Scholarship & Research
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Item Thermalization and exciton localization in 2D semiconductors(Montana State University - Bozeman, College of Letters & Science, 2023) Strasbourg, Matthew Christopher; Chairperson, Graduate Committee: Nick Borys; This is a manuscript style paper that includes co-authored chapters.2D semiconductors are a promising class of materials to investigate for applications in the next generation of photonic devices. They can be used to generate quantum light and also exhibit correlated many-body phenomena. Many of the novel optoelectronic properties of 2D semiconductors are associated with strongly-bound hydrogen-like states known as excitons. Excitons in 2D semiconductors have binding energies on the order of 100s of meV and are stable at room temperature. At low temperatures, higher-order excitonic states such as charged excitons and biexcitons--multiple-bound excitons that are like hydrogen molecules-- and localized excitons that emit quantum light are also observed. Whether excited optically or electronically, a diversity of high-energy excitons and free carriers are produced directly after excitation. The relaxation and thermalization of these initial states influence the formation of excitons, biexcitons, and localized excitons. Here, I present work that (i) investigates the thermalization of excited states in a prototypical 2D semiconductor, monolayer (1L-) WSe2, and reports the discovery that the generation of charged biexcitons is enhanced with increasing photoexcitation energy, (ii) shows the emergence of quantum emitters (QEs) in a new 2D QE platform: 1L-WSe2 nanowrinkle arrays induced by Au nano stressors, and (iii) uses a novel method to classify the excited-state dynamics of 2D QEs and differentiate emitter populations. A suite of low-temperature energy- and time- resolved optical spectroscopies are used to conduct this work. This work shows how excited state thermalization affects the formation of exciton and biexcitons and investigates the optical properties of an emergent class of 2D quantum light emitters.Item X-ray analysis and modeling of NGC 3227(Montana State University - Bozeman, College of Letters & Science, 2022) Newman, Jared James; Chairperson, Graduate Committee: Yves U. Idzerda and Sachiko Tsuruta (co-chair)The 1.5 Seyfert galaxy NGC 3227 has been observed by several X-ray missions. We carried out combined analysis of the data from a total of twenty one observations. Six of the observations were preformed by Suzaku, eight by XMM-Newton, and seven by NuStar. A unified model was constructed which is consistent with all twenty one of the observations by the three satellites with large intensity and spectral changes. The model consists of a hard power law which is interpreted as the Comptonized emission from the corona above an accretion disk. In the high flux states an additional soft excess component dominates, which is consistent with a model with either a steeper power law or a warm Comptonization component. These emissions from the central engine are absorbed by multiple distinct absorbers at various ionization levels. A reflection component and several emission lines are also present. This is the most robust model of this source to date.Item Novel models and observations of energetic events in the solar transition region(Montana State University - Bozeman, College of Letters & Science, 2021) Parker, Jacob Douglas; Chairperson, Graduate Committee: Charles C. Kankelborg; Dana Longcope was a co-author of the article, 'Modeling a propagating sawtooth flare ribbon as a tearing mode in the presence of velocity shear' in the journal 'Astrophysical journal' which is contained within this dissertation.; Charles Kankelborg was a co-author of the article, 'Determining the spectral content of MOSES images' submitted to the journal 'Astrophysical journal' which is contained within this dissertation.; Roy Smart, Charles Kankelborg, Amy Winebarger and Nelson Goldsworth were co-authors of the article, 'First flight of the EUV snapshot imaging spectrograph (ESIS)' submitted to the journal 'Astrophysical journal' which is contained within this dissertation.The solar atmosphere is an energetic and violent place capable of producing eruptions that affect us on earth. In order to better understand these events, so that we might improve out ability to model and predict them, we observe the sun from space to diagnose the local plasma conditions and track its evolution. The transition region, a thin region of the solar atmosphere separating the chromosphere from the corona, is where the solar atmosphere transitions rapidly from ten thousand, to one million kelvin and is therefore thought to play an important roll in the transfer of mass and energy to the hot corona. The sun's magnetic field, and magnetic reconnection, are thought to contribute to the increased temperature of the corona, since the cooler lower solar atmosphere cannot heat it via thermal conduction or convection. Explosive events, small solar eruptions likely driven by