Photon pairs produced through spontaneous parametric down-conversion exhibit entanglement in their time-energy degrees of freedom, offering sub-100 fs entanglement times while simultaneously exhibiting a joint energy resolution dictated by that of the continuous-wave pump laser. While entangled photon pairs have found many applications in sensing and imaging, taking advantage of their ultrafast correlations has proven to be more difficult.
\r\n\r\nIn this dissertation, we advance a number of practical aspects of spectroscopy with entangled pairs of photons. First, we show that the ultrafast correlations in photon pairs are useful for fluorescence lifetime measurements, enabling a CW laser to perform time-resolved measurements through a simple heralding scheme. Next, we develop bright, efficient, and single spatial mode sources of entangled photons using thin-film lithium niobate nanophotonics, bringing these devices to the visible and near-IR for the first time. In the process, we develop a source of UV light and investigate the performance of thin-film lithium niobate for evanescent sensing. Finally, we show promising results that two down-conversion processes in the same waveguide can be cascaded to generate entangled photon triplets with high efficiency, enabling pairs of photons to be heralded.
", "doi": "10.7907/j0x1-5742", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17581", "collection": "thesis", "collection_id": "17581", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07312025-212004631", "type": "thesis", "title": "Probing Quantum States in Low-Dimensional Materials via Laser-Assisted Scanning Tunneling Microscopy and Structured Light", "author": [ { "family_name": "Park", "given_name": "Akiyoshi", "orcid": "0000-0003-2383-1088", "clpid": "Park-Akiyoshi" } ], "thesis_advisor": [ { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This dissertation presents the development and application of a laser-assisted scanning tunneling microscope (STM) to probe and control emergent quantum phenomena in two-dimensional (2D) and topological materials. A custom-built STM system was designed to operate under ultra-high vacuum and cryogenic conditions, integrating electronic, mechanical, and optical subsystems to enable high-resolution tunneling spectroscopy with in situ optical excitation. This platform allows for the detection of light-induced tunneling photocurrents with polarization control, facilitating direct investigations of light\u2013matter interactions at the atomic scale.
\r\n\r\nUsing this instrument, we first investigate the dynamics of photoexcited quasiparticles in strained monolayer (ML) transition metal dichalcogenides (TMDs), specifically ML-MoS$_2$ grown on corrugated Au(111). Nanoscale strain induces local bandstructure modulation, which acts as a trapping potential for excitons, trions, and electron-hole plasmas. Optical excitation in these strained regions leads to strongly enhanced band renormalization effects, which we interpret through a tight-binding model that incorporates non-uniform strain and many-body interactions. These results establish a framework for manipulating quasiparticle interactions and optoelectronic properties in 2D materials via strain and light.
\r\n\r\nMoreover, we utilize STM/STS to explore magnetically doped topological insulators exhibiting the quantum anomalous Hall (QAH) effect. Scanning tunneling spectroscopy (STS) measurements on six-quintuple-layer films reveal a topologically non-trivial energy gap at low temperature. However, spatially inhomogeneous band alignment driven by many-body interactions, including electron-defect and electron-phonon coupling results in local band overlap and a breakdown of the insulating QAH state into a metallic phase, even below the Curie temperature. These findings highlight the role of microscopic disorder and finite-temperature renormalization in destabilizing topological phases.
\r\n\r\nFinally, we demonstrate angular momentum transfer from structured light to Rydberg excitons in monolayer MoSe\u2082. Optical vortex beams carrying orbital angular momentum (OAM) selectively couple to exciton degrees of freedom. At low light intensity, photonic OAM modifies the center-of-mass motion of excitons, while at higher light intensities, exchange-mediated processes transfer angular momentum of light to the internal excitonic orbitals. Photoluminescence measurements under Laguerre-Gaussian beam excitation reveal fingerprints of higher orbital Rydberg exciton states, providing a new pathway for controlling exciton orbital structure in solid-state systems.
\r\n\r\nTogether, these studies showcase how laser-assisted STM and structured light can be harnessed to probe, engineer, and control quantum states in low-dimensional materials, with implications for topological electronics, nanoscale optoelectronics, and quantum excitonic devices.
", "doi": "10.7907/p17k-3619", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17323", "collection": "thesis", "collection_id": "17323", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312025-001458670", "primary_object_url": { "basename": "peng_linqing_2025_thesis.pdf", "content": "final", "filesize": 9165870, "license": "other", "mime_type": "application/pdf", "url": "/17323/1/peng_linqing_2025_thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Harnessing Locality for Scalable Strongly Correlated Electron Simulations", "author": [ { "family_name": "Peng", "given_name": "Linqing", "orcid": "0000-0001-5682-2407", "clpid": "Peng-Linqing" } ], "thesis_advisor": [ { "family_name": "Chan", "given_name": "Garnet K.", "orcid": "0000-0001-8009-6038", "clpid": "Chan-Garnet-K-L" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Chan", "given_name": "Garnet K.", "orcid": "0000-0001-8009-6038", "clpid": "Chan-Garnet-K-L" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Materials-specific predictions of large, realistic molecules and materials with strong electron correlations have been a long-standing challenge in quantum chemistry. This dissertation addresses this challenge by leveraging three forms of physical and mathematical locality\u2014in space, energy, and rank\u2014to develop scalable, efficient, and accurate electronic structure methods.
\r\n\r\nIn Chapter 2, we use quantum embedding theory that exploits the spatial locality of electron correlations and reduces the computational cost of accurate correlated electronic structure methods, enabling accurate ab initio simulation of complicated correlated materials. In this work, we study Kondo physics, a prototypical many-body quantum phenomenon, with a full-cell extension of dynamical mean-field theory (DMFT). Our \\textit{ab initio} simulation of the Kondo correlations systematically converges towards the exact zero-temperature limit, yielding material-specific Kondo temperatures that reproduce the subtle exponential trends observed experimentally and offer new insight into the underlying physics.
\r\n \r\nChapter 3 explores the locality in energy in lanthanide single-ion magnets. Their multi-reference ground and excited states are generally challenging to compute, but fortunately, the states that govern the spin dynamics are local in the energy spectrum. We develop a theoretical protocol to compute their spin Hamiltonian by sampling only relevant states in this reduced Hilbert space, and particularly, the single-reference states accessible by the efficient density functional theory. This method surpasses the prohibitive cost of calculating multi-reference eigenstates, and with its mean-field scaling, enables studying realistic magnets of unprecedentedly large size at an accuracy comparable to the previous state-of-the-art method.
\r\n\r\nChapter 4 focuses on the locality in the rank structure of reduced density matrices (RDMs). The 1- and 2-RDMs are the crucial ingredients in estimating energies and observables in many classical and quantum simulation methods. Their intrinsic low-rank structure makes them compressible and can be exploited to significantly reduce the measurement cost. We analyze both noiseless and noisy measurement scenarios, including shot-noise-limited quantum algorithms, and show that in the context of Gaussian (shot) noise, a low-rank approximate reconstruction of RDMs effectively removes the high-rank noises and reduces the measurement cost by orders of magnitude, therefore enabling larger-scale simulations.
", "doi": "10.7907/6ffe-2j03", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17264", "collection": "thesis", "collection_id": "17264", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05222025-165729471", "primary_object_url": { "basename": "pham_kim_2024_thesis-final.pdf", "content": "final", "filesize": 41860246, "license": "other", "mime_type": "application/pdf", "url": "/17264/1/pham_kim_2024_thesis-final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Application of Ultrafast Spectroscopy Techniques to Probe Correlated Ion Hopping Mechanisms in Solid-State Ion Conductors", "author": [ { "family_name": "Pham", "given_name": "Kim Hoang", "orcid": "0000-0003-4053-6363", "clpid": "Pham-Kim-Hoang" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Stoltz", "given_name": "Brian M.", "orcid": "0000-0001-9837-1528", "clpid": "Stoltz-B-M" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Superionic conductors, or solid-state ion conductors that surpass the ionic con- ductivity of its liquid counterpart, can enable more energy dense batteries, robust artificial ion pumps, and optimized fuel cells. The mechanisms enabling superionic conductivity still remain elusive, though many-body correlations between the mi- grating ions, lattice vibrational modes, and charge screening clouds have all been posited to greatly enhance ionic conduction. Most spectroscopic techniques cannot directly probe and validate the role of such correlations due to their inability to transiently resolve these ultrafast dynamics occurring at picosecond timescales. In this work, we develop an ultrafast technique that measures the time-resolved change in impedance while a light source ranging from UV to THz frequencies selectively excites an ion-coupled correlation. The technique is used to compare the relative changes in impedance of a solid-state Li\u207a conductor Li0.5La0.5TiO3 (LLTO) before and after light excitation to elucidate the role of charge screening clouds, optical phonons, and acoustic phonons on ion migration. From our techniques, we deter- mine that electronic screening and rocking phonon-mode interactions significantly dominate the ion migration pathway of LLTO compared to acoustic phonons. Al- though we only present one case study, our technique can extend to O\u00b2\u207b, H\u207a, or other charge carrier transport phenomena where ultrafast correlations control transport. Furthermore, the temporal relaxation of the measured impedance can distinguish ion transport effects caused by many-body correlations, optical heating, correlation, and memory behavior.", "doi": "10.7907/825x-r459", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17245", "collection": "thesis", "collection_id": "17245", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05192025-200240351", "primary_object_url": { "basename": "Hwang_Emily_thesis_V1.pdf", "content": "final", "filesize": 97652885, "license": "other", "mime_type": "application/pdf", "url": "/17245/1/Hwang_Emily_thesis_V1.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Nonlinear Frequency Conversion in Lithium Niobate Nanophotonic Circuits for Quantum Spectroscopy", "author": [ { "family_name": "Hwang", "given_name": "Emily Yoonju", "orcid": "0000-0002-9541-5887", "clpid": "Hwang-Emily-Yoonju" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Marandi", "given_name": "Alireza", "orcid": "0000-0002-0470-0050", "clpid": "Marandi-A" }, { "family_name": "Vahala", "given_name": "Kerry J.", "orcid": "0000-0003-1783-1380", "clpid": "Vahala-K-J" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Quantum light sources are becoming an increasingly popular alternative to pulsed lasers for spectroscopy, microscopy, and sensing. The inherent quantum correlations of entangled photons present unique advantages in spectroscopy, enabling high signal-to-noise ratios, low excitation fluxes, and time-resolved measurements without requiring a pulsed laser. Entangled photon sources for spectroscopic measurements typically consist of bulk crystals or ion-diffused waveguides. Integrated platforms such as thin-film lithium niobate have potential for highly efficient, tailored, and compact entangled photon sources through periodically poled nanophotonic waveguides. The advantageous nonlinear optical properties of lithium niobate coupled with the nanophotonic thin film platform allows for frequency conversion, quantum state generation, state manipulation, and sample interaction all on a single compact chip, demonstrating thin-film lithium niobate's potential for compact and portable integrated spectrometers.
