Plasma and Beam Physics Commons^™

Electron Density And Electron Neutral Collision Frequency In The Ionosphere Using Plasma Impedance Probe Measurement, E. Spencer, S. Patra, T. Andriyas, C. Swenson, J. Ward, A. Barjatya

Publications

Swept Impedance Probe measurements in a sporadic E layer observed during the Sudden Atomic Layer (SAL) sounding rocket mission are analyzed to obtain absolute electron densities and electron neutral collision frequencies accurately. Three sets of upleg and downleg impedance data are selected for the analysis. Initial estimates of the plasma parameters are obtained through a least mean square fit of the measured impedance data against the analytical impedance formula ZB(f ) of Balmain (1969). These initial parameters are used as a starting point to drive a finite difference computational model of an antenna immersed in a plasma called PF-FDTD. The …

Observations Of Neutral Depletion And Plasma Acceleration In A Flowing High-Power Argon Helicon Plasma, C. Mark Denning, Matt Wiebold, John E. Scharer

Physics Faculty Publications

Neutral depletion effects are observed in a steady-state flowing argon helicon plasma with a magnetic nozzle for high rf input powers (up to 3 kW). Noninvasive diagnostics including 105 GHz microwave interferometry and optical spectroscopy with collisional-radiative modeling are used to measure the electron density (n_e), electron temperature (T_e), and neutral density (n_n). A region of weak neutral depletion is observed upstream of the antenna where increasing rf power leads to increased electron density (up to n_e = 1.6×10¹³ cm^-3) while T_e remains essentially constant and …

Characterizing Effects And Benefits Of Beam Defocus On High Energy Laser Performance Under Thermal Blooming And Turbulence Conditions For Air-To-Ground Engagements, Scott N. Long

Theses and Dissertations

This dissertation makes contributions towards knowledge of optimizing of laser weapon performance when operating in the air-to-ground (ATG) regime in thermal blooming conditions. Wave optics modeling techniques were used to represent laser weapon performance in a high fidelity sense to allow progress to be made toward improving lower-fidelity scaling laws that can be used in systems level analysis which has need for better representations of thermal blooming. Chemical-oxygen iodine laser (COIL) based weapon systems that operate near the ground will experience thermal blooming due to atmospheric absorption if output power is sufficiently high. The thermal lens in the ATG case …

Real-Time Plasma Controlled Chemistry In A Two-Frequency, Confined Plasma Etcher, Vladimir Milosavljevic, Albert R. Ellingboe, Cezar Gaman, John V. Ringwood

Articles

The physics issues of developing model-based control of plasma etching are presented. A novel methodology for incorporating real-time model-based control of plasma processing systems is developed. The methodology is developed for control of two dependent variables (ion flux and chemical densities) by two independent controls (27 MHz power and O2flow). A phenomenological physics model of the nonlinear coupling between the independent controls and the dependent variables of the plasma is presented. By using a design of experiment, the functional dependencies of the response surface are determined. In conjunction with the physical model, the dependencies are used to deconvolve the sensor …

Demonstration Of A Strategy To Perform Two-Dimensional Diode Laser Tomography, Ryan N. Givens

Theses and Dissertations

Demonstration of a strategy to perform two-dimensional diode laser tomography using a priori knowledge from symmetry arguments and computational fluid dynamic (CFD) calculations is presented for a flat flame burner. The strategy uses an optimization technique to determine flame diameter and location using a vector quantization approach. Next, the variance in a training set, produced from CFD calculations, is captured using principal components analysis. The information in the training set allows interpolation between beam paths resulting in temperature and density maps. Finally, the TDLAS temperature and density maps are shown to agree with traditional thermocouple measurements of the flat flame …

Modulation Response Of Twin Optically Coupled Diode Lasers, Eric M. Golden

Theses and Dissertations

Diode lasers are useful in military and commercial applications that have strict requirements for size, weight and power. This includes the use of diode lasers in optoelectronic and photonic integrated circuits, which can lead to new technologies in optical communications and optical interconnects in high performance computing systems. For these systems to be effective, the diode laser must be modulated at frequencies beyond current limits which are typically a few GHz. This barrier can be broken by optically coupling a diode laser with a similar laser. A set of single mode rate equations models the dynamics of twin optically coupled …

