Browsing by Author "Roberts, Jacob, committee member"
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Item Open Access Advancing the capability of high energy Yb:YAG lasers: multilayer coatings, pulse shaping and post compression(Colorado State University. Libraries, 2022) Wang, Hanchen, author; Rocca, Jorge, advisor; Roberts, Jacob, committee member; Lee, Siu Au, committee member; Marconi, Mario, committee memberRecently, cryogenically cooled Yb-doped amplifiers have been successfully scaled both in output energy and in repetition rate. The performance of such laser systems and their applications can be expanded by advancements in the development of optical coatings, that allow for scaling to higher pulse energies; as well as improvements in pulse shaping that include shorter pulse durations and the generation of programmable sequences of ultrashort pulses. This dissertation focuses on realizing the improvements mentioned above for cryogenic Yb:YAG amplifiers. First it reports the evaluation of ion beam sputtering (IBS) dielectric coatings for Yb:YAG at the environmental conditions in which cryogenic amplifiers are operated. The IBS coatings showed consistent performance in ambient, vacuum and cryogenic conditions, with damage threshold measured 20.4±0.6 J/cm2 for anti-reflection (AR) coating, and 27.4±1.3 J/cm2 for high reflector (HR) coating with 280 ps pulse duration at 77 K under the ISO:21254 standard. Second, a method for synthesizing trains of high energy compressed pulses was demonstrated and used to pump an 18.9 nm Ni-like Mo plasma-based soft x-ray laser more efficiently. The synthesized pulse increased the conversion efficiency of this spatially coherent soft x-ray source by 40%. Finally, femtosecond pulses were generated by post compression using a gas filled hollow core fiber (HCF), in which spectral broadening was achieved by self-phase modulation with an additional contribution from stimulated Raman scattering. Utilizing nitrogen gas as the non-liner medium, 300 mJ, 8 ps pulses were broadened to 3.7 nm and re-compressed to 460 fs by a grating compressor. The propagation and spectral broadening of high energy picosecond pulses in gas-filled HCFs were modeled and the results of simulations were compared with experiments.Item Open Access Applications of superatom theory in metal cluster chemistry(Colorado State University. Libraries, 2016) Tofanelli, Marcus A., author; Ackerson, Christopher J., advisor; Prieto, Amy L., committee member; Shores, Mathew, committee member; Farmer, Delphine, committee member; Roberts, Jacob, committee memberOne of the largest modern scientific debates is understanding the size dependent properties of a metal. While much effort has been performed on understanding metal particles from the top down to much less work has been accomplished from the bottom up. This has lead to a great deal of interest in metal clusters. Metal clusters containing 20 to 200 metal atoms are similar yet strikingly different to both to normal coordination chemistry and continuous bulk systems, therefore neither a classical understanding for bulk or molecular systems appears to be appropriate. Superatom theory has emerged as a useful concept for describing the properties of a metal cluster in this size range. In this model a new set of ‘superatomic’ orbitals arises from the valence electrons of all the metals in a cluster. From superatom theory the properties of a metal cluster, such as stability, ionization energy, reactivity, and magnetism, should depend on valence of the superatomic orbitals, similar to a normal atom. However superatom theory has largely been used to describe the high stabilities of metal clusters with completed electronic configurations. Thus many features of superatom theory have remained largely untested and the extent that the superatom model truly applies has remained in question for many years. Over the past decade increases in synthetic and analytical techniques have allowed for the isolation of a series of stable monodisperse gold thiolate monolayer protected clusters (MPCs) containing from 10 to 500 gold atoms. The wide range in sizes and high stability of gold thiolate clusters provides an instrumental system for understanding superatom theory and the transition from molecular-like cluster to bulk-like system. In the first part of this thesis the effects of the superatomic valence is investigated under superatomic assumptions. Au25(SR)18 (where SR= any thiolate) can be synthesized in 3 different oxidation states without any major distortions to the geometry of the cluster, thus it is possible to test 3 different superatomic configurations for a single cluster. These studies show that the superatom model correctly predicts changes observed in the stability, absorption spectrum, crystal structures, and magnetic susceptibility for each charge state of Au25(SR)18. In addition, the superatom model is shown to also apply to the isoelectronic PdAu24(SR)18 superatomic cluster. This work is discussed in Chapters 2, 3, and 4. The second part of this thesis focuses on the transition from superatomic metal clusters to metal nanoparticles. Au144(SR)60 is studied in order to understand this transition. Although the plasmon is not immediately apparent through linear absorption spectroscopy, a plasmonic feature is observed in transient absorption spectroscopy. This observation in combination with the absence of a HOMO-LUMO gap suggests that Au144(SR)60 can be treated