\r\n\r\nHere, we present our work in frequency conversion and sample interactions in thin-film lithium niobate. Most of the previous demonstrations of nanophotonic lithium niobate waveguides have focused on infrared wavelengths for applications in quantum communication and computing, leaving the shorter wavelengths that are of interest for spectroscopy still a largely unexplored space. In this work, frequency conversion in thin-film lithium niobate is investigated from ultraviolet through telecom wavelengths. Periodically poled lithium niobate nanophotonic waveguides are fabricated for second harmonic generation in the ultraviolet-A region and entangled photon generation at visible and near-infrared wavelengths. Using a violet continuous wave laser, a waveguide with a fluorescent dye-doped polymer cladding layer is investigated for sample interactions. Finally, preliminary work in entangled photon triplet generation down to telecom wavelengths is explored. This work represents a step towards compact, on-chip spectrometers and sensors through lithium niobate photonic integrated circuits.
", "doi": "10.7907/895c-5s83", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17243", "collection": "thesis", "collection_id": "17243", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05192025-180916338", "type": "thesis", "title": "Elucidating the Role of Transition Metal Electronic Structure in Catalysis and Spin Relaxation", "author": [ { "family_name": "Luedecke", "given_name": "Kaitlin Mary", "orcid": "0000-0002-8163-9417", "clpid": "Luedecke-Kaitlin-Mary" } ], "thesis_advisor": [ { "family_name": "Hadt", "given_name": "Ryan", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Hadt", "given_name": "Ryan", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Transition metal complexes are the workhorses of physical inorganic chemistry and have diverse applications in catalysis and quantum information science, especially. The primary descriptor of transition metal complexes, and a good predictor of their utility, is their electronic structure. Notably, rigorous characterization of the spin states, oxidation states, excited states, and magnetic properties of these complexes is necessary to gain mechanistic detail for these applications; this thesis focuses on elucidating the role of transition metal electronic structure in catalysis and spin relaxation. Chapter 1 introduces important transition metal electronic structure considerations and motivates these studies. Part I includes Chapters 2\u20134 and considers complexes relevant for CO\u2082 reduction chemistry and cross-coupling reactivity. Chapter 2 investigates the conditions under which a CO\u2082 reduction catalyst, Fe-p-TMA, undergoes speciation changes and characterizes its excited-state identities and lifetimes. Chapter 3 considers the electrochemical conditions under which highly reduced CO reduction products are generated in an iron porphyrin system, and important connections to photocatalysis are made. Chapter 4 compares the excited-state identities and reactivities of prototypical and tethered Ni(II)\u2013bpy aryl halide complexes. Part 2 includes Chapters 5\u20136 and focuses on spin relaxation, a key figure of merit in quantum information science. Chapter 5 investigates the effect of structural distortions in S = \u00bd copper porphyrin systems on their spin-lattice relaxation times, and Chapter 6 moves to identifying the mechanism of spin relaxation in an S = 1 Cr(o-tolyl)\u2084 system. Together, these compiled studies reveal the nuanced roles of transition metal electronic structure in catalysis and spin relaxation and highlight the importance of their characterization for developing optimized systems.", "doi": "10.7907/7t77-rd65", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17097", "collection": "thesis", "collection_id": "17097", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03272025-184257192", "type": "thesis", "title": "Investigation and Control of the Electrode/Electrolyte Interface in Electrochemical Systems", "author": [ { "family_name": "Lee", "given_name": "Brian Chansol", "orcid": "0000-0002-0898-0838", "clpid": "Lee-Brian-Chansol" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In electrochemical reactions, the electrode/electrolyte interface is of vital importance, as no reactivity occurs in the bulk electrode or the electrolyte. Often, the interface can be the difference between a successful reaction and a failure. In this thesis, we present three works wherein the electrode/electrolyte interface is studied and controlled to drive desired electrochemical reactivity. A Mg-In alloy is employed for Mg metal batteries to prevent Mg dendrite growth, which can cause cell shorting and failure. By coating the surface of Mg metal electrodes with the Mg-In alloy, the nucleation of Mg dendrites is suppressed and instead the Mg electroalloys into the surface alloy upon reduction, significantly increasing the cell life time. Next, the Li-intercalation material LiTiS\u2082 is studied for use in organic reductive electrosynthesis as counter anodes. Traditional metal sacrificial counter anodes are known to cause issues such as surface passivation, chemical reactivity, and cross-plating at the working electrode, which is deleterious to the desired organic reactivity. It is found that LiTiS\u2082 surface is less reactive in organic electrolytes, reducing both passivation and chemical reactivity. Further, Li\u207a de-intercalated from LiTiS\u2082 oxidation is found to be less susceptible to cross-plating than Zn, a common sacrificial anode. Finally, the effect of electrode material on the electrochemical reduction of \u1d57BuI is studied. Using electrochemical characterization, it is found that the reduction is catalyzed on Au and Ag through adsorption of the initial substrate, as well as the adsorption of the reactive intermediate tBu radical. The catalysis of \u1d57BuI reduction can have meaningful consequences for organic reactivity, driving the desirable generation of the carbanion nucleophile from alkyl halide reactants.", "doi": "10.7907/fz2d-pe37", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17006", "collection": "thesis", "collection_id": "17006", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02192025-011837407", "type": "thesis", "title": "Development and Characterization of a Table-Top Laser-Produced Plasma Source for In-Situ and Time-Resolved Soft X-Ray Absorption Spectroscopy", "author": [ { "family_name": "Nimlos", "given_name": "Danika Katherine", "orcid": "0000-0002-5414-0039", "clpid": "Nimlos-Danika-Katherine" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "X-ray absorption spectroscopy (XAS) has emerged as an indispensable tool in the fields of carbon capture and conversion, providing element-specific insights into electronic structure, oxidation states, and chemical bonding. Of particular interest are soft X-rays (SXRs), which can probe the X-ray water window, enabling detailed studies of carbon, nitrogen, and transition metal L-edges in aqueous environments. Traditionally, access to this technique and this energy range has been limited to large- scale facilities like synchrotrons and XFELs, which can only serve a small population of users in a given year. Furthermore, more complex techniques such as time-resolved and in-situ XAS are practically inaccessible to the majority of users. This thesis explores the development of a table-top laser-produced plasma (LPP) source based on a gaseous target to extend the reach of XAS techniques into laboratory settings. Such sources offer significant advantages in accessibility, flexibility, and cost, while advances in X-ray optics and detection systems have further enhanced their utility. The research presented here focuses on the utilization of gaseous LPP sources for both in-situ and time-resolved XAS, pushing the boundaries of table-top soft X-ray absorption capabilities.
\r\n\r\nKey achievements include exploration of the lower temporal limit of LPP sources for SXR emission, and the first demonstration of liquid-phase XAS measurements using a gaseous LPP source. Gas-phase measurements were also achieved using the system built in this work. Additionally, a novel UV-pump/SXR-probe technique was developed, enabling future time-resolved studies of charge transfer dynamics in transition metal oxides. These advances pave the way for detailed investigations of photodriven processes, interfaces, and catalytic mechanisms critical to carbon capture and conversion. By improving temporal resolution and expanding the scope of in-situ XAS techniques, this work addresses fundamental challenges in the field, bringing the power of synchrotron-like spectroscopy into everyday laboratories. Ultimately, the results presented here aim to democratize XAS, fostering a broader adoption of this technique in catalysis and materials research.
