Physical Sciences and Mathematics Commons^™

A Review Of Ball Lightning Models, Hasitha Mahabaduge

Georgia Journal of Science

Ball lightning is a natural phenomenon that occurs in the atmosphere. However due to its brevity and rarity, its occurrence is not well understood. Three models based on electromagnetic properties are discussed in this paper to explain the rare phenomenon of ball lightning. The first model incorporates the idea of electron bunching, electrons moving with different velocities. This creates a plasma bubble by recombining electrons with ionized gas to form plasma that is stabilized by a standing microwave. The second model explains the idea of streamers being tangled and linked in a magnetic field while stabilized by the conservation of …

Generating Electromagnetic Nonuniformly Correlated Beams, Milo W. Hyde Iv, Xifeng Xiao, David G. Voelz

Faculty Publications

We develop a method to generate electromagnetic nonuniformly correlated (ENUC) sources from vector Gaussian Schell-model (GSM) beams. Having spatially varying correlation properties, ENUC sources are more difficult to synthesize than their Schell-model counterparts (which can be generated by filtering circular complex Gaussian random numbers) and, in past work, have only been realized using Cholesky decomposition—a computationally intensive procedure. Here we transform electromagnetic GSM field instances directly into ENUC instances, thereby avoiding computing Cholesky factors resulting in significant savings in time and computing resources. We validate our method by generating (via simulation) an ENUC beam with desired parameters. We find the …

Effect Of Ar(3p54p; 2p)+M -> Ar(3p54s; 1s)+M Branching Ratio On Optically Pumped Rare Gas Laser Performance, Daniel J. Emmons Ii, David E. Weeks

Faculty Publications

Optically pumped rare gas laser performance is analyzed as a function of the Ar(3p⁵4p; 2p) + M → Ar(3p⁵4s; 1s) + M branching ratios. Due to the uncertainty in the branching ratios, a sensitivity study is performed to determine the effect on output and absorbed pump laser intensities. The analysis is performed using a radio frequency dielectric barrier discharge as the source of metastable production for a variety of Argon in Helium mixtures over pressures ranging from 200 to 500 Torr. Peak output laser intensities show a factor of 7 increase as the branching ratio is …

Charged Fusion Product Plasma Diagnostics In Spherical Tokamaks, Alexander Netepenko

FIU Electronic Theses and Dissertations

Charged fusion products from the D(d,p)t reaction, protons (p) and tritons (t), can be detected to obtain time and position dependent information on the fusion reaction profile in plasmas heated with neutral particles beams. We have developed a prototype instrument consisting of charged particle detectors with ion-implanted-silicon surface barrier detectors. Each detector is combined with two replaceable collimators in such a way that it can accept protons and tritons emitted from a well-defined area inside the plasma. The detectors thus provide curved views across the plasma volume.

Combining the data of all six detectors allows one to study changes in …

Experimental Testing Of A 3d-Printed Metamaterial Slow Wave Structure For High Power Microwave Generation, Antonio B. De Alleluia

Electrical and Computer Engineering ETDs

A metamaterial (MTM) high power microwave (HPM) vacuum electron device (VED) was developed using 3D printing technology. The specific geometric pattern of the source can produce both negative permittivity and permeability to interact with a relativistic electron beam. The electron beam is generated using a pulsed electron accelerator with a maximum energy of 700 keV and lasting approximately 16 ns. The design of this novel VED consists of a circular waveguide loaded with complementary split-ring resonators in a linear periodic arrangement in which the relativistic beam travels guided by a magnetic field. The electrons interact with the MTM producing electromagnetic …

Measurement Of Electron Density And Temperature From Laser-Induced Nitrogen Plasma At Elevated Pressure (1–6 Bar), Ashwin P. Rao [*], Mark Gragston, Anil K. Patnaik, Paul S. Hsu, Michael B. Shattan

Faculty Publications

Laser-induced plasmas experience Stark broadening and shifts of spectral lines carrying spectral signatures of plasma properties. In this paper, we report time-resolved Stark broadening measurements of a nitrogen triplet emission line at 1–6 bar ambient pressure in a pure nitrogen cell. Electron densities are calculated using the Stark broadening for different pressure conditions, which are shown to linearly increase with pressure. Additionally, using a Boltzmann fit for the triplet, the electron temperature is calculated and shown to decrease with increasing pressure. The rate of plasma cooling is observed to increase with pressure. The reported Stark broadening based plasma diagnostics in …

