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Articles 1 - 29 of 29
Full-Text Articles in Physics
Solid Phase Crystallization Of Vanadium Dioxide Thin Films And Characterization Through Scanning Electron Microscopy, Felipe Rivera
Solid Phase Crystallization Of Vanadium Dioxide Thin Films And Characterization Through Scanning Electron Microscopy, Felipe Rivera
Theses and Dissertations
Crystalline films of vanadium dioxide were obtained through thermal annealing of amorphous vanadium dioxide thin films sputtered on silicon dioxide. An annealing process was found that yielded polycrystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated single-crystal particles. Orientation Imaging Microscopy (OIM) was used to characterize and study the phase and the orientation of the vanadium dioxide crystals obtained, as well as to diferentiate them from other vanadium oxide stoichiometries that may have formed during the annealing process. There was no evidence of any other vanadium oxides present in the prepared samples. Indexing of the crystals for …
Investigation Of Radio Frequency Discharges And Langmuir Probe Diagnostic Methods In A Fast Flowing Electronegative Background Gas, Nathaniel P. Lockwood
Investigation Of Radio Frequency Discharges And Langmuir Probe Diagnostic Methods In A Fast Flowing Electronegative Background Gas, Nathaniel P. Lockwood
Theses and Dissertations
Discharges in a flowing background gas are used to produce charged and excited species for numerous applications including etching semiconductors and pumping gas discharge lasers (Pinhero and others, 1998). The effect of a flowing background gas on the charged and excited neutral species generation by an RF discharge in a flow tube and the diagnostics of the resulting plasma with a Langmuir probe have been investigated for pressures between 0.001 to 1 Torr and flow velocities up to 1000 m/s. This investigation was performed using a fluid method coupled to a chemical kinetic model and a hybrid Particle-In-Cell/Monte Carlo Collision …
Scandium Oxide Thin Films And Their Optical Properties In The Extreme Ultraviolet, Guillermo Antonio Acosta
Scandium Oxide Thin Films And Their Optical Properties In The Extreme Ultraviolet, Guillermo Antonio Acosta
Theses and Dissertations
This study reports on the physical and optical characterization of scandium oxide thin films. Thin films of scandium oxide, 20-40 nm thick, were deposited on silicon wafers, quartz slides, and silicon photodiodes by reactively sputtering scandium in an oxygen environment. These samples were characterized using ellipsometry, high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis. A 28.46 nm thick scandium oxide thin film was measured in the Extreme Ultraviolet (EUV) from 2.7 to 50 nm (459.3 to 24.8 eV) using synchrotron radiation at the Advanced Light Source Beamline 6.3.2 at the Lawrence Berkeley National Laboratory. In …
Construction Of A Calcium Matter-Wave Interferometer, Christopher Joseph Erickson
Construction Of A Calcium Matter-Wave Interferometer, Christopher Joseph Erickson
Theses and Dissertations
I describe the construction of a calcium matter-wave interferometer. The interferometer is based on a Ramsey-Borde scheme, and uses a thermal beam of atoms excited by an optical-frequency transition in calcium. In our experiment four pi/2 pulses of light are delivered to the atoms, which split and recombine the wave functions of the atoms. Our experimental design minimizes first-order Doppler shifts, and allows for the cancellation of systematic errors including phase shifts due to rotation and acceleration. I describe the individual components of the interferometer and its assembly. The requirements for the electronics used in the experiment as well as …
Error Sensor Placement For Active Control Of An Axial Cooling Fan, Benjamin M. Shafer
Error Sensor Placement For Active Control Of An Axial Cooling Fan, Benjamin M. Shafer
Theses and Dissertations
Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in …
Collision Broadening Using Alkali-Filled, Hollow Core Fibers, Luke P. Rodgers
Collision Broadening Using Alkali-Filled, Hollow Core Fibers, Luke P. Rodgers
Theses and Dissertations
