Theses and Dissertations from UMD
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Item HIGH THROUGHPUT STIMULATED BRILLOUIN SCATTERING SPECTROSCOPY(2024) Rosvold, Jake Robert; Scarcelli, Giuliano; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Brillouin light scattering arises from the coupled interaction between light and material acoustic phonons. The measurand of Brillouin scattering is the characteristic frequency difference between incident and scattered light which depends on the local longitudinal modulus of the material. Spontaneous Brillouin scattering has been used in combination with confocal microscopy to provide non-contact, label-free mapping at micron-scale resolution in biological media. To date, spontaneous Brillouin microscopy has reached the speed limit (~20-50ms per spectrum) as determined by the theoretical scattering efficiency. While a great deal of research has been directed to speeding up Brillouin microscopy acquisition times, spontaneous Brillouin scattering is fundamentally an inefficient process thus limiting the ability to study faster biological phenomena and rapid processes. To combat this limitation, its nonlinear counterpart, stimulated Brillouin scattering (SBS) has been proposed for microscopy applications. For decades, stimulated Brillouin scattering has been used in fiber sensing and all-optical pulse control and leverages a nonlinear interaction where two counterpropagating light beams stimulate a more efficient scattering relationship. However, the small interaction volumes and photodamage constraints presented in microscopy have hindered the translation of stimulated Brillouin scattering into the biological realm. Recently, continuous wave stimulated Brillouin microscopy has led to competitive acquisition times (~5ms per spectrum) when compared to the spontaneous alternative but has yet to be widely adopted. Due to a plethora of factors, such as an inefficient power balance between pump and probe beams, lack of proper commercial laser sources, and nonoptimal detection schemes, the complete picture of what SBS spectroscopy has to offer has yet to be revealed. As such, there is a need to customize light sources and detection schemes in order to fully take advantage of the enhanced Brillouin efficiency possible in SBS. Herein we introduce novel methodology to improve the acquisition speed of Brillouin microscopy by designing and developing proper laser sources and detection schemes for efficient SBS spectroscopy. First, we showcase the potential utility of our state-of-the-art continuous wave SBS technology in a flow cytometry application, highly suitable for the counterpropagating geometry of SBS where the laser position is fixed while the sample is being moved at high speeds. Additionally, we will present an optimized receiver design based on polarization detection which enables 100x faster spectral measurements in the low-gain regime relevant to biological materials. Finally, we demonstrate an optimal pulsed laser source specifically designed for SBS Brillouin microscopy.Item ENERGY TRANSFER DYNAMICS OF HIGH ENERGY MOLECULES(2023) Lukowski, Christopher; Mullin, Amy S; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation investigates the energy transfer dynamics of high-energy molecules excited electronically, vibrationally, and rotationally. The molecules studied in this thesis were excited electronically and vibrationally with UV photon absorption and rotationally with an optical centrifuge. The excited molecules are relaxed either by collisions or a chemical process. The products of the relaxation process are measured using high-resolution transient IR absorption spectroscopy to determine the state-resolved products and the energy partitioning. In the first study the collisional relaxation of highly vibrationally excited collidine with bath CO2 is investigated. The collidine was excited to an E_vib=38,552 cm-1 after absorption of a λ=266 nm photon and the full state-resolved distribution of the scattered CO2 is reported. The results are compared to previous studies done on methylated pyridines. The translational energy and rotational energy gain of the scattered CO2 is similar for the methylated pyridines, however, the integrated appearance rate constant for collidine-CO2 collisions is higher then the other methylated pyridine molecules. The effect that the donor complexity has on collisional relaxation is explored. For the second study, SO2 is electronically excited to the predissociative metastable C̃ electronic state. The SO product quantum yields, rotational distributions, and product energy partitioning show that translational energy is preferred by a 4:1 ratio over rotational energy for the photoproducts. The preference for translational energy is evidence that a linear transition state could be involved in the dissociation process. Theoretical calculations of the SO2 potential