", "doi": "10.7907/3e9t-xr72", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16551", "collection": "thesis", "collection_id": "16551", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07122024-082923823", "primary_object_url": { "basename": "Sekine_Ryoto_2024.pdf", "content": "final", "filesize": 106438025, "license": "other", "mime_type": "application/pdf", "url": "/16551/2/Sekine_Ryoto_2024.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Lithium Niobate Nanophotonic Circuits for Information Processing", "author": [ { "family_name": "Sekine", "given_name": "Ryoto", "orcid": "0000-0001-6135-8581", "clpid": "Sekine-Ryoto" } ], "thesis_advisor": [ { "family_name": "Marandi", "given_name": "Alireza", "orcid": "0000-0002-0470-0050", "clpid": "Marandi-A" } ], "thesis_committee": [ { "family_name": "Emami", "given_name": "Azita", "orcid": "0000-0002-6945-9958", "clpid": "Emami-A" }, { "family_name": "Scherer", "given_name": "Axel", "orcid": "0000-0002-2160-9064", "clpid": "Scherer-A" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Marandi", "given_name": "Alireza", "orcid": "0000-0002-0470-0050", "clpid": "Marandi-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In today's world, electronic information processors are ubiquitous. This dissertation explores an alternative paradigm of processing information using nanophotonics. We develop and investigate nanophotonic lithium niobate circuits leveraging strong \u03c7\u207d\u00b2\u207e nonlinearity for information processing. We demonstrate promising performance of nanophotonic circuits as building blocks of unconventional computing architectures that exploit the rich classical and quantum dynamics inherent to optics. Additionally, we introduce a new class of ultrafast nanophotonic sources, enabling novel opportunities for information processing. Ultimately, this dissertation puts forth the building blocks of next generation ultrafast photonic information processors in lithium niobate nanophotonics which may lead to photonic advantage.", "doi": "10.7907/8vxv-eb34", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16965", "collection": "thesis", "collection_id": "16965", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01282025-225116139", "primary_object_url": { "basename": "Caltech_Thesis.pdf", "content": "final", "filesize": 16689211, "license": "other", "mime_type": "application/pdf", "url": "/16965/15/Caltech_Thesis.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Classical Representation and Manipulation of Quantum Many Body States and High Dimensional Data", "author": [ { "family_name": "Peng", "given_name": "Ruojing", "orcid": "0000-0002-5293-7503", "clpid": "Peng-Ruojing" } ], "thesis_advisor": [ { "family_name": "Chan", "given_name": "Garnet K.", "orcid": "0000-0001-8009-6038", "clpid": "Chan-Garnet-K-L" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Chan", "given_name": "Garnet K.", "orcid": "0000-0001-8009-6038", "clpid": "Chan-Garnet-K-L" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis contains several developments in extending the capability of classical simulations for representing and manipulating quantum many-body states and high dimensional data. In Chapter 1, we introduce the different types of problems considered in quantum chemistry (with ab initio molecular Hamiltonian) and condensed matter physics (with lattice model Hamiltonian) as well as a classical scenario of high-dimensional function integration. In each case, we briefly introduce a corresponding anstaz for representing either the quantum many-body wavefunction or the classical high-dimensional integrand, which provides context for more detailed discussion in subsequent chapters.
\r\n\r\nChapter 2 describes a technical improvement on an existing formulation of the coupled cluster method, known as a popular wavefunction ansatz in quantum chemistry, for simulating finite-temperature non-equilibrium ab initio Hamiltonian dynamics. We adapt a technique from zero-temperature dynamics to the non-equilibrium finite-temperature coupled cluster method, thereby restoring conservation laws for 1-particle properties which were previously broken, and stabilizing the numerical behavior of the method for moderate time propagation. We demonstrated the capability of the method on both ab initio molecular systems such as field-driven H2 and electron transport in silicon cell, and model Hamiltonian such as the moderately interacting single impurity Anderson model (SIAM). We were able to perform stable dynamics simulation for sufficient amount of time to extract qualitatively correct physics, such as band population transport in silicon, and Kondo physics in the SIAM.
\r\n\r\nChapter 3 and Chapter 4 introduce developments in tensor network state (TNS) methods for lattice model Hamiltonian. Typically, TNS are constructed to correctly represent the entanglement structure of target physical state, whose computation of e.g., amplitude and expectation value, can only be performed approximately. A representative example is the projected entangled pair state (PEPS) for representing ground states on 2-dimensional lattices. In Chapter 3, we describe several aspects in PEPS (and TNS in general) construction and computation, including approximate contraction and derivative computation, as well as encoding of Abelian symmetry and fermion statistics. We also introduce a change of perspective of TNS ansatz that restores its exact variationality which was hitherto considered only approximate due to the need of approximate contraction. With such new perspective on TNS ansatz, Chapter 4 then focuses on stochastic optimization of TNS using variational Monte Carlo (VMC). In particular, we investigate the convergence behavior of first- and second order update methods under stochastic noise, which was in turn affected by several factors such as sample size, system size, wavefunction quality and variational expressivity of the ansatz. We hope that the developments described in Chapter 3 and Chapter 4 can allow efficient large scale PEPS simulation of highly entangled states on 2-dimensional lattices, such as spin liquids, ground state of fermi-Hubbard model, and phases of uniform electron gas.
\r\n\r\nChapter 5 introduces a constructive approach for representing high dimensional classical functions with tensor network, and perform integration with approximate contraction. Previous attempts of using tensor network for high dimensional integration typically fit a predetermined form of exactly contractable tensor network to the target function, where error is mainly due to the limited expressivity of the tensor network ansatz. On the other hand, our constructive approach is in principle free of representation error for any function that admits polynomial decomposition into small function blocks. The returned tensor network representation is of arbitrary geometry, where the error is mainly due to approximate contraction, which will benefit greatly from new developments in tenor network approximate contraction techniques.
", "doi": "10.7907/px31-5g53", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17334", "collection": "thesis", "collection_id": "17334", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012025-071545991", "type": "thesis", "title": "Anthropogenic Emissions and the Future of Our Atmosphere: I. Cyclohexanol Chemistry and Aerosol Formation in an Environmental Chamber \r\nII. K\u2082CO\u2083-Based Sorbent Development and Testing in a Packed Bed Reactor for CO\u2082 Capture", "author": [ { "family_name": "Szentkuti", "given_name": "Hannah Kate", "orcid": "0009-0000-2232-6333", "clpid": "Szentkuti-Hannah-Kate" } ], "thesis_advisor": [ { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Chapter 1 presents experimental studies conducted in an environmental chamber, alongside mechanistic modeling, to quantify aerosol formation from the gas-phase pollutant cyclohexanol. The calculated aerosol mass yields, which are higher than measured and predicted values of similar 6-carbon species, indicates the importance of functionalization, and interaction between functional groups (not just carbon number), on aerosol forming potential. Chapter 2 describes the construction and characterization of a mini-industrial scale packed-bed reactor, loaded with K\u2082CO\u2083-impregnated particles for CO\u2082 capture. Chapters 3 and 4 describe the formulation of durable high-capacity K\u2082CO\u2083-based sorbents using wet activated granulation and extrusion spheronization, respectively. In short, capture of point source CO\u2082 via K\u2082CO\u2083 sorbent is demonstrated to be feasible and even economical in the near future.
