Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 171-186). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.), Oregon Graduate Institute of Science & Technology, 1996.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Rebecca Richards-Kortum. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 157-168).

A fiber optic fluid level sensor based on light transmission attenuation due to bending losses is designed, built and tested. Fibers formed with reverse curvatures of decreasing radii will induce and increasing amount of lower order mode light loss to the cladding as the light propagates along the step index multimode fiber. The sensor is arranged in the fluid in a vertical position such that the light travels along the fiber from the bottom or low fluid point to the top or full point. As the fluid covers increasing lengths of the exposed fiber, it strips even more power from the cladding (assuming the fluid refractive index is greater than the cladding refractive index). Data taken with a sensor of this configuration show a monotonic decrease of the output intensity as a function of increasing fluid level. As much as a 14 dB change occurs over a one-foot fluid level change. A mathematical model, based on both field theory and geometrical optics, is developed to evaluate and predict the performance of this fiber optic fluid level sensor. Comparisons of the theoretical predictions and the experimental results under laboratory conditions show very good agreement.

Major advances in fiber optic transmissions have brought about a need for highly sensitive photodetectors. In order to detect this type of transmission, the photodetector must be able to detect one of the two low loss windows of the fiber optics transmission. The photodetector must also be characterized by a high gain and fast speed of response without generating excessive noise power. This report compares different types of high speed phodetectors with emphasis on the merits of using an avalanche photodiode. The report studies the avalanche multiplication and the signal-to-noise power ratio in the ternary InGaAs. The effects of the absorption coefficient, the depletion width, and the impurity concentration are studied. Finally, an optimization of the signal-to-noise power ratio is achieved by selecting the proper impurity concentration profile at suitable values of absorption coefficient and epitaxial width.

A novel detector for ultra-high energy cosmic rays, and its prototype are discussed. It detects events with primary energy greater than 100 PeV. (1 PeV = 1000 TeV; 1EeV = 1000 PeV.) The detector operates by sensing the near-ultraviolet scintillation light of ionized nitrogen molecules created by the passage of ionizing particles in extensive air showers. (The concept is loosely based on the highly successful Fly's Eye detector situated at Dugway, Utah.) Typical events should consist of 1 to 100 EeV primary energy showers, with near-vertical cores, passing through the detector's field-of-view at distances of 1 to 20 km. The optical field of view of the hypothetical detector would be 60 degrees wide by several (≈ 3) degrees high and would look in a near-horizontal direction at a distant mountain range or other suitably dark background roughly 20 Ian away. A typical good location would be the rim of a canyon, looking slightly downward at the other side. The field-of-view would be subdivided into 3 or more thinner ''wedges'', 60 degrees wide by, perhaps, 1 degree high. A single detector provides timing and brightness information only. Three widely-separated detectors with overlapping fields-of-view provide sufficient data to determine the core location, the zenith and azinruthal angles of the core axis, and the absolute luminosity of the cascade. Interpretation of the luminosity data would be a challenge, but it should be possible to estimate primary energy from it. The advantage of this new scheme is the enormous effective detector area per relatively low-cost detector module. Each triplet of detectors "sees" 300 square km with a typical core axis acceptance of roughly 1 sr. The construction and testing of a prototype unit has been accomplished. The field-of-view was 41 degrees wide by 2 degrees high. Light was collected by a 4.7 square meter mirror and focused onto a wave-shifter PMT system. 8 events with primary energies in the 0.1 to 1 EeV range were observed in an 8.5 hour period. Representative events are shown and preliminary data analysis is discussed.

The research described in this dissertation is the first evaluation and application of a new class of optical detectors, two-dimensional charge-coupled device (CCD), for low-light level chemiluminescence and other luminescence spectroscopies. This research conclusively demonstrates the superior qualitative and quantitative performance of spectrometric systems which employ these detectors. It is experimentally shown that a single detector element of a CCD has comparable or superior sensitivity to the most sensitive single channel detectors; photomultiplier tubes (PMT). The results from the application of the CCD detector system to molecular spectroscopies (fluorescence, chemiluminescence, fluorescence detection of high performance liquid chromatography (HPLC) effluents, and chemiluminescence detection of HPLC effluents) and atomic spectroscopies (spatially and spectrally resolved spark and direct current plasma are presented). The results of operating the CCD in specialized readout modes developed in this research termed charge dependent variable binning (CDVB), simultaneous variable binning (SVB), and continuous high speed spectral framing (CHSF) are described and applied. The CDVB and SVB techniques allow very sensitive quantitation of spectrally resolved and unresolved signals with very wide dynamic ranges without prior knowledge of the signal intensity. Finally, CHSF technique provides spectrally resolved temporal study of extended period luminescence emission with millisecond time resolution. The results of unique algorithms to restore the integrity of the image obtained with a two-dimensional CCD detector are described and applied. The algorithms implemented are for removing variations in detector sensitivity and responsivity and spectrometer efficiency, as well as providing digital image filtering.

A multispectral image data compression scheme has been investigated in which a scene is imaged onto a detector array whose elements vary in spectral sensitivity. The elements are staggered such that the scene is undersampled within any single spectral band, but is sufficiently sampled by the total array. Compression thus results from transmitting only one spectral component of a scene at any given array coordinate. The pixels of the mosaic array may then be directly transmitted via PCM or undergo further compression (e.g. DPCM). The scheme has the advantages of attaining moderate compression without compression hardware at the transmitter, high compression with low-order DPCM processing, and a choice of reconstruction algorithms suitable to the application at hand. Efficient spatial interpolators such as parametric cubic convolution may be employed to fill in the missing pixels in each spectral band in cases where high resolution is not a requirement. However, high-resolution reconstructions are achieved by a space-variant minimum-mean-square spectral regression estimation of the missing pixels of each band from the adjacent samples of other bands. In this case, reconstruction accuracy is determined by the local spectral correlations between bands, the estimates of which include the effects of interband contrast reversal. Digital simulations have been performed on three-band aerial and four-band Landsat multispectral images. Spectral regressions of mosaic array data can provide reconstruction errors comparable to second-order DPCM processing and lower than common intraband interpolators at data rates of approximately 2 bits per pixel. When the mosaic data is itself DPCM-coded, the radiometric accuracy of spectral regression is superior to direct DPCM for equivalent bit rates.

In this thesis the performance of a step quantum well infrared photodetector, designed by Kevin Lantz (June 2002) and experimentally studied by Michael Touse (September 2003) and Yeo Hwee Tiong (December 2004), was simulated in Matlab using the transfer matrix method. The results obtained by the Matlab program are compared with the experimental results in a try to make inferences about the optimum way of designing QWIP detectors. Simulation of the above implies numerical solution of the SchroÌ dinger equation, using algorithms and methods, which give accurate results. In our approach, the transfer matrix method is used with exponential and, Airy functions to represent the solutions to SchroÌ dinger equation under zero and nonzero bias, respectively. In the final section of the thesis we examine and simulate in Matlab the application of the extended Kalman filtering (EKF) to an infrared photodetector as a target tracking mechanism to both maneuvering and non-maneuvering targets.