Physics Commons^™

Modeling And Simulation Of Optical Characteristics Of Microelectromechanical Mirror Arrays, Peter C. Roberts

Theses and Dissertations

MEMS (Micro-Electro-Mechanical Systems) micromirror devices can be used to control the phase of a propagating light wavefront, and in particular to correct aberrations that may be present in the wavefront, due to either atmospheric turbulence or any other type of fixed or time and space varying aberrations. In order to shorten the design cycle of MEMS micromirror devices, computer software is developed to create, from MEMS micromirror device design data, a numerical model of the MEMS device. The model is then used to compute the far field diffraction pattern of a wavefront reflected from the device, and to predict the …

L-Shell Resonant Electron Transfer And Excitation In Cu18-19+ + H2 Collisions, Jeffrey A. Wroblewski

Masters Theses

Measurements of L-shell resonant electron transfer and excitation (RTE) were conducted for 45-72 MeV Cu^18-19+ (Na-like and Ne-like, respectively) ions colliding with H₂ using the Western Michigan University EN tandem Van de Graaff accelerator. The RTE process involves an electron-electron interaction between the projectile and the target where electron capture occurs simultaneously with projectile excitation. In previous measurements involving RTE with subsequent L x-ray relaxation for Nb^q+ (q=28-31) ions, the magnitudes of the RTE cross sections were found to be nearly a factor of two smaller than theory. In the analogous electron-ion process of dielectronic recombination, measurements …

Deconvolution From Wavefront Sensing Using Optimal Wavefront Estimators, Scott R. Maethner

Theses and Dissertations

A cost effective method to improve the space surveillance mission performance of United States Air Force (USAF) ground-based telescopes is investigated and improved. A minimum variance wavefront estimation technique is used to improve Deconvolution from Wavefront Sensing (DWFS), a method to mitigate the effects of atmospheric turbulence on imaging systems that does not require expensive adaptive optics. Both least-squares and minimum variance wavefront phase estimation techniques are investigated, using both Gaussian and Zernike polynomial elementary functions. Imaging simulations and established performance metrics are used to evaluate these wavefront estimation techniques for a one-meter optical telescope. Performance metrics include the average …

Laser-Induced Breakdown Spectroscopy On Solution Samples Using Surface Excitation, Leonard M. Berman

Theses and Dissertations

Laser-induced breakdown spectroscopy (LIBS) is a spectroscopic technique where output from a pulsed laser is focused onto a target in order to create an intense plasma. The optical emission is characteristic of the elements in the focal volume and can be used for elemental analysis. Research on the detection of nickel in solution in addition to solvent detection of CCl₄, CHCl₃, C2Cl₄, and C2HCl₃ has been performed. Breakdown was formed at the sample surface via a Q-switched Nd:YAG laser. Initially, operation of the laser was at 1064 nm/repetition rate of 5 Hz. Experiments …

Estimation Of Satellite Orientation From Space Surveillance Imagery Measured With An Adaptive Optics Telescope, Gregory E. Wood

Theses and Dissertations

The use of the matched filter to automatically estimate the pose of a Low Earth Orbiting satellite from imagery taken with an adaptive optics telescope is explored. This work represents the first effort to solve the satellite pose estimation problem while considering the broad range of atmospheric turbulence levels and target visual magnitudes that are encountered in ground based space surveillance operations. Several Algorithms are examined in an effort to determine the performance bounds on the matched filter for this application. Results are given over an extremely wide range of seeing conditions. These results are weighted based on historical data …

Investigation Of Ba, Bao, Sr And Sro Pulsed Laser-Induced Vapor Plumes In N2, O2, Microwave Discharged O2, And Vacuum At Low Laser Fluence, David L. Byers

Theses and Dissertations

Ba, BaO, Sr and SrO were ablated by 248 nm laser pulses at fluences ranging from 270 mJ-/sq cm to 575 mJ-/sq cm in vacuum and in 25 mtorr atmospheres of N2, O2 and microwave-discharged O2. The spectral emissions of these plumes were compared for indications of ionization due to Ba or Sr collisions with each gas. The addition of a background gas increased the ion and neutral signature across the spectrum. SrO band emission was observed at 16,600-16,900/cm and possible BaO band emissions were observed in the 18,250-18,400/cm, 19,000-19700/cm and 19,800-20,000/cm regions. A screened plate ion probe was use …