The goal of this research was to demonstrate the possibility of collision broadening in a cesium-filled, hollow-core fiber as an alternative to the proven technique of pressure broadening. Theoretically, alkali electrons should relax from the 2P3/2 to the 2P1/2 level and the absorption spectrum should collisionally broaden due to the presence of fiber walls, as opposed to the more common pressure broadening method. An absorption dip located at 852.34nm was recorded in a pressure broadened comparison leg. This data was used as a baseline during analysis of the fiber leg's data. While the fiber was successfully …
Time Resolution Of Collapse Events During The Progation Of Ultraviolet Filaaments, Teresa J. Fondren
Time Resolution Of Collapse Events During The Progation Of Ultraviolet Filaaments, Teresa J. Fondren
Theses and Dissertations
Long distance propagation, or filamentation, of short, intense laser pulses is suggested to be possible through the balance of two effects: self-focusing, when a nonlinear index of refraction of air is induced by high intensities, and de-focusing, due to the plasma created by the pulse. Applications for filamentation include areas such as remote sensing and directed energy. A split-step spectral propagation simulation is used to model the behavior of a high intensity ultraviolet laser pulse propagating through air. Convergence of femtosecond duration collapses that form on the leading edge of the pulse in the time domain is achieved with an …
A General Quantum Mechanical Method To Predict Positron Spectroscopy, Paul E. Adamson
A General Quantum Mechanical Method To Predict Positron Spectroscopy, Paul E. Adamson
Theses and Dissertations
The nuclear-electronic orbital (NEO) method was modified and extended to positron systems. NEO - second-order Moeller-Plesset perturbation (MP2) energies and annihilation rates were calculated for the positronium hydride (PsH) system, and the effects of basis set size on correlation energies captured with the NEO-MP2 and NEO-full configuration interaction (FCI) methods are compared and discussed. Equilibrium geometries and vibrational energy levels were computed for the LiX and e+LiX (X = H, F, Cl) systems at the MP2 and NEO-MP2 levels. It was found that anharmonicity plays a significant role, specifically in the differences between the vibrational energy levels of …
Phenomenological Model For Infrared Emissions From High-Explosive Detonation Fireballs, Kevin C. Gross
Phenomenological Model For Infrared Emissions From High-Explosive Detonation Fireballs, Kevin C. Gross
Theses and Dissertations
Time-resolved infrared spectra were recently collected via a Fourier-transform spectrometer (FTS) from the detonation fireballs of two types of conventional military munitions (CMM) as well as uncased TNT and four types of enhanced novel explosives (ENEs). The CMM spectra are dominated by continuum emission, and a single-temperature Planckian distribution, modified for atmospheric attenuation, captures most of the variation in the data. Some evidence of selective emission is identified by systematic patterns in the fit residuals. The behavior of these systematic residuals affords a distinction between the two types of CMMs studied. The uncased TNT and ENE spectra appear strongly influenced …
Development Of A Method For Calculating Delta Scuti Rotational Velocities And Hydrogen Beta Color Indices, Tabitha Christi Buehler
Development Of A Method For Calculating Delta Scuti Rotational Velocities And Hydrogen Beta Color Indices, Tabitha Christi Buehler
Theses and Dissertations
To add to the understanding of the structure and evolution of Delta Scuti stars, 167 Delta Scutis north of -01 degrees declination and brighter than 13th magnitude have been observed spectroscopically. A method for calculating rotational velocity values and Hydrogen-Beta color indices for the stars in the data set with no previously published values is developed, using the stars in the data set brighter than 7th magnitude. Rotational velocity values for four stars with previously unknown values and Hydrogen-Beta index values for five stars with previously unknown values are calculated.
