Physics Commons^™

Spectra Of Atmospheric And Astronomical Molecules, W. D. Cameron

Physics Theses & Dissertations

Spectroscopy techniques are focused on spectra of molecules of interest to the Earth’s atmosphere and/or astronomy and astrophysics. Laboratory spectroscopy as well as remote satellite sensing are applied. Using the Fourier transform spectrometer aboard the Atmospheric Chemistry Experiment (ACE) satellite to measure the absorption spectra of the Earth’s atmosphere through solar occultation limb observation demonstrates that volcanic eruption plumes can be located and tracked through their SO₂ content. The presence of those plumes is corroborated by overlaying infrared atmospheric aerosol extinction observed by the 1 μm imager on the same satellite. Tracking atmospheric aerosol movement with the ACE …

Experimental Investigation Of All-Optical Production Of Metastable Krypton, Joshua Carl Frechem

Physics Theses & Dissertations

Metastable production of noble gases requires significant energy due to their filled valence shells. These transitions from the ground state are in the vacuum ultraviolet and extreme ultraviolet, which are relatively inaccessible to lasers. This necessitates the use of either electron/ion bombardment via inefficient glow discharges or the use of high-power lasers and nonlinear processes. The all-optical production efficiency using these high-power lasers promises to be orders of magnitude higher than glow discharges, but far more costly. This work looks to improve all-optical production of metastable krypton (Kr*) through the use of a commercially available vacuum ultraviolet lamp with a …

Molecular Spectroscopy: A Study Of Molecules In Earth And Planetary Atmospheres, Mahdi Yousefi Atashgah

Physics Theses & Dissertations

The four most abundant isotopologues (N₂O, ¹⁵NNO, N¹⁵NO, and NN¹⁸O) of nitrous oxide have been measured in the Earth's atmosphere by infrared remote sensing with the Atmospheric Chemistry Experiment (ACE) Fourier transform spectrometer. These satellite observations have provided a near global picture of N₂O isotopic fractionation. The relative abundance of the heavier isotopologues increase with altitude and with latitude in the stratosphere as the air becomes older.

Near global 85°S{85°N atmospheric measurement of carbonyl sulfide (OCS), including the minor OC³⁴S and O¹³CS isotopologues, were made by the …

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 …

Optical Excitation Of Metastable Krypton And Photoassociative Spectroscopy Of Ultracold Rbar, Grady R. White

Physics Theses & Dissertations

In this presentation, we discuss results from two separate bodies of work. In the first, we investigate all-optical excitation methods to produce metastable-state krypton. The high energies required to excite rare gases out of their ground state present a unique challenge in the context of laser experiments. Laser physics work with rare gases often relies on excitation within an RF discharge. All-optical excitation is a promising replacement for RF discharges, avoids problems caused by ion production and may eventually allow for higher efficiencies. We examine three separate methods of all-optical metastable-state production: using an ArF excimer laser, using the third …

Fabrication Of An Apparatus For All-Optical Production Of Metastable Krypton, Lindsay M. Thornton

Physics Theses & Dissertations

Atom Trap Trace Analysis (ATTA) has made radiokrypton dating of polar ice and groundwater samples a possibility for scientists all over the world, allowing them to date samples further back in time and more accurately than other methods. However, this technique is hampered by the 36-hour cleaning process required for production of metastable-state krypton atoms via a radio-frequency driven plasma. Production of metastable krypton all-optically would dramatically increase the rate at which samples could be measured. Attempts to build an apparatus that could accomplish this have been done in the past but were lacking in aordability and practicality for widespread …

Investigation Of Multi-Photon Excitation In Argon With Applications In Hypersonic Flow Diagnostics, Jack L. Mills

Physics Theses & Dissertations

Non-intrusive flow diagnostics are essential for studying the physics of hypersonic flow wake regions. To advance the development of next generation hypersonic vehicles and to improve computational fluid dynamics techniques in the hypersonic regime, NASA needs a suitable non-intrusive diagnostic technique to measure velocity, density, and temperature. We will present our work on developing a seedless, non-intrusive diagnostic technique using excited state argon atoms, prepared via multi-photon excitation. In this dissertation, we report results on the first phase of this hypersonic wake measurement project. In particular, we have redesigned and characterized the performance of a high energy, nanosecond pulsed Ti:Sapphire …

Emergence Of Collective Light Scattering In Atomic 87Rb Samples, Kasie Jean Kemp

Physics Theses & Dissertations

Over the past half century, atomic ensembles have been used to create sensors, clocks, and quantum information systems. As these devices become more compact, and as the number of atoms increases to improve the sensitivity for detection, the atomic samples are increasing in density and optical depth. As such, the spectroscopic properties of the atomic media are modified due to interactions among the particles in the ensemble. We report investigation of near-resonance light scattering from a cold atomic sample of 87Rb. Initially prepared in a magneto-optical trap, the atoms are loaded into a far-off-resonance optical dipole trap (FORT) in which …