with bulk assumptions. However Au144(SR)60 shows quantized behavior and powder x-ray diffraction reveals that symmetry of the metal core does not represent what is observed in the bulk. Au144(SR)60 appears to show both superatomic and bulk behavior making it an instrumental tool for understanding the transition from superatomic to bulk behavior. This work is discussed in Chapters 2, 5, and 6.Item Open Access Barium extraction from liquid xenon on a cryoprobe for the nEXO experiment and a nucleon decay search using EXO-200 data(Colorado State University. Libraries, 2019) Craycraft, Adam B., author; Fairbank, William M., Jr., advisor; Roberts, Jacob, committee member; Wilson, Robert, committee member; Johnson, Thomas E., committee memberNeutrinoless double beta decay (0νββ) is a theorized decay that is beyond the standard model of particle physics. Observation of this decay would establish the Majorana nature of neutrinos and show violation of lepton number. Nucleon decay is another theorized decay that is beyond the standard model of particle physics that would violate baryon number. Observation of baryon number violation has been pursued for sometime in a wide variety of experiments. EXO-200 is an experiment that utilized a time projection chamber (TPC) filled with liquid xenon (LXe) enriched in the isotope xenon-136 to search for 0νββ. In this thesis, an analysis of EXO-200 data in search of evidence for triple-nucleon decays in ¹³⁶Xe is presented. Decay of ¹³⁶Xe to ¹³³Sb and decay to ¹³³Te were the particular decays searched for in this analysis. No evidence for either decay was found. Limits on the lifetimes of these decays were set that exceed all prior limits. The proposed nEXO experiment will be next generation LXe TPC search for 0νββ. In order to eliminate background events that are not associated with two neutrino double beta decay, a technique to tag the barium-136 decay daughter is under development. In this thesis, continued development is presented of a scheme to freeze the barium daughter in a solid xenon sample on the end of a cryoprobe dipped into LXe and subsequently tag it using its fluorescence in the solid matrix.Item Open Access Bulk and interface vibrational Raman spectroscopy with coherence modulated optical susceptibilities(Colorado State University. Libraries, 2010) Wilson, Jesse W., author; Bartels, Randy, advisor; Krapf, Diego, committee member; Marconi, Mario, committee member; Roberts, Jacob, committee memberThe effect on an ultrashort probe pulse of an impulsively prepared vibrational coherence is described by effective linear and nonlinear optical susceptibility perturbations. Linear susceptibility perturbations modulate both the amplitude and phase of a probe pulse. Three spectral interferometry methods are described for measuring this phase modulation, geared toward spectral resolution, noise suppression, and rapid data acquisition. Third-order nonlinear interactions perturbations may be used to acquire surface-specific Raman spectra. While second-order spectroscopy is an established surface-specific technique, odd-order methods have been passed over because the signal is generated in the bulk media. We show that through a surface Fresnel modulation, coherence-modulated third harmonic generation can be used to obtain surface-specific vibrational information. Bulk and interface contributions to the vibrational signal are separated by scanning the interface through the focus of the laser beam.Item Open Access Damping and switching in thin films and hetero-structures of magnetic materials and topological materials(Colorado State University. Libraries, 2020) Ding, Jinjun, author; Wu, Mingzhong, advisor; Camley, Robert, committee member; Field, Stuart, committee member; Roberts, Jacob, committee member; Shores, Matthew, committee memberYttrium iron garnet (Y3Fe5O12, YIG) materials have been widely used in microwave devices and have also shown high potential for magnonics and spintronics applications. This is because the fact that YIG materials have very low intrinsic damping and is electric insulating. The development of YIG-based spintronics demands YIG films that have a thickness in the nanometer (nm) range and at the same time exhibit low damping comparable to single-crystal YIG bulk materials. In this dissertation, the demonstration of using magnetron sputtering to grow high-quality polycrystalline nm-thick YIG films on gadolinium gallium garnet (Gd3Ga5O12, GGG) substrates is discussed in detail, which is of great technological significance as well as scientific research. The damping constant of the YIG films is the lowest among all the previous reports of nm-thick YIG films grown. Such demonstration of high-quality nm-thick YIG films proves the possibility of nanoscale patterning of YIG films and the future development of YIG-based nanoscale devices. Further, YIG thin films having a thickness of several nanometers and showing both strong perpendicular magnetic anisotropy (PMA) and low magnetic damping are realized in this dissertation. The phenomenon of spin pumping refers to the transfer of spins from precessional moments in a ferromagnet to a non-magnetic material. In a ferromagnetic/non-magnetic bi-layered system, spin pumping manifests itself as two distinct effects: (1) an enhancement in the damping in the ferromagnetic layer and (2) a pure spin current in the non-magnetic layer. This dissertation studies spin pumping effects in a ferromagnetic NiFe thin film