Browsing by Author "Marconi, Mario, committee member"

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Open Access
A study of the influence of process parameter variations on the material properties and laser damage performance of ion beam sputtered Sc2O3 and HfO2 thin films
(Colorado State University. Libraries, 2016) Langston, Peter F., author; Menoni, Carmen, advisor; Rocca, Jorge, committee member; Marconi, Mario, committee member; Yalin, Azer, committee member
This work is a study of the influence of process parameter variations on the material properties and laser damage performance of ion beam sputtered Sc2O3 and HfO2 thin films using a Vecco Spector ion deposition system. These parameters were explored for the purpose of identifying optically sensitive defects in these high index materials after the deposition process. Using a host of optical metrology and materials analysis techniques we report on the relationship between oxygen partial pressure in the deposition chamber during film growth and optical absorption in the grown material at 1 μm. These materials were found to be prone to excess oxygen incorporation. Positive identification of this excess oxygen is made and exactly how this oxygen is bound in the different materials is discussed. The influence of this defect type on the optical and mechanical properties of the material is also given and discussed. Laser damage results for these single layers are presented. The influence of higher and lower deposition energy was also studied to determine the potential for defect creation both at the surface and in the bulk of the material grown. Optimized thin films of HfO2, Sc2O3 and Ta2O5 were grown and tested for laser damage with a 1030 nm laser having a pulse width of ~375 ps and a nominal spot size of ~100 um FWHM. The laser damage threshold ranking of these materials followed fairly well with the band gap of the material when tested in air. When these same materials were tested in vacuum Sc2O3 was found to be very susceptible to vacuum mediated laser induced surface defect creation resulting in a greatly reduced LIDT performance. Ta2O5 showed much the same trend in that its in vacuum performance was significantly reduced from its in air performance but there was not as great of a difference between the in air and in vacuum performance as there was for Sc2O3. HfO2 also showed a large reduction in its in vacuum LIDT results compared with its in air LIDT values however, this material showed the smallest decrease of the three high index materials tested. A second contribution of this work is in the investigation of the impact of capping layers on the in air and in vacuum LIDT performance of single layer films. Ultra thin capping layers composed of different metal oxides were applied to 100 nm thick single layers of the same high index materials already tested, HfO2, Sc2O3 and Ta2O5. These capped samples were then LIDT tested in air and in vacuum. These ultra thin capping layers were shown to greatly influence the in air and in vacuum damage performance of the uncapped single layers. Damage probability curves were analyzed to retrieve surface and bulk defect densities as a function of local fluence. Methods for maximizing the LIDT performance of metal oxides based on our studied materials for use in air and in vacuum are discussed.
Open Access
Advancements in the optical damage resistance of ion beam sputter deposited interference coatings for high energy lasers
(Colorado State University. Libraries, 2015) Schiltz, Drew, author; Menoni, Carmen, advisor; Marconi, Mario, committee member; Bradley, Mark, committee member
The work presented in this thesis is dedicated toward investigating, and ultimately improving the laser damage resistance of ion beam sputtered interference coatings. Not only are interference coatings a key component of the modern day laser, but they also limit energy output due to their susceptibility to laser induced damage. Thus, advancements in the fluence handling capabilities of interference coatings will enable increased energy output of high energy laser systems. Design strategies aimed at improving the laser damage resistance of Ta2O5/SiO2 high reflectors for operation at one micron wavelengths and pulse durations of several nanoseconds to a fraction of a nanosecond are presented. These modified designs are formulated to reduce effects from the standing wave electric field distribution in the coating. Design modifications from a standard quarter wave stack structure include increasing the thickness of SiO2 top layers and reducing the Ta2O5 thickness in favor of SiO2 in the top four bi-layers. The coating structures were deposited with ion beam sputtering. The modified designs exhibit improved performance when irradiated with 4 ns duration pulses, but little effect at 0.19 ns. Scaling between the results from testing at these two pulse durations shows deviation from τ1/2 scaling, where τ is the pulse duration. This suggests possible differences in the initial damage mechanism. Also presented are results for at-wavelength optical absorption losses measured with photothermal common-path interferometry and surface roughness measurements with atomic force microscopy. Further studies on the damage thresholds of interference coatings operating at 1.6 micron wavelength and 2 picosecond pulse durations are presented. High reflection and anti-reflection coating structures were fabricated with varied high index materials: HfO2, Y2O3 and Ta2O5. For damage testing, an optical parametric chirped pulse amplifier was fabricated and implemented. This source is capable of producing ~5 millijoule pulses with a tunable wavelength between 1.5 and 2 micron. When investigated at 1.6 micron wavelength, the interference coatings exhibit ultra-low absorption losses and damage thresholds at ~7.0 J/cm2 and 3.5 TW/cm2 peak intensities, near that of the infrared grade fused silica substrates they are deposited on. Furthermore, interference effects and lower band gap materials do not impair the damage threshold. This behavior is significantly different than what has previously been observed at similar pulse durations and more common laser wavelengths around 0.8 to 1 micron. I show that conventional rate equation modeling proves inadequate at describing the obtained results.
