Sapphire fiber has been studied intensively for harsh environment sensing in the past two decades due to its supreme mechanical, physical and optical properties. It is by far the most reported and likely the best optical fiber based sensing technology for sensing applications in temperature beyond 1000°C. Several sensing schemes have been proposed and studied to date including sapphire fiber extrinsic and intrinsic Fabry-Perot interferometers, fiber Bragg gratings and long period gratings inscribed in sapphire fibers. Lacking the cladding, sapphire fiber is highly multi-moded which renders sapphire fiber based sensor fabrication much more difficult than those based on silica fibers. Among all the reported work on sapphire fiber sensing, the vast majority is for single point temperature measurement. In this work, different sensing schemes are proposed to enhance the capability of the sapphire fiber based sensing technology. For the single point sensing, a miniaturized sapphire fiber temperature sensor for embedded sensing applications was proposed and studied. The sensors are no more than 75 µm in diameter and are ideal for non-invasive embedded sensing applications. Unlike existing sapphire fiber sensors, the thin film sensors are batch-fabrication oriented and thus have a potential to permit mass production with low cost. In addition to single point sensors, multiplexed sapphire fiber sensing systems are investigated for the first time. Two multiplexed sensing solutions, named frequency-multiplexing and spatial-multiplexing, are proposed and studied to achieve multiplexed sensing based on sapphire fibers. / Ph. D.

This research provides the first known procedure for cleanly and consistently reducing the diameter of single-crystal sapphire optical fiber (SCSF) below the limits of standard production methods, including the first production of subwavelength-diameter optical fiber (SDF) composed of single-crystal sapphire. The first known demonstration of an air-clad single crystal sapphire optical fiber demonstrating single-mode behavior is also presented, and the single-mode cutoff wavelength and diameter are determined. Theoretical models describing and predicting the optical behavior of low modal volume sapphire optical fibers are also presented. These models are built upon standard weakly-guiding optical fiber theory, which is found to be accurate once experimentally-determined properties of the SCSF are substituted for theoretical values. Reduced modal dispersion is also observed in the form of decreased laser pulse broadening in reduced-diameter SCSF. The improvements in spatial resolution for distributed sensing systems such as Raman distributed temperature sensing are also predicted based on the measured decrease in pulse duration. This research also provides an enhanced understanding of the etching behavior of sulfuric and phosphoric acids on sapphire surfaces, including the first reporting of etching rates and activation energies for a-plane sapphire surfaces. Morphological changes of sulfuric and phosphoric acids at and beyond the temperature ranges used in etching were also tested and discussed in detail, especially regarding their practical impact on observed etching behavior. The demonstration of LMV single-crystal sapphire optical fibers enables the adaptation of numerous sensing schemes requiring low modal volume or single-mode behavior to be utilized in extreme environments. / Ph. D.

From the monitoring of deep ocean conditions to the imaging and exploration of the vast universe, optical sensors are playing a unique, critical role in all areas of scientific research. Optical fiber sensors, in particular, are not only widely used in daily life such as for medical inspection, structural health monitoring, and environmental surveillance, but also in high-tech, high-security applications such as missile guidance or monitoring of aircraft engines and structures. Measurements of physical parameters are required in harsh environments including high pressure, high temperature, highly electromagnetically-active and corrosive conditions. A typical example is fossil fuel-based power plants. Unfortunately, current optical fiber sensors for high-temperature monitoring can work only for single point measurement, as traditional fully-distributed temperature sensing techniques are restricted for temperatures below 800°C due to the limitation of the fragile character of silica fiber under high temperature. In this research, a first-of-its-kind technology was developed which pushed the limits of fully distributed temperature sensing (DTS) in harsh environments by exploring the feasibility of DTS in optical sapphire waveguides. An all sapphire fiber-based Raman DTS system was demonstrated in a 3-meters long sapphire fiber up to a temperature of 1400°C with a spatial resolution of 16.4cm and a standard deviation of a few degrees Celsius. In this dissertation, the design, fabrication, and testing of the sapphire fiber-based Raman DTS system are discussed in detail. The plan and direction for future work are also suggested with an aim for commercialization. / Ph. D.

