Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2006. / Ken Sandhage - Committee Chair, Robert Snyder - Committee Co-Chair, G. Paul Neitzel - Committee Member, Preet Singh - Committee Member, Robert Speyer - Committee Member Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains ix, 106 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 102-105).

Fiber optic sensors fabricated from standard silica fibers have many advantages over conventional sensors like small size, portability, durability and immunity to electromagnetic fields. Unfortunately, these sensors are not suitable for use in harsh environments where the temperatures are greater than 700°C and large working stresses are involved. Sapphire fiber-based sensors present an attractive alternative for use in such environments. The material properties of sapphire like high melting point, extreme hardness and relative imperviousness to chemical reactions, coupled with the advantages of optical fiber sensing, enhance the performance of these sensors for rugged use. Unfortunately, commercial sapphire fiber that is currently available has higher optical attenuation than silica fiber and is costlier. 0, it is prudent to use a small length of sapphire fiber as a sensor head, which is then spliced to a standard singlen10de silica fiber which acts a lead-in/lead-out fiber to the sapphire sensor head. This thesis investigates possible splicing techniques to fabricate such a sensor set-up. Comparative results from experiments performed on splices that have been obtained by each of these techniques, are presented. Furthermore, two different sensor configurations using a sapphire fiber, spliced to a silica fiber, are developed, and the results of preliminary tests are presented. / Master of Science

The kinetics of incongruent reduction between sapphire and oxygen-controlled Mg-Al melts was studied by measuring spinel-layer thickness, sample-weight change and sample-thickness change as a function of time at various temperatures. To eliminate the crucible contamination caused by impurities in commercial MgO crucibles, self-made high-purity MgO crucibles were achieved by gelcasting method, which is an attractive ceramic-forming technique for making high-purity ceramic parts. The oxygen-controlled alloys were obtained by the three-phase-equilibrium experiments at various temperatures. To avoid MgO formation, the oxygen-controlled alloys prepared at relatively lower temperatures were used for incongruent reaction at relatively higher temperatures. That is to say, the oxygen-controlled alloys prepared at 900°C, 1000°C, and 1100°C were used for spinel formation at 1000°C, 1100°C, and 1200°C, respectively. The experiments were conducted in a vertical furnace, and sapphire wafers were hung vertically in high-purity MgO crucibles so that the natural convection induced by the density change in the melt could be investigated. Experimental results obtained at 1000°C, 1100°C, and 1200°C showed that the spinel layer thickness on two kinds of sapphire wafers, namely {0001} and , followed orientation-independent parabolic kinetics, indicating the diffusion in spinel was one of the rate-limiting steps. In addition, the spinel layer thickness was not a function of position. The results of sample-thickness- change measurements also indicated that the effect of natural convection could be neglected. XPS, XRD, and TEM were also employed to characterize some samples in this study. Based on a simple model where the diffusion in spinel was the only rate-limiting step, the governing partial differential equations for diffusion and fluid dynamics were solved by the finite element method. The calculated theoretical parabolic constants at various temperatures were compared with these experimental results, and a good agreement was obtained. Some preliminary studies were also made on the morphologies of spinel particles at the nucleation stage. It was found that the triangular {111} faces of spinel particles were parallel to the surface of {0001} sapphire substrate. The product shape was consistent with the tetrahedron composed of {111} faces. The morphology of spinel particles on a sapphire substrate was more complicated in that the triangular {111} faces of spinel had to be inclined at a certain angle to the substrate in order to maintain the orientation relationship.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 114-122). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 114-122). Also available on the Internet.

Thesis (M.S.)--West Virginia University, 2004 / Title from document title page. Document formatted into pages; contains vi, 30 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 29-30).

Thesis (Ph.D.)--Ohio University, August, 2003. / Title from PDF t.p. Includes bibliographical references (leaves 188-194)

Advanced Laser Interferometric Gravitational Wave Detectors, based on current infrastructure (in particular, the Advanced LIGO detectors), are being planned to significantly increase the sensitivity to gravitational wave strain in the near future. To upgrade the existing detectors requests implementing very high optical power, as well as very high circulating power in the arm cavities; these measures will increase the sensitivity at the shot noise floor by one order of magnitude. However, such extremely high power circulation in the cavities will cause optical distortions in the test masses. Thermal distortions arise from the optical power absorption by defects or inhomogeneities in test masses, resulting in wavefront deformations, which have important consequences for the power buildup of the Radio-Frequency (RF) sidebands in the recycling cavities, thus degrading the performance of the detectors. The degree of this sensitivity degradation in the shot noise floor, due to optical distortions induced by defects or inhomogeneities (i.e. imperfections) in test masses in Advanced Laser Interferometric Gravitational-wave Detectors, is dependent on the test mass optical quality; while the sensitivity degradation in the thermal noise floor is dependent on the test mass mechanical properties. For this reason, it is compulsory to use high optical and mechanical quality test mass materials in the advanced interferometer detectors. Fused silica has been used for test masses in detectors, while sapphire has been planned to be used for test mass substrates in the proposed Large-scale Cryogenic Gravitational-wave Telescope (LCGT) project. Other materials, such as calcium fluoride (CaF2), are also attractive, especially for cryogenic detectors. However, for the state-of-theAbstract II art facilities, it is difficult to manufacture very uniform, defect-free, inhomogeneity-free, high-quality, and large-size samples. Thus, the qualities of sapphire and calcium fluoride single crystal samples were investigated and evaluated, to ensure that they have suitable properties for use in interferometer detectors, i.e. with an adequately low level of imperfections, but also with high mechanical quality factor (Q-factor). This thesis describes research done in the endeavour to investigate bulk defects or inhomogeneities in test masses, as well as their induced thermal distortions, which appear at a high optical power in Laser Interferometric Gravitational-wave Detectors. An Automatic Rayleigh Scattering Mapping System (ARSMS) to examine the optical property of large-size test masses is described. This ARSMS enables quantitative high-resolution 3D mapping of defects or inhomogeneities in optical materials. The measured 3D defect distribution mapping of optical materials can assist in the design of suitable configurations of test masses in high optical power interferometers. In addition, a very sensitive Hartmann wavefront sensor was used to actively monitor the thermal distortions due to bulk and coating absorption in test masses. A very strong thermal distortion in these test masses was observed in the Gingin facility, demonstrating that thermal distortions could be a critical issue in advanced interferometer detectors. A negative thermo-optical coefficient material, to be used in a thermal distortion compensation method, was investigated for the compensation of very localised distortions due to imperfections. This thesis also includes experimental and theoretical studies of the scattering, absorption, and birefringence mechanisms, thermal distortion effects, and optimal compensation methods for test masses.