Electrical Characterization Of Intrinsic And Induced Deep Level Defects In Hexagonal Sic, James D. Scofield

Theses and Dissertations

Deep level defects in hexagonal SiC were studied using digital deep level transient spectroscopy (DLTS) methods over the temperature range of 100 to 800 deg K. New centers were found in bulk and epitaxial 6H-SiC with ionization energies between 0.38 to 1.3 eV, and levels from 0.2 to 0.856 eV were identified in 4H-SiC epitaxy. Direct correlation between inequivalent lattice sites was identified for energetic pairs associated with both vanadium and ion implanted Mg impurities. Nonradioative carrier capture mechanisms were studied and deep level trapping was found to proceed via lattice relaxation multi-phonon emission, indicating efficient electronic lattice coupling in …

Theoretical Modeling Of Linear Absorption Coefficients In Si/Si1-Xgex Multiple Quantum Well Photodetectors, Kevin D. Greene

Theses and Dissertations

Si/Si_1-xGe_x MQW Infrared Photodetectors offer the promise of normal incidence photodetection tunable over the range of 3-12 micrometers wavelength range at temperatures above 40 K. This system is attractive because the Si_1-xGe_x offers greater compatibility with existing Si based signal processing circuitry. Band structures, momentum matrix elements and linear absorption coefficients are computed using a Luftinger-Kohn k/p analysis for Si/Si_1-xGe_x quantum wells grown in the 110 direction. The absorption coefficient as a function of energy and wavelength is calculated by two methods: a delta function fit to intersubband transitions, and a …

Demonstrating Optical Aberration Correction With A Mems Micro-Mirror Device, Shaun R. Hick

Theses and Dissertations

This research conducted the first demonstrated use of a micro-electro-mechanical structure (MEMS) mirror array to correct a static optical aberration. A well-developed technique in adaptive optics imaging systems uses a deformable mirror to reflect the incident wave front to the imaging stage of the system. By matching the surface of the deformable mirror to the shape of the wave front phase distortion, the reflected wave front will be less aberrated before it is imaged. Typical adaptive optics systems use piezo-electric actuated deformable mirrors. This research used an electrostatically actuated, segmented mirror array, constructed by standard MEMS fabrication techniques, to investigate …

Unfolding The High Energy Electron Flux From Crres Fluxmeter Measurements, Brian D. Mckellar

Theses and Dissertations

The Combined Release and Radiation Effects Satellite (CRRES) was launched on 25 July 1990 to collect measurements in the earth's radiation belts. One instrument, the High Energy Electron Fluxmeter (HEEF), measured the flux of electrons in 10 channels with energies between 1 MeV and 10 MeV. The channel sensitivities, Ri(E), have been calibrated and partially re-calibrated. We explore the errors introduced in unfolding the electron flux spectrum from the channel measurements and the propagation and growth of calibration and measurement errors. Using numerical experimentation, we fold the responses with known spectra to obtain simulated measurements, add random measurement and calibration …

Effects Of The Cardioprotective Drugs Dexrazoxane And Adr-925 On Doxorubicin Induced Ca2+-Release From The Sarcoplasmic Reticulum, Thomas Andreas Herzinger

Dissertations and Theses

The sarcoplasmic reticulum is the intramuscular organelle responsible for the regulation of cytoplasmic calcium levels in muscle. This thesis investigates the effects of the cardioprotective drug, dexrazoxane, and its metabolite ADR-925 on doxorubicin induced calcium release from skeletal sarcoplasmic reticulum. Doxorubicin is a widely used antineoplastic agent. One of the major side effects of doxorubicin usage is chronic cardiotoxicity. Doxorubicin is a potent activator of the calcium release mechanism from the SR. The interaction between doxorubicin and the calcium release channel has been proposed as the possible underlying mechanism behind cardiotoxicity. A short overview of different hypotheses describing doxorubicin induced …

A 2-D Numerical Simulation And Analysis Of A Simple Band Model For The Priz Spatial Light Modulator, Gary D. Barmore