Nonlinear Characterizing Of A New Titanium Nitride On Aluminum Oxide Metalens, Michael A. Cumming

Theses and Dissertations

A sample metalens generated from Titanium Nitride deposited onto Aluminum Oxide was designed to focus at 10 microns with a beam centered at 800nm, and when analyzed with high intensity illumination was found to have a focal length of 9.650 ±.003µm at an intensity of 16.93[MW/cm² ]. Analyzing this change by comparing it to a Fresnel Lens’ physics shows that for this lens, the effective nonlinear index of refraction is certainly greater than the nonlinear index of just Titanium Nitride itself, at −1.6239 × 10⁻¹⁵[m²/W] compared to the materials −1.3 × 10⁻¹⁵[m^{2 …}

Characterization Of Argon And Ar/Cl2 Plasmas Used For The Processing Of Niobium Superconducting Radio-Frequency Cavities, Jeremy J. Peshl

Physics Theses & Dissertations

The plasma processing of superconducting radio-frequency (SRF) cavities has shown significant promise as a complementary or possible replacement for the current wet etch processes. Empirical relationships between the user-controlled external parameters and the effectiveness of Reactive Ion Etching (RIE) for the removal of surface layers of bulk niobium have been previously established. However, a lack of a physical description of the etching discharge, particularly as the external parameters are varied, limits the development of this technology. A full understanding of how these external parameters affect both the amount of material removed and the physical properties of the plasma would aid …

Pulse Power Effects On Transient Plasma Ignition For Combustion, David Wayne Alderman Ii

Electrical & Computer Engineering Theses & Dissertations

Transient plasma ignition (TPI) uses highly non-equilibrium plasmas, driven by less than 100 nanosecond, high-voltage pulses, to initiate combustion. The effects of pulse repetition frequency (PRF) and ultrashort nanosecond rise times on TPI are investigated in this work using lean, stoichiometric, and rich air-fuel mixtures at atmospheric pressure. Experimental data show the transient plasmas driven by ultrashort rise time, high voltage pulses at high PRF’s enhance the combustion of lean or stoichiometric air-methane mixtures in a static chamber. In particular, increasing PRF enhances the combustion performance by means of reduced delay times independent of the equivalence ratio of the air-fuel …

Obituary: Anthony Starace (1945-2019)

Anthony F. Starace Publications

Anthony Starace, George Holmes University Professor of physics, died Sept. 5 from complications related to pancreatitis. He was 74.

Starace was born July 24, 1945, in the Queens borough of New York City. He graduated from Stuyvesant High School and earned his bachelor’s degree from Columbia University in 1966 before moving west to the University of Chicago, where he earned his doctorate under adviser Ugo Fano in 1971. It was in Chicago that he met Katherine Fritz of Beatrice, Nebraska, his wife of 51 years.

Following a postdoctoral appointment at Imperial College London, Starace moved to Lincoln as an assistant …

Numerical Simulation Of Unstable Laser Resonators With A High Gain Medium, Robert L. Lloyd

Theses and Dissertations

This research focused on the numeric simulation of unstable laser resonators with high gain media. In order to accomplish the research, the modes and eigenvalues for various bare cavity resonator were computed followed by modes of a resonator in the presence of gain. Using a Fourier Split Step Method in a Fox and Li iteration scheme, different laser outputs for various laser cavities with gain were computed. Various parameters defining positive branch confocal unstable resonators were chosen corresponding to four studies. The four studies focused on modifying laser cavity Fresnel number, gain medium parameters, gain cell position, and gain cell …

Measuring Length Of Electron Bunches With Optics In Lcls-Ii, Nathan Ahn, Alan Fisher

STAR Program Research Presentations

Since the launch of the LINAC Coherent Light Source (LCLS) in 2009, there have been over 1,000 publications enabling pioneering research across multiple fields. Advances include: harnessing the sun’s light, revealing life’s secrets and aiding drug development, developing future electronics, designing new materials and exploring fusion, customizing chemical reactions, and many more. These discoveries gathered worldwide attention, and now work has begun on a new revolutionary tool, LCLS-II. The LCLS-II will pulse at a million times a second, compared to the 120 pulses from the LCLS. Within the LCLS-II, there are two chicanes, serpentine curves. As the electron beam passes …