magnetic reconnection, are frequent in the transition region, making it an attractive area of the atmosphere to study and gather information on the processes. Using Computed Tomography Imaging Spectrographs (CTIS), capable of measuring spectral line profiles over a wide fields of view at every exposure, we find many eruptive events in the transition region to be spatially complex, three dimensional, and to evolve on rapid timescales. This demonstrates the utility of, and need to continue developing, CTIS style instruments for solar study since they provide a more complete picture of solar events, allowing us to improve our understanding of our closest star.Item Exploration of rare-earth ion transitions and host materials for spectral hole burning applications and quantum information science(Montana State University - Bozeman, College of Letters & Science, 2021) Marsh, Aaron Daniel; Chairperson, Graduate Committee: Rufus L. ConeDue to their capacity for generating and manipulating light, the rare-earths are a foundational part of many cutting-edge technologies, ranging from lighting to quantum communications. Optical applications based on rare-earth doped materials are restricted to their transition energies. There are large bands, including the telecom window, where available rare-earth transitions typically have poor properties at liquid helium temperatures. The limitations are determined by the fundamental interactions between rare-earth ions and their host materials; comprehension of the interactions can be leveraged to significantly improve the properties of rare-earth quantum states. Three unexplored rare-earth optical transitions are investigated in this thesis: the Tm 3+ 3 H6<-->3 F3 at ~690 nm, the Pr 3+ 3 H 4<-->3 F 3 at ~1584 nm, and the Tm 3+ 3 F4<-->3 H 4 at ~1451 nm. The first transition suppresses non-radiative relaxation through engineering of the host material phonon spectrum. The 3 F 3 lifetime is extended to ~100 microsecond in Tm 3+ :KPb 2Br 5. The material Tm 3+:LaF 3 is also prepared for high-contrast spectral filtering in ultrasound-optical medical imaging sensitive to blood oxygenation at ~690 nm. Narrow 380 kHz holes are burned; simulations of hole burning indicate that ~60 dB of filtering contrast at ~3MHz is possible. Likewise, non-radiative relaxation is suppressed on the Pr 3+ transition at ~1584 nm in the low-phonon energy host RbPb 2Br 5. Four sites are revealed, with ~2-5 GHz spectrally resolved inhomogeneous broadenings, ~0.5-1 ms T 1 lifetimes, pseudoquadrupole level storage, and ~750 ns coherence times. This material is discussed for use as an L-band quantum memory. The excited state transition of Tm 3+ at ~1451 nm is then explored for quantum memories. High-resolution spectroscopy finds ~1 GHz inhomogeneous broadenings, ~6 ms lifetimes, and laser-limited ~30 MHz holes are burned. Techniques for measuring the properties of excited state transitions are described. Throughout, experimental methods and applications demonstrate the close relationship between lanthanide research and devices. Rare-earth doped crystals are used as an all-optical, high-resolution sensor package for characterizing cryostats in situ, and spectral hole burning characterizes laser performance as a real-time, ~1 MHz resolution spectrum analyzer. The exploration of rare-earth transitions is found to enable new research and new applications, with many other transitions yet to be explored.Item Exploring the origin of the Magellanic periphery with SMASH photometric metallicities(Montana State University - Bozeman, College of Letters & Science, 2019) Miller, Amy Elizabeth; Chairperson, Graduate Committee: David L. NideverThe distribution of stellar metallicities across the Large and Small Magellanic Clouds is a key ingredient to understanding the processes that have shaped their evolution, and remains a rich ground for exploration. I use data from the Survey of Magellanic Stellar History (SMASH), a photometric survey of the Magellanic Clouds that contains approximately 400 million objects in 197 fields that were obtained with DECam on the CTIO Blanco 4m telescope. SMASH covers 2400 square degrees to 24th magnitude in ugriz, encompassing a depth of 2 magnitudes below the oldest main-sequence turnoff stars. The DECam u-band is sensitive to metallicity for main-sequence turn-off stars, which is calibrated using SDSS and LAMOST spectroscopy in overlapping regions. This analysis is used to make accurate metallicity maps of the main bodies of the Clouds and their peripheries. Ultimately, these metallicity maps will help us trace out population gradients in the Clouds and uncover the origin of their very extended stellar peripheries.Item Nonlinear correction of spectrally recovered, RF spectral features, readout with high frequency-chirped laser fields(Montana State University - Bozeman, College of Letters & Science, 2017) Oberto, Louis Joseph; Chairperson, Graduate Committee: Wm. Randall BabbittFrequency-chirped readout of spectral features from spatial-spectral (S2) materials, as a result of spectral hole-burning, has