Theses and Dissertations from UMD

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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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    PHYSICS AND APPLICATIONS OF EXTENDED AIR HEATING BY FEMTOSECOND LASER FILAMENTATION
    (2022) Larkin, Ilia; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Femtosecond laser pulses of sufficient energy can propagate as filaments in air due to a dynamic interplay between nonlinear self-focusing and ionization-induced defocusing. A filament in air is characterized by a narrow, 100 m diameter core propagating at high intensity for many Rayleigh ranges corresponding to the core diameter, surrounded by a lower intensity reservoir that exchanges optical energy with the core. The high intensity core ionizes the air and excites molecular rotational wavepackets in N2 and O2. Thermal relaxation of these excitations leads to air heating over very long and narrow volumes, launching acoustic waves and imprinting density profiles in air. These features enable longitudinal mapping of energy absorption, interaction with aerosols in air, guiding of high voltage discharges, and the generation of long air waveguides for subsequent laser pulses. All of these topics are detailed in this dissertation.In particular, we present: (1) Single shot axially resolved energy deposition measurements, using a synchronized array of microphones, to see on a shot-by-shot basis the effect of air turbulence on nonlinear pulse propagation. (2) Measurements of the pre-breakdown evolution of a laser triggered high voltage spark gap, induced by a density channel imprinted by femtosecond laser pulses. By interferometrically measuring air heating and current leakage through the spark gap we clarify the role of laser plasma vs laser air heating in triggering breakdowns. (3) Air waveguiding experiments extended to ranges up to 50 m from the original ~1 m experiments. (4) Fog droplet clearing experiments showing that in natural filamentation of a collimated beam, direct optical interactions are the dominant clearing mechanism rather than acoustic effects.
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    Experiments with Trapped Ions and Ultrafast Laser Pulses
    (2016) Johnson, Kale Gifford; Monroe, Christopher; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Since the dawn of quantum information science, laser-cooled trapped atomic ions have been one of the most compelling systems for the physical realization of a quantum computer. By applying qubit state dependent forces to the ions, their collective motional modes can be used as a bus to realize entangling quantum gates. Ultrafast state-dependent kicks [1] can provide a universal set of quantum logic operations, in conjunction with ultrafast single qubit rotations [2], which uses only ultrafast laser pulses. This may present a clearer route to scaling a trapped ion processor [3]. In addition to the role that spin-dependent kicks (SDKs) play in quantum computation, their utility in fundamental quantum mechanics research is also apparent. In this thesis, we present a set of experiments which demonstrate some of the principle properties of SDKs including ion motion independence (we demonstrate single ion thermometry from the ground state to near room temperature and the largest Schrodinger cat state ever created in an oscillator), high speed operations (compared with conventional atom-laser interactions), and multi-qubit entanglement operations with speed that is not fundamentally limited by the trap oscillation frequency. We also present a method to provide higher stability in the radial mode ion oscillation frequencies of a linear radiofrequency (rf) Paul trap--a crucial factor when performing operations on the rf-sensitive modes. Finally, we present the highest atomic position sensitivity measurement of an isolated atom to date of ~0.5 nm Hz^(-1/2) with a minimum uncertainty of 1.7 nm using a 0.6 numerical aperature (NA) lens system, along with a method to correct aberrations and a direct position measurement of ion micromotion (the inherent oscillations of an ion trapped in an oscillating rf field). This development could be used to directly image atom motion in the quantum regime, along with sensing forces at the yoctonewton [10^(-24) N)] scale for gravity sensing, and 3D imaging of atoms from static to higher frequency motion. These ultrafast atomic qubit manipulation tools demonstrate inherent advantages over conventional techniques, offering a fundamentally distinct regime of control and speed not previously achievable.