Raman Fiber Lasers And Amplifiers Based On Multimode Fibers And Their Applications To Beam Cleanup, Nathan B. Terry
Raman Fiber Lasers And Amplifiers Based On Multimode Fibers And Their Applications To Beam Cleanup, Nathan B. Terry
Theses and Dissertations
Raman fiber lasers (RFLs) and Raman fiber amplifiers (RFAs) in multimode fibers were explored. The RFL based on a graded-index fiber was shown to be very efficient relative to RFLs based on singlemode fibers. Several configurations of the RFL were examined; the beam quality of the Stokes beam depended on the reflectivity of the output coupler and the Stokes power. When used as a beam combiner, the RFL was a highly efficient brightness converter. RFL configurations which used dichroic mirrors were shown to be potentially useful for RFLs based on very large fibers. The forward- and backward-seeded geometries of an …
Optimization Of Control Source And Error Sensor Locations In Free Field Active Noise Control, Connor Raymond Duke
Optimization Of Control Source And Error Sensor Locations In Free Field Active Noise Control, Connor Raymond Duke
Theses and Dissertations
Previous work has shown that active noise control (ANC) can be applied to axial cooling fans. Optimization of the control source and error sensor placement is desired to maximize the attenuation using ANC. A genetic algorithm was developed to find the optimal placement of control sources for a given primary source. The optimal configuration of control sources around a single primary source was shown to be a linear arrangement of the sources. This holds true for both two-dimensional as well as three-dimensional configurations. The higher-order radiation of the linear arrangement has also been verified experimentally, but the improvement in the …
Development Of A New Ca Ii H And K Spectrophotometric Temperature Index, Kathleen Elizabeth Moncrieff
Development Of A New Ca Ii H And K Spectrophotometric Temperature Index, Kathleen Elizabeth Moncrieff
Theses and Dissertations
We are developing a new spectrophotometric temperature index based on the Ca II H and K lines. Because these lines are present even in very cool stars and because the Ca II H line is blended with the H-epsilon line in hot stars, this index should cover a very broad range of spectral types. Our data set consisted of 95 stars with spectral types ranging from O9 to M1. We examined five different indices based on the Ca II H + H-epsilon and K lines, as well as single-wavelength indices centered on each of the H-delta and H-gamma lines, which …
The Effect Of Nonlinear Propagation On Near-Field Acoustical Holography, Micah Raymond Shepherd
The Effect Of Nonlinear Propagation On Near-Field Acoustical Holography, Micah Raymond Shepherd
Theses and Dissertations
Near-field acoustical holography (NAH) has been used extensively for acoustical imaging of infinitesimal-amplitude (or small-amplitude) sources. However, recent interests are in the application of NAH to image finite-amplitude (or high-amplitude) sources such as jets and rockets. Since NAH is based on linear equations and finite-amplitude sources imply nonlinear effects, which cause shock formation and consequently an altered spectral shape, a feasibility study is carried out to determine the effect of nonlinear propagation on NAH. Jet and rocket sources typically have a distinct spectral shape resembling a ‘haystack’ and center frequencies varying from 30 to 300 Hz. To test the effect …
On Stability And Evolution Of Solutions In General Relativity, Stephen M. Taylor
On Stability And Evolution Of Solutions In General Relativity, Stephen M. Taylor
Theses and Dissertations
This thesis is concerned with several problems in general relativity and low energy string theory that are pertinent to the time evolution of the gravitational field. We present a formulation of the Einstein field equations in terms of variational techniques borrowed from geometric analysis. These equations yield the evolution equations for the Cauchy problems of both general relativity and low energy string theory. We then proceed to investigate the evolutionary linear stability of Schwarzschild-like solutions in higher dimensional relativity called black strings. These objects are determined to be linearly unstable. This motivates a further stability analysis of the charged p-brane …
Development Of A Mevva Based Beryllium-7 Plasma Source, David K. Olson
Development Of A Mevva Based Beryllium-7 Plasma Source, David K. Olson
Theses and Dissertations
We have designed a new type of plasma gun ion source for a Malmberg-Penning trap based on Metal Vapor Vacuum Arc (MeVVA) ion source designs. Our primary intent with this MeVVA-type source is to create a confinable beryllium-7 (7-Be) plasma. 7-Be is a peculiar isotope due to its varying radioactive decay half-life in different electro-chemical configurations. It is also found in an unexpected abundance at high altitudes of the Earth's atmosphere. It is possible ioniziation affects the radioactivity of the isotope, partly explaining this discrepancy with atmospheric models. The short half-life of 7-Be requires us to replace the sample inside …
Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics, Nicole Brimhall
Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics, Nicole Brimhall