associated with topological surface states (TSS) in a neighboring topological Dirac semimetal α-Sn thin film. Large damping enhancement due to the TSS of the Dirac semimetal alpha-Sn thin film is observed. Moreover, the spin current generated in the alpha-Sn film was utilized to switch a magnet through spin-orbit torque (SOT). The switching efficiency is comparable to that in topological insulators, which paves the way for the application of alpha-Sn thin films in future SOT-based magnetic memory. When a topological insulator (TI) is interfaced with a magnetic insulator (MI), it may host the anomalous Hall effect (AHE) and the quantum AHE associated with Berry-phase curvature in momentum space. This dissertation reports a bona fide topological Hall effect (THE) in a single magnetic phase TI/MI heterostructure (Bi2Se3/BaFe12O19) where the electrical transport is exclusively confined to the TI layer. Experimental observations are consistent with a THE originating from skyrmions in BaFe12O19 that are formed due to interfacial Dzyaloshinskii–Moriya interaction.Item Open Access Dark Matter annihilation cross-section limits of dwarf spheroidal galaxies with the high altitude water Cherenkov (HAWC) gamma-ray observatory and on the design of a water Cherenkov detector prototype(Colorado State University. Libraries, 2016) Proper, Megan Longo, author; Harton, John, advisor; Mostafa, Miguel, advisor; Buchanan, Kristen, committee member; Roberts, Jacob, committee member; Marconi, Mario, committee memberI present an indirect search for Dark Matter using the High Altitude Water Cherenkov (HAWC) gamma-ray observatory. There is significant evidence for dark matter within the known Universe, and we can set constraints on the dark matter annihilation cross-section using dark matter rich sources. Dwarf spheroidal galaxies (dSphs) are low luminosity galaxies with little to no gas or dust, or recent star formation. In addition, the total mass of a dwarf spheroidal galaxy, as inferred from gravitational effects observed within the galaxy, is many times more than the luminous mass, making them extremely dark matter rich. For these reasons dSphs are prime targets for indirect dark matter searches with gamma rays. Dark matter annihilation cross-section limits are presented for 14 dSphs within the HAWC field of view, as well as a combined limit with all sources. The limits presented here are for dark matter masses ranging from 0.5 TeV to 1000 TeV. At lower dark matter masses, the HAWC-111 limits are not competitive with other gamma-ray experiments, however it will be shown that HAWC is currently dominating in the higher dark matter mass range. The HAWC observatory is a water Cherenkov detector and consists of 300 Water Cherenkov Detectors (WCDs). The detector is located at 4100 m above sea level in the Sierra Negra region of Mexico at latitude 18deg 59'41" N and longitude 97deg 18'28" W. Each WCD is instrumented with three 8 inch photomultiplier tubes (PMTs) and one 10 inch high efficiency PMT, anchored to the bottom of a 5 m deep by 7.3 m diameter steel tank. The tank contains a multilayer hermetic plastic bag, called a bladder, which holds 200,000 L of ultra-purified water. I will also present the design, deployment, and operation of a WCD prototype for HAWC built at Colorado State University (CSU). The CSU WCD was the only full-size prototype outside of the HAWC site. It was instrumented with 7 HAWC PMTs and scintillator paddles both under and above the volume of water. In addition, the CSU WCD was equipped with the same laser calibration system that is deployed at the HAWC site, as well as the same electronics and data acquisition system. The WCD prototype served as a testbed for the different subsystems of the HAWC observatory. During the three different installations of the prototype, many aspects of the detector design and performance were tested including: tank construction, bladder installation and performance, PMT installation and performance, roof design, water filtration and filling, muon coincidence measurements and calibration system. The experience gained from the CSU prototype was invaluable to the overall design and installation of the HAWC detector.Item Open Access Design, optimziation and fabrication of an integrated optoelectronic sensing chip with applications in groundwater contaminant detection and biosensing(Colorado State University. Libraries, 2014) Erickson, Timothy, author; Lear, Kevin L., advisor; Roberts, Jacob, committee member; Notaros, Branislav, committee member; Collins, George, committee memberThe LEAC (Local Evanescent Array Coupled) chip is a CMOS-compatible, waveguide-based, label-free, optoelectronic sensor, which can function as a biosensor or environmental sensor. Unique among optoelectronic sensors, the ~1 cm2 LEAC chip features an integrated photodetector array, which increases device portability, enables multi-analyte detection on a single waveguide, and simplifies system instrumentation. At its core, the LEAC chip is simply a precision refractometer, which can sense very small changes in refractive index (~5x10-6) in its multiple upper cladding sensing regions. The chip can be functionalized for detection of biomarkers or groundwater contaminants, which bind or diffuse into the waveguide's upper cladding sensing region, thereby producing a measurable change in refractive index. The research conducted during my doctoral studies has addressed two important goals. The first was to optimize