Plasma Processing Of Superconducting Radio Frequency Cavities, Janardan Upadhyay

Physics Theses & Dissertations

The development of plasma processing technology of superconducting radio frequency (SRF) cavities not only provides a chemical free and less expensive processing method, but also opens up the possibility for controlled modification of the inner surfaces of the cavity for better superconducting properties. The research was focused on the transition of plasma etching from two dimensional flat surfaces to inner surfaces of three dimensional (3D) structures. The results could be applicable to a variety of inner surfaces of 3D structures other than SRF cavities. Understanding the Ar/Cl₂ plasma etching mechanism is crucial for achieving the desired modification of Nb …

Cebaf Upgrade Bunch Length Measurements, Mahmoud Mohamad Ali Ahmad

Physics Theses & Dissertations

Many accelerators use short electron bunches and measuring the bunch length is important for efficient operations. CEBAF needs a suitable bunch length because bunches that are too long will result in beam interruption to the halls due to excessive energy spread and beam loss. In this work, bunch length is measured by invasive and non-invasive techniques at different beam energies. Two new measurement techniques have been commissioned; a harmonic cavity showed good results compared to expectations from simulation, and a real time interferometer is commissioned and first checkouts were performed. Three other techniques were used for measurements and comparison purposes …

Catalysis Of Stark-Tuned Interactions Between Ultracold Rydberg Atoms, Aye Lu Win

Physics Theses & Dissertations

We present the study of the catalysis effect in the resonant energy transfer between ultracold ⁸⁵Rb Rydberg atoms. We have investigated the energy transfer process of 34p + 34p → 34s + 35s, and observed Stark-tuned Forster resonances. When additional Rydberg atoms of 34d state are included in the interaction, an increase in the population of 34s states atoms is observed. Although the 34d state atoms do not directly participate in the resonant energy transfer that produces 34s state atoms, they add an additional interaction channel 34p + 34 …

Photoassociative Spectroscopy Of Ultracold Argon And Krypton Confined In A Magneto Optical Trap, Maha Khaled Omar

Physics Theses & Dissertations

Creating ultracold molecules has attracted considerable interest in the last decade. Once created, such molecules can be used for precision spectroscopy or to study chemical reactions at ultracold tem peratures. Several techniques have been developed to produce ultracold molecules; the most common is photoassociation where two ultracold atoms collide in the presence of light that induces a free-bound transition to an excited molecular state. Photoassociation can also be used to perform spectroscopy in order to map out the ro-vibrational levels of a molecular state. In this dissertaiotn, we report on our Photoasociative Spectroscopy (PAS) studies conducted separately in argon and …

Case Studies In Many-Body Physics, Ana Samolov

Physics Theses & Dissertations

The many-body problem refers to any physical problem made of more than two interacting particles. With increasing number of particles in a system, their coupling and entanglement becomes more complex, and there is no general analytic solution even for a three-body classical or quantum systems. However, some of the most fascinating phenomena in nature are products of collective effects. Therefore, significant efforts have been made in both experiment and theory to unravel some specific many-body problems. If we look at still unanswered physics questions we see that for most of these problems addressing the many-body interactions is a key issue. …

Spectroscopic Study Of Ultracold Rubidium Atoms In An Optical Dipole Force Trap, Eman Mohammed Ahmed

Physics Theses & Dissertations

The interaction of light with atoms and molecules is of fundamental interest in many branches of science. In atomic physics, this interaction can be used to cool and spatially confine (trap) atoms. These traps can be used as the starting point for other experiments, but the dynamics of the cooling and trapping processes is itself of interest. In order to better understand the physics of trapping atoms in an optical dipole force trap, we have conducted a series of spectroscopic measurements of ultracold rubidium atoms in such a trap. The trap was created at the focus of a Nd:YAG laser …

Characterization Of Microwave Cavity Discharges In A Supersonic Flow, Dareth Janette Drake

Physics Theses & Dissertations

A partially ionized gas is referred to as either a plasma or a discharge depending on the degree of ionization. The term discharge is usually applied to a weakly ionized gas, i.e. mostly neutrals, where as a plasma usually has a larger degree of ionization. To characterize a discharge the plasma parameters, such as the rotational temperature, vibrational temperature, and electron density, must be determined. Detailed characterization of supersonic flowing discharges is important to many applications in aerospace and aerodynamics. One application is the use of plasma-assisted hydrogen combustion devices to aid in supersonic combustion. In conditions close to the …