Production And Characterization Of Femtosecond-Laser-Induced Air Plasma, David R. Armbruster

Theses and Dissertations

The purpose of this research was to produce, characterize, and optimize laser induced air plasma as a preliminary step in using the plasma as a source of terahertz radiation. An 800 nanometer, 50 femtosecond, 0.75 Watt, pulsed Ti:Sapphire laser system was used as the source infrared beam. A beam expander was used to expand the beam to a diameter of approximately 6.5 mm, and the beam was focused through a 25 mm focal length achromatic lens to produce laser-induced plasma in ambient air. A 40 kHz ultrasonic transducer was used to detect the plasma. A second harmonic generation crystal was …

Ultrafast Spectroscopy Of Mid-Infrared Semiconductors Using The Signal And Idler Beams Of A Synchronous Optical Parametric Oscillator, Richard M. Derbis

Theses and Dissertations

Mid-Wave Infrared (MWIR) semiconductors are of use to the Air Force for several applications. Ultrafast spectroscopy can be used to better quantify the effectiveness of semiconductor opto-electronic devices. The objective of this thesis was to improve the procedure for taking ultrafast, time-resolved measurements of photoluminescence from MWIR semiconductors. Previous work has used a mode-locked titanium sapphire (Ti:Saph) laser to excite the semiconductor sample and to upconvert the photoluminescence from the semiconductor. Work completed in this thesis improved on the techniques developed during previous work. A synchronous Optical Parameter Oscillator (OPO) will be used to convert the Ti:Saph laser (0.830 µm) …

Measuring Dispersion In Laser Cavity Mirrors Using White-Light Interferometry, Allison S. Goodspeed

Theses and Dissertations

Terahertz radiation is an emerging field that has far reaching applications. There is a need for portable and affordable terahertz sources that may be used for detection of structural weaknesses in aerospace composites. One possibility for terahertz generation is a femtosecond Cr:LiSAF laser. However, controlling intracavity dispersion is necessary in order to get the ultrashort pulses needed to generate terahertz radiation. This research measures dispersion of the chirped femtosecond intracavity mirrors by employing white-light interferometry and explains the theory behind the curve-fitting process used to calculate dispersion. To compensate for the narrow reflectivity band of the mirrors, a CaF_{2 …}

Cold Atmospheric Pressure Air Plasma Jet For Medical Applications, Juergen Friedrich Kolb, A.-A H. Mohamed, R. O. Price, R. J. Swanson, A. Bowman, R. L. Chiavarini, Michael W. Stacey

Bioelectrics Publications

By flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, we were able to generate a 2 cm long plasma jet. With increasing flow rate, the flow becomes turbulent and temperatures of the jet are reduced to values close to room temperature. Utilizing the jet, yeast grown on agar can be eradicated with a treatment of only a few seconds. Conversely, animal studies show no skin damage even with exposures ten times longer than needed for pathogen extermination. This cold plasma jet provides an effective mode of treatment for yeast infections of the skin.

Interactions Of Electrons And Rydberg Atoms In Ultra-Cold Plasmas, Cristian Vesa

Honors Theses

This thesis discusses an experimental technique for investigating electron temperature control by Rydberg atoms in ultra-cold plasmas. The objective we set ourselves was twofold. Firstly, we sought to gain an insight into the processes whereby the creation of Rydberg atoms within the plasma lengthens the lifetime of the plasma. To this end, we created the plasma using a Littman dye laser and subsequently, at a variable time delay, we excited neutral atoms in the plasma to specific Rydberg states using a narrow bandwidth pulsed dye laser. Secondly, we employed radio-frequency (rf) electric fields to excite electron oscillations within the plasma …

A Mode-Locked Vertical Extended Cavity Surface Emitting Laser, Aoife Deburca

Theses

Surface emitting lasers are a competitive and flexible alternative to edge emitting lasers. The surface-emitting laser has many useful characteristics, which make it beneficial for many applications. These characteristics include the ease of testing during the growth and the fundamental mode output that is effortlessly achieved

The thesis is focused on the Vertical External Cavity Surface Emitting Laser due to its increased flexibility beyond that of the Vertical Cavity Surface Emitting Laser. A wide range of possible parameters are detailed allowing for flexibility in design and applications.