", "doi": "10.7907/n0mg-9c43", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16267", "collection": "thesis", "collection_id": "16267", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12152023-235139391", "primary_object_url": { "basename": "Ware_thesis_final.pdf", "content": "final", "filesize": 24589417, "license": "other", "mime_type": "application/pdf", "url": "/16267/1/Ware_thesis_final.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Nonaqueous Electrolyte Design for Energy Storage and Electrosynthesis", "author": [ { "family_name": "Ware", "given_name": "Skyler Danielle", "orcid": "0000-0002-3249-1946", "clpid": "Ware-Skyler-Danielle" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Reisman", "given_name": "Sarah E.", "orcid": "0000-0001-8244-9300", "clpid": "Reisman-S-E" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "3MT Competition (Caltech)" }, { "literal": "div_chem" } ], "abstract": "Electrochemically driven metal redox has enabled advances in both academic and industrial processes, including production of metals from their ores, storage of renewable energy in batteries and fuel cells, and greener chemical synthesis conditions. While many electrochemical reactions are performed in aqueous solutions, applications in energy storage and organic synthesis often require extreme applied potentials that lie outside the electrochemical stability window of water or necessitate water-free conditions to prevent undesirable side reactions. Herein, we develop tailored non-aqueous electrolytes for applications in both energy storage and organic electrosynthesis and analyze the effects of electrolyte composition on interfacial and electrochemical reactions. First, a series of highly concentrated solvate electrolytes is developed for Li-S batteries, and interfacial reactivity between the solvate electrolytes and the Li anode is investigated in detail. The addition of a fluoroether cosolvent limits electrolyte decomposition at the Li surface, improving cycling stability and enabling new high-temperature applications. Next, samarium(III)/(II) redox is investigated in a variety of non-aqueous electrolytes to support an electrocatalytic cycle for samarium-mediated carbon-carbon bond formation. The coordination environment of the samarium salt, which can be tuned through anion exchange between the electrolyte and the samarium precursor, strongly affects the reversibility and reducing power of the samarium redox couple. Third, electrolyte additives are studied to increase the desolvation barrier of Zn\u00b2\u207a. When Zn sacrificial anodes are used in organic electrosynthesis, such additives may prevent deleterious cross-plating of Zn\u00b2\u207a at the cathode. Finally, a detailed guide to troubleshooting metal sacrificial anodes is presented with special attention to issues commonly encountered in reductive electrosynthesis.", "doi": "10.7907/kx7f-2065", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16151", "collection": "thesis", "collection_id": "16151", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08032023-213853772", "primary_object_url": { "basename": "Hickam_Bryce_2023.pdf", "content": "final", "filesize": 28267294, "license": "other", "mime_type": "application/pdf", "url": "/16151/1/Hickam_Bryce_2023.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Exploring How Entangled Photon Correlations Can Enhance Spectroscopy", "author": [ { "family_name": "Hickam", "given_name": "Bryce Patrick", "orcid": "0000-0003-2120-4769", "clpid": "Hickam-Bryce-Patrick" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Quantum light sources consisting of highly correlated or \"entangled\" photon pairs are increasingly becoming popular alternatives to classical light sources to perform microscopy and spectroscopy. Entangled photon pairs can replicate and enhance spectroscopic signals and have practical advantages compared to the pulsed laser systems that are typically utilized to perform these measurements. For instance, entangled photons are inherently low-flux, enabling measurements to be performed without undesired photoeffects, such as sample heating and degredation or nonideal photoinduced sample behavior. In addition, entangled photon sources can be generated and manipulated on much smaller physical footprints than state-of-the-art pulsed laser systems with comparable frequency bandwidths and time resolutions. Together, these capabilities could allow for the development of spectroscopic instruments that do not rely on bulky, expensive pulsed laser systems that necessitate teams of specialists to maintain. In turn, this instrument development could enable more widespread access to exotic forms of atomic and material characterization.
\r\n\r\nDespite a growing body of theoretical work, the field of experimental entangled photon spectroscopy is still nascent and entangled light-matter interactions have yet to be fully characterized in laboratory settings. Here, we investigate entangled photon light-matter interactions towards the goal of developing entangled spectroscopic techniques. A broadband entangled photon source with femtosecond coherence times is designed and characterized to perform these measurements. Using this source and an entangled photon spectrometer, characterization of the entangled photon enhancement to two-photon absorption are attempted by in studies of two different molecular dyes, Rhodamine 6G and zinc tetraphenylporphyrin. The entangled photon two-photon absorption enhancement is determined to be below previously reported values due to the presence of single photon scattering signals. Finally, entangled photons are utilized to replicate fluorescence lifetime measurements using a continuous wave pump laser and the temporal correlations inherent to entangled photon pairs. As the first experimental demonstration of this technique, the fluorescence lifetimes of indocyanine green in three solvent systems are measured.
", "doi": "10.7907/ez5h-qp07", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16274", "collection": "thesis", "collection_id": "16274", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01082024-171459002", "primary_object_url": { "basename": "Lin_Haw_Wei_2024_Thesis.pdf", "content": "final", "filesize": 21762497, "license": "other", "mime_type": "application/pdf", "url": "/16274/1/Lin_Haw_Wei_2024_Thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Nonlinear and Multidimensional Terahertz Spectroscopy of Liquids and Crystalline Solids", "author": [ { "family_name": "Lin", "given_name": "Haw-Wei", "orcid": "0000-0002-5208-7385", "clpid": "Lin-Haw-Wei" } ], "thesis_advisor": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The delocalized and correlated nuclear degrees of freedom in the terahertz (THz) regime strongly influences the room temperature chemical and physical properties of condensed matter systems, yet detailed understanding of the photo-induced dynamics and anharmonicities of the vibrational modes have remained elusive. In hydrogen-bonded liquids, these information facilitates the development of accurate force field models to aid simulations of biological processes of proteins and DNAs. In the field of nonlinear phononics, anharmonic lattice vibrations form the foundation for ultrafast coherent control of material properties, which has become an indispensable technique in the engineering toolbox for quantum materials. In this thesis, we demonstrate the development and application of nonlinear 1D THz Kerr effect (TKE) and 2D THz-THz-Raman (2D-TTR) ultrafast THz spectroscopies, which are specially designed to induce resonant coherent excitations of the correlative nuclear degrees of freedom in liquids and crystalline solids. By analyzing the temporal evolution of the nuclear THz-driven dynamics, insights into the excitation mechanisms, nonlinear coupling interactions, and the dominant source(s) of anharmonicity may be determined. Specifically, we developed a nonlinear imaging method based on the third-order response of electro-optic crystal GaP, which significantly improved the alignment consistency and the signal strength of 2D-TTR spectroscopy. Further, we extended an echelon-based single-shot detection scheme, originally developed in 1D TKE spectroscopy, to 2D-TTR spectroscopy, which led to up to two orders-of-magnitude reduction in acquisition time. Armed with these instrument advancements, we measured 2D-TTR spectra of liquid halogenated methanes with significantly improved signal-to-noise and a larger temporal window, which led to the identification of a novel competing sum-frequency THz excitation pathway. On the other hand, we investigated resonant driven-dynamics of the phonon-polariton modes in semiconductor LiNbO$_3$, which revealed nonlinear coupling interactions between two phonon branches that are attributed to mechanical anharmonicity. In addition, we directly observed photo-induced coherent phonon wavepackets for the layered semiconductors transition metal dichalcogenide using 1D TKE spectroscopy, which are attributed to the sum-frequency excitation pathway. These works highlight the rigorous experimental considerations and careful spectral analysis required to extract essential insight into excitation mechanisms and anharmonic contributions, while avoiding spectral artifacts due to the instrument response function. In order to provide clarity to these often misunderstood spectroscopies in the THz regime, this thesis further summaries the theories behind 1D TKE and 2D-TTR spectroscopies and the lessons we have learned from experimental realization of these exotic instruments and the analysis of complex spectral features.", "doi": "10.7907/2qt0-mg05", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16303", "collection": "thesis", "collection_id": "16303", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02262024-021912071", "primary_object_url": { "basename": "he_manni_2024_thesis_submit.pdf", "content": "final", "filesize": 31075794, "license": "other", "mime_type": "application/pdf", "url": "/16303/2/he_manni_2024_thesis_submit.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Entanglement-Enhanced Bioimaging and Sensing", "author": [ { "family_name": "He", "given_name": "Manni", "orcid": "0009-0001-4237-900X", "clpid": "He-Manni" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Wei", "given_name": "Lu", "orcid": "0000-0001-9170-2283", "clpid": "Wei-Lu" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Hong", "given_name": "Elizabeth J.", "orcid": "0000-0003-3866-418X", "clpid": "Hong-Elizabeth-J" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Studies of entangled light-matter interactions have been gaining momentum because of their potential applications in bioimaging and sensing. Entangled photons are predicted to linearize nonlinear optical processes and offer orders of magnitude of enhancement to the interaction cross sections. To investigate the validity of entanglement-enhanced bioimaging techniques, a continuous wave (CW)-powered, on-chip, broadband entangled light source based on periodically poled lithium tantalate (ppLT) was designed and characterized. This light source achieved femtosecond entangled correlation times comparable to classical ultrafast lasers with an unprecedented power of ~100 nW in near-infrared (NIR), which is a crucial first step toward fully integrated, thin-film lithium niobate (TFLN)-based, visible to NIR entangled photon sources. This light source was then used for subsequent spectroscopy/microscopy experiments to systematically investigate the feasibility of entanglement-enabled microscopy techniques such as entangled two-photon absorption (ETPA) microscopy and entangled fluorescence lifetime measurements. A novel method was developed to measure fluorescence from ETPA using a spectrotemporally resolved Michelson interferometer which is good at eliminating false signals due to one-photon absorption and scattering. Careful experimental attempts at detecting virtual-state mediated ETPA from rhodamine 6G (R6G) and resonance-enhanced ETPA from indocyanine green (ICG) were made, and the ETPA signals were found to be below the instrument detection limits and often masked by one-photon effects such as scattering and linear absorption. Instead, experimental upper bounds were placed on the ETPA cross sections of the studied molecules, with an emphasis on continued improvement of the light source and instrument detection limits. On-chip entangled fluorescence lifetime imaging microscopy (entangled-FLIM) has also been identified as a new future development focus. The feasibility of the technique was demonstrated via a proof-of-principle experiment which measured the fluorescence lifetime of ICG in various solvents. Using entangled photons produced from a CW laser, the lifetime measurement scheme achieved a temporal resolution of 50 ps and a minimum measurable lifetime of 365 ps, which can be used to distinguish most biologically relevant fluorophores in the corresponding wavelength range. This experiment is a critical first step toward scalable, high-throughput, wavelength-multiplexed, and on-chip FLIM or lifetime measurements which could be used in label-free health monitoring technologies.", "doi": "10.7907/3zg0-4135", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16375", "collection": "thesis", "collection_id": "16375", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05082024-165921385", "type": "thesis", "title": "Measuring Charge Carrier and Structural Photodynamics at Solar Energy Material Surfaces Using Transient Extreme Ultraviolet Reflection Spectroscopy", "author": [ { "family_name": "Michelsen", "given_name": "Jonathan Malte Zschiegner", "orcid": "0000-0002-7420-5610", "clpid": "Michelsen-Jonathan-Malte-Zschiegner" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Electronic and vibrational degrees of freedom, and their interactions, control the chemical and physical properties of solids. Core-level spectroscopies, such as transient extreme ultraviolet (XUV) spectroscopy, provide detailed information on the electronic structure and local coordination environment of a material. In this work, we employ transient XUV reflection spectroscopy to measure surface carrier and structural dynamics in solar energy materials. To interpret experimental spectra, excited state valence effects are incorporated into the OCEAN code (Obtaining core excitations from ab initio electronic structure and the NIST Bethe-Salpeter equation solver). The modeling of core-level spectra from first principles enables the extraction of carrier kinetics via the robust assignment of spectral features. Moreover, this thesis explores experimental and theoretical methods for understanding carrier-structural coupling in solids relevant to solar energy applications.