Theses and Dissertations
We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux directional EUV source has available wavelengths between 8 nm and 62 nm and easily rotatable linear polarization. The polarimeter will aid researchers at BYU in characterizing EUV thin films and improving their understanding of materials for use in EUV optics. This first-time workhorse application of laser high harmonics enables polarization-sensitive reflection measurements not previously available in the EUV. We have constructed a versatile positioning system that places harmonics on the microchannel plate detector with an accuracy of 0.3 mm, which allows …
Parallel Fast Multipole Method For Molecular Dynamics, Reid G. Ormseth
Parallel Fast Multipole Method For Molecular Dynamics, Reid G. Ormseth
Theses and Dissertations
We report on a parallel version of the Fast Multipole Method (FMM) implemented in the classical molecular dynamics code, NAMD (Not Another Molecular Dynamics program). This novel implementation of FMM aims to minimize interprocessor communication through the modification of the FMM grid to match the hybrid force and spatial decomposition scheme already present in NAMD. This new implementation has the benefit of replacing all-to-all communications broadcasts with direct communications between nearest neighbors. This results in a significant reduction in the amount of communication compared to earlier attempts to integrate FMM into common molecular dynamics programs. The early performance of FMM …
An Infrared Camera Simulation For Estimating Spatial Temperature Profiles And Signal-To-Noise Ratios Of An Airborne Laser-Illuminated Target, David F. Orth
Theses and Dissertations
Airborne Laser testing and evaluation can be aided by developing a spectrally-based infrared camera simulation to explore how the target surface's specular and diffuse reflectivities affect the observed signal-to-noise ratio (SNR) and how the target's temperature in the laser spot can estimated. This simulation provides for the observed irradiance, scaled by atmospheric absorption, to consist of the target's self-emission, reflected background emission, and the path emission from the observer to the target. The observed irradiance is scaled and distributed onto a focal plane array by way of a simulated optical system, whose effects are described by modulation transfer functions. The …
Coupling Down Converted Light Into Single Mode Fibers, David A. Niemi
Coupling Down Converted Light Into Single Mode Fibers, David A. Niemi
Theses and Dissertations
We investigate the influence of the pump and collection mode parameters on the collection efficiency of Type I down converted photons into single mode fibers. For best single and coincidence counting rates, we find that the mode sizes should be close to the same size and that the mode waists should be located near the down-conversion crystal. Larger collection waists give higher collection efficiencies, but lower singles counts.
Stimulated Brillouin Scattering Beam Cleanup And Beam Phasing Through Two Passive Channels, Omar Gamboa
Stimulated Brillouin Scattering Beam Cleanup And Beam Phasing Through Two Passive Channels, Omar Gamboa
Theses and Dissertations
Stimulated Brillouin scattering (SBS) beam cleanup and SBS piston correction properties are explored. This research measures the beam cleaning and phase-conjugating properties of stimulated Brillouin scattering in an optical fiber. The first stage of this research began by coupling an aberrated beam into a long multimode 62.5 micron core fiber to demonstrate its beam cleanup properties. The Stokes beam obtained was shown to be the fundamental fiber mode, LP01. The second stage spatially divided the pump beam into two equal halves. Each half was then sent through two different channels. The path length of one channel remained fixed while the …
Portable Diode Pumped Femtosecond Laser, David A. Jones
Portable Diode Pumped Femtosecond Laser, David A. Jones
Theses and Dissertations
This thesis discusses the work to make ultrashort pulsed lasers smaller and more economical. While sharing many of the basic properties of normal beam optics there are some specific properties in both creating and exploiting those pulses that must be understood. The discussion will focus on mode locking as the primary way of producing ultrashort pulses. Particular attention will be paid to intracavity group velocity dispersion and how to correct it inside the cavity. The discussion then turns to the basis of our work including initial cavity design and component selection with focus on the specific crystals used in the …
A Study Of Bi-Directional Reflectance Distribution Functions And Their Effects On Infrared Signature Models, Samuel I. Harkiss
A Study Of Bi-Directional Reflectance Distribution Functions And Their Effects On Infrared Signature Models, Samuel I. Harkiss
Theses and Dissertations
Since 2004, AFIT has been developing a trend-analysis tool to assess large commercial aircraft infrared (LCAIR) signatures. In many cases, this code predicted signatures to within 10% of measured data. However, other results indicated that the single-bounce, specular-reflection algorithm being used failed to adequately simulate interactions between aircraft parts where either the specular component is dominated by diffuse reflection or part-to-part multiple-bounce reflections contribute significantly to the signature. This research incorporates Bi-Directional Reflectance Distribution Functions (BRDF's) and multiple-bounce calculations into the LCAIR model. A physical aircraft model was constructed from aluminum, and measurements were taken before and after a surface …
