Theses and Dissertations from UMD
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Item Dynamics and applications of long-distance laser filamentation in air(2024) Goffin, Andrew; Milchberg, Howard; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Femtosecond laser pulses with sufficient power will form long, narrow high-intensity light channels in a propagation medium. These structures, called “filaments”, form due to nonlinear self-focusing collapse in a runaway process that is arrested by a mechanism that limits the peak intensity. For near-infrared pulses in air, the arrest mechanism is photoionization of air molecules and the resulting plasma-induced defocusing. The interplay between plasma-induced defocusing and nonlinear self-focusing enables high-intensity filament propagation over long distances in air, much longer than the Rayleigh range (~4 cm) corresponding to the ~200 µm diameter filament core. In this thesis, the physics of atmospheric filaments is studied in detail along with several applications. Among the topics of this thesis: (1) Using experiments and simulations, we studied the pulse duration dependence of filament length and energy deposition in the atmosphere, revealing characteristic axial oscillations intimately connected to the delayed rotational response of air molecules. This measurement used a microphone array to record long segments of the filament propagation path in a single shot. These results have immediate application to the efficient generation of long air waveguides. (2) We investigated the long-advertised ability of filaments to clear fog by measuring the dynamics of single water droplets in controlled locations near a filament. We found that despite claims in the literature that droplets are cleared by filament-induced acoustic waves, they are primarily cleared through optical shattering. (3) We demonstrated optical guiding in the longest-filament induced air waveguides to date (~50 m, a length increase of ~60×) using multi-filamentation of Laguerre-Gaussian LG01 modes with pulse durations informed by experiment (1). (4) We demonstrated the first continuously operating air waveguide, using a high-repetition-rate laser to replenish the waveguide faster than it could thermally dissipate. For each of the air waveguide experiments, extension to much longer ranges and steady state operation is discussed.Item A prototype miniature mass spectrometer for in situ analysis of trace elements on planetary surfaces(2021) Farcy, Benjamin Jacob; Arevalo, Ricardo D; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Interrogation of the chemical composition of rocky planets provides a deeper understanding of the history and evolution of the solar system. While laboratory studies of returned samples and remote sensing surveys of planetary surfaces can give insight into planetary history, one technique that has delivered major insights to planetary geology is in situ measurements of a planetary surface via mass spectrometry. Here, a new approach to spaceflight mass spectrometry is discussed, including an overview of the pursued scientific questions, the analytes targeted, and the prototype hardware in development. This effort constitutes the scientific and technological foundation of a landed planetary mission. This dissertation focuses on the history and evolution of the Earth-Moon system as recorded by trace elements. Specifically, the abundance and distribution of the heat producing elements (HPEs: K, Th, U) and their implications for mantle dynamics is considered. The radiogenic heat produced from K, Th, and U drives mantle convection, volcanism, and planetary dynamos. To understand better the chemical dynamics of radiogenic heat distribution in the Earth, the HPE abundance of a series of oceanic basalts was statistically analyzed. This analysis revealed the K/U ratio of the mantle and how it changes due to the enrichment or depletion of incompatible elements. The HPE abundance of the lunar interior was also discussed as a target of a future investigation, along with a series of trace element proxies meant to probe the lunar farside mantle. Further, an analysis of lunar farside craters provides a series of landing sites for an in situ mission, specifically for their surficial exposure of upper mantle material and later emplacement of lunar basalts. To access the trace element systems discussed in this dissertation, a prototype miniature inductively coupled plasma mass spectrometer (ICPMS) was developed to analyze trace elements in situ for landed planetary missions. First, the capability of the plasma to atomize and ionize input material was investigated. A plasma operating at reduced pressure can achieve 99\% ionization efficiency of most elements on the periodic table, with as much as a 50 to 100 times reduction in gas load and forward power compared to commercial systems for both He and Ar based plasma ion sources. The plasma system was integrated with a quadrupole mass spectrometer via a series of DC ion optics and vacuum housing, with its ion current and peak resolution optimized. Quantative data for an analyte spectrum of Kr demonstrates