\r\n\r\nSpecifically, we explore the chemical and physical information contained in core-level spectra for various solar energy material systems and present guiding principles for designing a core-level electronic spectroscopy experiments to determine photoexcited carrier and structural dynamics. We report on experimental measurements of ultrafast surface carrier and structural dynamics in photocathodes zinc telluride and copper iron oxide. Further, complementary excited state theory is presented to extract excited state valence dynamics from experimental core-level spectra based on ground state implementations of the Bethe-Salpeter equation.
", "doi": "10.7907/73h7-kg35", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16391", "collection": "thesis", "collection_id": "16391", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05192024-000137690", "primary_object_url": { "basename": "KVirgil_Thesis_2023.pdf", "content": "final", "filesize": 2810434, "license": "other", "mime_type": "application/pdf", "url": "/16391/1/KVirgil_Thesis_2023.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Polarization-Resolved, Oblique Incidence Terahertz Spectroscopy of Highly Uniform 2D Hybrid Perovskite Films", "author": [ { "family_name": "Virgil", "given_name": "Kyle Allan", "clpid": "Virgil-Kyle-Allan" } ], "thesis_advisor": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis details the development and optimization of thin film THz transmission measurements to extract spectrally resolved vibrational anisotropy in high quality layered hybrid perovskite materials. After an introduction in Chapter 1, Chapter 2 details the design, construction, and characterization of a terahertz time-domain spectrometer from scratch. Generalized THz propagation models are presented which enable accurate and diverse implementation of THz analysis. In Chapter 3, hybrid perovskite materials are introduced and our efforts towards reliably synthesizing high quality thin film perovskites using spin coating techniques are discussed. We find that optimized thin films are achieved from tailored synthetic conditions which depend on perovskite composition. In Chapter 4, we present our investigation into the elusive yet highly influential THz vibrational properties of 2D hybrid perovskite systems. A novel implementation of oblique-incidence THz transmission measurements reveals previously unseen vibrational excitations which provide valuable insight into the fundamental photodynamics that govern perovskite optoelectronics. We conclude in Chapter 5. This thesis serves to enhance the accessibility of powerful THz spectroscopic techniques as well as support the realization of promising perovskite renewable energy technologies.", "doi": "10.7907/cr97-p373", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16401", "collection": "thesis", "collection_id": "16401", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05202024-220341626", "primary_object_url": { "basename": "2024_0523_WenChao_Thesis_Final.pdf", "content": "final", "filesize": 10139571, "license": "other", "mime_type": "application/pdf", "url": "/16401/1/2024_0523_WenChao_Thesis_Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Spectroscopy and Kinetics of Reactive Intermediates in the Atmosphere of Venus: the Catalytic Role of Chlorine Atoms", "author": [ { "family_name": "Chao", "given_name": "Wen", "orcid": "0000-0003-0602-1606", "clpid": "Chao-Wen" } ], "thesis_advisor": [ { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" }, { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Chlorine chemistry plays essential roles in both industrial and academic fields due to the special reactivity required to initiate or catalyze important reactions in our daily life. For example, Cl atoms are the most common oxidation agents in combustion and are famous for the catalyzed destruction of ozone that eventually leads to the ozone hole.
\r\n\r\nAs terrestrial planets, Venus and Earth\u2019s atmospheres have similar origins but very different evolutions. Compared to Earth, Venus suffers strong water loss in hydrodynamics escape due to its distinct distance from the Sun; as a result, high abundances of chlorine and sulfur species are not trapped in the sea and survive in Venus\u2019 atmosphere. For example, a dense cloud, made with sulfuric acid, has been observed at the middle altitude (50 - 70 km) and the concentration profiles for distinct species (SO\u2082, CO, CO\u2082, O\u2082 ..., etc.) have been measured during the Venus Express mission operated by the European Space Agency. Digging into the discrepancy between the observations and model simulations, a few important questions arose, and further laboratory studies are needed to solve the puzzles, including (1) the unknown UV absorber, (2) the SO\u2082 concentration inversion at high altitude and (3) the extremely low O\u2082 and high CO\u2082 abundances, wherein a reactive chlorine atom is proposed for explaining these phenomena.
\r\n\r\nIn this thesis, we performed the pulsed-laser photolysis experiments with a homemade time-resolved broadband UV-Vis transient-absorption spectroscopy coupled with a temperature- and pressure-controlled flow reactor to study the spectroscopic and kinetic\r\nproperties of key intermediates (ClSO, ClCO and ClCO\u2083) in the oxidation process of sulfur and carbon to ultimately form SO\u2082 and CO\u2082. The recorded spectra are analyzed, and highlevel ab initio calculations were performed to rationalize the electronic structures of target molecules to reveal the catalysis role of Cl atoms. In addition, key reaction rate coefficients\r\n(ClSO + Cl, kClSO+Cl(292 K) = (1.48 \u00b1 0.42)x10-11 cm\u00b3 molecule-1 s-1; ClCO + O\u2082,\r\nkClCO+O\u2082(0) = (9.0 \u00b1 2.3) \u00d7 10-32 cm\u2076 s-1 a cm\u00b3 molecule-1 s-1, and thermodynamic property (Cl + CO \u21cc ClCO, Keq = 1.8 x10-18 molecules cm\u207b\u00b3) have been measured to\r\nfurther assist the model simulations.
\r\n\r\nThis thesis not only offers essential data for model simulations to understand the complex chemistry in Venus' atmosphere but also provide new insights to guide future tasks to explore Venus, e.g. DAVINCI+ and VERITAS by NASA.
", "doi": "10.7907/v9ey-m476", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:15013", "collection": "thesis", "collection_id": "15013", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08292022-044824279", "primary_object_url": { "basename": "Honglie_Ning_2023_Thesis.pdf", "content": "final", "filesize": 27843215, "license": "other", "mime_type": "application/pdf", "url": "/15013/1/Honglie_Ning_2023_Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Ultrafast Optical Control of Order Parameters in Quantum Materials", "author": [ { "family_name": "Ning", "given_name": "Honglie", "orcid": "0000-0003-4867-0751", "clpid": "Ning-Honglie" } ], "thesis_advisor": [ { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "thesis_committee": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Developing protocols to realize quantum phases that are not accessible thermally and to manipulate material properties on demand is one of the central problems of modern condensed matter physics. Impulsive electromagnetic stimulus provides an extensive playground not only to exert desired control over the material macroscopic properties but also to optically detect the underlying microscopic mechanisms. Two indispensable components form the cornerstone to realize these goals: a meticulous comprehension of light-induced phenomena and a suitable and versatile platform.
\r\n\r\nAbundant photoinduced phenomena emerge upon light irradiation. A collective oscillation of order parameter can be launched and probed in the weak perturbation regime; further increasing light intensity can transiently modulate the free-energy landscape, inducing a suppression, enhancement, reversal, and switch of order parameters; in the strong non-perturbative excitation regime, the system can be driven nonlinearly with microscopic coupling parameters modified. Understanding these light driven emergent phenomena lays the foundation of optical control and novel functionalities.
\r\n\r\nQuantum materials, embodying a large portfolio of topological and strongly correlated compounds, afford an exceptional venue to realize optical control. Owing to the complex interplay between the charge, spin, orbital, and lattice degrees of freedom, a rich phase diagram can be generated with various phases that are selectively and independently accessible via optical perturbations. They hence offer a wealth of opportunities to not only improve our comprehension of the underlying physics but also develop the next generation of ultrafast technologies.