Theses and Dissertations

This dissertation discusses the development of and analyzes the first complete, 2-D numerical simulation of the PRIZ. The simulation is based upon a simple band model of the PRIZ: a single donor, a single trap, and free electron carriers. Modeled mechanisms include photogeneration, energy level transitions, injection, drift currents, diffusion currents, photorefraction and diffraction. The model goes beyond the previous charge and field dynamics of 1-D numerical models to include optical effects, and it eliminates the oversimplifications and assumptions used in earlier mathematical models with closed solutions. Sensitivity analyses and selected simulations provide a better understanding of the dynamic imaging …

Luminescence Study Of Ion-Implanted Gallium Nitride, Eric Silkowski

Theses and Dissertations

Luminescence and absorption measurements were used to demonstrate the efficacy of ion implantation for introducing various classes of dopants into GaN. A wide range of implantation and annealing studies were performed with several dopant species (Ar, Zn, C, O, Si, Be, Mg, Nd, Er). Room temperature ion implantation was performed on MOCVD- and MBE-grown GaN samples at energies between 100 and 1150 keV with doses ranging from 1 x 10¹³ to 1 x 10¹⁵/cm^-2. Conventional furnace annealing in flowing NH₃ or N₂ gas resulted in good implantation damage recovery at an annealing temperature …

Surface Phenomena On The Tin-Dioxide Polycrystalline Layers, Andrei A. Fluerasu

Theses

Polycrystalline tin-dioxide is widely used in the detection of reducing gases (such as H₂, CO, CH₄, C₂H₅OH,...) in air by measuring its conductivity changes. The advantage of gas sensors based on such sensing devices is low cost and high sensitivity. In contrast to their widespread applications and to their successful empirical research and development work, the present understanding of the chemical sensing mechanisms is still immature.

In this thesis, for gas sensors based on thick and porous tin-dioxide layers, a study of the response function upon variation of the partial pressure of …

Design Of A Two-Chamber-No₂-Fluorescence-Cell, Volker Schmid

Dissertations and Theses

Nitrogen oxides control the photochemical production of ozone O₃ in the lower atmosphere and influence the concentration of the hydroxyl radical HO in the troposphere. As an important member of the nitrogen oxide family, NO₂ plays a significant role in serving as the only known source of ozone (through photolysis) in the lower atmosphere and as sink for HO via formation of nitric acid. Therefore, accurate measurements of nitrogen dioxide are essential for the understanding of the processes that determine the distribution of tropospheric ozone and for assessing the impact of human activity on the troposphere.

Although reliable and …

Calibration Of A Ccd Camera And Correction Of Its Images, Armin Rest

Dissertations and Theses

Charge-Coupled-Device (CCD) cameras have opened a new world in astronomy and other related sciences with their high quantum efficiency, stability, linearity, and easy handling. Nevertheless, there is still noise in raw CCD images and even more noise is added through the image calibration process. This makes it essential to know exactly how the calibration process impacts the noise level in the image. The properties and characteristics of the calibration frames were explored. This was done for bias frames, dark frames and flat-field frames at different temperatures and for different exposure times.

At first, it seemed advantageous to scale down a …

Distribution Coefficients Of Ionized And Un-Ionized Halogenated Phenols In An Octanol-Water System And Their Relationship To Molecular Structure, Sven Hensler

Dissertations and Theses

Life supporting biological membranes are barriers to toxic chemicals. One of the factors determining the toxicity of chemical compounds is their distribution between membranes and their an environment. An octanol-water system is frequently used as a model for biological membranes to estimate the toxic potency of environmental pollutants. The distribution of a chemical between the octanol and the water phase is described by the octanol-water partition coefficient K_OW. This study is concerned with the relationship between K_OW and the molecular structure of the toxic chemical.