energy surfaces for the ground state and the excited state show that for SO2 photodissociation to occur near the dissociation threshold the SO2 in the C̃ state becomes linear and that coupling to the repulsive triplet state lowers the height of the energy barrier so dissociation can proceed. The third study used a tunable optical centrifuge to rotationally excite N2O into extreme rotational states. The optical centrifuge was tuned to selectively populate rotational states between J=100-200. N2O IR transitions for the (0001-0000) band are known up to J=100 for the R-branch. Line center profiles were collected over each IR transition between J=100-200 to identify the IR transition frequencies. The newly identified N2O transitions and the tunable optical centrifuge were used to maximize the population in N2O J=140 and J=165, using two different optical traps, to determine the relaxation dynamics in this region. Doppler-broadened line profiles show that rotational states below the maximized population have higher translational temperatures than rotational states near the peak of the distribution. From the near nascent distributions, the relaxation rate of the N2O was measured to be 65 % of the gas kinetic collision rate for both optical traps. This result is compared with a previous study on CO relaxation dynamics.Item PHYSICAL CONDITIONS OF THE MULTI-PHASE INTERSTELLAR MEDIUM IN NEARBY GALAXIES FROM INFRARED AND MILLIMETER-WAVE SPECTROSCOPY(2022) Tarantino, Elizabeth; Bolatto, Alberto D; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gas and dust in the interstellar medium (ISM) cools and condenses, gravitationally collapses, and forms stars. At the same time, stars can heat and ionize their surroundings, influencing the physical conditions of the nearby ISM. In this thesis, I take a multi-wavelength, spectroscopic approach to investigate the physical conditions of the multi-phase ISM in nearby galaxies. The [CII] fine-structure transition at 158 micron is frequently the brightest far-infrared line in galaxies and can trace the ionized, atomic, and molecular phases of the ISM. I present velocity-resolved [CII] observations from SOFIA in the nearby galaxies M101 and NGC 6946 and determine that [CII] emission is associated with the atomic and molecular gas about equally, with little contribution from the ionized gas. Using the [CII] cooling function, I calculate the thermal pressure of the cold neutral medium and find that the high star formation rates in our sample can drive large thermal pressures, consistent with predictions from analytical theory. Next, I investigate the properties of the ionized gas around one of the hottest and most luminous Wolf-Rayet (WR) stars in the Small Magellanic Cloud. I use spatially resolved mid-infrared Spitzer and far-infrared Herschel spectroscopy to establish the physical conditions of the ionized gas. Using the photoionization code Cloudy, I construct models with a range of constant densities between n_H = 4 - 12 cm^-3 and a stellar wind-blown cavity of 15 pc that reproduce the intensity and spatial distribution of most ionized gas emission lines. The higher ionization lines cannot be produced by the models --- however, I show that wind-driven shocks or a harder ionizing WR spectrum can explain their intensities. Lastly, I explore the properties of molecular clouds in a large (170x350 pc) map of an active star-forming region in the Large Magellanic Cloud. Using 12CO(2-1) and 13CO(2-1) observations from the ALMA ACA, I decompose the emission into individual cloud structures and determine their sizes, linewidths, mass surface densities, and virial parameters. Almost all of the clouds are gravitationally bound or marginally bound and share similar properties to molecular clouds in the Milky Way. I do not find evidence that the surrounding star formation significantly influences the kinematic properties of the clouds through stellar feedback.Item Experimental Atomic Spectroscopy of Iron Group Elements for Astrophysics(2021) Ward, Jacob Wolfgang; Nave, Gillian; Rolston, Steve; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The quality of modern astrophysical spectra has made it clear that there is a lack of sufficiently accurate and robust laboratory atomic reference data sets. Particularly for spectra of the iron-group elements, the growing demand for critically evaluated sets of comprehensive atomic data is a direct result of advancing stellar astrophysics models and fundamental physics problems probing beyond the standard model. My thesis reports on my critical evaluation of the Ni V spectrum and the recent laboratory measurements I have conducted to improve the state of available reference data for astrophysical applications that rely on observations of Ni V. Additionally, I report my laboratory measurements of Fe II branching fraction values in the UV/VUV. Using high-resolution grating spectroscopy