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 member
Recently, 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.
Open Access
Analysis and modeling of cells, cell behavior, and helical biological molecules
(Colorado State University. Libraries, 2011) Benoit, Steven Richard, author; Putkaradze, Vakhtang, advisor; Shipman, Patrick, committee member; Estep, Don, committee member; Marconi, Mario, committee member; Tobet, Stuart, committee member
Mathematical models of biological systems have evolved over time and through the introduction and growth of computer simulation and analysis. Models have increased in sophistication and power through the combination of multi-scale approaches, molecular and granular dynamics simulations, and advances in parallelization and processing speed. However, current cell models cannot accurately predict behaviors at the whole-cell scale, nor can molecular models predict accurately the complex shape assumed by large biological molecules including proteins, although significant progress is being made toward this goal. The present work introduces new models in three domains within biological systems modeling. We first discuss a phenomenological model of observed cell motions in developing tissue that characterizes cells according to a best-fit generalized diffusion model and combines this data with Voronoi diagrams to effectively visualize patterns of cell behavior in tissue. Next, we present a series of component models for cells and cell structure that support simulations involving tens to hundreds of cells in a way that captures behaviors ignored by existing models, including pseudopod formation, membrane mechanics, cytoskeletal polymerization / depolymerization, and chemical signal transduction. The resulting models exhibit many of the behaviors of real-world cells including polarization and chemotaxis. Finally, we present a method for analysis of biological molecules that form helical conformations that includes long-range electrostatic interactions as well as short-range interactions to prevent self-intersections. We consider the stability of molecules with repeating monomers that include off-axis charge concentrations and derive energy landscapes to identify stable conformations, then analyze helical stability using geometric methods.
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 member
The 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.
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 member
I 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.
Open Access
Demonstration of filament-guided electrical discharges from a high average power 1 kHz picosecond laser
(Colorado State University. Libraries, 2023) Dehne, Kristian A., author; Rocca, Jorge, advisor; Marconi, Mario, committee member; Brewer, Samuel, committee member
The atmospheric propagation of ultrashort, high energy laser pulses is of interest for applications including remote sensing, directed energy, and the guiding of lightning. In this thesis, the filamentation of high energy picosecond laser pulses at repetition rates up to 1 kHz is demonstrated and the guiding of electrical discharges in air at high repetition rates is studied. The design and performance of the diode-pumped Yb:YAG chirped pulse amplification (CPA) system utilized for this experiment is also described. Diode-pumped solid state lasers in a CPA layout have emerged as the modern choice for the generation of high pulse energies at high repetition rates. For the work presented in this thesis, a high average power diode-pumped Yb:YAG laser system utilized for filament formation is de- tailed. The compact CPA system, which combines a room temperature regenerative amplifier and cryogenically cooled Yb:YAG amplifiers, results in compressed pulses of < 5 ps duration with up to 1.1 J of energy at 1 kHz repetition rate. This record Joule-level 1 kHz repetition rate picosecond laser (average power output of more than 1 kW) has enabled the results described herein. The application of this high average power Yb:YAG system for producing laser guided electrical discharges is the main focus of this thesis. The compressed output pulses from the Yb:YAG laser induce filamentation in air, resulting from the counterbalance between Kerr self-focusing and plasma refraction defocusing. The hydrodynamic response of the atmospheric air results in a density depression of similar geometry