Optically pumped pulsed cavity configurations were investigated in relation to intra-cavity devices and …

Hypersonic Boundary Layer Receptivity To Acoustic Disturbances Over Cones, Kursat Kara

Mechanical & Aerospace Engineering Theses & Dissertations

The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifth-order weighted essentially non-oscillatory (WENO) scheme with third-order total-variation-diminishing (TVD) Runge-Kutta method. Hypersonic boundary layer receptivity to free-stream acoustic disturbances in slow and fast modes over 5-degree, half-angle blunt cones and wedges are numerically investigated. The free-stream Mach number is 6.0, and the unit Reynolds number is 7.8×106/ft. Both the steady and unsteady solutions are obtained …

Sublethal And Killing Effects Of Atmospheric-Pressure, Nonthermal Plasma On Eukaryotic Microalgae In Aqueous Media, Ying Zhong Tang, Xin Pei Lu, Mounir Laroussi, Fred C. Dobbs

OES Faculty Publications

In-depth studies on the interaction of nonthermal plasmas with microorganisms usually focus on bacteria; only little attention has been given to their effects on more complex eukaryotic cells. We report here nonthermal plasma's effects on cell motility, viability staining, and morphology of eukaryotic microalgae, with three marine dinoflagellates and a marine diatom as major targets. The effects on motility and viability staining depended on the time of exposure to plasma and the species of microalgae. We observed a strong pH decrease in aqueous samples (marine and freshwater algal cultures, their culture media, and deionized water) after exposure to plasma, and …

Electron Density And Temperature Measurement Of An Atmospheric Pressure Plasma By Millimeter Wave Interferometer, Xinpei Lu, Mounir Laroussi

Electrical & Computer Engineering Faculty Publications

In this paper, a 105 GHz millimeter wave interferometer system is used to measure the electron density and temperature of an atmospheric pressure helium plasma driven by submicrosecond pulses. The peak electron density and electron-neutral collision frequency reach 8 X 10¹² cm^-3 and 2.1 X 10¹² s^-1, respectively. According to the electron-helium collision cross section and the measured electron-neutral collision frequency, the electron temperature of the plasma is estimated to reach a peak value of about 8.7 eV.

Plasma Medicine, Mounir Laroussi, Alexander Fridman

Electrical & Computer Engineering Faculty Publications

Recent demonstrations of plasma technology in the treatment of living cells, tissues, and organs are creating a newfield at the intersection of plasma science and technology with biology and medicine - Plasma Medicine.

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 …

Practical Sensor For Measurement Of Nitrogen, Dusan Popovic, Vladimir Milosavljevic, Steven Daniels

Articles

This paper presents a method for precise measurement of atomic and molecular nitrogen in an oxygen-nitrogen dc plasma. This is achieved by monitoring the intensities of the atomic nitrogen spectral line at 821.6 nm and the molecular nitrogen bandhead at 337.1 nm, relative to the atomic oxygen spectral line at 844.7 nm. Oxygen is one of the most frequently used gases for surface chemical treatment, including deposition and etching, therefore the ability to measure and control the process and chemical composition of the process is essential. To validate this oxygen actimometry method for N2-xO2 (where x varies from 0 to …

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 …

Bactericidal Effects Of Cold Plasma Technology On Geobacillus Stearothermophilus And Bacillus Cereus Microorganisms, Angela D. Morris, Gayle B. Mccombs, Susan L. Tolle, Mounir Laroussi, Wayne L. Hynes

Dental Hygiene Faculty Publications

Cold plasma is a state of matter that contains a large number of particles that are electrically charged. Plasmas generate chemically reactive species and ultraviolet radiation making them useful in decontamination applications (Kong & Laroussi, 2003). Research regarding the inactivation of gram-positive bacteria by cold plasma has been studied by Laroussi et al (2003); however, there is limited research regarding the germicidal effectiveness of cold plasma on Geobacillus stearothermophilus and Bacillus cereus microorganisms. The purpose of this study was to determine if cold plasma technology inactivates Geobacillus stearothermophilus and Bacillus cereus vegetative cells and spores. This study consisted of 981 …