at the National Institute of Standards and Technology, I have carried out an analysis of quadruply ionized iron and nickel (Fe V & Ni V) in the vacuum ultraviolet (VUV) region by both recording new spectra and critically evaluating previously published data sets. My analysis has resulted in highly accurate wavelengths, presented with calculated oscillator strengths, for roughly 1500 Ni V lines, 200 of which have uncertainties that are almost an order of magnitude lower than in previous publications. Additionally, I present over 300 Ni V energy levels derived from my evaluated wavelengths. This section of my thesis focuses on the large improvements made in the analysis of Ni V, but my work also strongly supports the previous evaluations of Fe V by another author. With the extreme accuracy requirements of modern astrophysics problems, confirming the wavelength scale and uncertainty evaluation of previous Fe V data sets is still significant. In addition to the above work, my thesis also presents measurements of singly ionized iron (Fe II) branching fractions (BFs) in the VUV using high-resolution Fourier-transform spectroscopy. BFs are essential values for interpreting complex astrophysical spectra, but are notoriously difficult to measure in the VUV; for this reason, VUV BFs of Fe II have only been reported by one other research group for just seven levels. My thesis reports accurate BFs for 11 Fe II levels, involving approximately 100 spectral lines (16 in the VUV), which roughly doubles the amount of reported Fe II BFs in VUV.Item Transient Infrared Absorption Studies of Molecular Super Rotors Prepared in a Tunable Optical Centrifuge(2021) Michael, Tara; Mullin, Amy S.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the work presented here, an ultrafast, angularly accelerating optical trap, called an optical centrifuge, rotationally excites gas-phase molecules such as N2O, CO, and CO2 to extremely high-J rotational levels with oriented angular momentum. Molecules in highly energetic rotational levels are known as super rotors and relax to thermal equilibrium. The state-resolved collision dynamics are investigated using polarization-sensitive high-resolution transient infrared absorption spectroscopy. Three different optical centrifuge traps are used to impart angular momentum to the gas-phase molecules: a full optical bandwidth, a reduced optical bandwidth, and a tunable optical bandwidth. New IR spectral lines of N2O with J=140-205 (E_rot=8,200-17,400 cm^(-1)) are reported. Polarization-dependent transient measurements of N2O in J=195 reveal high orientational anisotropy of r=0.85 produced by the centrifuge. The nearly-nascent rotational distributions of CO are investigated using two pressures and two optical centrifuge bandwidths. The shapes of the distributions beyond the peak at J=62 mimic the intensity profile in the fall-off region of the shaped optical pulses. The capture and acceleration efficiencies of CO and CO2 at comparable angular frequencies using three clipped chirps are also investigated. Nascent rotational distributions show that CO2 and CO exhibit narrow and broad distributions, respectively, due to differences in molecular polarizability anisotropy. Surprisingly, the ratio of [CO2]:[CO] trapped by the centrifuge is nearly 1.5, despite CO2 having twice as many states as CO and about 3-fold larger polarizability anisotropy. The relaxation dynamics of CO and N2O with He and Ar buffer gases indicate that He is more efficient at rotational quenching than is Ar, and leads to products with larger recoil.Item SPECTROSCOPY OF TWO LEVEL DEFECTS & QUASIPARTICLES IN SUPERCONDUCTING RESONATORS(2021) Kohler, Timothy; Osborn, Kevin D; Anlage, Steven; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Superconducting films are inherently limited by losses due to two-level system (TLS) defects within the amorphous oxide layers surrounding them and from quasiparticles in the film. In this thesis I will discuss novel theoretical and experimental methods toward understanding superconducting resonator loss from deleterious surface TLS defects as well as a loss transition from non-equilibrium quasiparticles in granular TiN. I will show using finite element solver software that a resonator with submicron linewidth and linespacing can be used to better characterize and simulate surface TLS as part of a circuit QED system. I have observed individual surface TLS and found coupling values in the range of g/2π =50 kHz -280 kHz with a maximum dipole moment pz-max = 4.5 Debye (.93 eÅ). I have found in in simulation of experiment that over 80% of the strongly coupled TLS reside within 50 nm of the corner between the Metal-Substrate (MS) and Substrate-Air (SA) interface. Additionally I have studied a loss transition from non-equilibrium quasiparticles in TiN films. These films exhibit an anomalous loss dependence on substrate treatment and film