Digital Commons Network^™

Single-Mode Raman Fiber Laser In A Multimode Fiber, Matthew B. Crookston

Theses and Dissertations

The feasibility of a transverse single-mode Raman fiber laser using a multimode fiber has been investigated. The Raman fiber laser operates in low-order transverse modes despite the fact the fiber supports multimode beam propagation. The performance characteristics of the Raman fiber laser are compared with those of the single-pass SRS beam.

Effect Of Multi-Mode Vibration On Signature Estimation Using A Laser Vibration Sensor, Ngoya Pepela

Theses and Dissertations

A laser vibration sensor (LVS) can be used to determine the vibrational spectrum of targets such as vehicles using heterodyne laser Doppler velocimetry. The vibrational spectra of exterior skin of vehicles are known to have characteristic resonances due to the physical structure driven by motor gears and other moving parts. Each particular class of vehicle has a unique vibrational spectrum. This research shows how a body vibrating in higher order modes has the opportunity to eliminate spectral content of the target's vibrational spectrum while using an LVS to perform spectrum estimation. This is due to roughly equal amounts of laser …

Building Blocks For Time-Resolved Laser Emission In Mid-Infrared Quantum Well Lasers, Gabriel D. Mounce

Theses and Dissertations

The objective of this research is to improve the performance of mid-infrared semiconductor quantum-well lasers. Lasers operating in the mid-infrared are useful for many Air Force applications which include infrared (IR) countermeasures in particular. Countermeasure applications require lasers that are compact, and able to emit at high powers while operating at room temperature. Limits to power increases are seen in the transverse modal development of laser oscillation. These modes typically form in the waveguiding active region contributing to the laser output. However, competing modes outside of this region also develop when the confining structural layers have the right characteristics. These …

Detection Of Special Nuclear Material With High Purity Germanium (Hpge) And Mercuric Iodide (Hgi2) Gamma Detectors, Michael B. Nelson

Theses and Dissertations

The Defense Threat Reduction Agency (DTRA) contracted for two gamma radiation detectors: mercuric iodide (HgI₂) and electromechanically cooled (EMC) high purity germanium (HPGe) to support arms control inspection efforts. This project investigated whether these detectors could measure the quality and quantity of special nuclear material (SNM), particularly Pu-239 for the treaty verification mission. The project investigated two areas of detector capabilities: 1) HgI₂ and HPGe detector performance necessary to characterize the quality of plutonium and the presence of shielding materials and 2) HgI₂ and EMC HPGe detector performance degradation by high noise levels and EMC HPGe …

Phasing A Dual Optical Path System Using An Optical Fiber As A Phase Conjugate Mirror, Shawn M. Willis

Theses and Dissertations

Phase conjugation properties of stimulated Brillouin scattering (SBS) in a short multimode fiber have been investigated with an eye towards its application for a multi-channel double pass master oscillator power amplifier (MOPA) system. In particular, properties of the SBS beam to compensate for the axial and transverse phase distortion between individual channels in a multi-channel amplifier system were studied. Two optical paths were created by covering half of the laser beam with a microscope slide, and also by spatially splitting the wavefronts with a 4 prism set-up. The Stokes beams that traversed the same optical paths as the pump beams …

Optical Characterization Of Antimony-Based, Types-I And Ii, Multiple Quantum-Well Semiconductor Structures For Mid-Infrared Laser Applications, Edward G. Ferguson

Theses and Dissertations

This experiment characterizes antimony-based, multiple quantum-well, types-I and -II, semiconductor samples designed for laser applications. The samples emit light in the 3-5-micron range to exploit an atmospheric transmission window, making them ideal for infrared (IR)-seeking missile countermeasures. Photoluminescence (PL) spectra were collected and yielded bandgap (E(sub g)) dependence-on-temperature relationships. The type-I sample was found to follow the Varshni equation, while the type-II samples showed a rise with temperature in a portion of the curve that should be linear according to the Varshni equation. The type-II samples followed the Varshni equation well at higher temperature. The PL study indicated that the …

Scattering Of Ultra Wide Band X-Wave Pulses By A Sphere, Maged Fayez Moawad

Archived Theses and Dissertations

No abstract provided.

Afm, Cafm, And Efm Studies Of The Gan System, John C. Dickinson

Theses and Dissertations

This thesis discusses a variety of techniques based on the atomic force microscope (AFM), and their application to the GaN materials system. In particular, the local conductivity and contact potential of surfaces have been measured using the techniques of Conductive AFM (CAFM) and Surface Potential Electric Force Microscopy (SPEFM), respectively. CAFM studies of GaN surfaces have revealed that prismatic planes around islands and pits on surfaces can lead to enhanced conductivity, which may be related to leakage problems in device applications. With regard to SP-EFM work, the change in surface potential associated with inversion domains on Ga-polar GaN has been …

