UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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Item MULTI-GEV LASER WAKEFIELD ACCELERATION IN OPTICALLY GENERATED PLASMA WAVEGUIDES(2023) Shrock, Jaron E; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasma based electron accelerators offer a promising path to overcoming the significant technological and economic challenges facing the evolution to higher energies by radiofrequency (RF) accelerator technology. In particular, laser-driven wakefield acceleration (LWFA) in plasmas can produce accelerating gradients 1000 times larger than linear RF accelerators, enabling the production of GeV-scale electron bunches in just a few centimeters of acceleration. Efficient LWFA of electrons to this energy scale requires the use of optical guiding to maintain drive laser intensity over much longer distances than the characteristic diffraction length of the pulse. In this dissertation, I will present the first successful implementations of optically generated plasma waveguides in multi-GeV laser wakefield acceleration. I will focus on three primary topics: (1) experimental considerations for generating and diagnosing meter-scale plasma waveguides and the wakefield acceleration process, (2) the experimental demonstration of electron bunches accelerated up to 5 GeV in an all-optical LWFA, and (3) development of a model of drive pulse evolution and electron injection in agreement with a broad range of our experimental results, including the demonstration of localized electron injection through modification of the waveguide properties.Item APPLICATIONS OF INTENSE MID-INFRARED LASER-PLASMA INTERACTIONS(2020) Woodbury, Daniel; Milchberg, Howard; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intense laser-plasma interaction, generally characterized by focused laser intensities exceeding ~1 TW/cm2, is a major pillar of plasma physics and nonlinear optics with broad applications, including high energy charged particle and photon sources, the generation and study of high energy density physics conditions, fusion energy sources, remote detection techniques, and self-guided nonlinear propagation. For many important applications, longer wavelength lasers provide favorable scaling for laser-plasma interactions, and in several cases enable entirely new phenomena. In this dissertation we present experimental and computational results for three laser-plasma-based applications using ultrashort mid-infrared (mid-IR or MIR) and long-wave-infrared (LWIR) laser pulses. In the first laser wakefield acceleration (LWFA) experiment at mid-IR wavelengths, we demonstrate acceleration of electron bunches driven by relativistic self-focusing collapse of mid-IR laser pulses in near-critical density gas jet targets, and compare scaling of bunch charge and energy to those from common near-infrared systems. Second, we demonstrate that single-electron-seeded avalanche breakdown driven by picosecond mid-IR lasers is an ultrasensitive technique for measuring extremely low plasma densities in gases. We use this technique in two applications. First, we first demonstrate standoff detection of radioactive materials, with avalanche measurements enabling determination of source location and estimates of the radioactivity level. We then use the technique to measure ionization yield induced by an auxiliary laser in atmospheric pressure range gases over 14 orders of magnitude, a record range achievable with no other technique we are aware of. Finally, we present theory and simulations of nonlinear propagation of high power MIR and LWIR multi-picosecond pulses in air, demonstrating that self-guided propagation at moderate intensity is mediated by an ensemble of discrete avalanche plasmas seeded by aerosols.Item HIGH REPETITION RATE LASER-DRIVEN ELECTRON ACCELERATION TO MEGA-ELECTRON-VOLT ENERGIES(2019) Salehi, Fatholah; Milchberg, Howard M; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Laser-driven particle accelerators have the potential to be a compact and cost-effective replacement for conventional accelerators. Despite the significant achievements of laser wakefield acceleration in the last two decades, more work is required to improve the beam parameters such as the energy spread, emittance, repetition rate, and maximum achievable energy delivered by these advanced accelerators to values comparable to what conventional accelerators offer for various applications. The goal of this dissertation is to lower the threshold of the laser pulse energy required for driving a wakefield and in turn enable higher repetition rate particle acceleration with current laser technology. In the first set of electron acceleration experiments presented in this dissertation, we show that the use of a thin gas jet target with near critical plasma density lowers the critical power for relativistic self-focusing and leads to electron acceleration to the ~MeV range with ~1pC charge per shot, using only ~1mJ energy drive laser pulses delivered by a 1kHz repetition rate laser system. These electron beams accelerated in the self-modulated laser wakefield acceleration (SM-LWFA) regime have a thermal energy distribution and a rather large divergence angle (>150mrad). In order to improve the energy spread and the divergence, in the second set of the experiments, we employ a few-cycle laser pulse with a ~7fs duration and ~2.5mJ energy as the driver, to perform wakefield acceleration in the bubble regime using near critical plasma density targets. The results show a significant improvement in the energy spread and divergence of the beam. The electron bunches from this experiment have a quasi-monoenergetic peak at ~5MeV with an energy spread of ΔE/E≃0.4 and divergence angle of ~15mrad. These results bring us closer to the use of tabletop advanced accelerators for various scientific, medical, and industrial applications.