thickness. The films of interest are ones grown thin on oxidized substrates, which exhibit an order of magnitude decrease in internal quality factor (Qi) relative to either thicker ˝films or films grown without the oxidized substrate. These films additionally exhibit a grain size on average of 7.5 nm, a higher inhomogeneous gap, a transition to lower stress and a preference for the [111] crystal growth. The temperature dependence of the conductivity is fit and a factor of two difference in quasiparticle lifetime is found between the two films where the thinner film has a shorter lifetime. A two gap quasiparticle trapping model is fit to the temperature dependent loss data. The data is consistent with a model where non-equilibrium quasi-particles are trapped in low gapped grains on the inside of the films. From these works and others presented in my thesis the understanding of TLSs on surfaces and non-equilibrium quasiparticles in TiN has improved. This will help illuminate some of the most important absorption mechanisms plaguing superconducting qubits and resonators.Item TAILORING LOCALIZED SURFACE PLASMON RESONANCES IN METALLIC NANOANTENNAS(2020) Zhang, Kunyi; Rabin, Oded; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The strong localized electromagnetic field achievable with metallic nanoantennas provides new opportunities for harmonics generation and label-free chemical sensing. In this work, the localized surface plasmon resonances (LSPRs) of metallic nanoarcs on dielectric substrates have been systematically investigated with visible and infrared spectroscopy, with the goal of elucidating the relationship between the structural and material parameters of the nanoarcs and their resonances. The transmission spectra provide rich information regarding the fundamental and higher order LSPR modes. Experimental results and numerical simulations demonstrate that the LSPR wavelengths are governed by the mid-arc length of the nanoarcs, and the extinction cross-sections of the different order modes are controlled by the central angle of the nanoarc and the symmetry of the mode. The fundamental and second order LSPR wavelengths can be tuned independently through the design of a non-uniform arc-width profile. Several relationships between features of the LSPR modes and the geometric parameters of nanoarcs are also confirmed by transformation optics analysis. The newly found relationships are then utilized as guidelines for the realization of plasmonic nanoarc antennas exhibiting efficient second harmonic generation (SHG). In another application, strong coupling between LSPRs and molecular vibrations is evident in the IR spectra of plasmonic nanoarcs placed in contact with a thin film of polymer, a native oxide layer or a thiol monolayer, enhancing the vibrational mode signals. This observation suggests that by appropriately tuning the frequency of the LSPR modes, the localized electromagnetic field around nanoarcs can resonantly couple to another emitter to boost its far-field radiation, which could benefit applications requiring highly localized, sensitive and selective chemical detection.Item WATER IN THE EARLY SOLAR SYSTEM: INFRARED STUDIES OF AQUEOUSLY ALTERED AND MINIMALLY PROCESSED ASTEROIDS(2017) McAdam, Margaret; Sunshine, Jessica M; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis investigates connections between low albedo asteroids and carbonaceous chondrite meteorites using spectroscopy. Meteorites and asteroids preserve information about the early solar system including accretion processes and parent body processes active on asteroids at these early times. One process of interest is aqueous alteration. This is the chemical reaction between coaccreted water and silicates producing hydrated minerals. Some carbonaceous chondrites have experienced extensive interactions with water through this process. Since these meteorites and their parent bodies formed close to the beginning of the Solar System, these asteroids and meteorites may provide clues to the distribution, abundance and timing of water in the Solar nebula at these times. Chapter 2 of this thesis investigates the relationships between extensively aqueously altered meteorites and their visible, near and mid-infrared spectral features in a coordinated spectral-mineralogical study. Aqueous alteration is a parent body process where initially accreted anhydrous minerals are converted into hydrated minerals in the presence of coaccreted water. Using samples of meteorites with known bulk properties, it is possible to directly connect changes in mineralogy caused by aqueous alteration with spectral features. Spectral features in the mid-infrared are found to change continuously with increasing amount of hydrated minerals or degree of alteration. Building on this result, the degrees of alteration of asteroids are estimated in a survey of new asteroid data obtained from SOFIA