In the study the following trihalophenols were included: 2,4,6-trifluorophenol (TriFP), 2,4,6-trichlorophenol (TriCP); …

Silcom Quantum Walls: Fabrication And Opticla Analysis, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the,anddirection, and each slab surfaces is extended in the-plane and normal to thedirection. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of the phonons is highly dependent on …

Design Of A Device Independent Computer Graphic Software Package, An-Shyang Chu

Physics & Astronomy ETDs

The fabrication and optical analysis of well-defined Si quantum walls (periodic slabs) are presented. Using a unique combination of interference lithography and wet-­chemical KOH etching, vertically-standing, periodic Si rectangular slabs are fabricated with a slab thickness ranging from a few nm to ~ 200 nm. Each slab has its three principal axes in the <110>, <112> and <111> direction, and each slab surfaces is extended in the <110>-<112> plane and normal to the <111> direction. These samples are used to study the effects of the size confinement on the crystal properties of Si. Raman scattering experiment is carried out because the scattering of …

Ionization And Charge Changing In 0.5 - 8 Qmev Li^Q+ + He (Q=1,2,3) Collisions And Setup Of An Electron Spectrometer Control System, Oliver Woitke

Dissertations

Projectile charge changing and target ionization cross sections are measured for 0.5 to 8 qMeV Li^q+ + He (q=1,2,3) collisions. Total cross sections for single-electron capture (for L i^1,2,3+) and single-electron loss (for L i^1,2+) are obtained and compared to existing experimental and theoretical data. Also, single and double target ionization of He associated with specific outgoing projectile charge states are identified using coincidence techniques. Cross sections for target ionization associated with no projectile charge change (direct ionization), single-electron capture, and single-electron loss are measured and compared to existing experimental data and to available calculations. Double-to-single target ionization ratios R …

Design Of Gradient Index Optical Thin Films, Jeffrey J. Druessel

Theses and Dissertations

Gradient index thin films provide greater flexibility for the design of optical coatings than the more conventional 'layer' films. In addition, gradient index films have higher damage thresholds and better adhesion properties. This dissertation presents an enhancement to the existing inverse Fourier transform gradient index design method, and develops a new optimal design method for gradient index films using a generalized Fourier series approach. The inverse Fourier transform method is modified to include use of the phase of the index profile as a variable in rugate filter design. Use of an optimal phase function in Fourier-based filter designs reduces the …

Electrical Characterization Of Gasb Based Semiconductors For 2-4 Micrometers Diode Laser Applications, Daniel K. Johnstone

Theses and Dissertations

Deep Level Transient Spectroscopy (DLTS) was used to characterize the band offsets and deep levels in MBE grown GaSb-based semiconductors that are used in 2-4 µm laser diode structures. One of several deep level traps found in Al_xGa_1-xAs_ySb_1-y (x=0, 0.5, 0.6, 1.0) is a GaSb double acceptor trap. Progress is also made in establishing the model for the DX center in this material. The degree of compensation of the donor related DX center by GaSb affect where donors are situated, giving preference to one configuration over the many other possible configurations. One minority …

Degradation And Breakdown In Ultra-Thin Silicon Oxides, Christopher Franck

Theses

Emerging trends in the semiconductor device industry call for detailed knowledge of the properties of devices whose dimensions are small enough to exploit Quantum Mechanical effects. This thesis presents a complete picture of oxide degradation in MOS direct tunnel diodes (t0 <3.4 nm). It is demonstrated that for structures fabricated at different facilities and stressed with either gate or substrate injection, a universal degradation mode is revealed which is manifested as the build up of positive charge in the oxide. The data gathered demonstrates that the positive charging phenomena in sub-3.5 nm oxides is independent of oxide thickness, and is characterized by a voltage threshold and two-regime temperature dependence. Further, the catastrophic failure, or breakdown, of these oxides was studied and the strongest evidence to date is presented which links the positive charging phenomena to the oxide breakdown. This thesis concludes with the presentation of a novel device design which can exploit the properties of degradation and breakdown, in thin oxides, to achieve an EEPROM memory cell of superior endurance.

Design And Fabrication Of A Miniature Pressure Sensor Head Using Direct Bonded Ultra-Thin Silicon Wafers, Chad Eugene Statler

Theses

A miniature pressure sensor head is designed and fabricated using an ultra-thin silicon membrane directly bonded to an excimer laser micromachined substrate. The pressure sensor head has its intended implementation as part of an optically interrogated device with sensitivity to pressures ranging from 0.5 to 4.0 MPa. The pressure range design is shown to be easily adjusted by tailoring the thickness of the membrane wafer. The fabrication process features numerous advantages over existing pressure sensor construction technology including a maskless procedure and no chemical etching or mechanical thinning necessary to form the membrane after bonding. An optic lever is constructed …

