Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Fabrication, Characterization and Application of High Density Gas Targets for Intense Laser Interaction Experiments(2019) Tay, Yuan Yan; Kim, Ki-Yong; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We report on the generation and characterization of submillimetric Argon gas jets with peak density higher than 10^21 atoms/cm3 from capillary nozzles of varying throat diameter in the range of 50-450 μm. The use of gas jet targets to generate a suitably dense, reliable, and reproducible interaction medium is particularly important in the broad field of laser-plasma interactions, in areas such as high energy density physics (HEDP), plasma waveguides, electron/ion acceleration and x-ray generation. Here, it is essential to place those targets in the laser focus with subwavelength accuracy and have control over the gas flow using a sonic or supersonic nozzle to provide the desired interaction density. The use of a sonic or supersonic gas flow provides a Gaussian like or plateau neutral density profile. By changing the gas pressure and temperature, one can change the initial neutral density and by using a combination of gases, one can obtain plasmas with multiple ions species, which is needed to localize electrons injection for innovative laser-plasma accelerator schemes. In this thesis, we present a study of the specific characteristics of gas jets produced by micron-sized nozzles in the context of laser-plasma physics. The study is based on experimental work on gas jets of varying sizes and parameters such as backing pressure and temperature. The thesis is organized as follows: Chapter 1 examines the motivation for generating such high density gas jets in the context of laser wakefield acceleration and the flow physics of supersonic gas jets. Chapter 2 presents the work in manufacturing the nozzles and characterizing the gas jets produced from the straight capillary nozzles using interferometry methods to measure the density profiles and Rayleigh Scattering to identify clusters in the target. Chapter 3 explores the possible applications of the gas jets in terms of generating gas targets in atmospheric conditions, producing icy filament targets by cooling and demonstrating multi-nozzle arrays.Item Energy Deposition in Femtosecond Filamentation: Measurements and Applications(2017) Rosenthal, Eric Wieslander; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Femtosecond filamentation is a nonlinear optical propagation regime of high peak power ultrashort laser pulses characterized by an extended and narrow core region of high intensity whose length greatly exceeds the Rayleigh range corresponding to the core diameter. Providing that a threshold power is exceeded, filamentation can occur in all transparent gaseous, liquid and solid media. In air, filamentation has found a variety of uses, including the triggering of electric discharges, spectral broadening and compression of ultrashort laser pulses, coherent supercontinuum generation, filament-induced breakdown spectroscopy, generation of THz radiation, and the generation of air waveguides. Several of these applications depend on the deposition of energy in the atmosphere by the filament. The main channels for this deposition are the plasma generated in the filament core by the intense laser field and the rotational excitation of nitrogen and oxygen molecules. The ultrafast deposition acts as a delta function-like pressure source to drive a hydrodynamic response in the air. This thesis experimentally demonstrates two applications of the filament-driven hydrodynamic response. One application is the ‘air waveguide’, which is shown to either guide a separately injected laser pulse, or act as a remote collection optic for weak optical signals. The other application is the high voltage breakdown of air, where the effect of filament-induced plasmas and hydrodynamic response on the breakdown dynamics is elucidated in detail. In all of these experiments, it is important to understand quantitatively the laser energy absorption; detailed absorption experiments were performed as a function of laser parameters. Finally, as check on simulations of filament propagation and energy deposition, we measured the axially resolved energy deposition of a filament; in the simulations, this profile is quite sensitive to the choice of the nonlinear index of refraction (n2). We found that using our measured values of n2 in the propagation simulations results in an excellent fit to the measured energy deposition profiles.Item COMPACT LASER DRIVEN ELECTRON AND PROTON ACCELERATION WITH LOW ENERGY LASERS(2017) Hine, George Albert; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Laser-driven particle accelerators offer many advantages over conventional particle accelerators. The most significant of these is the magnitude of the accelerating gradient and, consequently, the compactness of the accelerating structure. In this dissertation, experimental and computational advances in laser-based particle acceleration in three intensity regimes are presented. All mechanisms investigated herein are accessible by “tabletop” ultrashort terawatt-class laser systems found in many university labs, with the intention of making them available to more compact and high repetition rate laser systems. The first mechanism considered is the acceleration of electrons in a preformed plasma “slow-wave” guiding structure. Experimental advances in the generation of these plasma guiding structures are presented. The second mechanism is the laser-wakefield acceleration of electrons in the self-modulated regime. A high-density gas target is implemented experimentally leading to electron acceleration at low laser pulse energy. Consequences of operating in this regime are investigated numerically. The third mechanism is the acceleration of protons by a laser-generated magnetic structure. A numerical investigation is performed identifying operating regimes for experimental realizations of this mechanism. The key advances presented in this dissertation are: The development and demonstration of modulated plasma waveguide generation using both mechanical obstruction and an interferometric laser patterning method The acceleration of electrons to MeV energy scales in a high-density hydrogen target with sub-terawatt laser pulses and the generation of bright, ultra-broadband optical pules from the interaction region 3D particle-in-cell (PIC) simulations of self-modulated laser wakefield acceleration in a plasma, showing the generation of broadband radiation, and the role of “direct laser acceleration” in this regime 3D PIC simulations of laser wakefield acceleration in the resonant regime, identifying spatio-temporal optical vortices in a laser-plasma system 3D PIC simulations of proton acceleration by magnetic vortex acceleration using TW-class laser pulses