Graduation date: 1997

Doppler-free saturation spectroscopy in an optically thick atomic vapor is used in an optical-feedback configuration for two semiconductor diode laser systems. One laser system consists of an unmodifed, commercially available diode laser. The other laser system consists of a diode laser initially stabilized by optical feedback from a diffraction grating. In both cases a portion of a 780-nm diode laser beam passes through a heated rubidium cell and is retroreflected back to the laser. The optical feedback causes the laser frequency to be stabilized to a hyperfine transition within the Rb D��� line. The linewidth of the laser is also reduced as a result of the optical feedback. / Graduation date: 1995

This thesis outlines two advancements in the field of limited data absorption tomography. First, a novel reconstruction algorithm integrating the use of level set methods is presented that incorporates the additional a priori knowledge of a distinct interface between the species of interest and co-flow. The added a priori further reduces the ill-posedness of the system to produce a final concentration distribution that explains the laser absorption measurements and is qualitatively consistent with advection/diffusion transport. The algorithm is demonstrated by solving a simulated laser tomography experiment on a turbulent methane plume, and is compared with the current state-of-the-art reconstruction algorithm. Given the limited number of attenuated measurements, accurate reconstructions are also highly dependent on the locations sampled by the measurement array. This thesis displays how the mathematical properties of the coefficient matrix, A, formed by the locations of the lasers, are related to the information content of the attenuation data using a Tikhonov reconstruction framework. This formulation, in turn, becomes a basis for a beam arrangement design algorithm that minimizes the reliance on additional assumed information about the concentration distribution. Using genetic algorithms, beam arrangements can be optimized for a given application by incorporating physical constraints of the beam locations. The algorithm is demonstrated by optimizing unconstrained and constrained arrangements of light sources and detectors. Simulated experiments are performed to validate the optimality of the arrangements.

No description available.

This thesis describes the development of a sensing technique for temperature nonuniformity along the line of sight through combustion exhaust, geared for gas turbine applications. Tunable diode laser absorption spectroscopy is used to measure three absorption lines and compute a variable to characterize the level of temperature nonuniformity along the laser path. Nonuniformity information is obtained from one line of sight sensor because the absorption has a nonlinear dependence on temperature. This dependence is analyzed to determine the behaviour, shape, and response of absorption lines measured through mediums with nonuniform temperature profiles. Based on this analysis a new line selection process for nonuniformity sensing is developed. A sensor for temperature nonuniformity is proposed and demonstrated through computer simulations and experiments in the exhaust of a laboratory-scale combustor. The nonuniformity variable, U, is shown to monotonically track the level of temperature nonuniformity along the laser path. The capabilities of this sensing technique are determined based on a comprehensive analysis of errors and their effect on sensor performance. Methods to mitigate these errors are described, and the overall sensor capability is determined based on the characteristics of state of the art diode laser and absorption sensor technology. Such a sensor is capable of measuring minimum temperature deviations of 17% or more, which is well within the needed capabilities for industrial applications. Furthermore, the results and knowledge presented in this thesis apply to other absorption based sensing techniques.

Reproduction de : Thèse de doctorat : Chimie inorganique : Reims : 2005. / Titre provenant de l'écran titre. Bibliogr. f. 213-228.

Thèse de doctorat : Médecine. Nutrition et métabolisme : Université de Nantes : 2006. / Bibliogr.

Thesis (M. Sc.)--Cambridge. / Typescript.

Thesis (Ph. D.)--University of Michigan, 1933. / From Physical review, v. 42, December 1, 1932.

Thesis (M.S. in Physics)--Washington State University. / Includes bibliographical references.