the ability for this instrument to resolve individual mass peaks, which lead to an accuracy and precision measurement of isotope ratios. This effort represents an end-to-end prototype miniature ICPMS, successfully demonstrating a viable instrument for landed planetary missions.Item Characteristics of Plasma Solitons Produced by Small Orbital Debris(2020) Truitt, Alexis; Hartzell, Christine; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sub-centimeter orbital debris is currently undetectable using ground-based radar and optical methods. However, pits in Space Shuttle windows produced by paint chips demonstrate that small debris can cause serious damage to spacecraft. Recent analytical, computational and experimental work has shown that charged objects moving quickly through a plasma will cause the formation of plasma density solitary waves, or solitons. Due to their exposure to the solar wind plasma environment, even the smallest space debris will be charged. Depending on the debris size, charge and velocity, debris may produce plasma solitons that propagate along the debris velocity vector and could be detected with existing sensor technology. Plasma soliton detection would be the first collision-free method of mapping the small debris population. The first major contribution of this thesis is the identification of orbital locations where solitons will be produced, as a function of debris size and speed. Using the Chan & Kerkhoven pseudospectral method, we apply the Forced Korteweg-de Vries equation to describe the amplitude, width, and production frequency of solitons that may be produced by mm-cm scale orbital debris, as a function of the debris' size, velocity, and location (altitude, latitude, longitude) about Earth. Analytical solutions result in solitons that propagate forever without damping, assuming a uniform plasma environment. However, Earth's space plasma is complex, with processes that could cause the solitons to dampen. Damped solitons will have a limit to the distance they will travel before becoming undetectable. For our second major contribution, we calculated the propagation distance of solitons in the presence of damping processes. We applied the Damped Forced Korteweg-de Vries equation to calculate the damping rate of the solitons, and estimate the resulting soliton propagation distance. We demonstrate that Landau damping dominates over collisional damping for these solitons. It is necessary to understand the damping of solitons in order to assess the feasibility of on-orbit debris detection. In our first contribution, we demonstrate that one dimensional simulations are sufficient to model the orbital debris solitons that propagate along the debris velocity vector. However, in order to fully understand the soliton signatures in a 3D spatial environment, it is necessary to extend the Damped Forced Korteweg-de Vries model to three spatial dimensions. For our final major contribution, we apply the Damped Forced Kadomtsev-Petviashvili Equation, which is a natural extension for waves described by the Damped Forced Korteweg-de Vries equation. Transverse solitonic perturbations extend across the width of the debris, with predictable amplitudes and speeds that can be approximated by the one dimensional Damped Forced Korteweg-de Vries equation at the transverse soliton location. The transverse perturbations form soliton rings that advance ahead of the debris in the three dimensional simulations, allowing for additional opportunity for detection. With the current absence of a dedicated, calibrated, on-orbit debris detection sensor, plasma soliton detection would be the first collision-free method of mapping the small debris population. The characteristics of plasma solitons described here are necessary to evaluate the feasibility of orbital debris detection via soliton detection with future debris detection systems.Item Ionospheric Turbulence Near the Upper Hybrid Layer: Theory and Experiment(2016) Najmi, Amir Christopher; Papadopoulos, Konstantinos; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The thesis presents experimental results, simulations, and theory on turbulence excited in magnetized plasmas near the ionosphere’s upper hybrid layer. The results include: The first experimental observations of super small striations (SSS) excited by the High-Frequency Auroral Research Project (HAARP) The first detection of high-frequency (HF) waves from the HAARP transmitter over a distance of 16x10^3 km The first simulations indicating that upper hybrid (UH) turbulence excites electron Bernstein waves associated with all nearby gyroharmonics Simulation results that indicate that the resulting bulk electron heating near the upper hybrid (UH) resonance is caused primarily by electron Bernstein waves parametrically excited near the first gyroharmonic. On the experimental side we present two sets of experiments performed at the HAARP heating facility in Alaska. In the first set of experiments, we present the first detection of super-small (cm scale) striations (SSS) at the HAARP facility. We detected density structures smaller than 30 cm for the first time through a