\r\n\r\nIn Chapter I of this thesis, I will first cover a multitude of light-induced emergent phenomena in quantum materials under the framework of time-dependent Landau theory, Keldysh theory, and Floquet theory, and then introduce several canonical microscopic models to quantitatively rationalize the intra- and interactions between different degrees of freedom in quantum materials. As the necessary theoretical background is established, three main experimental techniques that have been extensively utilized in my research: time-resolved reflectivity and Kerr effect, time-resolved second harmonic generation rotational anisotropy, and coherent phonon spectroscopy will be introduced in Chapter II. In Chapter III, I will demonstrate that a light-induced topological phase transition can be engendered concomitant with an inverse-Peierls structural phase transition in elemental Te. In Chapter IV, I will describe signatures of ultrafast reversal of excitonic order in excitonic insulator candidate Ta2NiSe5 and substantiate a manipulation of the reversal as well as the Higgs mode with tailored light pulses. In Chapter V, a light-induced switch of spin-orbit-coupled quadrupolar order in multiband Mott insulator Ca2RuO4 will be introduced. In Chapter VI, a Keldysh tuning of nonlinear carrier excitation and Floquet bandwidth renormalization in strongly driven Ca2RuO4 will be covered.
", "doi": "10.7907/yxa0-6884", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15080", "collection": "thesis", "collection_id": "15080", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12282022-061839565", "type": "thesis", "title": "Electronic Structure and Reactivity of Metal Complexes", "author": [ { "family_name": "Barth", "given_name": "Alexandra Teresa", "orcid": "0000-0002-1813-4029", "clpid": "Barth-Alexandra-Teresa" } ], "thesis_advisor": [ { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" } ], "thesis_committee": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Transition metals are at the core of addressing global energy needs. Functioning as catalysts, these systems have long demonstrated competency to promote thermodynamically challenging reactions, lowering energetic barriers and facilitating desired transformations with applied light or potential. Employing infrared, visible, ultraviolet, and x-ray spectroscopy, chemists are afforded insight into the electronic structures of transition metal complexes, investigating ligand field strengths and metal-ligand interactions. Addition of time-resolved techniques affords resolution of dynamic processes in molecular species, such as electron transfer pathways.
\r\n\r\nChapter 1 reviews the electronic structure and reactivity of homoleptic tungsten(0) arylisocyanides W(CNAr)\u2086 to provide the foundation for much of this work.
\r\n\r\nIn Chapter 2, application of W(CNAr)\u2086 species for one- and two-photon photoredox catalysis are explored. The two-photon absorption cross-sections of W(CNAr)\u2086 are remarkably large (\u03b4\u2088\u2081\u2080 = 180\u20131900 GM) and enable these photocatalysts to operate under excitation from visible or near infrared light. Photoredox activity is evaluated via base-promoted homolytic aromatic substitution (BHAS) reaction of thermodynamically challenging substrates. In Chapter 3, solvent perturbations enhance visible light-activated BHAS catalysis from W(CNAr)\u2086. Increased solvent dielectric (benzene to 1,2-difluorobenzene) and solvated electrolyte combine to increase *W(CNAr)\u2086 quenching rates up to one order of magnitude with greater cage-escape yields.
\r\n\r\nIn Chapter 4, the electronic structure of linear gold(I) arylisocyanide complexes ([Au(CNDipp-R)\u2082]\u207a; CNDipp = 2,6-diisopropylphenylisocyanide) are assigned using insights from UV-visible spectroscopy and time-dependent density functional theory (TD-DFT) calculations. In Chapter 5, the electronic structure of Fe(II) and Co(II) quaterpyridine photo-/electro-catalysts for CO\u2082 reduction are evaluated using UV-visible-NIR, \u00b9H NMR, M\u00f6ssbauer, and infrared spectra. Assignment of the absorption transitions are supported by TD-DFT calculations.
", "doi": "10.7907/k66v-1c93", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15198", "collection": "thesis", "collection_id": "15198", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05202023-131846404", "type": "thesis", "title": "Ultrafast Dynamics of Photo-Doped Mott Antiferromagnets", "author": [ { "family_name": "Mehio", "given_name": "Omar", "orcid": "0000-0001-7923-2178", "clpid": "Mehio-Omar" } ], "thesis_advisor": [ { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "thesis_committee": [ { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Lee", "given_name": "Patrick A.", "orcid": "0000-0001-7809-8157", "clpid": "Lee-Patrick-A" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Strong coupling between spin and charge degrees of freedom in two-dimensional spin-1/2 Mott antiferromagnets (AFMs) creates a rich platform to study quantum many-body physics. For decades, the consequences of these interactions have been intensely studied in thermal equilibrium, where the introduction of charge carriers through chemical doping has been shown to generate a vibrant phase diagram rich with unconventional types of charge, spin, and orbital ordering. In recent years, however, attention has grown to include the study of these materials as they are driven far from equilibrium using intense pulses of light produced by femtosecond laser sources. In addition to fundamental interest in the resultant dynamics, recent experimental and theoretical studies have suggested that driven Mott insulators can host states of matter that cannot be accessed in thermal equilibrium.
\r\n\r\nWhile many driving protocols have been developed---spanning from the selective excitation of bosonic modes to photon-dressing via coherent time-periodic driving---the simplest conceptual approach to engineering Mott insulators with light is known as photo-doping. In this procedure, the material is impulsively driven resonantly with a transition from a filled band to an empty band, transiently producing charge carriers. Given the impact of chemical doping in thermal equilibrium, photo-doping has garnered interest as an important tool in the study of driven Mott insulators. Early successes in the study of photo-doped Mott AFMs include the observation of ultrafast demagnetization and the prediction of non-thermal magnetic states, charge density waves, and superconductivity. Photo-doping thus holds promise to generate an out-of-equilibrium phase diagram that is equally rich to that found in equilibrium.
\r\n\r\nYet, many open questions about the basic properties of photo-doped Mott insulators remain unresolved. Whether charge instabilities exist as a result of interactions between the photo-dopants has yet to be examined. Moreover, while theoretical studies have suggested that antiferromagnetic correlations can enhance attractive interactions between photo-dopants, evidence of the resultant bound states remain elusive. Even the light-matter interactions that generate the photo-dopants are in need of investigation, as the fate of a Mott insulator driven by strong electric fields remains a fundamental open theoretical and experimental problem.
\r\n\r\nIn this thesis, I present a series of experiments designed to answer each of these questions. After describing the properties of Mott insulators in Chapter 1, I present the experimental details of the tools that enable these studies in Chapter 2. Taking a multi-messenger approach to ultrafast spectroscopy, a suite of ultrafast probes simultaneously track the spin and charge degrees of freedom to paint a holistic picture of the out-of-equilibrium state. In Chapter 3, I use ultrafast THz conductivity to establish the existence of an insulating photo-excited fluid of Hubbard excitons (HEs), which are bound states that are thought to form as a result of attractive spin-mediated interactions. This magnetic binding mechanism is studied in more detail in Chapter 4 by examining the properties of these HEs in the magnetic critical region of several materials that lie in different magnetic universality classes. In Chapter 5, I study the effects of HE formation on the ultrafast demagnetization that is known to occur following photo-doping. Finally, I turn my attention towards the photo-dopant generation mechanism in Chapter 6, exploring the effects of strong electric field driving in Mott insulators. I find signatures of the so-called Keldysh crossover from a multiphoton-absorption- to a quantum-tunneling-dominated pair production regime. Altogether, this work establishes photo-doped Mott insulators as a rich playground to engineer non-equilibrium phases of matter and study quantum many-body dynamics.
", "doi": "10.7907/fsbz-pd46", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15078", "collection": "thesis", "collection_id": "15078", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12132022-201432142", "primary_object_url": { "basename": "thesis_final.pdf", "content": "final", "filesize": 184003401, "license": "other", "mime_type": "application/pdf", "url": "/15078/3/thesis_final.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Understanding the Origins of Photoexcited XUV Spectra", "author": [ { "family_name": "Klein", "given_name": "Isabel McMillan", "orcid": "0000-00016134-6732", "clpid": "Klein-Isabel-McMillan" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Fu", "given_name": "Gregory C.", "orcid": "0000-0002-0927-680X", "clpid": "Fu-G-C" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A full measurement of photoexcited dynamics, from excitation to recombination, is required to understand the photochemical processes at the heart of solar energy materials and devices. Measuring these complete dynamics is often unachievable with a single experimental tool. Transient X-ray spectroscopies, however, have proven to be powerful techniques as they can separately measure electron and hole dynamics, as well as vibrational and structural modes, all with elemental specificity. The interpretation of these measurements is still challenging, as the core-hole created following a core-level transition distorts the measured spectrum. This thesis aims to develop complementary experimental and computational techniques to measure and interpret transient X-ray spectra. Initially, the measured photoexcited dynamics of ZnTe and CuFeO\u2082, which reveal polaron formation and lattice coupling, as well as electron and hole kinetics and band gap dynamics, are presented. Following this experimental work, we develop an ab initio computational method for modeling transient X-ray and extreme ultraviolet (XUV) spectra. The ab initio method is a Bethe-Salpeter equation (BSE) approach based on the previously developed Obtaining Core Excitations from Ab initio electronic structure and the NIST BSE solver (OCEAN) code. Building on the foundations of the OCEAN code, we incorporate photoexcited states for a range of transition metal oxides and demonstrate the method\u2019s ability to simulate the effects of state filling, isotropic thermal expansion and polaron states on XUV absorption spectra. Importantly, our method is also able to fully decompose the calculated spectra into the constituent components of the X-ray transition Hamiltonian, providing further insight into the origins and nature of spectral features. The XUV absorption spectra for the ground, photoexcited, and polaron states of \u03b1-Fe\u2082O\u2083, as well as for the ground, photoexcited, and thermally expanded states of other first row transition metal oxides \u2013 TiO\u2082, \u03b1-Cr\u2082O\u2083, \u03b2-MnO\u2082, Co\u2083O\u2084, NiO, CuO, and ZnO \u2013 are calculated to demonstrate the accuracy of our approach. This method is easily generalized to K, L, M, and N edges to provide a general approach for analyzing transient X-ray absorption or reflection data.
