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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

An optical probe of thin film and surface contamination based on surface plasmon resonance.

Wang, Ran-Hong Raymond. January 1990 (has links)
The microcontamination of optical surfaces or optical thin films affects many of their properties. In this work, we investigated several measurement systems to detect many types of surface contamination of coatings based on the surface plasmon resonance (SPR) phenomenon. The attenuated total reflection (ATR) coupling, also known as the Kretschmann configuration, excited the nonradiative surface plasmon wave for SPR measurement. Several microcontamination layers thinner than 10 nm were studied. The results showed that in all the cases SPR curves shifted to larger incident angles. From the amount of angle shift, the thickness of contamination was determined with a sensitivity of as little as one angstrom. The optical constants of those contamination layers were also derived. The shifts of the SPR curves served as an index for the efficiency of cleaning processes. It was found that the contamination by moisture can be removed with Iso-propyl alcohol by the ultrasonic cleaning process, while acetone was the more effective solvent in removing the contamination left by strippable coating residue show that the contamination layer was roughened by ultrasonic cleaning. In studies of island-like discontinuous thin layers of Ag, Al, and MgF₂, we found that the refractive index of MgF₂, a dielectric film material, slightly decreased as the thickness decreased, but for discontinuous metal films, the optical constants changed rapidly and became more dielectric in nature. Direct detection of contamination by coating processes in a small vacuum chamber was also carried out. In a chamber with high backstreaming from a diffusion pump, a broad SPR curve for an Ag film revealed obvious optical constant changes. Measuring and comparing the shift indicates that a significant amount of contamination was occurring right after the coating was completed. This suggests that for good evaporated optical thin films, it is important to have a more tightly controlled evaporation process. Finally, particulate, as well as layered, contamination can also be measured. A radiative SPR wave was generated by illuminating a contaminated surface. Similar radiative SPR waves also can be observed by adding a rough contaminant layer on an Ag film.
22

Lanthanide trifluoride thin films: Structure, composition, and optical properties.

Lingg, Linda Jeanne. January 1990 (has links)
This study characterizes thin films of eleven lanthanide trifluorides which are potentially useful for optical applications. The natural and controlled transparency and real refractive index of single layers of these trifluorides are examined and accompanied by studies of composition and crystal structure of the films which are made by conventional, high temperature, and ion-assisted thermal evaporation. Additionally, since these particular fluoride compounds provide an excellent opportunity for doing so, the mechanisms active in film modification through high temperature and ion-assisted thermal evaporation are explored.
23

Fluorescence enhancement and angular scattering by selected cylindrical particles.

Abromson, David, 1961- January 1990 (has links)
An examination of light scattering and emissions from a fluorescent dye confined within small hollow core quartz fibers has revealed several interesting phenomena. First, backscattered fluorescent emissions increased as the fiber's inner diameter decreased below 23 microns. Second, interference between the inner and outer fiber walls created angular scattering intensity oscillations in the elastic scattered light and fluorescent emissions. The interference induced oscillations produced large intensity changes in less than a degree. Third, fiber immersion in an index-matched fluid removed the interference oscillations, and fourth, the fiber immersion also decreased the backscattered fluorescent emissions for the same fiber. These research results can be used to optimize the design of fluorescence measuring devices used in capillary zone electrophoresis (CZE). A CZE device measures the fluorescence spectrum from biological material within small hollow core fibers. The small amount of fluorescent material makes it desirable to find an optimum viewing angle to maximize signal and avoid spurious results from selective wavelength enhancement and intensity variations in angular scattering caused by the fiber.
24

An observational comparison of mercury and the moon.

Sprague, Ann Louise. January 1990 (has links)
Observations of the neutral sodium (Na) and neutral potassium (K) atoms in the tenuous atmospheres of the Moon and Mercury have been made, analyzed and interpreted. An atmospheric number density of ∼300 times more Na and ∼100 times more K are observed at Mercury than at the Moon. This is not consistent with a meteoritic source for these constituents unless losses and recycling are very different. Potassium observations in the lunar atmosphere indicate fewer accommodated atoms than expected from thermalization of the extended component through gas-surface interactions. A mechanism for redistributing the thermal and non-thermal populations is presented. Thermal infrared observations between 7.5 and 12.5 μm have been made at both bodies in an attempt to gain understanding of the relationship of the surfaces to the alkali atmospheres. Mercury has been found to have a surface composition at three locations more felsic than that of the lunar south-polar highlands. Spectral indications of high alkali feldspar have been observed. One mafic location on Mercury's surface has been determined. Calculations using a grain-boundary and regolith diffusion model have shown that the differences in abundances of Na and K and the ratios of Na/K at both bodies can be explained by a supply of atoms diffusing upward through the sub-surface materials over geologic time. Enhancements in K seen at the longitude of Caloris and the antipodal point of up to five (5) and four (4) respectively, point to a sub-surface source for at least part of the tenuous alkali atmosphere at Mercury.
25

In-flight methods for satellite sensor absolute radiometric calibration.