On The Pulsed Laser Ablation Of Metals And Semiconductors, Todd A. Van Woerkom

Theses and Dissertations

This dissertation covers pulsed laser ablation of Al, Si, Ti, Ge, and InSb, with pulse durations from tens of picosecond to hundreds of microseconds, fluences from ones of J/cm² to over 10,000 J/cm², and in ambient air and vacuum. A set of non-dimensional scaling factors was created to interpret the data relative to the laser and material parameters, and it was found that pulse durations shorter than a critical timescale formed craters much larger than the thermal diffusion length, and longer pulse durations created holes much shallower than the thermal diffusion length. Low transverse order Gaussian beams …

Increasing The Functionality Of Additive Manufacturing Through Atmospheric Microplasma And Nanotechnology, Alexander Jon Ulrich

Doctoral Dissertations

Additive Manufacturing (AM) has been changing the manufacturing landscape for the last 20 years. As the interest and demand for both polymer and metal-based 3D printing has grown, the materials and machines used have increased in capabilities. Despite the growth and advancement, there are still a large number of improvements that can be made to add functionality to 3D printers. Metal AM, a subcategory of 3D printing, has garnered much attention among industrial applications with large companies such as General Electric trying to implement the technology to increase innovative designs for motors. Some of the limitations on AM have to …

Polarization Properties Of Airy And Ince-Gaussian Laser Beams, Sean Michael Nomoto

Graduate Theses and Dissertations

The description of polarization states of laser light as linear, circular polarization within the paraxial scalar wave approximation is adequate for most applications. However, this description falls short when considering laser light as an electromagnetic wave satisfying Maxwell's equations. An electric field with a constant unit vector for direction of the field and a space dependent complex scalar amplitude in the paraxial wave approximation does not satisfy Maxwell equations which, in general, requires all three Cartesian components of electric and magnetic fields associated for a nonzero laser beam to be nonzero.

Physical observation of passing a linearly polarized laser through …

Plasma Spectroscopy Of Titanium Monoxide For Characterization Of Laser Ablation, Todd A. Van Woerkom, Glen P. Perram, Christian G. Parigger, Brian D. Dolasinski, Charles D. Phelps, Patrick A. Berry

Faculty Publications

Ablation of titanium wafers in air is accomplished with 60 µs pulsed, 2.94 µm laser radiation. Titanium monoxide spectra are measured in the wavelength range of 500 nm to 750 nm, and molecular signatures include bands of the C3 Δ → X3 Δ α, B3 Π → X3 Δ γ', and A3 Φ → X3 Δ γ transitions. The spatially and temporally averaged spectra appear to be in qualitative agreement with previous temporally resolved studies that employed shorter wavelengths and shorter pulse durations than utilized in this work. The background signals in the current study are possibly due to particulate …

Effects Of Pulse Width On He Plasma Jets In Contact With Water Evaluated By Oh(A-X) Emission And Ohaq Production, Shutong Song, Esin B. Sözer, Chunqi Jiang

Bioelectrics Publications

Nanosecond pulsed helium plasma jets impinging on water produce hydroxyl radicals both in gas- and liquid-phase. In this study, the effects of pulse width on a repetitively pulsed plasma jet in contact with water are evaluated via OH(A-X) emission and OH_aq production in water for various pulse widths ranging from 200 to 5000 ns. The maximal energy efficiency of OH(A-X) emission is obtained for pulse widths of 600-800 ns whereas the maximal efficiency of OH_aq production is at 200 ns. Temporally-resolved emission spectroscopy shows that more than 40% of OH(A-X) emission is produced during the first 200 ns …

Slow Light With Interleaved P-N Junction To Enhance Performance Of Integrated Mach-Zehnder Silicon Modulators, Marco Passoni, Dario Gerace, Liam O'Faolain, Lucio Claudio Andreani

Cappa Publications

Slow light is a very important concept in nanophotonics, especially in the context of photonic crystals. In this work, we apply our previous design of band-edge slow light in silicon waveguide gratings [M. Passoni et al, Opt. Express 26, 8470 (2018)] to Mach-Zehnder modulators based on the plasma dispersion effect. The key idea is to employ an interleaved p-n junction with the same periodicity as the grating, in order to achieve optimal matching between the electromagnetic field profile and the depletion regions of the p-n junction. The resulting modulation efficiency is strongly improved as compared to common modulators based on …