Measurement Of The Neutron (Helium-3) Spin Structure Functions At Low 4-Momentum: A Connection Between The Bjorken And Gerasimov-Drell-Hearn Sum Rule, Pibero Kisa Djawotho

Dissertations, Theses, and Masters Projects

This dissertation presents results of experiment E94-010 performed at Jefferson Laboratory (simply known as JLab) in Hall A.;The experiment aimed to measure the low Q2 evolution of the Gerasimov-DrellHearn (GDH) integral from Q 2 = 0.1 to 0.9 GeV2. The GDH sum rule at the real photon point provides an important test of Quantum Chromodynamics (QCD). The low Q2 evolution of the GDH integral contests various resonance models, Chiral Perturbation Theory (chiPT) and lattice QCD calculations, but more importantly, it helps us understand the transition between partonic and hadronic degrees of freedom. at high Q2, beyond 1 GeV2, the difference …

Chemical Bonding In Hard And Elastic Amorphous Carbon-Nitride Films, W. Jason Gammon

Dissertations, Theses, and Masters Projects

In this study, the chemical bonding in hard and elastic amorphous carbon nitride (a-CNx) films is investigated with x-ray photoelectron spectroscopy (XPS) and 15N, 13C, and 1H nuclear magnetic resonance (NMR) spectroscopy. The films were deposited by DC Magnetron sputtering in a pure nitrogen discharge on Si(001) substrates at 300--400??C. Nanoindentation measurements reveal an elastic modulus of ∼50 GPa and a hardness of ∼5 GPa, thus confirming our films are highly elastic but resist plastic deformation.;Our 13C NMR study demonstrates the absence of sp 3-bonded carbon in this material. Collectively, our N(1s) XPS, 13C NMR, and 15N NMR data suggest …

The Effect Of An Adsorbate Upon Secondary Emission Properties Of Low -Energy Ion Bombarded Metallic And Semiconductor Substrates, Wendy Sara Vogan

Dissertations, Theses, and Masters Projects

The absolute probabilities for low energy ion bombardment induced secondary emission of electrons and anions have been measured as a function of adsorbate coverage of the surface. The primary ion beams were incident at less than 500 eV on metallic, semiconducting and insulating surfaces. The adsorbate used was chiefly oxygen, and the coverage range studied was zero to about one monolayer. The presence of an adsorbate was observed to significantly enhance secondary emission of electrons and anions in the case of O - and Na+ impacting metallic (W, Al) and semiconducting (Si) substrates; the effect of the adsorbate was little …

Performance Advantages Of Maximum Likelihood Methods In Prbs-Modulated Time-Of-Flight Energy Loss Spectroscopy, Zhongyu Yang

Electronic Theses and Dissertations

This thesis describes the design, experimental performance, and theoretical simulation of a novel time-of-flight analyzer that was integrated into a high resolution electron energy loss spectrometer (TOF-HREELS). First we examined the use of an interleaved comb chopper for chopping a continuous electron beam. Both static and dynamic behaviors were simulated theoretically and measured experimentally, with very good agreement. The finite penetration of the field beyond the plane of the chopper leads to non-ideal chopper response, which is characterized in terms of an "energy corruption" effect and a lead or lag in the time at which the beam responds to the …

Crevassing And Calving Of Glacial Ice, James Patrick Kenneally

Electronic Theses and Dissertations

Calving of ice is a relatively new area of research in the still young field of glaciology. In the short time that calving has been studied, it has been mainly treated as an afterthought, with the predominant mode of thinking being that it will happen so to concern oneself with why is not important. Many studies dealt with observations of calving front positions over time vs. ice velocity in an attempt to quantify the calving rate as the difference between the two, while others have attempted to deduce some empirical relationship between calving rate and variables such as water depth …

Renormalization-Group Studies Of Three Model Systems Far From Equilibrium, Ivan T. Georgiev

Electronic Theses and Dissertations

This thesis describes the development of analytical and computational techniques for systems far from equilibrium and their application to three model systems. Each of the model systems reaches a non-equilibrium steady state and exhibits one or more phase transitions. We first introduce a new position-space renormalization-group approach and illustrate its application using the one-dimensional fully asymmetric exclusion process. We have constructed a recursion relation for the relevant dynamic parameters for this model and have reproduced all of the important critical features of the model, including the exact positions of the critical point and the first and second order phase boundaries. …

An Information Theoretic Study Of The Ising Antiferromagnet With Quenched Dilution On A Triangular Lattice, Matthew D. Robinson

Electronic Theses and Dissertations

This investigation applies information theoretic techniques to study the ordering and structure of the Ising antiferromagnet with quenched disorder on a triangular lattice. The pure system shows no phase transition due to the high degree of frustration present. However, when quenched vacancies are introduced randomly into this geometrically frustrated system, a phase transition at finite temperature, to an ordered phase, can arise. If the vacancies are introduced on all three sublattices of the triangular lattice, then a two-dimensional spin-glass transition occurs. If dilution takes place on only one sublattice, then the other two sublattices develop magnetiza- tions below the critical …