Comparative Study Of Forward And Diffusely Scattered Light In A Coherently Prepared Ultracold Rubidium Gas, Rocio Gisel Olave Gonzalez

Physics Theses & Dissertations

A comparison between forward and diffusely scattered light propagating in a coherently prepared ultracold ⁸⁷Rb atomic vapor is presented. This research is part of the ongoing effort to characterize the processes, such as diffusion, that contribute to coherence loss in atomic media under conditions of electromagnetically induced transparency, for applications in realistic systems. Toward this end, a magneto optical trap (MOT) of ⁸⁷Rb has been built, and the atomic vapor sample characterized in terms of atomic density, shape and size, temperature, and optical depth. Next, two co-propagating beams were sent through the sample, to establish an electromagnetically induced …

Light Scattering In Ultracold High Density Rubidium Vapor, Salim Balik

Physics Theses & Dissertations

Recent developments in laser cooling and trapping opened the door to a world full of new opportunities for research in atomic, molecular and optical physics as well as condensed matter physics. It became possible to do experiments under conditions that are hard to achieve in condensed matter systems but recently have been observed in atomic systems. Bose Einstein Condensation, the Mott insulator transition, and superfluidity are examples of such achievements. Another considerable interest to both condensed matter and atomic physics is Anderson localization of light. The localization phenomenon is named after P. W. Anderson who suggested the possibility of localization …

Investigation Of (E, 2e) Collisions And Related Phenomena, Jason Manuel Martinez

Physics Theses & Dissertations

In this thesis I investigate (e, 2e) processes, or electron impact ionization, using several theoretical methods. I first examine the problem using the Born approximations, particularly the Distorted Wave Born Approximation (DWBA), focusing on the underlying processes that dominate for ionization of the 2p state of Argon and Magnesium. I investigate as well the ionization of helium and hydrogen and use the simplicity of the approximation to probe the incident particle effects on the Helium cross section. In both cases the results are compared with experiment. I also produce cross section results for ions near threshold, a regime that …

Photoassociative Spectroscopy Of Ultracold Metastable Argon And Study Of Dual Species Trap Loss In A Rubidium-Metastable Argon Mot, Michael K. Shaffer

Physics Theses & Dissertations

This dissertation presents the findings of two experimental investigations in ultracold atomic and molecular physics: The study of the dual species trap loss in a rubidium - metastable argon magneto-optical trap and the photoassociative spectroscopy of ultracold metastable argon. The interspecies trap loss rate coefficients have been measured for ultracold collisions between ⁸⁵Rb and ⁴⁰Ar* in a dual-species magneto-optical trap (MOT) and the two rates have been found to be approximately equal over the range of intensities studied with values of β'_Rb–Ar* = 3.0 ± 1.3 × 10^-11 cm³/s and β'_Ar*–Rb = 1.9 …

Investigation Of Ultracold Rubidium Atoms In A Pulsed Far Off Resonance Trap, Minarni Minarni

Physics Theses & Dissertations

This dissertation reports on the design, construction, and investigation of a pulsed optical dipole force trap which uses laser light to confine ultracold rubidium (Rb) atoms. Because the laser frequency is detuned far from the atomic resonance frequency, the optical dipole force trap is also called a "far-off-resonance trap" (FORT). The use of pulsed laser light to create an optical trap may find application in expanding the number of atomic species which can be confined. The experiments reported here are principally aimed, however, at understanding the physics of pulsed FORT dynamics in anticipation of using the free electron laser (FEL) …

Experimental Investigation Of A Rubidium-Argon Dual Species Magneto-Optical Trap, Hauke Christian Busch

Physics Theses & Dissertations

The first simultaneous cooling and confinement of two different atomic species from opposite sides of the periodic table in a dual magneto optical trap (DMOT) has been accomplished. The alkali-metal ⁸⁵Rb and the noble gas ⁴⁰Ar* have been simultaneously confined, characterized, and interspecies interaction parameters have been measured. The DMOT confined 1.2 × 10^{6 85}Rb atoms at a density of 1 × 10¹⁰/cm³ and 1.4 × 10^{6 40}Ar* atoms with a density of 1.2 × 10¹⁰/cm³. A collisional loss rate coefficient for Rb-Ar* has been determined to …

Measurement Of Proton Transfer Reaction Rates In A Microwave Cavity Discharge Flowing Afterglow, George M. Brooke Iv