Performance Of Plastic Electron Optics Components Fabricated Using A 3d Printer, Phillip Wiebe, Peter Beierle, Hua-Chieh Shao, Bret Gergely, Anthony F. Starace, Herman Batelaan

Anthony F. Starace Publications

We show images produced by an electron beam deflector, a quadrupole lens and a einzel lens fabricated from conducting and non-conducting plastic using a 3D printer. Despite the difficulties associated with the use of plastics in vacuum, such as outgassing, poor conductivity, and print defects, the devices were used successfully in vacuum to steer, stretch and focus electron beams to millimeter diameters. Simulations indicate that much smaller focus spot sizes might be possible for such 3D-printed plastic electron lenses taking into account some possible surface defects. This work was motivated by our need to place electron optical components in difficult-to-access …

Analytic Generalized Description Of A Perturbative Nonparaxial Elegant Laguerre-Gaussian Phasor For Ultrashort Pulses In The Time Domain, Andrew Vikartofsky, Ethan C. Jahns, Anthony F. Starace

Anthony F. Starace Publications

An analytic expression for a polychromatic phasor representing an arbitrarily short elegant Laguerre-Gauss (eLG) laser pulse of any spot size and LG mode is presented in the time domain as a nonrecursive, closed-form perturbative expansion valid to any order of perturbative correction. This phasor enables the calculation of the complex electromagnetic fields for such beams without requiring the evaluation of any Fourier integrals. It is thus straightforward to implement in analytical or numerical applications involving eLG pulses.

Analytic Description Of High-Order Harmonic Generation In The Adiabatic Limit With Application To An Initial S State In An Intense Bicircular Laser Pulse, M. V. Frolov, N. L. Manakov, A. A. Minina, A. A. Silaev, N. V. Vvedenskii, M. Yu. Ivanov, Anthony F. Starace

Anthony F. Starace Publications

An analytic description of high-order harmonic generation (HHG) is proposed in the adiabatic (low-frequency) limit for an initial s state and a laser field having an arbitrary wave form. The approach is based on the two-state time-dependent effective range theory and is extended to the case of neutral atoms and positively charged ions by introducing ad hoc the Coulomb corrections for HHG. The resulting closed analytical form for the HHG amplitude is discussed in terms of real classical trajectories. The accuracy of the results of our analytic model is demonstrated by comparison with numerical solutions of the time-dependent Schrödinger equation …

Optical Response Analysis Of Thz Photoconductive Antenna Using Comsol Multiphysics, Jose Isaac Santos Batista

Electrical Engineering Undergraduate Honors Theses

A THz photoconductive antenna consists of antenna pads laid over a photoconductive substrate. These types of antennas are excited through the application of an optical pump (laser), which generates carriers inside the semiconductor. The acceleration and recombination of these carriers produce photocurrent that excites the antenna and generates THz pulse. This thesis focuses on analyzing the optical response of a photoconductive antenna, which consist of the interaction of the incident electric field of a laser pump with the radiating device. It develops the amplitude modulation process of a plane wave of light into a laser pump. It also takes into …

Optical Enhancement In Periodic Plasmonic Gratings For Sers And Metal-Semiconductor-Metal Photodetectors (Msm-Pds) Applications, Ahmad Aziz Darweesh

Graduate Theses and Dissertations

This dissertation is aimed to numerically study the effect of plasmonic grating electrodes on the efficiency of metal-semiconductor-metal photodetectors (MSM PDs) and the sensitivity of Surface Enhanced Raman Spectroscopy (SERS). This research can benefit many areas of nanoscience and optics, including plasmonic applications, such as, super lenses, nano-scale optical circuits, optical filters, surface plasmon enhanced photo-detectors solar cells, imaging sensors, charge-coupled devices (CCD), and optical-fiber communication systems. Several parameters, wire widths and thickness, gap space, taper angle, and the incident wavelength and angle, were investigated. The goal of this research is to utilize the plasmonic phenomenon by using plasmonic gratings …

The Population Densities Of Argon Metastable Levels, Nada Khogeer, Chelsy Gonzalez, Milka Nikolic