combination of satellite and ground based measurements. In the second set of experiments, we present the results of a novel diagnostic implemented by the Ukrainian Antarctic Station (UAS) in Verdansky. The technique allowed the detection of the HAARP signal at a distance of nearly 16 Mm, and established that the HAARP signal was injected into the ionospheric waveguide by direct scattering off of dekameter-scale density structures induced by the heater. On the theoretical side, we present results of Vlasov simulations near the upper hybrid layer. These results are consistent with the bulk heating required by previous work on the theory of the formation of descending artificial ionospheric layers (DIALs), and with the new observations of DIALs at HAARP’s upgraded effective radiated power (ERP). The simulations that frequency sweeps, and demonstrate that the heating changes from a bulk heating between gyroharmonics, to a tail acceleration as the pump frequency is swept through the fourth gyroharmonic. These simulations are in good agreement with experiments. We also incorporate test particle simulations that isolate the effects of specific wave modes on heating, and we find important contributions from both electron Bernstein waves and upper hybrid waves, the former of which have not yet been detected by experiments, and have not been previously explored as a driver of heating. In presenting these results, we analyzed data from HAARP diagnostics and assisted in planning the second round of experiments. We integrated the data into a picture of experiments that demonstrated the detection of SSS, hysteresis effects in simulated electromagnetic emission (SEE) features, and the direct scattering of the HF pump into the ionospheric waveguide. We performed simulations and analyzed simulation data to build the understanding of collisionless heating near the upper hybrid layer, and we used these simulations to show that bulk electron heating at the upper hybrid layer is possible, which is required by current theories of DAIL formation. We wrote a test particle simulation to isolate the effects of electron Bernstein waves and upper hybrid layers on collisionless heating, and integrated this code to work with both the output of Vlasov simulations and the input for simulations of DAIL formation.Item THE DESIGN AND STUDY OF THE SUB-MILLIMETER WAVE LENGTH GYROTRON AND FUNDAMENTAL AND SECOND CYCLOTRON HARMONICS(2015) Pu, Ruifeng; Granatstein, Victor L.; Nusinovich, Gregory S.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation documents research activities directed toward designing high power, high efficiency gyrotrons to operate in the sub-millimeter wavelength region. The gyrotron is to produce pulsed RF power at 670 GHz, with possible application to a novel scheme for detecting concealed radioactive materials. High efficiency is to be achieved by designing a cavity resonator in which the electrons interact with the high-order TE31,8 mode. The choice of resonating mode helps to alleviate Ohmic losses in the cavity walls, and simulation results show that the output efficiency could be more than 30%. The design study takes into account a variety of known effects that could affect efficiency, such as orbital velocity spread, voltage depression and after-cavity interaction. The 670GHz gyrotron was built using the resonator design; operation confirmed that record high efficiency was achieved at an output power level of about 200 kilowatts. In addition, the issue of radial spread in electron guiding centers, which is related to the design of the magnetron injection gun used in the 670GHz gyrotron, was also examined. This spread degrades the interaction between the electrons and the RF field. This often overlooked issue is important for future electron gun designs; this thesis presents analytical methods for estimating how much the degradation affects gyrotron efficiency. The analytical method was verified with numerical simulation, showing that the efficiency's sensitivity to spread in guiding centers is highly dependent on the location of an annular electron beam: when the beam is injected in the inner peak of the desired mode, the radial spread should be kept to less than 1/3 of the RF wavelength. Finally, the dissertation investigates the possibility of further extending the operating parameters of the gyrotron by using the second harmonic of the electron cyclotron resonance. An average output power could be increased by operating the gyrotron continuously rather than in pulses. Using the second cyclotron harmonic allows the magnetic field requirement for resonance condition to be reduced by a factor of two, so that in 670 GHz gyrotrons the pulsed solenoid can be replaced with a cryo-magnet. The investigation shows that for the TE31,8 mode at the second cyclotron harmonic, the operating mode has only one competing mode at the fundamental cyclotron harmonic that could present a mode stability issue. Numerical simulation shows that this mode is TE11,6, the operating mode can suppress this mode, while achieving 20% interaction efficiency. Results also reveal that the resonator for the operating mode at second cyclotron harmonic must be modified to increase the Q-factor. Continuously operating gyrotrons using cryo-magnets have been used for plasma heating in controlled thermonuclear fusion research, albeit at lower frequency than the 670 GHz of the current study.Item STUDY OF THE FEMTOSECOND DYNAMICS AND SPECTROSCOPY OF LASER IONIZED PLASMAS.