", "doi": "10.7907/s8qe-4s74", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15249", "collection": "thesis", "collection_id": "15249", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312023-235401985", "primary_object_url": { "basename": "Ober_Douglas_2023_Thesis.pdf", "content": "final", "filesize": 4433994, "license": "other", "mime_type": "application/pdf", "url": "/15249/12/Ober_Douglas_2023_Thesis.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Laser Spectroscopy of Hydrocarbons for Applications in Atmospheric and Space Science", "author": [ { "family_name": "Ober", "given_name": "Douglas Clifford", "orcid": "0009-0005-2257-5029", "clpid": "Ober-Douglas-Clifford" } ], "thesis_advisor": [ { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" }, { "family_name": "Beauchamp", "given_name": "Jesse L.", "orcid": "0000-0001-8839-4822", "clpid": "Beauchamp-J-L" }, { "family_name": "Hodyss", "given_name": "Robert P.", "orcid": "0000-0002-6523-3660", "clpid": "Hodyss-Robert-P" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis describes applications of spectroscopy and mass spectrometry towards applications of in situ sensing, chemical kinetics, and photodissociation processes of hydrocarbon species. Both mass spectrometry and cavity ring-down spectroscopy are used in this work. Irradiation of protonated coronene was used to study photodissociation process of polycyclic aromatic hydrocarbons (PAHs), with the power, irradiation time, and fragmentation studied to elucidate a photofragmentation mechanism. Biomolecules were ionized via Direct Analysis in Real Time (DART) to explore the feasibility and sensitivity of the ionization technique for different chemical species for in situ measurement in simulated extraterrestrial conditions. Photofragmentation and DART ionization were combined to quantify mixtures of isobaric PAHs, providing a tunable and complimentary technique for in situ analysis of mixtures. Finally, frequency-stabilized cavity ring-down spectroscopy was used to analyze precise \u00b9\u00b3CH\u2084, CH\u2083D, and CH\u2082D\u2082 to CH\u2084 isotologue ratios using optically-switched dual-wavelengths, allowing for sensitive measurement of the kinetic isotope effect of methane oxidation with O(\u00b9D).
", "doi": "10.7907/x42v-ry39", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15190", "collection": "thesis", "collection_id": "15190", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05182023-163804024", "primary_object_url": { "basename": "overholts_thesis_submit.pdf", "content": "final", "filesize": 11126390, "license": "other", "mime_type": "application/pdf", "url": "/15190/1/overholts_thesis_submit.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A Novel Platform for Mechanochemical Multicolor Lithography and Models for Solution-Phase Mechanophore Activation", "author": [ { "family_name": "Overholts", "given_name": "Anna Camille", "orcid": "0000-0002-0593-6903", "clpid": "Overholts-Anna-Camille" } ], "thesis_advisor": [ { "family_name": "Robb", "given_name": "Maxwell J.", "orcid": "0000-0002-0528-9857", "clpid": "Robb-M-J" } ], "thesis_committee": [ { "family_name": "Reisman", "given_name": "Sarah E.", "orcid": "0000-0001-8244-9300", "clpid": "Reisman-S-E" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Nelson", "given_name": "Hosea M.", "orcid": "0000-0002-4666-2793", "clpid": "Nelson-H-M" }, { "family_name": "Robb", "given_name": "Maxwell J.", "orcid": "0000-0002-0528-9857", "clpid": "Robb-M-J" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The use of mechanical force to trigger chemical reactions has generated many exciting applications in stimuli-responsive materials. Advancement of this area of study requires the development of fundamental models for mechanical activation as well as the design of new force-responsive units, termed mechanophores. This thesis investigates models for solution-phase activation kinetics and activation efficiency and details the development of a novel mechanophore platform for multicolor mechanochemical lithography.", "doi": "10.7907/px5z-aj53", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15141", "collection": "thesis", "collection_id": "15141", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04172023-221653165", "primary_object_url": { "basename": "Dutton_Thesis_Final.pdf", "content": "final", "filesize": 47710578, "license": "other", "mime_type": "application/pdf", "url": "/15141/1/Dutton_Thesis_Final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Chirped Pulse Rotational Spectroscopy of Small Molecule Clusters", "author": [ { "family_name": "Dutton", "given_name": "Sarah Emily", "orcid": "0000-0002-9587-5971", "clpid": "Dutton-Sarah-Emily" } ], "thesis_advisor": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "thesis_committee": [ { "family_name": "Wei", "given_name": "Lu", "orcid": "0000-0001-9170-2283", "clpid": "Wei-Lu" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Fu", "given_name": "Gregory C.", "orcid": "0000-0002-0927-680X", "clpid": "Fu-G-C" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Despite the ubiquity of water and alcohol mixtures in every realm of science, the hydrogen bond network governing the unique properties of these mixtures is still under investigation. To aid in the determination of hydrogen bond energetics and dynamics in alcohol and water mixtures, herein a ground up approach studying small alcohol:water clusters is presented. Novel instrumentation for chirped pulse Fourier-transform microwave spectroscopy was developed, and subsequently benchmarked against the detection and characterization of ethanol and water trimers. From there, cluster size was gradually increased, first studying ethanol and water tetramers, then switching to methanol for larger cluster studies of pentamers and hexamers. Throughout this thesis, the over-arching questions as to microaggregation in clusters and trends in geometry and relative energy ordering were investigated, and evidence supporting the facile mixing of small alcohols and water is presented at the few-molecule cluster scale. In the final studies of methanol and water hexamers, the first `3-dimensional' bonding motifs of methanol and water clusters are observed, marking the transition from the planar conformers of small clusters to the complex and higher cooperativity bonding patterns in larger clusters and in bulk mixtures.", "doi": "10.7907/dxsp-c265", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15279", "collection": "thesis", "collection_id": "15279", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-055053747", "type": "thesis", "title": "Complex Charge Compensation Mechanisms in Lithium-Rich Chalcogenide Cathodes", "author": [ { "family_name": "Zak", "given_name": "Joshua Joseph", "orcid": "0000-0003-3793-7254", "clpid": "Zak-Joshua-Joseph" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Giapis", "given_name": "Konstantinos P.", "orcid": "0000-0002-7393-298X", "clpid": "Giapis-K-P" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Lithium-ion batteries have revolutionized the world by enabling long-lasting portable electronics, electrified transportation, and grid storage solutions for renewable energy implementation. However, current commercialized technologies are limited by the one electron transfer per transition metal paradigm utilized by cathode materials that operate with an intercalation-based charge storage mechanism. Finding ways to increase the charge storage capabilities of the cathode into the multielectron regime has long been a focus of research efforts, and involvement of structural anions in the redox has been demonstrated as a promising way to accomplish multielectron storage. Layered lithium-rich oxide materials have been shown to afford dramatic improvements to overall storage capacity but are plagued by complex mechanisms and unwanted side reactions that lead to poor cycling stability and characterization difficulties. This thesis expands upon previous understanding of oxide-based anion redox materials and extends the exploration into sulfide and selenide systems, which allow the study of anion redox without the side processes that affect oxides. First, a dynamic charge compensation mechanism of late group metal-poor, lithium-rich oxide, Li2Ru0.3Mn0.7O3, is uncovered and found to involve an irreversible anion oxidation that leads to involvement of redox states on transition metals previously thought to be unavailable. Second, active electrolyte additives are explored as a method of stabilizing the cathode-electrolyte interface of anion redox material, Li2RuO3. Third, reversible anion redox is demonstrated in alkali-rich sulfides, Li2FeS2 and LiNaFeS2, and proven to occur through oxidation of sulfides (S2-) to persulfides ([S2]2-). Understanding of the structural ramifications of anion oxidation in Li2FeS2 is further expanded through computational and experimental methods. Fourth, the role of metal-anion covalency is systematically investigated through anion substitution of Li2FeS2 with S2-, highlighting the importance of a holistic understanding of changes to the electronic and physical structure of anion redox materials to predict long-term performance. Finally, detailed perspectives and future outlooks on sulfur redox in lithium battery systems are offered with an exhaustive survey of thermodynamically stable binary and ternary persulfide materials.