Biggar, Stuart Frick. January 1990 (has links)
Three methods for the in-flight absolute radiometric calibration of satellite sensors are presented. The Thematic Mapper (TM) on the Landsat satellites and the HRV on the SPOT satellite have been calibrated using the three methods at the White Sands Missile Range in New Mexico. Ground and airborne measurements of ground reflectance, radiance, atmospheric, and weather parameters are made coincident with satellite image acquisition. The data are analyzed to determine inputs to radiative transfer codes. The codes compute the radiance at the sensor entrance pupil which is compared to the average digital count from the measured ground area. The three methods are the reflectance-based, radiance-based and irradiance-based methods. The relevant theory of radiative transfer through an atmosphere is reviewed. The partition of extinction optical depth into Rayleigh, aerosol and absorption optical depths is discussed. The reflectance-based method is described along with the assumptions made. The reflectance-based method accuracy is no better than the measurement of the ground reflectance which is made in reference to a standard of spectral reflectance. The radiance-based method is described. The standard for the radiance method is a standard of spectral irradiance used to calibrate a radiometer. The calibration of a radiometer is discussed along with the use of radiative transfer computations to correct for the residual atmosphere above the radiometer. The irradiance-based method is described. It uses the measurement of the downward direct and total irradiance at ground level to determine the apparent reflectance seen by a sensor. This method uses an analytic approximation to compute the reflectance without the use of an "exact" radiative transfer code. The direct-to-total irradiance ratio implicitly gives the description of the scattering normally calculated from the size distribution and assumption of Mie scattering by the aerosols. The three methods give independent results which should allow for the detection of possible systematic errors in any of the methods. All three methods give results within the estimated errors of each method on most calibration dates. We expect the results of our sensor calibrations are within five percent of the actual value.
26

Saturn's atmosphere in the visible and near-infrared, 1986-1989.

Karkoschka, Erich. January 1990 (has links)
This work describes observations of Saturn's atmosphere in the visible and near infrared (450-1000 nm) including four hydrogen quadrupole lines, 17 methane absorption bands ranging over three orders of magnitude in absorption strength, an ammonia absorption band, and the absolute calibrated continuum spectrum. All observations have complete coverage of Saturn's disk, in latitude as well as in center-to-limb position. The accuracy of the data is comparable or better than previous data. This data set gives a quite complete description of Saturn's atmosphere in the visible and near infrared at the spatial resolution of ground based observations. While the main data were acquired in 1988, small changes between 1986 and 1989 were determined also. An atmospheric model is given which fits all observations within estimated errors. It has clear gas at the top of the atmosphere, an extended haze layer and a reflective cloud at the bottom. Pressure levels and the haze optical depth were determined as a function of latitude. The single scattering albedo spectrum of the particles (most likely ammonia ice crystals) is also given for each latitude. The methane mixing ratio is (3.0 ± 0.6) x 10⁻³, the ammonia mixing ratio is (1.2 + 0.8/-0.6) x 10⁻³ below the ammonia condensation level. Room temperature methane absorption spectra do not fit the observed spectra for any cloud structure. A cold temperature methane absorption spectrum is determined under the assumption that methane band strengths are temperature invariant, but not necessarily the absorption coefficients at each location across the band. It indicates that the absorption coefficients are typically 20-30 per cent stronger in the center of a band and up to a factor of two weaker in the wings. This spectrum should be useful in the interpretation of methane observations of all the giant planets and Titan.
27

Factors influencing lesion detection in medical imaging.

Rolland, Jannick Paule Yvette. January 1990 (has links)
An important goal in medical imaging is the assessment of image quality in a way that relates to clinical efficacy. An objective approach is to evaluate the performance of diagnosis for specific tasks, using ROC analysis. We shall concentrate here on classification tasks. While many factors may confine the performance achieved for these tasks, we shall investigate two main limiting factors: image blurring and object variability. Psychophysical studies followed by ROC analysis are widely used for system assessment, but it is of great practical interest to be able to predict the outcome of psychophysical studies, especially for system design and optimization. The ideal observer is often chosen as a standard of comparison for the human observer since, at least for simple tasks, its performance can be readily calculated using statistical decision theory. We already know, however, of cases reported in the literature where the human observer performs far below ideal, and one of the purposes of this dissertation is to determine whether there are other practical circumstances where human and ideal performances diverge. Moreover, when the complexity of the task increases, the ideal observer becomes quickly intractable, and other observers such as the Hotelling and the nonprewhitening (npw) ideal observers may be considered instead. A practical problem where our intuition tells us that the ideal observer may fail to predict human performance occurs with imaging devices that are characterized by a PSF having long spatial tails. The investigation of the impact of long-tailed PSFs on detection is of great interest since they are commonly encountered in medical imaging and even more generally in image science. We shall show that the ideal observer is a poor predictor of human performance for a simple two-hypothesis detection task and that linear filtering of the images does indeed help the human observer. Another practical problem of considerable interest is the effect of background nonuniformity on detectability since, it is one more step towards assessing image quality for real clinical images. When the background is known exactly (BKE), the Hotelling and the npw ideal observers predict that detection is optimal for an infinite aperture; a spatially varying background (SVB) results in an optimum aperture size. Moreover, given a fixed aperture size and a BKE, an increase in exposure time is highly beneficial for both observers. For SVB, on the other hand, the Hotelling observer benefits from an increases in exposure time, while the npw ideal observer quickly saturates. In terms of human performance, results show a good agreement with the Hotelling-observer predictions, while the performance disagrees strongly with the npw ideal observer.
28

Long slit CCD observations of active and normal galaxies.