the chip's sensing performance. The second goal was to run proof of concept experiments, in order to demonstrate its utility in practical sensing applications. By incorporating multiple engineering improvements, the sensing performance of the LEAC chip has been improved to the point where it may be competitive with low-end surface plasmon resonance (SPR) systems for bulk refractive index sensing. We have demonstrated the LEAC sensing platform for both environmental and biosensing applications. These include sensing aromatic hydrocarbons such as benzene, toluene and xylenes in groundwater at sub-ppm concentrations and detection of the cardiac infarction biomarker TroponinI. Research results have been communicated in peer-reviewed journals and presented at conferences, as summarized in Appendix J. Additionally, the intellectual property that was developed during the course of research activities has served as the basis for several patent filings. This dissertation provides a comprehensive account of research conducted on the LEAC sensing platform, while working as a graduate student in Dr. Kevin Lear's laboratory. It is structured in the following manner. In Chapter 1, the basic functionality of LEAC chip is introduced, while providing the necessary background to motivate its development. Chapter 2 provides a comprehensive and comparative overview of other label-free biosensors and groundwater aromatic hydrocarbon contaminant sensors. It reviews the requirements of other sensing systems and demonstrates the uniquely portable aspects of LEAC chip technology. It is provided for completeness, in order to summarize the state-of-the-art in the field of portable sensing and highlight some of the unique advantages of the LEAC sensor. In Chapter 3, the engineering aspects of performance optimization over prior art are described in detail. Whereas the 1st generation LEAC chip was fabricated at Avago Technologies, all 2nd generation LEAC chips have been fabricated by myself in the CSU cleanroom or at the Colorado Nanofabrication Lab in Boulder. The development of 2nd generation LEAC chips, including device physics, modeling, and fabrication is rigorously described. In Chapter 4, the bulk refractive index sensing capabilities of the chip are demonstrated as well as the chip's capacity to perform multi-analyte dry sensing assays . Through design improvements, it is quantitatively shown that the 2nd generation chip is over two orders of magnitude more sensitive than the 1st generation chip. In Chapter 5, the environmental sensing capabilities of the LEAC chip are presented. Teflon AF is first characterized as a unique film for sensing BTX (benzene, toluene, and xylene) contaminants in water using near-IR surface plasmon resonance. Then LEAC chips functionalized with Teflon AF are demonstrated for BTX sensing in water at sub-ppm concentrations. Interference from potential matrix interfering contaminants is evaluated. In Chapter 6, the biosensing capabilities of the LEAC chip are discussed. The LEAC chip is validated for detection of Troponin I. In Chapter 7, areas for future improvements to the LEAC sensing platform are briefly touched upon along with concluding remarks. A number of appendices related to very specific technical aspects of my work have been included as helpful documentation. These appendices include fabrication process flows, the data acquisition system, transimpedance amplifier design, grating coupler designs, mask designs (including testing structures), and other protocols. A list of publications and conferences is provided at the end of this report in Appendix I.Item Open Access Detection of small numbers of barium ions implanted in solid xenon for the EXO experiment(Colorado State University. Libraries, 2012) Cook, Shon, author; Fairbank, William, advisor; Lee, Siu Au, committee member; Roberts, Jacob, committee member; Bartels, Randy, committee memberIn an effort to discover the yet-unknown absolute masses of neutrinos, the goal of the Enriched Xenon Observatory is to observe neutrinoless double beta decay of 136Xe. Identification of this very rare decay may be difficult even with the best conventional efforts to reduce and reject radioactive background, thus requiring additional background rejection via detection of the daughter 136Ba nucleus. One method of detection is laser-induced fluorescence of the barium atom in solid xenon. Spectra of very small numbers of barium atoms in solid xenon, as few as 3 atoms, are reported for the first time. Demonstration of detection of Ba atoms with large fluorescence efficiencies gives promise for detecting single atoms in the near future. Results from experiments involving implantation of Ba+ ions in solid xenon are discussed. One narrow excitation peak was discovered from ion beam deposition that was not found in neutral deposits. Five new emission lines are found with this same excitation spectrum. Bleaching, annealing, and laser dependence of these lines are studied. The identification of the new Ba species as Ba+ or as a barium molecule is discussed.Item Open Access Development and testing of a multiplexing system for laser ignition of large bore natural gas engines(Colorado State University. Libraries, 2011) Reynolds, Adam Robert, author; Yalin, Azer, advisor; Willson, Bryan, committee member; Roberts, Jacob, committee memberConventional electric spark plugs present a hindrance to the continuing goals of higher efficiency and reduced emissions for