to the filament. The result is a preferential path which both triggers and guides electrical discharges. The majority of previous laser-guided discharge studies have been conducted at repetition rates of 10 Hz, where the medium completely recovers before the next laser pulse arrives. This thesis reports on the physics of laser filament-guided electric discharges in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of ∼7 ps duration at repetition rates up to 1 kHz. A breakdown voltage reduction of up to 4.2 X was measured and determined to result primarily from the perturbation caused by a single laser pulse, with cumulative effects playing only a secondary role. A current proportional to the laser pulse energy arises as soon as the laser pulse arrives, initiating a high impedance phase of the discharge channel evolution. Full breakdown, characterized by impedance collapse and the onset of high current conduction, occurs 100s of ns to a few μs later. The gaps between the filamentary plasma channel and the electrodes are observed to play a role in the delay between arrival of the laser pulse and the onset of a discharge. The breakdown voltages measured for 100 Hz and 1 kHz repetition rates are shown to be nearly equivalent. This is consistent with the results of interferometric analysis which shows that the filament formed by a single laser shot causes a deep density depression up to 75%, compared with the 20% density depression measured 10 μs prior to the arrival of a laser pulse in a sustained 1 kHz sequence. The physical insight gained from this work on the formation of laser filament-guided discharges in air at 1 kHz repetition rate can be expected to contribute to their use in applications.
Open Access
Development and implementation of near-infrared ultrafast laser sources generated by nonlinear fiber propagation
(Colorado State University. Libraries, 2015) Domingue, Scott R., author; Bartels, Randy, advisor; Krummel, Amber, committee member; Krapf, Diego, committee member; Marconi, Mario, committee member
This dissertation is broken up into three parts: (I) generating high-quality ultrafast pulses around 1060 nm, (II) using the pulses from part (I) to generate pulses around 1300 nm, and (III) analyzing newly developed experimental theories and methods utilizing these pulses for linear and nonlinear microscopy. The majority of the work in this dissertation is choreographing the dance between nonlinear spectral broadening in optical fiber and the associated complexity in accumulated spectral phase. We have developed and employed several systems which manage to accomplish this task quite elegantly due to our technological contributions, producing high-quality pulses with high oscillator-type pulse energies both at 1060 and 1250 nm. In addition to developing some theory and techniques extending current types of nonlinear microscopy, we have as a capstone an experimental microscope cascading several of our primary source and application technologies to conduct an entirely new form of spectroscopic absorption imaging.
Open Access
Development of a high energy diode-pumped chirped pulse amplification laser system for driving soft x-ray lasers
(Colorado State University. Libraries, 2012) Reagan, Brendan A., author; Rocca, Jorge, advisor; Menoni, Carmen, committee member; Marconi, Mario, committee member; Krueger, David, committee member
There is significant interest in the development of compact high repetition rate soft x-ray lasers for applications. This dissertation describes the development of a high energy, laser diode pumped, chirped pulse amplification laser system for driving soft x-ray lasers in the 10-20 nm spectral region. The compact laser system combines room temperature and cryogenically-cooled Yb:YAG amplifier to produce 1.5 Joule pulses at up to 50 Hz repetition rate. Pulse compression results in 1 J pulses of 5 ps duration. A room temperature pre-amplifier maintains bandwidth for short pulse operation and a novel cryogenic cooling technique for the power amplifier was developed to enable high average power operation of this laser. This laser was used to drive a soft x-ray laser on the 18.9 nm line of nickel-like molybdenum. This is the first demonstration of a soft x-ray laser driven by an all diode-pumped laser.
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 member
Laser 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.