Physics Theses & Dissertations

The reaction rate coefficients between the hydronium ion and the molecules ethene (C₂H₄), propene (C₃H₆), 1-butene (C₄H₈) and hydrogen sulfide (H₂S) were measured at 296 K. The measured reaction rates were compared to collision rates calculated using average dipole orientation (ADO) theory. Reaction efficiency depends primarily upon the proton affinity of the molecules. All the measurements were obtained using the newly developed microwave cavity discharge flowing afterglow (MCD-FA) apparatus. This device uses an Asmussen-type microwave cavity discharge ion source that is …

Coherent Backscattering Of Light From An Ultra Cold Gas Of Rubidium-85 Atoms, Pasad B. Kulatunga

Physics Theses & Dissertations

This thesis reports on the experimental study of coherent radiative transport in an ultracold gas of ⁸⁵Rb atoms confined in a magneto-optic trap. Measurements are made of the polarization dependence of the spatial and spectral profile of light backscattered from the sample. The results shows an interferometric enhancement sensitive to coherent multiple scattering in the atomic gas, and strong variations with the polarization of the incident and detected light. Effects due to coherent enhancement of weak non-resonant transitions are also observed. Comparison of the measurements with realistic quantum Monte Carlo simulations of Kupriyanov, et al [1] yield very good …

Field Emission Based Sensors Using Carbon Nanotubes, Changkun Dong

Physics Theses & Dissertations

A number of sensitive applications would be greatly benefited by the development of better cold cathodes that employ the electron field emission process. Among the many kinds of field emitters that could be tried, carbon nanotubes (CNT) have a number of distinct advantages because of their unique geometrical structure, chemical inertness, mechanical stiffness, and high thermal and electrical conductivities. This dissertation describes research in which CNT cathodes were fabricated and their emission characteristics were measured.

Multi-walled carbon nanotubes (MWNT) were grown by chemical vapor deposition (CVD) on various substrates: Ni and Hastelloy gauze, 304 stainless steel (SS) plates, and Ni-coated …

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. …

Decomposition Of Carbon Dioxide In A Capacitively Coupled Radio Frequency Discharge, Thao Hoang Dinh

Physics Theses & Dissertations

Decomposition of CO₂ was studied in a capacitively coupled radio frequency discharge using Martian Simulant Gas mixture that contains 95% CO₂. The discharge was operated at a gas pressure of 3 to 6 Torr and a discharge power density of less than 2.0 W/cm³. The main mechanism of the CO₂ decomposition process is the electron impact dissociation and the rate of the process depends on the electron density, Ne, the concentration of CO₂, and the reduced electric field, E/N. A self-consistent model was established to describe the CO …

Experimental Investigation Of Long-Lived "Zeke" Rydberg States In Ultracold Argon, Gambhir Ranjit

Physics Theses & Dissertations

There is considerable interest in the dynamics of ultracold plasmas and ultracold Rydberg gases. Ultracold plasmas are typically formed by photo-excitation of ultracold atoms to an energy region near (both above and below) an ionization threshold. Excitation to bound, highly-excited Rydberg states can lead to formation of a plasma via several processes, including collisions between Rydberg atoms. Three-body recombination in an ultracold plasma can also result in the production of ultracold Rydberg atoms. Understanding the dynamics of ultracold Rydberg gases is therefore important for understanding the dynamics of ultracold plasmas. In this dissertation, we have investigated the formation and survival …

Characterization Of Iron Oxides And Atmospheric Corrosion Of Steel, Sei Jin Oh

Physics Theses & Dissertations

The study of corrosion behavior was performed using three different analytical techniques, which provided information on the formation, development and layering of iron oxides on the corrosion products as a function of atmospheric conditions, exposure time and type of steel. In particular, the protective layer formed on weathering steel was investigated as a function of different amounts of alloying elements in the steel, atmospheric conditions and exposure times. Combined together, the results provided a better understanding of the atmospheric corrosion behavior of steel, and formed a part of database of the atmospheric corrosion characteristics.

Accurate characterization of the iron oxides …

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, …

Measurement Of Hyperfine Coupling Constants Of The 5d²D₃/₂ And 5d²D₅/₂ Levels In Atomic Cesium Using Polarization Quantum Beat Spectroscopy, Wo Yei

Physics Theses & Dissertations

Accurate measurements of hyperfine constants have revealed effects that can not be explained by a simple hydrogenic picture of the alkali atoms such as cesium [1-3]. More precise experimental results and theoretical treatments are in demand for the alkali elements, especially for atomic cesium because of its wide range of applications. Therefore, it is essential to understand its atomic and nuclear structure. Precision measurement of its excited-states properties such as hyperfine structure provides global information on nuclear charge and current distributions and also serves as a check to the theory and a calibration of calculated excited state wave functions. Accurate …