Physics and Astronomy

In this experiment, we used the optical emission spectroscopy (OES) method to obtain the main properties of low temperature Argon plasma. The experiment was sustained in powers and pressures that ranges from 30-100 W and 15-100 mTorr. We used numerical methods for the Argon kinetic model to calculate metastable levels and resonant states for the first excited states in low temperature Argon plasma. By finding the ratio of two spectral lines and finding another ratio from a different upper energy level that goes down to the same two lower energy levels, we can construct a system of two nonlinear equations. …

The Non-Mechanical Beam Steering Of Light In Reflective Inverse Diffusion, Eric K. Nagamine

Theses and Dissertations

Wavefront shaping is a technique that uses spatial light modulators to conjugate the phase of light incident on a rough surface, such that the light will refocus after reflection. This refocusing effect is called reflective inverse diffusion. There currently are two different approaches used to achieve reflective inverse diffusion: iterative methods and matrix methods. Iterative methods find one phase mask which allows for reflected light to be focused at a single, specific position, with results that are immediately available and continuously improving. Matrix methods calculate the complex matrix which describes the rough surface and allows for reflected light to be …

Development Of A Model For 11C Production Via The 14N(P,Α) Reaction Using A Ge Pettrace Cyclotron, Amy C. Hall

Theses and Dissertations

The GE PETtrace 800 Series cyclotron at the Missouri University Research Reactor (MURR) facility is used extensively for medical and research radioisotope production. However, no model exists of its radioisotope production performance, and the energy, full intensity, and spatial profile of the cyclotron proton beam has never been measured. To improve production planning for research and medical isotopes, a MCNP6 model of the isotope production process was developed to maximize efficiency in target design and better understand irradiation conditions. Since the cyclotron beam energy and profile has a significant impact on the types of reactions that take place and the …

Global Ionosonde And Gps Radio Occultation Sporadic-E Intensity And Height Comparison, Joshua Y. Gooch

Theses and Dissertations

A global, multi-year comparison of low and mid-latitude COSMIC GPS radio occultation (RO) sporadic-E (E_s) plasma frequency and altitude and Digisonde blanketing frequency (fbEs) and altitude within 150 km and 30 minutes of each other. RO methods used to estimate the intensity of the E_s layer include the scintillation index S4, total electron content (TEC) with both a constant and variable E_s cloud thickness, and an Abel transform. The S4 and TEC with varying thickness techniques both under-represent the fbEs values while the TEC with constant thickness and Abel transform better estimate Digisonde fbEs values. …

Violation Of Centrosymmetry In Time-Resolved Coherent X-Ray Diffraction From Rovibrational States Of Diatomic Molecules, Hua-Chieh Shao, Anthony F. Starace

Anthony F. Starace Publications

Owing to increasing applications of time-resolved coherent x-ray scattering for the investigation of molecular reaction dynamics, we develop a theoretical model for time-dependent x-ray diffraction from molecular and/or electronic motion in molecules. Our model shows that the violation of centrosymmetry (VOC) is a general phenomenon in time-resolved diffraction patterns. We employ our theoretical model to illustrate the VOC in time-resolved coherent x-ray diffraction from two oriented diatomic molecules undergoing rovibrational motion: lithium hydride (LiD) and hydrogen (HD). Our simulations show asymmetric x-ray diffraction images that reflect the directions of the molecular motions.

Generation Of Broadband Thz Pulses By Laser Wakefield At Radial Boundary Of Plasma Column, Serge Y. Kalmykov, Alexander Englesbe, Jennifer Elle, Andreas Schmitt-Sody

Serge Youri Kalmykov

Experimental Study: Underwater Propagation Of Super-Gaussian And Multi-Gaussian Schell-Model Partially Coherent Beams With Varying Degrees Of Spatial Coherence, Svetlana Avramov-Zamurovic, Charles L. Nelson, Milo W. Hyde Iv

Faculty Publications

We report on experiments where super-Gaussian and flat-top, multi-Gaussian Schell-model spatially partially coherent beams, with varying degrees of spatial coherence, were propagated underwater. Two scenarios were explored—calm and mechanically agitated water. The main objective of our study was the experimental comparison of the scintillation statistics. For a similar degree of coherence widths, the results show a potentially improved performance of scintillation index for the multi-Gaussian Schell-model beams as compared to the super-Gaussian beams. It should be noted that the presented results pertain only to the given experimental scenarios and further investigation is necessary to determine the scope of the findings.