Open Access
Development of a high power high energy ultrafast laser
(Colorado State University. Libraries, 2021) Chi, Han, author; Rocca, Jorge, advisor; Menoni, Carmen, committee member; Marconi, Mario, committee member; Lee, Siu Au, committee member
This dissertation describes the development of high energy, high repetition rate laser technology based on cryogenically cooled diode-pumped Yb:YAG laser amplifiers. The key challenges of thermal management, the generation of high energy green pulses at high repetition rate, and the design of an ultrafast laser amplifier that uses the green pulses as pump are discussed in this dissertation. To aid the development of thermal management solutions, an accurate, in situ, noninvasive optical technique to generate three-dimensional (3-D) temperature maps of cryogenic amplifiers during operation at high average power was demonstrated. The temperature is determined by analyzing the fluorescence spectra of the laser material (Yb:YAG) with a neural network algorithm. The accuracy of the technique relies on a calibration that does not depend on simulations. Results are presented for a cryogenic Yb:YAG active mirror laser amplifier operating at different pump conditions, which include kW pump power level operation. Based on this temperature measurement technique, an analysis of the thermal behavior of a high-energy kilowatt-average-power diode-pumped cryogenically cooled Yb:YAG active mirror laser amplifier is presented. Maps of the temperature distribution in the laser amplifier crystal at pump powers up to 1kW were obtained for the first time by spectrally resolving the fluorescence induced by a scanning probe beam. The cryo-temperature measurement technique is applicable to other solid-state lasers materials. The wavefront distortions resulting from the front surface deformation and the overall deformation of the gain medium assembly were measured using a Mach–Zehnder interferometer. The measured deformations agree well with the results of finite element thermomechanical modeling simulations, and with the results of focal length shift measurements. The relative contributions to the optical path difference (OPD) of the mechanical deformations, refractive index changes, and electronic contribution are discussed. The pump-induced mechanical deformations of the assembly dominate the OPD changes in the kilowatt-average-pump-power cryogenically cooled Yb:YAG active mirror laser investigated. The generation of green (λ= 515 nm) Joule-level pulses at 1 kHz repetition rate was demonstrated. This was achieved by frequency doubling 1.2 J, 2 ns temporally shaped square pulses from a cryogenically cooled Yb:YAG laser in an LBO crystal. The generation of 0.94 J second-harmonic pulses at 1 kHz was demonstrated with 78% conversion efficiency. The unconverted light was sent through a second LBO crystal to generate an additional >100 mJ second-harmonic pulses to reach a total green average power of 1.04kW. A higher conversion efficiency of 89% was also achieved for 0.58 J green pulses at 1 kHz. An application of this green laser is the pumping of high average power ultrafast laser amplifiers. The design of a two-stage water-cooled Ti:Sapphire amplifier system to generate 300 mJ pulses pre-compression using this green laser as pump is discussed. The simulation of the gain and thermal distribution of the 1st and 2nd stage amplifier are presented. The first experimental results of the operation of the first amplification stage of this laser system are discussed.
Open Access
Extreme ultraviolet time-of-flight mass spectrometry for the characterization of actinides
(Colorado State University. Libraries, 2017) Green, Tyler, author; Menoni, Carmen, advisor; Crick, Dean, committee member; Marconi, Mario, committee member
Many scientific disciplines, as well as several technologies, have a great demand for analytical tools capable of assessing chemical composition and imaging chemical content that are highly sensitive and have sub-micron spatial resolution. Laser ablation mass spectrometry meets both of these requirements and as such is broadly used for chemical analyses and chemical mapping of atomic and molecular species on solid samples. This thesis describes results on the characterization of Extreme Ultraviolet Time-of-Flight Laser Ablation Mass Spectrometry (EUV TOF) for analysis of trace actinides and for high lateral resolution imaging of inorganic samples. We demonstrate that this technique, with a nominal sensitivity around 50 ppm and a lateral resolution of 80 nm, is already competitive with other well-established mass spectrometry techniques that focus on analytical isotopic imaging. The thesis also details the diagnosis and determination of causes of noise that compromise sensitivity in the mass spectra. These results enable EUV TOF to properly orient itself in the field of mass spectrometry and allow multiple disciplines to conduct high resolution compositional mapping quickly and with minimal isobaric interferences.