Temperature sensing is one of the most common and needed sensing technique, especially in harsh environment like a coal gasifier or an airplane engine. Single crystal sapphire has been studied in the last two decades as a candidate for harsh environment sensing task, due to its excellent mechanical and optical properties under extreme high temperature (over 1000°C). In this research, a sapphire wafer based Fabry-Perot (FP) interferometer sensor has been proposed, whose functional temperature measurement can go beyond 1600°C. The size of the sensors can be limited to a 2cm-length tube, with 2mm outer diameter, which is suitable for a wide range of harsh environment applications. The sensors have shown linear sensing response during 20~1200°C temperature calibration, with high sensitivity and resolution, and strong robustness, which are ready for the field test in real-world harsh environment. / Master of Science

To meet the requirements of precise temperature monitoring at high temperatures in extremely corrosive environments, such as in coal gasifiers, a new sensor technology has been developed. This optical, ultra high temperature measurement system utilizes single crystal sapphire as a sensing element. A series of experiments was performed to determine the corrosion resistance of single crystal sapphire and single crystal fully stabilized cubic zirconia at high temperatures in coal slag and soda lime glass. The amount of corrosion of sapphire and zirconia in corrosive slags was measured at 1200°C, 1300°C, and 1400°C for different exposure times. The microstructural features at the interface of sapphire and zirconia were investigated using SEM and EDX analysis. The experimental measurements as well as SEM micrographs show very little or no degradation of sapphire and zirconia samples in corrosive slags. An interesting phenomenon was observed in the EDX scans of sapphire in the coal slag: the iron from the slag appears to have completely separated from the silicon and deposited at the sapphire surface. This interesting observation can be further explored to study whether this iron layer can be used to control the corrosion of sapphire. / Master of Science

National Programme on Micro and Smart Materials and Systems (NPMASS) / A computer-aided technique is developed in this thesis to systematically generate concepts for sensors of a wide variety. A database of building blocks, based on physical laws and effects that capture the transduction rules underlying the working principles of sensors, has been developed to synthesize concepts. The proposed method uses the database to first create a concept-space graph and then selects concepts that correspond to paths in the graph. This is in contrast to and more efficient than existing methods, such as, compositional synthesis and graph-grammar synthesis, where solution paths are laid out first and then a concept-space graph is generated. The research also explores an approach for synthesis of concepts for closed-loop sensors, where a quantity is sensed indirectly after nullifying its effect by using negative feedback. These sensors use negative feedback to increase the dynamic range of operation without compromising the sensitivity and resolution. According to the literature, generation of un-interesting solutions is a major drawback of the building block-based synthesis approaches. In the proposed approach, this shortcoming is mitigated substantially by using some rules. For a number of the concepts generated, in the sensor problems attempted, we found that those concepts were already implemented in existing patents; thus emphasising the usefulness of the concepts produced. The synthesis approach proposed new, feasible sensor concepts, thereby indicating its potential as a stimulator for enhancing creativity of designers. Another important problem is to improve the robustness of designs. Robustness can be achieved by minimizing the side effects. Side effects are defined as unwanted effects that affect the intended working of the sensor. The research presents an algorithm that (a) predicts the potential side effects for the synthesized concepts of sensors; (b) aids in quantifying the magnitude of the side effects, thus helping the designer to predict the significant side effects; and (c) suggests ways to improve the robustness of the design.

We report the possibility to control the tilting of nanoneedles and nanowires by using structured sapphire substrates. The advantage of the reported strategy is to obtain well oriented growth along a single direction tilted with respect to the surface normal, whereas the growth in other directions is suppressed. In our particular case, the nanostructures are tilted with respect to the surface normal by an angle of 58°. Moreover, we demonstrate that variation of the nanostructures shape from nanoneedles to cylindrical nanowires by using SiO2 layer is observed.