and IRTF as well as archived the Spitzer Space Telescope data. 75 observations of 73 asteroids are analyzed and presented in Chapter 4. Asteroids with hydrated minerals are found throughout the main belt indicating that significant ice must have been present in the disk at the time of carbonaceous asteroid accretion. Finally, some carbonaceous chondrite meteorites preserve amorphous iron-bearing materials that formed through disequilibrium condensation in the disk. These materials are readily destroyed in parent body processes so their presence indicates the meteorite/asteroid has undergone minimal parent body processes since the time of accretion. Presented in Chapter 3 is the spectral signature of meteorites that preserve significant amorphous iron-bearing materials and the identification of an asteroid, (93) Minerva, that also appears to preserve these materials.Item Wide Field of View Spectroscopy Using Fabry-Perot Interferometers(2016) Nikoleyczik, Jonathan Allen; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We present a high resolution spectrometer consisting of dual solid Fabry-Perot Interferometers (FPIs). This work is intended to be an all inclusive documentation of the instrument including discussion of the design of this instrument, the methods used in data reduction, and the analysis of these data. Each FPI is made of a single piece of L-BBH2 glass which has a high index of refraction n~2.07 with a thickness on the order of 100 μm. Each is then coated with partially reflective mirrors to create a resonant cavity and thus achieve a spectral resolution of R~30,000. Running the FPIs in tandem reduces the overlapping orders and allows for a much wider free spectral range and higher contrast. We will also discuss the properties of the FPIs which we have measured. This includes the tuning of the FPIs which is achieved by adjusting the temperature and thus changing the FPI gap and the refractive index of the material. The spectrometer then moves spatially in order to get spectral information at every point in the field of view. We select spectral lines for further analysis and create maps of the line depths across the field. Using this technique we are able to measure the fluorescence of chlorophyll in plants and attempt to observe zodiacal light. In the chlorophyll analysis we are able to detect chlorophyll fluorescence using the line depth in a plant using the sky as a reference solar spectrum. This instrument has possible applications in either a cubesat or aerial observations to measure bulk plant activity over large areas.Item Modeling Optically Thick Molecular Emission Spectra of Comets Using Asymmetric Spherical Coupled Escape Probability(2014) Gersch, Alan Michael; A'Hearn, Michael F; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Comets are frozen remnants from the formation of the Solar System. As such, their chemical composition is of great significance to understanding the origin of the planets and the distribution of important molecules, including water and other volatiles, throughout the Solar System. Recent observations, in particular those of the Deep Impact and EPOXI Missions, have provided better spectra of a cometary coma than were previously available. These observations include spectra with high spatial resolution very near to the nucleus. The purpose of this research is to better understand the abundances, distributions and creation mechanisms of various volatiles observed in cometary comae, in particular those of comet 9P/Tempel 1, the target of the Deep Impact Mission, and 103P/Hartley 2, the subject of the EPOXI mission. In order to do so, I have built a computer model of the spectrum of the comet's coma which includes the difficult and often ignored problem of accurately including radiative transfer to account for the potentially optically thick coma (or regions of the coma) near the nucleus. I have adapted Coupled Escape Probability, a new exact method of solving radiative transfer problems, from its original plane-parallel formulation for use in asymmetrical spherical situations. My model is designed specifically for use in modeling optically thick cometary comae, although not limited to such use. By providing for asymmetric geometry in the coma, the model is able to include the morphology of the near nucleus coma, as observed by the Deep Impact spacecraft for Tempel 1 and Hartley 2, and include this in the modeling of radiative transfer. This method enables the accurate modeling of comets' spectra even in the potentially optically thick regions nearest the nucleus, such as those seen in Deep Impact observations of 9P/Tempel 1 and EPOXI observations of 103P/Hartley 2. This model will facilitate analyzing the actual spectral data from the Deep Impact and EPOXI missions to better determine abundances of key volatile species, including CO, CO2 and H2O, as well as remote sensing data on active comets.