Open Access
Highly relativistic laser interactions with ordered nanostructures
(Colorado State University. Libraries, 2019) Hollinger, Reed, author; Rocca, Jorge J., advisor; Prieto, Amy L., committee member; Menoni, Carmen, committee member; Marconi, Mario, committee member
Heating high density matter to extreme temperatures has been one of the primary motivations behind the construction of high power laser facilities around the world. The creation of simultaneously hot (multi-keV) and dense (on the order of a solid) plasma with small scale and mid-scale lasers is a difficult problem due to the barrier that the critical electron density imposes to optical lasers, typically limiting the heating to a very thin plasma into which the laser is inefficiently coupled. Experiments conducted at Colorado State University with joule level laser pulses have demonstrated that using high contrast, relativistic laser pulses it is possible to efficiently heat near solid density nanowire arrays volumetrically to multi-keV temperatures. This dissertation extends these results to the highly relativistic regime, demonstrating extremely high ionization states for volumes >5μm in depth. These relatively large volume plasmas have longer hydrodynamic cooling times while their radiative cooling time is greatly decreased due to the near solid electron densities. This results in very efficient conversion of optical laser light into x-rays since the plasma is able to radiate away more of its' energy as x-rays before cooling due to hydrodynamic expansion. With this technique, an x-ray conversion efficiency of nearly 20% was measured for photon energies greater than 1keV. After a significant upgrade to the laser, these interactions were explored at highly relativistic intensities up to 4x1021 Wcm−2, nearly 1000 times higher than initial experiments. Measurements of the energy deposition dynamics, including the time limit for energy coupling and the volume of the nanowire plasma were carried out in comparison to solid targets. The results show that at these intensities, it is possible to generate unprecedented degrees of ionization never before obtained with ultrashort pulse lasers, such as H-like Ni (27 times ionized) and Ne-like Au (69 times ionized).
Open Access
Homotopy continuation methods, intrinsic localized modes, and cooperative robotic workspaces
(Colorado State University. Libraries, 2012) Brake, Daniel Abram, author; Putkaradze, Vakhtang, advisor; Maciejewski, Tony, advisor; Marconi, Mario, committee member; Bates, Dan, committee member; Shipman, Patrick, committee member
This dissertation considers three topics that are united by the theme of application of geometric and nonlinear mechanics to practical problems. Firstly we consider the parallel implementation of numerical solution of nonlinear polynomial systems depending on parameters. The program written to do this is called Paramotopy, and uses the Message Passing Interface to distribute homotopy continuation solves in another program called Bertini across a supercomputer. Paramotopy manages writing of Bertini input files, allows automatic re-solution of the system at points at which paths failed, and makes data management easy. Furthermore, parameter homotopy nets huge performance gains over fresh homotopy continuation runs. Superlinear speedup was achieved, up to hard drive throughput capacity. Various internal settings are demonstrated and explored, and the User's Manual is included. Second, we apply nonlinear theory and simulation to nanomechanical sensor arrays. Using vibrating GaAs pillars, we model Intrinsic Localized Modes (ILMs), and investigate ILM-defect pinning, formation, lifetime, travel and movement, and parameter dependence. Intrinsic Localized Modes have been analyzed on arrays of nonlinear oscillators. So far, these oscillators have had a single direction of vibration. In current experiments for single molecule detection, arrays made of Gallium Arsenide will be innately bidirectional, forced, dissipative. We expand previous full models to bidirectionality, and simulate using ODE solvers. We show that small regions of a very large parameter space permit strong ILM formation. Additionally, we use Hamiltonian mechanics to derive new simplified models for the monodirectional ILM travel on an infinite array. This monodirectional ILMs of constant amplitude have unrealistic behavior. Permitting the amplitude of the ILM to vary in time produces much more realistic behavior, including wandering and intermittent pinning. The final set of problems concerns the application of numerical algebraic geometric methods to untangle the phase space of cooperating robots, and optimize configuration for fault tolerance. Given two robots in proximity to each other, if one experiences joint failure, the other may be able to assist, restoring lost workspace. We define a new multiplicity-weighted workspace measure, and use it to solve the optimization problem of finding the best location for an assistance socket and separation distance for the two robots, showing that the solution depends on robot geometry, which link is being grasped, and the choice of objective function.
