFe wires that support stationary domain walls, and NiFe shapes that yield mobile domains. Interactions between these particles, the underlying stationary or mobile magnetic domains, and external magnetic fields give rise to tunable, ordered micro-particle arrays (clusters) that can be remotely activated and maneuvered. Seamless schemes to self-assemble, disassemble, transport, and reconstruct ordered planar arrays of fluid-borne microspheres are illustrated with the CoFe wires while their Brownian fluctuations are shown to provide an elegant means to probe the local energy landscape in which the spheres are constrained to move. Finally, a magneto-optical micro grating is developed using mobile domains in NiFe to modulate inter-particle spacing and thus diffract and steer photon beams with high precision. The potential for a magneto-optical lock and other photonic applications with this approach are discussed.

Committee: Ratnasingham Sooryakumar (Advisor); Ciriyam Jayaprakash (Committee Member); Fengyuan Yang (Committee Member); Amy Hill (Committee Member) Subjects: Condensed Matter Physics; Physics

PHD, Kent State University, 2015, College of Arts and Sciences / Chemical Physics

We demonstrate a camera combined with a large angle non-mechanical image steering device based on primary a Pancharatnam phase device. The device consists of primary Pancharatnam phase beam deflectors and liquid crystal polarization rotators (LCPRs). The image steering device can change the view direction of a camera to ±30° and ±10° while the image quality using this device is only slightly degraded at large angles. We explore the diffraction efficiency limit of double twist Pancharatnam phase deflectors (DTPPD) with large deflection angles. We show that a Pancharatnam phase device with a dual twist structure can deflect light up to 60 degrees with nearly perfect efficiency. This was beyond the limits previous thought for these types of devices. In this dissertation we consider the range of parameters that will allow for high efficiency and show results for a structure that demonstrates up to 80 degree deflection. We then explore the light propagation through these devices to point out interesting intensity variations in the deflected mode of light as it traverses the deflecting layer. Finally, we offer that a key to understanding the efficiency of these devices, is not the typical parameters important for traditional diffractive devices, but is the control of the polarization state of light. Liquid crystal polarization rotators (LCPRs) are another key component in digital image steering devices. To extend fast response LCPRs from switchers to display applications, we propose and demonstrate a fast response liquid crystal (LC) variable optical retarder, or attenuator with several transmission levels. The fast response LC optical device consists of dual pi-cells. The device is designed so that the transition between any two states is controlled by the application of an increased voltage level, rather than by applying a lower level. This design offers transition times in the range of 10s of microseconds between any transmission states. The combination of (open full item for complete abstract)

Committee: Philip Bos J. (Advisor); Hiroshi Yokoyama (Committee Member); Lian-Chy Chien (Committee Member); Deng-Ke Yang (Committee Member); Achintya Bhowmik (Committee Member); James Gleeson T. (Committee Member); Mark Manley (Committee Chair) Subjects: Optics; Physics

Doctor of Philosophy, University of Akron, 2014, Civil Engineering

A heavy duty riveted steel grating is an open grid deck system used in movable bridge construction and rehabilitation projects. They are lightweight and easy to install when compared to conventional slab systems and is thus preferred when the load carrying capacity of an existing bridge needs to be increased. Empirical methods have been used in the past due to limited information about their design and behavior. Open grid decks have been used in a number of bridges with the majority being welded decks. A major problem encountered with these decks is the development of fatigue cracks resulting in increased maintenance cost. Observations in the field when heavy duty riveted steel gratings are used and results from experiments indicate better fatigue performance than welded decks. The fatigue characterization of the heavy duty riveted grating has not been established and there are no provisions to govern the design in the AASHTO LRFD Specifications. The current research examines the fatigue behavior of heavy duty riveted steel decks under AASHTO H20 truck loading and also establishes an effective width to be considered during design. Preliminary tests were conducted on two large panels of 37R5 lite to investigate the static behavior and the nature of stress distribution on major components of the grating. A 3D finite element model was calibrated to laboratory data to simulate experimental tests and used for parametric studies in estimating stresses in various components. Fatigue testing of six structural panels with simulated H20 design truck tire loads and of 26 smaller panels at stress ranges of 20ksi, 25ksi, 30ksi and 35ksi was performed. A fracture mechanics approach was used to estimate the fatigue life of the gratings. Results showed that the primary strip width provided in the AASHTO LRFD specifications for the design of open grid decks under predicted the stresses on main bearing bars. An effective width is proposed and involves the length or width of the t (open full item for complete abstract)