Le présent mémoire s'intéresse aux représentations de la colère dans la littérature des femmes africaines-américaines du 20e siècle. Il cherche à comprendre de quelles manières cette émotion taboue et honteuse investit Passing de Nella Larsen, Sula de Toni Monison et Push de Sapphire, trois œuvres écrites à différentes époques-clés de l'histoire littéraire noire états-unienne au féminin (les années 1920 et la Renaissance de Harlem; les années 1970 et l'émergence du féminisme noir et de sa critique littéraire; les années 1990 et la consécration institutionnelle des black women's studies). Il s'agit de voir comment, dans ces romans où prédominent des enjeux liés aux oppressions de sexe, de race et de classe, la colère joue le rôle de moteur textuel, d'émotion-source : elle dirige les actions et propos des personnages, dirige les intrigues, dirige l'écriture. Elle semble ainsi constituer une impulsion, un paradigme traversant la tradition littéraire féministe noire. L'étude d'un corpus diachronique permet d'entrevoir une évolution singulière : le passage d'une colère nommée et thématisée à une colère-discours. La colère constituant une émotion du désordre et du spectaculaire, j'analyse les stratégies narratives qui permettent de faire surgir l'excès et le théâtral dans les œuvres à l'étude. Ma réflexion se décline en quatre temps. Je me penche dans un premier chapitre sur les articulations entre rapports d'oppression et colère. J'interroge les liens entre sexe et colère, puis entre race et colère, pour enfin présenter les fondements théoriques du féminisme noir et les écrits de féministes noires sur la question. Les trois autres chapitres sont consacrés aux romans analysés : le deuxième traite de Passing et de la colère qui prend possession de l'intrigue grâce à quelques stratégies du double; le troisième montre que la colère, dans Sula, se manifeste selon deux mouvements simultanés (une transmission entre plusieurs générations de personnages et un détournement dans la narration) et par le recours à la métaphore du feu; le quatrième s'intéresse à Push et à son esthétique de l'excès, laquelle imprègne à la fois les corps des protagonistes et la narration. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : colère, excès, violence, littérature afro-américaine, littérature américaine, féminisme noir, Nella Larsen, Toni Morrison, Sapphire.

[Truncated abstract] This thesis is split into two parts. In part one; A 50 K dual mode oscillator, the aim of the project was to build a 50 K precision oscillator with frequency stability on the order of 1014 from 1 to 100 seconds. A dual-mode temperature compensation technique was used that relied on a turning point in the frequency-temperature relationship of the difference frequency between two orthogonal whispering gallery modes in a single sapphire crystal. A cylindrical sapphire loaded copper cavity resonator was designed, modelled and built with a turning point in the difference frequency between an E-mode and H-mode pair at approximately 52.5 K . . . The frequencies and Q-factors of whispering spherical modes in the 3-12 GHz range in the fused silica resonator are measured at 6, 77 and 300 K and the Q-factor is used to determine the loss tangent at these temperatures. The frequency and Q-factor temperature dependence of the TM2,1,2 whispering gallery mode at 5.18 GHZ is used to characterise the loss tangent and relative permittivity of the fused silica from 4-300 K. Below 22 K the frequency-temperature dependence of the resonator was found to be consistent with the combined effects of the thermal properties of the dielectric and the influence of an unknown paramagnetic impurity, with a spin resonance frequency at about 138 ± 31 GHz. Below 8 K the loss tangent exhibited a 9th order power law temperature dependence, which may be explained by Raman scattering of Phonons from the paramagnetic impurity ions. A spherical Bragg reflector resonator made from multiple concentric dielectric layers loaded in a spherical cavity that enables confinement of field in the centre of the resonator is described. A set of simultaneous equations is derived that allow the calculation of the required dimensions and resonance frequency for such a resonator and the solution is confirmed using finite element analysis. A spherical Bragg reflector resonator is constructed using Teflon and free-space as the dielectric materials. A Q-factor of 22,000 at 13.87 GHz was measured and found to compare well with the design values.

Thesis (M.S.); Submitted to the University of California, Berkeley, CA (US); 1 Dec 2003. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--54185" Sugar, Joshua D. USDOE Director. Office of Science. Basic Energy Sciences (US) 12/01/2003. Report is also available in paper and microfiche from NTIS.