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 member
The 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.
Open Access
Instrumentation for ultra-intense laser matter interaction studies at high repetition rates
(Colorado State University. Libraries, 2022) Nedbailo, Ryan, author; Rocca, Jorge, advisor; Marconi, Mario, committee member; Yalin, Azer, committee member
A new class of high-repetition rate (HRR) Peta-Watt-class (PW) laser systems make it possible to study laser matter interaction processes, like laser ion acceleration (LIA) and laser plasma instabilities (LPI), at unprecedented rates. These systems have the potential to generate immense amounts of data through rapid multivariable parameters scans of laser energy, pulse shape, spot size and others, in order to better diagnose and characterize the conditions underlying LPI and LIA. However, detection media, typically image plates, film, CR-39, presently limits the repetition rate at which data can be collected from these systems. Rep-rated diagnostics are being redesigned to match the capabilities of current multi-Hz present and near future, PW-class laser systems. Here we present the development of a compact Thomson Parabola Ion Spectrometer capable of characterizing various ion species of multi-MeV ion beams from >10^20 W/cm^2 laser produced plasmas at rates commensurate with the laser operation rates. This diagnostic makes use of a Polyvinyltoluene (PVT) based fast plastic scintillator (EJ-260), where the emitted light is collected by an optical imaging system coupled to a thermoelectrically cooled scientific complementary metal–oxide–semiconductor (sCMOS) camera. This offers a robust solution for data acquisition at HRR while avoiding the added complications and non-linearities of microchannel plate (MCP) based systems. Different ion energy ranges can be probed using the modular magnet setup, variable electric field, and a varying drift-distance. We have demonstrated operation and data collection with this system at up to 0.2 Hz from plasmas created by irradiating a solid target, limited only by the motorized target motion system. With the appropriate software and the use of machine learning techniques, on-the-fly ion spectral analysis will be possible, enabling real-time experimental control. The diagnostic design, calibration, and results from experiments at the ALEPH laser facility at Colorado State University (CSU) are presented. In addition, we describe the results of the development of a novel scheme for the generation of spike trains of uneven delay (STUD) laser pulses using an array of hexagonal mirrors. By individually driving the offset of each mirror segment, we can divide the wavefront of the laser creating a pulse train of arbitrary delay. This pulse-train forming device can be used to conduct experiments related to a proposed method of mitigating the effects of LPI for inertial confinement fusion (ICF). By periodically turning on and off the laser drive of the ICF process, it has been postulated that the growth of parametric instabilities can be mitigated by allowing damping during the off-cycle of the STUD pulses. The use of the pulse-train forming scheme demonstrated here will allow us to study the effects of pulse train delay and duration best suited to LPI mitigation.
Open Access
Nanometer-scale machining with extreme ultraviolet lasers
(Colorado State University. Libraries, 2013) Bravo, Herman, author; Yalin, Azer, advisor; Rocca, Jorge J., advisor; Marconi, Mario, committee member
This thesis demonstrates the feasibility of direct machining in the nanometer scale using Extreme Ultraviolet (EUV) laser radiation. Laser machining of materials has been widely used for the development of micromechanical components and devices. Advances in technology further motivate the extension of laser machining of microstructures to smaller dimensions. The advent of high repetition rate table top EUV lasers has opened the possibility of extending laser machining to the nanometer-scale. It has been previously demonstrated that single laser shots from a 46.9 nm wavelength capillary discharge laser can ablate very clean holes with a diameter as small as 82 nm on polymethyl methacrylate (PMMA) photoresist. This thesis extends previous work by demonstrating nanometer-scale machining of polymers with a focused EUV laser beam. Sub-200 nm wide trenches several micrometers in length were machined on PMMA. These are,to our knowledge, the smallest ablated trenches machined with a focused laser beam. This work also discusses the study of warm plasmas created by EUV laser irradiation of solid targets in which single-photon photoionization is the dominant energy absorption mechanisms. Low-absorption (silicon, Z=14) and high-absorption (chromium, Z=24, and silver, Z=47) targets were heated by ~ 1 ns duration pulses from a 46.9 nm wavelength EUV laser. The spectra obtained agree with 1 1/2 dimension simulations in showing that the Si plasmas are significantly colder and less ionized, confirming that in contrast to plasmas created by optical lasers the plasma properties are largely determined by the absorption coefficient of the target material.