Committee: Craig Menzemer Dr. (Advisor); Anil Patnaik Dr. (Committee Member); David Roke Dr. (Committee Member); T.S. Srivatsan Dr. (Committee Member); Desale Habtzghi Dr. (Committee Member) Subjects: Civil Engineering; Design; Engineering; Mechanical Engineering

PhD, University of Cincinnati, 2011, Engineering and Applied Science: Chemical Engineering

Advanced sensors and controllers have been actively sought for enhancing energy efficiency, lowering operation cost, and reducing pollutant emission in fossil fuel power plants. Compared to conventional electrochemical and semiconductor sensors, fiber optic chemical sensors (FOCS) are attractive for applications in the harsh environments involved in fossil energy systems due to their advantages in miniature, immunity to electromagnetic interferences, robustness and capability of remote operation. FOCS has the potential to meet many analytical challenges in high temperature, high pressure, dusty, and corrosive environments associated with the fossil fuel energy processes where current gas sensors may fail to function effectively. This dissertation aims to develop and demonstrate two types of FOCS fabricated by physically and functionally integrating chemically sensitive nanomaterials with long-period fiber gratings (LPFG): one is the perovskite type doped ceramic thin film coated-LPFG sensor for in situ high temperature H2 detection in fossil fuel derived syngas streams; the other is surface-acidified zeolite thin film integrated-LPFG sensor for potential uses for NH3 detection in biomass-derived syngas and environmental monitoring. Three representative perovskite-type doped ceramics, i.e. the cerate-based SrCe0.95Tb0.05O3-d (SCTb), the ceria-zirconia solution based SrCe0.8Zr0.1Y0.1O3-d (SCZY), and the zirconate-based SrZr0.95Y0.05O3-d (SZY) have been specifically evaluated to identify the appropriate sensing material for high temperature H2 detection in the harsh environments. The H2 sensing materials have been initially evaluated through the measurement and analysis of the material stability in different atmospheres, the high temperature H2 uptake/sorption, and the thin film total electrical conductivity in H2 with and without CO2. Results of these studies on the material chemical and physical properties suggest that the SCTb has the best sensitivity for H2 detect (open full item for complete abstract)

Committee: Junhang Dong PhD (Committee Chair); Hai Xiao PhD (Committee Member); Anastasios Angelopoulos PhD (Committee Member); William Connick PhD (Committee Member); Vadim Guliants PhD (Committee Member) Subjects: Engineering

PhD, University of Cincinnati, 2010, Engineering : Electrical Engineering

Details of the design, fabrication, and characterization of silicon-on-insulator (SOI) nanophotonic devices are presented. Shallow etched rectangular profile gratings are demonstrated to couple free space light into planar SOI waveguides with efficiencies exceeding 20%. Parabolic planar solid immersion mirror (PSIM) couplers are shown to inject light into SOI photonic crystal waveguides with efficiencies exceeding 99%. Wavelength dependent low-loss propagation through SOI photonic crystal waveguides is reported, and the incorporation of nonlinear materials is considered.

Committee: Joseph Thomas Boyd PhD (Committee Chair); David Klotzkin PhD (Committee Member); Howard Everett Jackson PhD (Committee Member); Jason Heikenfeld PhD (Committee Member); Thomas Mantei PhD (Committee Member) Subjects: Electrical Engineering

PhD, University of Cincinnati, 2002, Engineering : Electrical Engineering

We have investigated the capability of focused ion beam (FIB) in the microfabrication of photonic devices. Novel liquid metal ion sources (LMIS) for FIB have been developed. With these LMIS, implantation-doping of different ion species into semiconductors for local modification of their electrical and photonic properties has been studied. FIB micromachining of semiconductors has also been investigated. Methods of micromilling of microgratings, photonic band-gap (PBG) structures, micromirrors, microlenses, Bragg type grating structures have been developed. An approach to form microstructures on an arbitrary angled facet has been invented. The application of FIB milling of microgratings has been pioneered, and a prototype of a wavelength-division multiplexing (WDM) demultiplexer utilizing the micrograting and optical fiber technologies has been demonstrated.

Committee: Dr. Andrew Steckl (Advisor) Subjects:

Master of Science, University of Toledo, 2012, Chemistry

Biomolecular imaging enables localization and characterization of biomolecules at the cellular and tissue levels in order to better understand their roles in biological organisms. Although a plethora of imaging techniques is available, there is a need to improve current imaging methodologies and apply them for selective analyses of complex biological specimens. The work described in this thesis is related to development and applications of spectral imaging and imaging mass spectrometry (IMS) methodologies. Spectral imaging uses either labeling dyes or native chromophores to visualize biomolecules in cells and tissues under a specialized light microscope, while IMS provides direct detection and analysis of biomolecules on tissue surfaces with preserved spatial distribution. In this initial study, multimodal spectral imaging of cells, cellular organelles, and tissues was performed on a light microscope upon the addition of a transmission diffraction grating. The instrument concurrently recorded spectral images by fluorescence, darkfield, brightfield, and differential interference contrast (DIC) spectral microscopy. Fluorescence signals originating from fluorescently labeled biomolecules in cells were collected through triple or single filter cubes, separated by the grating, and were imaged using a charge-coupled device (CCD) camera. Cellular components such as nuclei, cytoskeleton, and mitochondria were spatially separated by the fluorescence spectra of the fluorophores present in them, providing detailed multi-colored spectral images of cells. Additionally, the grating-based spectral microscope enabled measurement of scattering and absorption spectra of unlabeled cells and stained tissue sections using darkfield and brightfield spectral microscopy, respectively. In the second project, matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) was utilized to visualize the protein spatial distribution on tissue surfaces. Our study has been focused on (open full item for complete abstract)

Committee: Dragan Isailovic PhD (Committee Chair); Surya Nauli PhD (Committee Member); Jon Kirchhoff PhD (Committee Member); Terry Bigioni PhD (Committee Member) Subjects: Biochemistry; Chemistry

Doctor of Philosophy, The Ohio State University, 2006, Astronomy

I present an investigation into the local warm-hot gaseous environment of the Milky Way as observed through highly ionized metal absorption lines in ultraviolet and X-ray spectra. These X-ray lines (primarily OVII) had been reported at redshifts consistent with zero in previous studies of background quasars; however, it has been unclear whether this gas exists close to the Galaxy (within a few tens of kpc) or extends far out into intergalactic space, thereby comprising most of the mass in the local universe. Additionally, highly-ionized OVI high-velocity clouds (HVCs), some of which are associated with the ubiquitous extended neutral hydrogen HVCs seen around the Galaxy, had been extensively studied. However, the distance to the OVI HVCs, and their relation to the X-ray lines, remained undetermined. With three of the highest-quality Chandra grating spectra of extragalactic sources to date, a large number of z=0 absorption lines are detected; the FUSE spectra of these same objects show low- and high-velocity OVI absorption. Using advanced curve-of-growth and ionization balance analysis, limits are placed on the velocity dispersion, temperature, and density of the warm-hot gas along these lines of sight. In none of these cases can the absorption be placed conclusively at Galactic or extragalactic distances. However, in two of the three cases (Mrk 421 and Mrk 279), the observed OVI UV absorption components are found to be inconsistent with the X-ray absorber, indicating that the X-ray absorption is either extragalactic or traces a previously undiscovered Galactic component. The third sightline (PKS 2155-304) exhibits absorption with properties more similar to Mrk 421 than Mrk 279; thus, there may be more than one physical process contributing to the observed absorption along any given sightline. While the X-ray components of this research exclusively employ Chandra data, the XMM-Newton mission can in principle be used for the same purpose. XMM's effectiveness in observ (open full item for complete abstract)

Committee: Smita Mathur (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, Miami University, 2006, Chemistry and Biochemistry

The major thrust of this dissertation is the study of a new type of optical sensor, the long period grating (LPG). As a general rule the evanescent wave from the LPG will not travel more than l/10 e. Therefore, the use of novel nanomaterials to provide the selective coating on an LPG is required. The chapters in this dissertation either extend our knowledge of the LPG applicability to analytical measurements or the feasibility of using specific nanomaterials on LPG to create the desired sensor. The major findings in this dissertation are: 1. Gold nanoislands respond the same way as colloidial gold nanoparticle solutions. Both colloidial and nanoislands showed a reversible color change when exposed to ozone. 2. Ozone shifts the surface plasmon resonce of gold nanoparticles, but without aggregation which has been hypothesized as the primary reason for the surface plasmon resonance shifts. 3. The ozone surface plasmon resonace shift is reversible. 4. A flow-through LPG system was designed and demonstrated. 5. LBL coatings do work on LPG. 6. LPG/LBL systems did not respond in a way similar to prior membrane swelling systems thereby suggesting that the LBL was changing the refractive index in ways other than only swelling. The significance of findings 1-3 are that previous methods for ozone detection either were complex multi-step titrations or were non-reversible processes that destroyed the analytical reagents during measurement. The construction of a flow-through LPG system in findings 4, allows for more reproducible measurements. The flow-through cell also allows for more sensitive measurements, due to the elimination of strain measurements that would be present if the fiber is handled. Finally, the significance of findings 5 and 6 allow for the combination of a very sensitive refractive index sensor by amplifying optical changes in LBL film changes.

Committee: Gilbert Pacey (Advisor) Subjects: Chemistry, Analytical