(2015) Elle, Jennifer; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ultra-short laser pulses are used to ionize gas in different configurations and study the plasma and ionization dynamics. The variation in non-linear index of refraction as a function of time is used to diagnose laser-plasma interactions. First, a proposed novel method to stimulate lasing in the atmosphere is studied. A few mJ pulse is used to ionize nitrogen gas in a long column without dissociating the molecular nitrogen. A 140ps laser is used to heat the resulting electron population in an attempt to generate a population inversion between the C3u and B3g states of molecular nitrogen. No evidence of lasing from this transition is observed. Next, a few mJ pulse is used to ionize xenon gas, creating Xe+ plasma. Ionization in Xe+ is observed far below the threshold predicted by multiphoton ionization theory due to resonant multiphoton ionization of collisionally excited states. To my knowledge, this is the first observation of resonant ionization involving multiple resonances. Finally, construction of an experiment to detect predicted birefringence in a relativistic laser-plasma interaction is described, with preliminary testing of diagnostics included.Item Microwave Emission and Electron Temperature in the Maryland Centrifugal Experiment(2013) Reid, Remington R.; Ellis, Richard F; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of two magnetised plasma waves as electron temperature diagnostics for the Maryland centrifugal ecperiment (MCX) are explored. First, microwave emission in the whistler mode is examined and ultimately found to be a poor candidate for diagnostic purposes owing to reflections from elsewhere in the plasma confusing the signal. Second, the electron Bernstein wave is found to offer promise as means to measure the radial electron temperature profile. Several numeric codes are developed to analyze the observed microwave emission and calculate the elec- tron temperature profile. Measurements of electron Bernstein wave emission indicate that the electrons in the plasma attain temperatures close to 100 eV. Clear evidence is shown that the measurements are not influenced by reflections or emission from hot (Te > 1keV) superthermal electrons. The measured electron temperature is shown to be in reasonable agreement with recent measurements of the plasma ion temperature.Item Structured Plasma Waveguides and Deep EUV Generation Enabled by Intense Laser-Cluster Interactions(2012) Layer, Brian; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Using the unique properties of the interaction between intense, short-pulse lasers and nanometer scale van-der-Waals bonded aggregates (or `clusters'), modulated waveguides in hydrogen, argon and nitrogen plasmas were produced and extreme ultraviolet (EUV) light was generated in deeply ionized nitrogen plasmas. A jet of clusters behaves as an array of mass-limited, solid-density targets with the average density of a gas. Two highly versatile experimental techniques are demonstrated for making preformed plasma waveguides with periodic structure within a laser-ionized cluster jet. The propagation of ultra-intense femtosecond laser pulses with intensities up to 2x1017 W/cm2 has been experimentally demonstrated in waveguides generated using both methods, limited by available laser energy. The first uses a `ring grating' to impose radial intensity modulations on the channel-generating laser pulse, which leads to axial intensity modulations at the laser focus within the cluster jet target. This creates a waveguide with axial modulations in diameter with a period between 35 μm and 2 mm, determined by the choice of ring grating. The second method creates modulated waveguides by focusing a uniform laser pulse within a jet of clusters with flow that has been modulated by periodically spaced wire obstructions. These wires make sharp, stable voids as short as 50 μm with a period as small as 200 μm within waveguides of hydrogen, nitrogen, and argon plasma. The gaps persist as the plasma expands for the full lifetime of the waveguide. This technique is useful for quasi-phase matching applications where index-modulated guides are superior to diameter modulated guides. Simulations show that these `slow wave' guiding structures could allow direct laser acceleration of electrons, achieving gradients of 80 MV/cm and 10 MV/cm for laser pulse powers of 1.9 TW and 30 GW, respectively. Results are also presented from experiments in which a nitrogen cluster jet from a cryogenically cooled gas valve was irradiated with relativistically intense (up to 2x1018 W/cm2) femtosecond laser pulses. The original purpose of these experiments was to create a transient recombination-pumped nitrogen soft x-ray laser on the 2p3/2→1s1/2 (λ = 