Open Access
Nanometer-thick yttrium iron garnet film development and spintronics-related study
(Colorado State University. Libraries, 2017) Chang, Houchen, author; Wu, Mingzhong, advisor; Celinski, Zbigniew, committee member; Field, Stuart, committee member; Marconi, Mario, committee member; Patton, Carl, committee member
In the last decade, there has been a considerable interest in using yttrium iron garnet (Y3Fe5O12, YIG) materials for magnetic insulator-based spintronics studies. This interest derives from the fact that YIG materials have very low intrinsic damping. 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 similar to single-crystal YIG bulk materials. This dissertation reports comprehensive experimental studies on nm-thick YIG films by magnetron sputtering techniques. Optimization of sputtering control parameters and post-deposition annealing processes are discussed in detail. The feasibility of low-damping YIG nm-thick film growth via sputtering is demonstrated. A 22.3-nm-thick YIG film, for example, shows a Gilbert damping constant of less than 1.0 × 10-4. The demonstration is of great technological significance because sputtering is a thin film growth technique most widely used in industry. The spin Seebeck effect (SSE) refers to the generation of spin voltage in a ferromagnet (FM) due to a temperature gradient. The spin voltage can produce a pure spin current into a normal metal (NM) that is in contact with the FM. Various theoretical models have been proposed to interpret the SSE, although a complete understanding of the effect has not been realized yet. In this dissertation the study of the role of damping on the SSE in YIG thin films is conducted for the first time. With the thin film development method mentioned in the last paragraph, a series of YIG thin films showing very similar structural and static magnetic properties but rather different Gilbert damping values were prepared. A Pt capping layer was grown on each YIG film to probe the strength of the SSE. The experimental data show that the YIG films with a smaller intrinsic Gilbert damping shows a stronger SSE. The majority of the previous studies on YIG spintronics utilized YIG films that were grown on single-crystal Gd3Ga5O12 (GGG) substrates first and then capped with either a thin NM layer or a thin topological insulator (TI) layer. The use of the GGG substrates is crucial in terms of realizing high-quality YIG films, because GGG not only has a crystalline structure almost perfectly matching that of YIG but is also extremely stable at high temperature in oxygen that is the condition needed for YIG crystallization. The feasibility of growing high-quality YIG thin films on Pt thin films is explored in this dissertation. This work is of great significance because it enables the fabrication of sandwich-like NM/YIG/NM or NM/YIG/TI structures. Such tri-layered structures will facilitate various interesting fundamental studies as well as device developments. The demonstration of a magnon-mediated electric current drag phenomenon is presented as an example for such tri-layered structures.
Open Access
Near-resonant and resonant light in ultracold gases
(Colorado State University. Libraries, 2020) Gilbert, Jonathan, author; Roberts, Jacob, advisor; Yost, Dylan, committee member; Bradley, Mark, committee member; Marconi, Mario, committee member
This dissertation describes experiments and calculations involving light manipulation of atoms and light propagation in ultracold gases. There are three major sections to this dissertation. Each section presents a research topic connected to the main subject of near-resonant and resonant light in ultracold gases. First, this dissertation details the theoretical description and experimental implementation of a novel cooling technique for ultracold atoms trapped in a confining potential. Manipulating the internal states of atoms by applying near-resonant laser pulses at specified times leads to high energy atoms being preferentially selected and then slowed to achieve cooling. We call the technique "spatially truncated optical pumping (STOP) cooling." Advantages of the technique include its straightforward adaptability into experiments already using a magneto-optical trap; its applicability to any species that can be laser cooled and trapped in a confining potential; it does not depend on highly specific transitions for cooling; it does not depend on number loss for cooling. We present experimental results from applying the technique to an ultracold gas of 87Rb. We also present theoretical predictions of expected cooling rates, along with possible improvements to our apparatus that could lead to further cooling. Next, this dissertation details numerical calculations of near-resonant light propagation through a highly absorptive elongated ultracold gas. The confined gas modeled by these calculations are representative of gases commonly found