Self-Organization In Cathode Boundary Layer Discharges, Nobuhiko Takano

Electrical & Computer Engineering Theses & Dissertations

Cathode boundary layer (CBL) discharge, which has been developed as a UV light source, operates in a direct current between a planar cathode and a ring-shape anode that are separated by a dielectric with an opening of the same diameter as the anode. The nonthermal CBL discharges operate in a medium pressure range down to 30 Torr, emitting excimer radiation when operated with noble gases. The radiant excimer emittance at 172 nm in xenon reaches 1.7 W/cm², and a maximum excimer efficiency of 6 % has been obtained. The high excimer radiant emittance, in addition to low cost …

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 …

Hot Electron And X-Ray Production From Intense Laser Irradiation Of Wavelength-Scale Polystyrene Spheres, H. A. Sumeruk, S. Kneip, D. R. Symes, I. V. Churina, A. V. Belolipetski, G. Dyer, J. Landry, G. Bansal, A. C. Bernstein, Thomas D. Donnelly, A. Karmakar, A. Pukhov, T. Ditmire

All HMC Faculty Publications and Research

Hot electron and x-ray production from solid targets coated with polystyrene-spheres which are irradiated with high-contrast, 100 fs, 400 nm light pulses at intensity up to 2×10¹⁷ W/cm² have been studied. The peak hard x-ray signal from uncoated fused silica targets is an order of magnitude smaller than the signal from targets coated with submicron sized spheres. The temperature of the x-rays in the case of sphere-coated targets is twice as hot as that of uncoated glass. A sphere-size scan of the x-ray yield and observation of a peak in both the x-ray production and temperature at a …

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 …

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

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 …

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 …

Control Of Strong-Laser-Field Coupling To Electrons In Solid Targets With Wavelength-Scale Spheres, H. A. Sumeruk, S. Kneip, D. R. Symes, I. V. Churina, A. V. Belolipetski, Thomas D. Donnelly, T. Ditmire

All HMC Faculty Publications and Research

Irradiation of a planar solid by an intense laser pulse leads to fast electron acceleration and hard x-ray production. We have investigated whether this high field production of fast electrons can be controlled by introducing dielectric spheres of well-defined size on the target surface. We find that the presence of spheres with a diameter slightly larger than half the laser wavelength leads to Mie enhancements of the laser field which, accompanied by multipass stochastic heating of the electrons, leads to significantly enhanced hard x-ray yield and temperature.

Reactive Oxygen Emission From Microwave Discharge Plasmas, S. Popovic, M. Rašković, S. P. Kuo, L. Vuskovic

Physics Faculty Publications

Metastable oxygen atoms and molecules have received increased interest because of their function in surface modification, bio-decontamination and many other industrial applications, in addition to the role in the upper atmospheric layer chemistry. We review work on production and detection of metastable oxygen and we describe our experiments, including the development of techniques for measurement of metastable molecular oxygen. We show that either metastable oxygen molecules or metastable oxygen atoms can be produced in large quantities in electrical discharges, carefully tailored to promote the required kinetics. Although the two species may coexist, colder discharge regimes favor production of molecules, while …

Plasma Treatment Of Bulk Nb Surface In The Ar/Cl2 Discharge, M. Rašković, L. Vuskovic, S. Popovic, A.-M. Valente-Feliciano, L. Phillips

Physics Faculty Publications

The preparation of the cavity walls has been one of the major challenges in the superconducting radio-frequency (SRF) accelerator technology. Therefore, constant research and development effort is devoted to develop surface preparation processes that will improve roughness and lower the level of impurities, like hydrogen or oxygen, embedded in bulk Nb, having in the same time reasonable etching rates. Plasma based surface modification provides an excellent opportunity to achieve these goals. We present Ar/Cl₂ discharge treatment of bulk Nb where we achieved etching rates comparable to the rates obtained with the electropolishing method without introducing impurities in Nb. The …