24.779 Å) and 2p1/2→1s1/2 (λ = 24.785 Å) transitions in H-like nitrogen (N6+). Although no amplification was observed, trends in EUV emission from H-like, He-like and Li-like nitrogen ions in the 15 - 150 Å spectral range were measured as a function of laser intensity and cluster size. These results were compared with calculations run in a 1-D fluid laser-cluster interaction code to study the time-dependent ionization, recombination, and evolution of nitrogen cluster plasmas.Item Controlling and Enhancing Atmospheric Optical/Plasma Filaments(2011) Varma, Sanjay Ramesh; Milchberg, Howard M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As intense laser pulses propagate in atmosphere, they experience dramatic self-focusing, spectral broadening and phase modulation, and they ionize atmospheric molecules. The self-focusing and ionization-induced defocusing are competing effects that keep parts of the beam, called filaments, at high intensity over many Rayleigh lengths. Optical filaments and the plasma filaments that follow them are useful tools for remote sensing and ionization, atmospheric monitoring, terahertz generation, guiding of electrical discharges and optical pulse compression even to the few-cycle regime. Some of these applications may only be realized when the filamentation process is stabilized and plasma density is enhanced. Our experiments have shown that the rotational response of atmospheric nitrogen and oxygen is large enough and fast enough to dominate Kerr-induced self-focusing for optical pulses propagating with FWHM time duration > 40 fs. Moreover, our measurements have pointed to a way to greatly enhance the filament electron density by controlling the alignment of ambient N2 and O2 molecules and thereby controlling the optical nonlinearity or air. In addition, our group pointed out for the first time that quantum effects could dominate the propagation of intense femtosecond pulses in the atmosphere. This effect was demonstrated in our experiment that showed the quantum beats from laser-excited rotational wavepackets were able to steer, enhance or destroy laser filaments, depending on laser pulse timing. Our more recent work demonstrates that these quantum effects can increase the length of the plasma filament by a factor of three and can also promote soliton-like behavior of the pulse, cleaning and compressing it temporally. We performed direct measurements of the plasma density left behind by the filamenting optical pulses to confirm enhancement and extension of the electron density and laser intensity. Compression was measured with SPIDER, a technique for measuring the complex envelope and phase of optical pulses with sub-5 fs features.Item Blood Coagulation Inducing Synthetic Polymer Hydrogel(2010) Casey, Brendan John; Kofinas, Peter; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Uncontrolled hemorrhaging, or blood loss, accounts for upwards of 3 million deaths each year and is the leading cause of preventable deaths after hospital admission around the world. Biological-based hemostatics are quite effective at controlling blood loss, but prohibitively expensive for people in developing countries where over 90 % of these deaths are occurring. Synthetic-based hemostatics are less expensive, yet not nearly as effective as their biological counterparts. A better understanding of how synthetic materials interact with and affect the body's natural clotting response is vital to the development of future hemostatic material technology which will help millions around the world. Initial in vitro experimentation focused on investigating the key chemical and structural material properties which affect Factor VII (FVII) activation in citrated human plasma. Enzyme-linked assays were utilized to confirm the ability of specifically formulated charged hydrogels to induce FVII activation and provided insight into the critical material parameters involved in this activation. Dynamic mechanical analysis was used to establish a correlation between polymeric microstructure and FVII activation. Experiments utilizing coagulation factor depleted and inhibited plasmas indicated that FVII, FX, FII, and FI are all vital to the process outlining the general mechanism of fibrin formation from the onset of FVII activation. The ability of the polymer to induce fibrin formation in "artificial plasma" explicitly lacking calcium, TF, and platelets suggested that a specifically designed material surface has the capability to substitute for these vital cofactors. Clinical diagnostic experimentation using sheep blood indicated that hydrogels containing higher amounts of electrostatic positive charge and lower cross-link density were able to induce faster, more robust clot formation in the presence of a coagulation cascade activator. Subsequent in vivo animal experimentation clearly demonstrated the ability of such hydrogels to aggregate platelets and erythrocytes promoting the formation of an effective hemostatic seal at the wound site. Moreover, in vivo testing confirmed the viability of such a charged polymer hydrogel to effectively control blood loss in a clinically relevant model.