large-bore natural gas engines. In order to achieve these goals, higher compression ratios and higher air-to-fuel ratios must be achieved relative to those currently allowed by conventional spark plugs. Laser ignition has been shown to work farther into the lean limit, and contrary to conventional electric spark plugs, laser sparks are easier to produce at higher pressures. Laser ignition has also been shown to reduce NOx emissions. This work presents efforts to design, build, and test a single-laser-to-multiple-cylinders multiplexed laser ignition system for use with a large bore natural gas engine. A fiber based laser delivery system was found to work for laser ignition on the bench-top. Results of bench top tests are presented.Item Open Access Development of a high power chirped pulse amplification laser for driving secondary sources(Colorado State University. Libraries, 2019) Baumgarten, Cory M., author; Rocca, Jorge, advisor; Roberts, Jacob, committee member; Lee, Siu Au, committee member; Marconi, Mario, committee memberLaser applications which require high energy ultrashort laser pulses have been limited in repetition rate. This dissertation describes the development of high repetition rate, high energy, all diode pumped ultrashort pulse Yb:YAG lasers and their use in two selected applications. Yb:YAG is an attractive gain medium for high average power, ultrashort pulse laser operation. This material, with long upper level lifetime, is well suited for direct pumping by high power, narrow bandwidth laser diodes, and combined with a small quantum defect, minimal heating of the material is produced. Additionally, the thermal conductivity and optical properties of Yb:YAG dramatically improve when cooled to cryogenic temperatures. The main focus of this dissertation is the development of an all diode-pumped, chirped pulse amplification, ultrashort pulse laser based on a cryogenically-cooled Yb:YAG amplifier design. This laser system operates at λ = 1.03 μm and is capable of producing 1.4 J pulses before compression at 500 Hz and 1 kHz repetition rate. During 500 Hz operation, the laser used a combination of room temperature and cryogenically-cooled Yb:YAG amplifiers to generate pulses of 1 J energy compressed to sub- 5ps duration. At 1 kHz, pulse energies of 1 J with sub-10ps transform limited pulse durations were obtained. The simultaneously high pulse energies and repetition rates obtained in this work will be beneficial for a host of applications including tabletop sources of coherent short wavelength radiation, high power femtosecond sources operating in the near and mid-infrared, and high gradient laser plasma accelerators. The work in this dissertation specifically demonstrates the use of cryogenically cooled Yb:YAG lasers in the development of soft x-ray lasers and a near-infrared optical parametric amplifier for the testing damage threshold of multilayer coatings.The generation of coherent radiation in the soft x-ray regime was historically limited to 10 Hz. Compact, table-top soft x-ray lasers have enabled a range of applications including nano- scale imaging and lithography, the investigation of hot dense plasmas, and nano-scale fabrication. Recently, compact sources of coherent soft x-ray laser radiation were demonstrated at repetition rates of one hundred shots per second using the laser technology described in this dissertation. As a demonstration of the Yb:YAG laser's excellent beam quality and high average power, this system was used to pump a high repetition rate soft x-ray laser. The optical pump laser and the resulting soft x-ray laser, operated at a record 400 Hz repetition rate with strong lasing in the λ = 18.9 nm line of Ni-like Mo. This work also demonstrates a Yb:YAG laser driven, optical parametric chirped pulse amplification (OPCPA) laser system operating at 100 Hz in the near-infrared, which was used to per- form laser induced damage threshold measurements of optical coatings. OPCPAs have emerged as a next generation ultrafast laser source for generating sub-femtosecond laser pulses useful for probing molecular electron dynamics as well as creating ultra-intense, femtosecond laser pulses for exploring exotic states of matter and for the development of next generation laser plasma accelerators. The OPCPA developed as part of this work operates at wavelengths ranging from λ = 1.5-2 μm with final amplification stages pumped at 100 Hz with a chirped pulse amplification laser based on cryogenically-cooled Yb:YAG. The OPCPA was used to obtain damage thresholds of optical coatings in what to our knowledge constitutes the first results of picosecond damage performed in this wavelength range.Item Open Access High-power deep-UV laser for improved and novel experiments on hydrogen(Colorado State University. Libraries, 2019) Burkley, Zakary Neumann, author; Yost, Dylan, advisor; Roberts, Jacob, committee member; Bradley, Mark, committee member; Menoni, Carmen, committee memberThis dissertation details the design, performance, and cavity enhancement of a novel, high-power coherent 243.1 nm laser system, and through simulations, its ability to trap hydrogen in a magic wavelength optical trap. This wavelength of light is necessary to address the 1S–2S two-photon transition in hydrogen, and the primary motivation behind development of this laser system is obtaining high enough 243.1 nm powers for two-photon cooling of hydrogen. Due to the light mass of hydrogen, high precision spectroscopy