in ultracold atom experiments. The spatial density distribution and spatial extent of these gases leads to a substantial gradient in the index of refraction. In addition, these gases can have a smaller spatial extent than that of the cross section of a laser beam that illuminates them. We present calculations that show the index variation in these systems can lead to frequency-dependent focusing or defocusing of incident near-resonant light. In some cases, focusing results in light intensities inside of the gas that are over an order of magnitude higher than the incident value. Additionally, we show that refraction and diffraction of the light results in non-intuitive patterns forming in the directions perpendicular to the light propagation. Lastly, this dissertation details the theoretical treatment and experimental measurements of the time-dependent absorption and phase response of an ultracold gas that is suddenly illuminated by near-resonant light. These studies focus on dynamics occurring over timescales on the order of an atomic excited state lifetime. Because the atoms cannot respond instantaneously to the applied light, both the absorption response and phase response require time to develop, with the phase response being slower than the absorption response. Related polarization effects such as Faraday rotation are due to phase shifts imparted by the gas, and therefore these effects also require time to develop. We detail our experimental measurements of the time-dependent development of Faraday rotation in an ultracold gas of 85Rb and compare the results to predictions using a theoretical approach based on solving optical Bloch equations. We identify how parameters such as the applied magnetic field strength and optical thickness of the gas influence the response timescales of the gas.
Open Access
Nonlinear spin waves in magnetic thin films - foldover, dispersive shock waves, and spin pumping
(Colorado State University. Libraries, 2016) Janantha, Pasdunkorale Arachchige Praveen, author; Wu, Mingzhong, advisor; Eykholt, Richard, committee member; Marconi, Mario, committee member; Patton, Carl, committee member
Three nonlinear phenomena of spin waves and the spin Seebeck effect in yttrium iron garnet (YIG)/Pt bi-layer structures are studied in this thesis and are reported in detail in Chapters 4-7. In the fourth chapter, the first observation of foldover effect of nonlinear eigenmodes in feedback ring systems is reported. The experiments made use of a system that consisted of a YIG thin film strip, which supported the propagation of forward volume spin waves, and a microwave amplifier, which amplified the signal from the output of the YIG strip and then fed it back to the input of the strip. The signal amplitude vs. frequency response in this ring system showed resonant peaks which resulted from ring eigenmodes. With an increase in the resonance amplitude, those resonant peaks evolved from symmetric peaks to asymmetric ones and then folded over to higher frequencies. The experimental observations were reproduced by theoretical calculations that took into account the nonlinearity-produced frequency shift of the traveling spin waves. The fifth chapter presents the first experimental observation of the formation of envelope dispersive shock wave (DSW) excitations from repulsive nonlinear spin waves. The experiments used a microwave step pulse to excite a spin-wave step pulse in a YIG thin film strip, in which the spin-wave amplitude increases rapidly. Under certain conditions, the spin-wave pulse evolved into a DSW excitation that consisted of a train of dark soliton-like dips with both the dip width and depth increasing from the front to the back and was terminated by a black soliton that had an almost zero intensity and a nearly 180 degree phase jump at its center. The sixth chapter reports on the spin pumping due to traveling spin waves. The experiment used a micron-thick YIG strip capped by a nanometer-thick Pt layer. The YIG film was biased by an in-plane magnetic field. The spin waves pumped spin currents into the Pt layer, and the later produced electrical voltages across the length of the Pt strip through the inverse spin Hall effect (ISHE). Several distinct pumping regimes were observed and were interpreted in the frame work of the nonlinear three-wave splitting processes of the spin waves. The seventh chapter presents the first experimental work on the roles of damping in the spin Seebeck effect (SSE). The experiments used YIG/Pt bi-layered structures where the YIG films exhibited very similar structural and static magnetic properties but very different damping. The data indicate that a decrease in the damping of the YIG film gives rise to an increase in the SSE coefficient, and this response shows quasi-linear behavior. The data also indicate that the SSE coefficient shows no notable dependences on the enhanced damping due to spin pumping.