Magnetohydrodynamic Turbulence: The Development Of Lattice Boltzmann Methods For Dissipative Systems, Angus Ian Duncan Macnab

Dissertations, Theses, and Masters Projects

Computer simulations of complex phenomena have become an invaluable tool for scientists in all disciplines. These simulations serve as a tool both for theorists attempting to test the validity of new theories and for experimentalists wishing to obtain a framework for the design of new experiments. Lattice Boltzmann Methods (LBM) provide a kinetic simulation technique for solving systems governed by non-linear conservation equations. Direct LBMs use the linearized single time relaxation form of the Boltzmann equation to temporally evolve particle distribution functions on a discrete spatial lattice. We will begin with a development of LBMs from basic kinetic theory and …

Development Of A Portable Carbon Monoxide Sensor Based On An External Cavity Diode Laser At 1565 Nm, Eva Shirley Norris

Theses

Carbon monoxide is a major trace gas pollutant with road traffic being responsible for most emissions. Work has been done on the development of a carbon monoxide sensor, which is potentially capable of measuring the gas in vehicle exhaust emissions. This is based on tunable diode laser absorption spectroscopy The device must distinguish carbon monoxide from other gas species and from particulate matter. The device should also operate with a response time of the order of one second, have the potential for portability and a capacity for remote operation. Experimental work presented compares and contrasts the characteristics of the free-running …

Trace Analysis Of Organic Substances, Alan Giltinan

Theses

One of the major challenges facing the pharmaceutical industry is the control of the amount of trace contaminants during the manufacture of organic substances. Lowering the level of contamination improves the quality of the product and reduces possible side effects.

One of the main techniques used to detect trace contaminants is UV-VIS spectroscopy, where the unique absorption fingerprint of a chemical reveals its presence. UV-VIS absorption is based upon the Beer-Lambert Law. The critical point to note about this law is that the absorption is exponentially dependent on both the concentration of the absorber and the pathlength traversed by the …

Extracting Movement Patterns Using Fuzzy And Neuro-Fuzzy Approaches, Haci Mustafa Palancioglu

Electronic Theses and Dissertations

Several applications generate large volumes of data on movements including vehicle navigation, fleet management, wildlife tracking and in the near future cell phone tracking. Such applications require support to manage the growing volumes of movement data. Understanding how an object moves in space and time is fundamental to the development of an appropriate movement model of the object. Many objects are dynamic and their positions change with time. The ability to reason about the changing positions of moving objects over time thus becomes crucial. Explanations on movements of an object require descriptions of the patterns they exhibit over space and …

Multinuclear Nmr Studies Of Relaxor Ferroelectrics, Donghua Zhou

Dissertations, Theses, and Masters Projects

Multinuclear NMR of 93Nb, 45Sc, and 207Pb has been carried out to study the structure, disorder, and dynamics of a series of important solid solutions: perovskite relaxor ferroelectric materials (1-x) Pb(Mg1/3Nb 2/3)O3-x Pb(Sc1/2Nb1/2)O 3 (PMN-PSN).;93Nb NMR investigations of the local structure and cation order/disorder are presented as a function of PSN concentration, x. The superb fidelity and accuracy of 3QMAS allows us to make clear and consistent assignments of spectral intensities to the 28 possible nearest B-site neighbor (nBn) configurations, (NMg, NSc, NNb), where each number ranges from 0 to 6 and their sum is 6. For most of the …

Time-Resolved Optical Studies Of Colossal Magnetoresistance And Charge -Density Wave Materials, Yuhang Ren

Dissertations, Theses, and Masters Projects

This thesis presents measurements of collective modes and ultrafast carrier relaxation dynamics in charge-density-wave (CDW) conductors and colossal magnetoresistance (CMR) manganites. A femtosecond laser pump pulse excites a broad frequency spectrum of low-energy collective modes and electron-hole pairs thereby changing its optical properties. The low-energy collective excitations and quasiparticle relaxation and recombination processes are monitored by measuring the resulting photoinduced absorption as a function of probe pulse wavelength and time delay.;A general model was developed for the photogeneration and detection mechanism of collective modes based on light absorption in two-color pump-probe experiments. A broad spectrum of collective modes (phasons and …

Shock Wave Dispersion In Weakly Ionized Gas, Prasong Kessaratikoon

Physics Theses & Dissertations

Electrodeless microwave (MW) discharge in two straight, circular cylindrical resonant cavities in TE_1,1,1 and TM_0,1,2 modes were introduced to perform additional experimental studies on shock wave modification in non-equilibrium weakly ionized gases and to clarify the physical mechanisms of the shock wave modification process. The discharge was generated in 99.99% Ar at a gas pressure between 20 and 100 Torr and at a discharge power density less than 10.0 Watts/cm³. Power density used for operating the discharge was rather low in the present work, which was determined by evaluating the power loss inside the resonant cavity. …