of hydrogen is limited by unwanted motional effects, which could be mitigated with laser cooling and confinement in an optical trap. Besides laser cooling, a high power deep-UV laser system at this wavelength has great utility for improving spectroscopy of hydrogen and other exotic simple systems. High-power fiber lasers from 1-1.2 µm have flourished as a result of advances in ytterbium(Yb)-doped fiber amplifiers. In addition, high-power Yb-fiber lasers between 975-980 nm have also been developed—a notable accomplishment due to gain competition in the > 1 µm spectral region. These systems initially lacked sufficiently narrow spectral bandwidth for efficient harmonic generation, motivating further development since there is significant interest in frequency doubling and quadrupling these sources to produce coherent blue radiation and deep-UV radiation. Here, we generate coherent, high-power deep-UV radiation through frequency quadrupling of a high-power, highly coherent Yb-fiber amplifier at 972.5 nm. The Yb-fiber amplifier system consists of a frequency stabilized master oscillator power amplifier (MOPA) that can be referenced to a coherent frequency comb. This MOPA can be amplified to > 10 W of narrow linewidth power at 972.5 nm in the Yb-fiber amplifier. This is a technically challenging and notable result for this wavelength as gain is much more readily obtained in Yb-doped fibers at the absorption/emission cross-section peak near 975 nm and in the > 1 µm spectral region where the emission cross-section is much larger than the absorption cross-section. This system successfully combated unwanted gain at these wavelengths by using a relatively short (≈ 10 cm), angle-polished Yb-fiber with a large core-cladding ratio, along with aggressive spectral filtering and large amounts of seed power at 972.5 nm. With this narrow linewidth Yb-fiber amplifier, efficient frequency conversion of high power 972-976 nm radiation to 243-244 nm radiation is possible through intracavity doubling. Through successive resonant doubling stages, this system demonstrates > 1 W of highly stable, continuous-wave (CW) 243.1 nm power. To the author's knowledge, this is a record amount of CW deep-UV power below 266 nm, and is made possible thanks to advances in the production of a relatively new non-linear crystal for robust deep-UV generation, cesium lithium borate (CLBO). The precise frequency control of this radiation is established via excitation of the 1S–2S transition in hydrogen, and the viability for two-photon laser cooling on this transition is shown through enhancement of this power to > 30 W of intracavity power in a deep-UV enhancement cavity. At these powers, UV-induced mirror degradation was observed and mitigated by flushing the enhancement cavity mirrors with ultra-pure oxygen. With these powers, rapid two-photon laser cooling of a hydrogen atomic beam approaches reality. The 243.1 nm powers offered by this laser system also offer unique methods for capturing hydrogen in an optical trap. Explored via simulations, single optical scatter capture of hydrogen in a magic wavelength dipole trap is demonstrated, promising exciting new avenues for high precision spectroscopy of hydrogen.Item Open Access Hodge and Gelfand theory in Clifford analysis and tomography(Colorado State University. Libraries, 2022) Roberts, Colin, author; Shonkwiler, Clayton, advisor; Adams, Henry, committee member; Bangerth, Wolfgang, committee member; Roberts, Jacob, committee memberThere is an interesting inverse boundary value problem for Riemannian manifolds called the Calderón problem which asks if it is possible to determine a manifold and metric from the Dirichlet-to-Neumann (DN) operator. Work on this problem has been dominated by complex analysis and Hodge theory and Clifford analysis is a natural synthesis of the two. Clifford analysis analyzes multivector fields, their even-graded (spinor) components, and the vector-valued Hodge–Dirac operator whose square is the Laplace–Beltrami operator. Elements in the kernel of the Hodge–Dirac operator are called monogenic and since multivectors are multi-graded, we are able to capture the harmonic fields of Hodge theory and copies of complex holomorphic functions inside the space of monogenic fields simultaneously. We show that the space of multivector fields has a Hodge–Morrey-like decomposition into monogenic fields and the image of the Hodge–Dirac operator. Using the multivector formulation of electromagnetism, we generalize the electric and magnetic DN operators and find that they extract the absolute and relative cohomologies. Furthermore, those operators are the scalar components of the spinor DN operator whose kernel consists of the boundary traces of monogenic fields. We define a higher dimensional version of the Gelfand spectrum called the spinor spectrum which may be used in a higher dimensional version of the boundary control method. For compact regions of Euclidean space, the spinor spectrum is homeomorphic to the region itself. Lastly, we show that the monogenic fields form a sheaf that is locally homeomorphic to the underlying manifold which is a prime candidate for solving the Calderón problem using analytic continuation.Item Open Access In-situ laser tagging of barium ions in liquid xenon for the EXO experiment(Colorado State University. Libraries, 2012) Hall, Kendy, author; Fairbank, William, advisor; Toki, Walter, committee member; Marconi, Mario, committee member; Roberts, Jacob, committee