been in use as a radio-frequency (RF) spectrum analyzer for well over a decade. Previously, a signal processing deconvolution algorithm had been developed that enabled faster chirping, such that the chirp rate 'K' could be much greater than the desired resolution bandwidth (RBW). This broke past conventional limits for spectroscopic detection, which states that one needs to dwell on a spectral feature of width gamma for a time 1/gamma. For a chirp, this would mean that the square root of the chirp rate would need to be less than the RBW. For chirp rates on the order of gamma 2 or higher, nonlinearities begin to appear in detected signals depending on optical absorption depth, the chirp rate, and burned hole depths. Even with this algorithm, distortions still persist when very deep holes are burned in a high absorbing material, while the chirp rate is still very high. However, resolving spectral features under these conditions is desirable to increase the dynamic range of the SA. A new nonlinear signal processing technique that removes the nonlinearity has been developed, recovering the distorted signals. It was applied to RF signals spectrally absorbed in two different Tm 3+: YAG crystals, with measured absorption lengths of 1.9 and 2.5. The new algorithm is shown to work on multiple spectral holes simultaneously. Signals as wide as 1 MHz and as small as 300 kHz were recovered for a chirp rate of about 11.88 MHz/microsecond. These results show that very fast chirp rates could be used for highly absorbing materials, with deeply burned spectral holes. This could enable ultra-sensitive readout of a spectrum spanning hundreds of gigahertz, while pushing the dynamic range higher.Item Mesoscale, radiometrically referenced, multi-temporal hyperspectral data for CO 2 leak detection by locating spatial variation of biophysically relevant parameters(Montana State University - Bozeman, College of Letters & Science, 2017) McCann, Cooper Patrick; Chairperson, Graduate Committee: Kevin S. RepaskyLow-cost flight-based hyperspectral imaging systems have the potential to provide valuable information for ecosystem and environmental studies as well as aide in land management and land health monitoring. This thesis describes (1) a bootstrap method of producing mesoscale, radiometrically-referenced hyperspectral data using the Landsat surface reflectance (LaSRC) data product as a reference target, (2) biophysically relevant basis functions to model the reflectance spectra, (3) an unsupervised classification technique based on natural histogram splitting of these biophysically relevant parameters, and (4) local and multi-temporal anomaly detection. The bootstrap method extends standard processing techniques to remove uneven illumination conditions between flight passes, allowing the creation of radiometrically self-consistent data. Through selective spectral and spatial resampling, LaSRC data is used as a radiometric reference target. Advantages of the bootstrap method include the need for minimal site access, no ancillary instrumentation, and automated data processing. Data from a flight on 06/02/2016 is compared with concurrently collected ground based reflectance spectra as a means of validation achieving an average error of 2.74%. Fitting reflectance spectra using basis functions, based on biophysically relevant spectral features, allows both noise and data reductions while shifting information from spectral bands to biophysical features. Histogram splitting is used to determine a clustering based on natural splittings of these fit parameters. The Indian Pines reference data enabled comparisons of the efficacy of this technique to established techniques. The splitting technique is shown to be an improvement over the ISODATA clustering technique with an overall accuracy of 34.3/19.0% before merging and 40.9/39.2% after merging. This improvement is also seen as an improvement of kappa before/after merging of 24.8/30.5 for the histogram splitting technique compared to 15.8/28.5 for ISODATA. Three hyperspectral flights over the Kevin Dome area, covering 1843 ha, acquired 06/21/2014, 06/24/2015 and 06/26/2016 are examined with different methods of anomaly detection. Detection of anomalies within a single data set is examined to determine, on a local scale, areas that are significantly different from the surrounding area. Additionally, the detection and identification of persistent anomalies and non-persistent anomalies was investigated across multiple data sets.Item A dielectric and nuclear magnetic resonance study of lithium hydrazinium sulfate and its deuterated isomorph(Montana State University - Bozeman, College of Letters & Science, 1971) Parker, Robert SanfordItem Optical characterization of perturbed sites and C₃i sites in rare earth doped oxide crystals(Montana State University - Bozeman, College of Letters & Science, 2003) Reinemer, Gregory DonaldItem Optical coherent transients and hole burning of the �₀�₀transition in Eu(OH)₃(Montana State University - Bozeman, College of Letters & Science, 1984) Otteson, Michael Stephen