Optical Tracking For Relative Positioning In Automated Aerial Refueling, James H. Spencer
Optical Tracking For Relative Positioning In Automated Aerial Refueling, James H. Spencer
Theses and Dissertations
An algorithm is designed to extract features from video of an air refueling tanker for use in determining the precise relative position of a receiver aircraft. The algorithm is based on receiving a known estimate of the tanker aircraft's position and attitude. The algorithm then uses a known feature model of the tanker to predict the location of those features on a video frame. A corner detector is used to extract features from the video. The measured corners are then associated with known features and tracked from frame to frame. For each frame, the associated features are used to calculate …
Development Of An H-Alpha Index For The Detection Of Pms Candidates In Young Open Clusters, Liberty Rae Evanko
Development Of An H-Alpha Index For The Detection Of Pms Candidates In Young Open Clusters, Liberty Rae Evanko
Theses and Dissertations
One phase of formation of medium- and low-mass stars is the optically visible phase known as the pre-main-sequence or PMS phase. In order to further the understanding of this phase, more of these PMS objects need to be identified and classified. Previous techniques have used photometry to identify possible PMS objects by their characteristic Hα emission. Once identified these objects can be studied spectroscopically yielding complete PMS classification. This study develops a method to locate these emission objects that overcomes two limitations of previous techniques. The first limitation is the need for the creation of reddening maps. It is eliminated …
Direct Diode Pumped Raman Amplifier Based On A Multimode Graded Index Fiberr, Charles James Baird
Direct Diode Pumped Raman Amplifier Based On A Multimode Graded Index Fiberr, Charles James Baird
Theses and Dissertations
The direct pumping of a Raman fiber amplifier (RFA) was attempted using an array of four 25W, fiber pigtailed diodes at 936nm, combined via a 7 channel fiber beam combiner. The initial attempt was conducted using a 1.8 km, 100 micron core, GRIN fiber with an NA of .29 and attenuation 3.6 dB/km at 936nm. While amplification was not achieved, over 200mW of conversion was shown, with 10.4W of pump power and 3.5W of seed. This corresponds to an average conversion efficiency of 2.2%. The subsequent effort utilized a 2km long, 200 micron core, GRIN fiber, with NA of .27 …
Thermally Activated, Variable Blazed Grating For Coherent Beam Steering, Matthew T. Johnson
Thermally Activated, Variable Blazed Grating For Coherent Beam Steering, Matthew T. Johnson
Theses and Dissertations
The ability to perform non-mechanical optical beam steering is of critical importance in laser communication and remote sensing; it is as vital as a phased-array antenna is for RADAR. Directed energy transmission and direction-selective reception increase performance and produce tactical advantage in DoD applications. However, specific geometric features of non-mechanical beam steering devices must be designed in proportion to the wavelength of the monochromatic light to be steered. Also, the ability to handle higher energies by reducing the energy per unit requires large areas of uniform properties on the micrometer scale. These challenges have been addressed in the past using …
Cafm Studies Of Epitaxial Lateral Overgrowth Gan Films, Vishal P. Kasliwal
Cafm Studies Of Epitaxial Lateral Overgrowth Gan Films, Vishal P. Kasliwal
Theses and Dissertations
This thesis uses the techniques of atomic force microscopy (AFM) and conductiveAFM (CAFM) to study defect sites on GaN films. In particular, these defect sites demonstrate current leakage under reverse-bias conditions that are detrimental to device fabrication. Two growth techniques that were used to improve this leakage behavior for samples in this study included: epitaxial lateral overgrowth (ELO) and nano-ELO using a Si3N4 film. Both techniques decrease defects such as threading dislocations by controlling the nucleation and growth behavior of the GaN films. The EL0 technique uses a patterned dielectric film to laterally grow micron-wide regions (referred to as 'wings') …
Raman Scattering In Gan And Zno, Shinobu Nagata
Raman Scattering In Gan And Zno, Shinobu Nagata
Theses and Dissertations
The Micro-Raman scattering technique has been used for the study of GaN and ZnO. Capabilities of the Raman technique and existing literature on Raman spectroscopy in GaN and ZnO are reviewed. About 50 GaN and ZnO samples with a wide range of properties are studied. From the analysis of positions of the E2H and A1(LO) phonon modes, biaxial stress and plasmon coupling of the Al(LO) mode are observed and compared to a bulk GaN sample. The stress-related shift rate for the AI(LO) mode in hexagonal GaN is established to be 2.7 ± 0.4 cm-1/GPa through series of GaN with low …