memberThe goal of the Enriched Xenon Observatory (EXO) collaboration is to measure the half-life of neutrino-less double beta decay using a ton size liquid 136Xe detector with zero back-ground. Zero background detection can only be achieved if the daughter nucleus, 136Ba, can be tagged. The EXO collaboration is investigating several techniques to tag the 136Ba daughter. The goal of this thesis is to investigate the prospects of directly observing a single 136Ba+ ion in the liquid using a laser aimed at the decay site, hence in-situ laser tagging. Because the energy levels of Ba+ ions are expected to be altered from the vacuum configuration, in-situ laser tagging can only be accomplished if the spectroscopy of the Ba+ ions in liquid xenon is understood. An ultra-pure liquid xenon test apparatus with a liquid xenon purity monitor has been built to study the spectroscopy of the Ba+ ions. An unexpected discovery of the nonresonant multiphoton ionization of liquid xenon using pulsed UV lasers was made while characterizing the purity monitor. The discovery was vital to the ability to accurately measure the purity of the liquid xenon. The spectroscopy of Ba+ ions in liquid xenon and the multiphoton ionization studies are the two key topics that are presented in this thesis.Item Open Access Maximal curves, zeta functions, and digital signatures(Colorado State University. Libraries, 2011) Malmskog, Beth, author; Pries, Rachel, advisor; Achter, Jeffrey, committee member; Penttila, Tim, committee member; Roberts, Jacob, committee memberCurves with as many points as possible over a finite field Fq under the Hasse-Weil bound are called maximal curves. Besides being interesting as extremal objects, maximal curves have applications in coding theory. A maximal curves may also have a great deal of symmetry, i.e. have an automorphism group which is large compared to the curve's genus. In Part 1, we study certain families of maximal curves and find a large subgroup of each curve's automorphism group. We also give an upper bound for the size of the automorphism group. In Part 2, we study the zeta functions of graphs. The Ihara zeta function of a graph was defined by Ihara in the 1960s. It was modeled on other zeta functions in its form, an infinite product over primes, and has some analogous properties, for example convergence to a rational function. The knowledge of the zeta function of a regular graph is equivalent to knowledge of the eigenvalues of its adjacency matrix. We calculate the Ihara zeta function for an infinite family of irregular graphs and consider how the same technique could be applied to other irregular families. We also discuss ramified coverings of graphs and a joint result with Michelle Manes on the divisibility properties of zeta functions for graphs in ramified covers. Part 3 is joint work with Jeremy Muskat. Gauss's curve, with equation x2t2 + y2t2 + x2y2 - t4 = 0 defined over Fp was the subject of the last entry in Gauss' mathematical diary. For p equivalent to 3 ≡ 4, we give a proof that the zeta function of C is ZC(u) = (1 + pu2)(1 + u)2/(1 - pu)(1 - u). Using this, we find the global zeta function for C. The best algorithms for solving some lattice problems, like finding the shortest vector in an arbitrary lattice, are exponential in run-time. This makes lattice problems a potentially good basis for cryptographic protocols. Right now, lattices are especially important in information security because there are no known quantum computer algorithms that solve lattice problems any faster than traditional computing. The learning with errors problem (LWE) is provably as hard as certain lattice problems. Part 4 of the dissertation is a description of a digital signature scheme based on the learning with errors problem over polynomial rings. The search version of LWE is to find a hidden vector s, given access to many pairs of noisy inner products with random vectors (ai, bi = ai • s + ei). The context can be shifted to a polynomial ring over Z/q, giving rise to the problem of learning with errors over a ring (R-LWE). In this joint work with Kristin Lauter, Michael Naehrig, and Vinod Vaikuntanathan, we devise a digital signature scheme based on R-LWE and outline a proof of security for certain parameter choices.Item Open Access Precision measurement and symmetry properties of metastable hydrogen(Colorado State University. Libraries, 2022) Rasor, Cory M., author; Yost, Dylan, advisor; Roberts, Jacob, committee member; Mooney, Michael, committee member; Bartels, Randy, committee memberHydrogen has been an indispensable system to study during the development of quantum mechanics due to the simplicity of its atomic structure. Hydrogen maintains its utility today as an important tool for determining fundamental values such as the Rydberg and fine structure constants, as well as the proton charge radius. The work described in this thesis aims to use hydrogen for determining the proton Zemach radius, to search for anomalous spin-dependent forces, and to provide means for measuring the degree of parity violation within this simple system. An overview of a 2S1/2 hyperfine interval measurement is described, followed by a description of the apparatus used and finally a discussion of the systematic effects to be characterized. A proposed parity violation experiment is also described.Item Open Access Probing molecular kinetics using higher-order fluorescence correlation spectroscopy(Colorado State