Carone, Timothy Edward. January 1990 (has links)
This work presents a comparative study between a sample of Seyfert galaxies and a control sample of galaxies that was done to determine if the presence of an active nucleus would in any way effect its host galaxy. An obvious manifestation of such an effect would be changes in the star formation properties of the Seyfert galaxies relative to the control sample. Since the star formation rate is directly related to the amount of Hα emission, the Hα luminosity along the major axis of each program galaxy was measured. The result of this work was twofold. First, a highly optimized CCD camera system was developed for use as a facility instrument. This camera system was then used to spectroscopically survey 15 Seyfert and 15 normal galaxies. Hα emission was measured in 12 Seyfert and 12 normal galaxies. It was found that after comparing a number of different quantities all dependent on the star formation process, there was no discernible difference between the sample of Seyfert galaxies and the sample of normal galaxies. In particular, the total Hα emission, line ratios and various properties of the sites of star formation and their spatial distribution were similar between the two samples. This implies that the disk regions of Seyferts are identical to the disks of normal spirals as determined by the properties of their giant HII regions.
29

Beam propagation and shift-variant optics.

Eckhardt, Stephen Karl. January 1990 (has links)
The goal of the research described in this dissertation is to be able to model propagation of light through shift-variant optics. Shift-variant optical elements have a point spread function which is a function of the transverse coordinates. This shift-variance can be caused by aberration or by the first order properties of the optical system. In this work the latter is emphasized. Specifically, this dissertation discusses propagation through lenses and prisms and between tilted planes or a plane and a spherical surface. Extension to other types of shift-variant optical elements is possible. Two methods for performing the propagation are described. One, the beam division model, divides the beam into isoplanatic patches, separately propagates the patches and recombines them on the observation surface. The second method, the mapping model, maps the beam into a space in which the propagation is shift-invariant, propagates and then maps back into real space. Experimental verification of these methods is demonstrated by means of the Talbot effect. The setup consists of a collimated laser beam passing through a Ronchi ruling of about ten cycles per millimeter. With no intervening optics, Talbot images of the ruling are formed which are parallel to the wavefronts. When a prism at minimum deviation is placed in the outgoing beam, it causes the Talbot images to be tilted with respect to the wavefronts. If a stigmatic unit magnification telescope replaces the prism, the Talbot images are formed on surfaces congruent to the Petzval surface.
30

Cryomagmatism in the outer solar system.

Kargel, Jeffrey Stuart. January 1990 (has links)
Cryovolcanism has played an important role in the geological histories of many icy satellites. Cryovolcanism, like the more familiar silicate volcanism on Earth and the other terrestrial planets, takes many forms. Many individual cryovolcanic landforms are morphologically surprisingly similar to terrestrial volcanic landforms and can be explained with similar mechanisms. However, assemblages of cryovolcanic, tectonic, and impact structures form unique and varied landscapes quite alien in their collective expression. Many variables can affect the cryovolcanic style of a satellite but none more so than cryolava composition. This work considers the compositional variable in considerable detail. This work summarises existing knowledge of phase equilibria and physical properties of cosmochemically relevant unary, binary, and multi-component chemical systems, and where published knowledge was found lacking, the author presents his own measurements of the physical chemistry of volatile mixtures. The author then takes the reader on a brief tour of cryovolcanic landscapes, and applies knowledge of the physical chemistry of volatile mixtures to problems of cryovolcanological interest. Aqueous cryolavas may range in composition from salt-water brines to cryogenic ammonia-water-rich multi-component solutions possibly involving methanol, ammonium sulfide, alkali chlorides, and many other potential components. Cryomagmatic distillation can greatly accentuate the importance of trace and minor constituents of icy satellites. The viscosities, densities, and other physical properties of these liquids vary considerably and depend sensitively on their exact compositions. These properties affect everything from cryovolcanic eruptive styles and landforms, to the way cryovolcanic crusts respond to tectonic stresses. It is believed that the compositional variable is directly or indirectly implicated in a wide variety of geomorphic aspects of contrast among the icy satellites. Thus, even though we can not as yet confidently attribute any specific morphology to a specific composition (for lack of in situ compositional analyses), there appears to be a powerful link between the composition of the ices originally accreted by a satellite and its subsequent interior evolution and exterior geomorphic appearance.

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