Distribution Of Ionized And Neutral Halogenated Phenols In An Octanol-Water Membrane Model System, Robert Word

Dissertations and Theses

The accumulation of xenobiotics, such as halogenated phenols, in soils, sediments, and living organisms is primarily a partitioning process between an aquatic and organic phase. It is traditional to use a bulk octanol-water system to model the partitioning of a compound between complex biological lipid membranes and aqueous media. The octanol-water partition coefficient K_OW successfully approximates the lipid membrane-water partition coefficient K_LipW of neutral compounds. However, the ionized species of substituted phenols were shown to have a higher affinity for lipid membranes than predicted from octanol-water results.

Data on the octanol-water partition coefficients of molecular ions is limited. …

A Study Of The Gradient Drift Instability In The High-Latitude Ionosphere Using The Utah State University Time Dependent Ionospheric Model, Mahesh Subramanium

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Research over the years has established that the Gradient Drift Instability process causes small-scale irregularities, mostly along the edges of the high-latitude polar cap patches. Studying these irregularities will help in the development of a Global Scale Ionospheric model, which is a central part of a global space weather forecast system. Much theoretical work has been done with varying degrees of complexity to study this instability in the high latitude patches.

In this work we have used the Utah State University Time Dependent Ionospheric Model to model the high-latitude patches, calculate the growth rate of the instability, and perform a …

An Instrument For Experimental Secondary Electron Emission Investigations, With Application To The Spacecraft Charging Problem, Robert Davies

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Secondary electron emission (SEE) and incident-particle backscattering are important processes accompanying the impact of energetic electrons and ions on surfaces. The phenomena play a key role in the buildup of electrical charge on spacecraft surfaces. and are therefore of particular interest to scientists attempting to model spacecraft charging. In response to a demonstrated need for data, techniques for determining total secondary electron (SE) and backscatter (BS) yields S and n, and associated scattering-angle-resolved, scattering-energy-resolved, and simultaneous angle-energy-resolved yields have been developed. Further, an apparatus capable of making the necessary measurements for experimental determination of these quantities-for conducting materials in …

Characterization Of Spatial And Temporal Anisotropy In Turbulent Mixing Layers Using Optical Techniques, Patrick J. Gardner

Theses and Dissertations

The optical aberrations induced by mixing layers of dissimilar gases are recorded and analyzed in order to characterize the spatial and temporal properties of the flow. Laser light was propagated through a mixing layer of Helium and Nitrogen gas, having velocities of 8.5 m/sec and 1.5 m/sec, respectively. The light was propagated in a direction perpendicular to the plane of the mixing layer. The mixing layer was evaluated in two experimental regimes: free turbulent mixing, where the mixing layer spreads into the surrounding air; and channel flow, where the mixing layer is confined to a rectangular channel. The optical perturbations …

Gamma-Ray Optical Studies Of ⁷³Ge And ⁵⁷Fe, Walter Carlton Mcdermott Iii

Physics Theses & Dissertations

The research described herein is among the first attempts to test one of the more popular theories for development of a gamma-ray laser. This work is a "marriage" between the Borrmann effect, which is a consequence of the dynamical theory of x-ray diffraction, and time-filtering which comes from time-domain Mossbauer spectroscopy.

Our experiments involved the search for a nuclear Borrmann effect and the subsequent time-filtering effect using ⁵⁷Fe and ⁷³Ge. In both cases, no nuclear Borrmann effect was observed; however, the methodology and criteria necessary for such an observation with any isotope were documented. The procedures necessary for …

Two-Photon Quantum Interference Polarization Spectroscopy: Measurements Of Transition Matrix Elements In Atomic Rubidium, Alexander I. Beger

Physics Theses & Dissertations

The estimation of the adequacy of theoretical calculations on the atomic structure requires availability of the precise experimental data on radiative properties of the atoms. Such data is also required in astronomy and some important areas of technology. The lack of precision of traditional spectroscopic studies of atom presents a fundamental obstacle for progress in these areas. For example, in atomic rubidium, the best precision of the traditional spectroscopic results is on the order of about 1 - 5%, which does not allow for clear assessment of the latest sophisticated theoretical calculations on atomic rubidium structure, with emphasis on different, …