University. Libraries, 2019) Abdollah-Nia, Farshad, author; Gelfand, Martin P., advisor; Van Orden, Alan, advisor; Krapf, Diego, committee member; Prasad, Ashok, committee member; Roberts, Jacob, committee memberFluorescence correlation spectroscopy (FCS) is a powerful tool in the time-resolved analysis of non-reacting or reacting molecules in solution, based on fluorescence intensity fluctuations. However, conventional (second-order) FCS alone is insufficient to measure all parameters needed to describe a reaction or mixture, including concentrations, fluorescence brightnesses, and forward and reverse rate constants. For this purpose, correlations of higher powers of fluorescence intensity fluctuations can be calculated to yield additional information from the single-photon data stream collected in an FCS experiment. To describe systems of diffusing and reacting molecules, considering cumulants of fluorescence intensity results in simple expressions in which the reaction and the diffusion parts factorize. The computation of higher-order correlations in experiments is hindered by shot noise and common detector artifacts, the effects of which become worse with increasing order. We introduce a technique to calculate artifact-free higher-order correlation functions with improved time resolution, and without any need for modeling and calibration of detector artifacts. The technique is formulated for general multi-detector experiments and verified in both two-detector and single-detector configurations. Good signal-to-noise ratio is achieved down to 1 μs in correlation curves up to order (2,2). Next, we demonstrate applications of the technique to analyze systems of fast and slow reactions. As an example of slow- or non-reacting systems, the technique is applied to resolve two-component mixtures of labeled oligonucleotides. Then, the protonation reaction of fluorescein isothiocyanate (FITC) in phosphate buffer is analyzed as an example of fast reactions (relaxation time < 10 μs). By reference to an (apparent) non-reacting system, the simple factorized form of cumulant-based higher-order correlations is exploited to remove the dependence on the molecular detection function (MDF). Therefore, there is no need to model and characterize the experimental MDF, and the precision and the accuracy of the technique are enhanced. It is verified that higher-order correlation analysis enables complete and simultaneous determination of number and brightness parameters of mixing or reacting molecules, the reaction relaxation time, and forward and reverse reaction rates. Finally, we apply the technique to analyze the conformational dynamics of DNA hairpins. Previous FCS measurements of DNA hairpin folding dynamics revealed at least three conformational states of the DNA are present, distinguished by the brightness of fluorescent dye-quencher labels. Rapid fluctuations between two of the states occurred on time scales observable by FCS. A third state that was static on the FCS time scale was also observed. We show that conventional FCS alone cannot uniquely distinguish the conformational states or assign their roles in the observed mechanism. The additional information offered by higher-order FCS makes it possible (i) to uniquely identify the static and rapidly-fluctuating states; and (ii) to directly measure the brightnesses and populations of all three observed states. The rapid fluctuations occurring on the FCS time-scale are due to a reversible reaction between the two lowest brightness levels, attributed to the folded and random-coil conformations of the DNA. The third state, which is the brightest, is attributed to spatially extended unfolded conformations that are isolated from the more compact conformations by a substantial energy barrier. These conformations attain a maximum equilibrium population of nearly 10% near physiological temperatures and salt concentrations.Item Open Access SMOKE+: a video dataset for automated fine-grained assessment of smoke opacity(Colorado State University. Libraries, 2024) Seefried, Ethan, author; Blanchard, Nathaniel, advisor; Sreedharan, Sarath, committee member; Roberts, Jacob, committee memberComputer vision has traditionally faced difficulties when applied to amorphous objects like smoke, owing to their ever-changing shape, texture, and dependence on background conditions. While recent advancements have enabled simple tasks such as smoke detection and basic classification (black or white), quantitative opacity estimation in line with the assessments made by certified professionals remains unexplored. To address this gap, I introduce the SMOKE+ dataset, which features opacity labels verified by three certified experts. My dataset encompasses five distinct testing days, two data collection sites in different regions, and a total of 13,632 labeled clips. Leveraging this data, we develop a state-of-the-art smoke opacity estimation method that employs a small number of Residual 3D blocks for efficient opacity estimation. Additionally I explore the use of MAMBA blocks in a video based architecture, exploiting their ability to handle spatial and temporal data in a linear fashion. Techniques developed during the SMOKE+ dataset creation were then refined and applied to a new dataset titled CSU101, designed for educational use in Computer Vision. In the future I intend to expand further into synthetic data, incorporating techniques into Unreal Engine or Unity to add accurate opacity labels.