", "doi": "10.7907/1k50-3811", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15097", "collection": "thesis", "collection_id": "15097", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01312023-221353362", "primary_object_url": { "basename": "orourke_matthew_thesis_final.pdf", "content": "final", "filesize": 10598009, "license": "other", "mime_type": "application/pdf", "url": "/15097/1/orourke_matthew_thesis_final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Towards High-Accuracy Simulations of Strongly Correlated Materials Using Tensor Networks", "author": [ { "family_name": "O'Rourke", "given_name": "Matthew John", "orcid": "0000-0002-5779-2577", "clpid": "Orourke-Matthew-John" } ], "thesis_advisor": [ { "family_name": "Chan", "given_name": "Garnet K.", "orcid": "0000-0001-8009-6038", "clpid": "Chan-Garnet-K-L" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Chan", "given_name": "Garnet K.", "orcid": "0000-0001-8009-6038", "clpid": "Chan-Garnet-K-L" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Accurate and verifiable computation of the properties of real materials with strong electron correlation has been a long-standing challenge in the fields of chemistry, physics, and material science. Most existing algorithms suffer from either approximations that are too inaccurate, or fundamental computational complexity that is too high. In studies of simplified models of strongly-correlated materials, tensor network algorithms have demonstrated the potential to overcome these limitations. This thesis describes our research efforts to develop new algorithms for two-dimensional (2D) tensor networks that extend their range of applicability beyond simple models and toward simulations of realistic materials.
\r\n\r\nWe begin by describing three algorithms for projected entangled-pair states (PEPS, a type of 2D tensor network) that address three of their major limitations: numerical stability, long-range interactions, and computational efficiency of operators. We first describe (Ch. 2) a technique for converting a PEPS into a canonical form. By generalizing the QR matrix factorization to entire columns of a PEPS, we approximately generate a PEPS with analogous properties to the well-studied canonical 1D tensor network. This connection enables enhanced numerical stability and ground state optimization protocols. Next, we describe (Ch. 3) a technique to efficiently represent physically realistic long-range interactions between particles in a 2D tensor network operator, a projected entangled-pair operator (PEPO). We express the long-range interaction as a linear combination of correlation functions of an auxiliary system with only nearest-neighbor interactions. This allows us to represent long-range pairwise interactions with linear scaling in the system size. The third algorithm we present (Ch. 4) is a method to rewrite the 2D PEPO in terms of a set of quasi-1D tensor network operators, by exploiting intrinsic redundancies in the PEPO representation. We also report an on-the-fly contraction algorithm using these operators that allows for a significant reduction in computational complexity, enabling larger scale simulations of more complex problems.
\r\n\r\nWe then move on to describe (Ch. 5) an extensive study of a \"synthetic 2D material\"---a two-dimensional square array of ultracold Rydberg atoms---enabled by some of the new algorithms. We investigate the ground state quantum phases of this system in the bulk and on large finite arrays directly comparable to recent quantum simulation experiments. We find a greatly altered phase diagram compared to earlier numerical and experimental studies, and in particular, we uncover an unexpected entangled nematic phase that appears in the absence of geometric frustration.
\r\n \r\nFinally, we finish by describing (Ch. 6) a somewhat unrelated, but topically similar project in which we investigate the feasibility of laser cooling small molecules with two metal atoms to ultracold temperatures. We study in detail the properties of the molecules YbCCCa and YbCCAl for application in precision measurement experiments.
", "doi": "10.7907/wwka-as73", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14499", "collection": "thesis", "collection_id": "14499", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02162022-092446660", "type": "thesis", "title": "Entangled Photon Interferometry: Development of Photonic Systems Towards Quantum Spectroscopy", "author": [ { "family_name": "Szoke", "given_name": "Szilard", "orcid": "0000-0001-7860-4638", "clpid": "Szoke-Szilard" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Marandi", "given_name": "Alireza", "orcid": "0000-0002-0470-0050", "clpid": "Marandi-A" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Entangled photon spectroscopy is an emergent field offering the potential to perform nonlinear and non-classical measurements at low photon fluxes. The entangled photon pairs which are generated using a continuous-wave laser pumped spontaneous parametric downconversion (SPDC) process simultaneously display strong correlations in time and anti-correlations in frequency space. Measuring changes in these correlations provides classical and non-classical information about the underlying dynamics and fluctuations of the sample-system. Further, because these two variables are not Fourier conjugates, entangled photon spectroscopy makes it possible to exploit the spectral resolution of continuous-wave lasers, while leveraging the temporal relationship of the near-simultaneously generated photon pairs which effectively mimics an ultrafast pulsed laser experiment. Nonlinear and ultrafast measurements can therefore be performed with low-power sources while also achieving superior signal-to-noise ratios due to the underlying quantum statistics. As photons in a pair can be separately manipulated, spectroscopic setups using these quantum states of light have marked benefits in contrast to measurements performed using traditional single photon states.
\r\n\r\nHere, we describe our efforts towards implementing quantum interferometers to test the abilities of entangled photon pairs in nonlinear spectroscopic studies. Specifically, we present work on the development of free-space, fiber-optic, and nanophotonic systems that leverage nonlinear materials to generate narrow to broadband entangled photon pairs via SPDC. The numerical methods used for designing and tailoring these entangled photon sources are outlined together with associated experimental limitations. The spectral-temporal correlations of the two-photon states are characterized using fourth-order interferometry, demonstrating Hong-Ou-Mandel interference with picoseconds to femtoseconds coherence times, and wavelengths ranging from the IR to the UV. A monolithic nanophotonics architecture is proposed for completely on-chip, entangled, ultrafast, and nonlinear spectroscopy.
", "doi": "10.7907/brct-zh28", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14462", "collection": "thesis", "collection_id": "14462", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01032022-154242981", "type": "thesis", "title": "High-Resolution Imaging of Chemistry in Extreme Interstellar Environments", "author": [ { "family_name": "Wilkins", "given_name": "Olivia Harper", "orcid": "0000-0001-7794-7639", "clpid": "Wilkins-Olivia-Harper" } ], "thesis_advisor": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "thesis_committee": [ { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "de Kleer", "given_name": "Katherine R.", "orcid": "0000-0002-9068-3428", "clpid": "de-Kleer-K-R" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Advancements in imaging technologies have changed the ways in which we see and understand our chemical universe. Given the extreme distances between Earth, from which we observe the wider chemical universe, and the molecular clouds where stars are born, we cannot resolve the chemical structure of these interstellar laboratories on the same scales as we can with samples on Earth. Nevertheless, with the advent of larger and more sophisticated telescopes, such as the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, we can now look at interstellar chemistry on scales much smaller than the solar system. The research presented here uses ALMA to investigate the chemistry in (massive) star-forming regions in different parts of the Milky Way with high spatial resolution.
\r\n\r\nThis thesis first focuses on the nearby Orion Kleinmann-Low nebula (Orion KL), the closest (at about 400 parsecs away) massive star-forming region to us, at spatial scales smaller than those of typical planetary systems. Using methanol and methyl cyanide as molecular probes, we provide new insight into the physical structure\u2014especially the thermal structure\u2014of the nebula by mapping physical parameters derived from observed spectra. We also use different isotopologues of methanol to understand its chemistry, specifically after it forms on the surfaces of icy dust grains. This work provides a new view of Orion KL by providing high-angular-resolution maps of parameters such as abundance and temperature, whereas much of the existing literature provides a single set of parameters for a region.
\r\n\r\nHowever, Orion KL is only one interstellar laboratory, and it is part of a cohort of star-forming regions that are the targets of repeated astrochemical observations. The second part of this thesis ventures into the so-called molecular ring, a region 4-8 kiloparsecs from the galactic center that has remained relatively unexplored in the context of astrochemistry. Using the Atacama Compact Array (ACA) component of ALMA, we observed a slew of millimeter-emitting objects across 11 giant molecular clouds at higher angular resolutions than most previous observations of our sample, and we characterize their chemistry for the first time. This pilot survey establishes a catalogue of interstellar laboratories for future higher-angular-resolution observations. Over time, this catalogue will drive a better understanding of the chemistry in molecular-ring young stellar objects, allowing us to see whether (and if so, how) chemistry varies across distance from the galactic center and significantly increasing the number of targets for astrochemical observations.
", "doi": "10.7907/rwj8-8683", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14069", "collection": "thesis", "collection_id": "14069", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02012021-171503477", "primary_object_url": { "basename": "JacobBagley_ThesisPDF.pdf", "content": "final", "filesize": 11019676, "license": "other", "mime_type": "application/pdf", "url": "/14069/1/JacobBagley_ThesisPDF.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Fabrication of Pristine and Doped Graphene Nanostripes and their Application in Energy Storage", "author": [ { "family_name": "Bagley", "given_name": "Jacob David", "orcid": "0000-0001-9490-1341", "clpid": "Bagley-Jacob-David" } ], "thesis_advisor": [ { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "thesis_committee": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Fossil fuel usage causing rising CO2 levels and leading to climate change is, perhaps, the most pressing issue of our time. However, our economic dependence on energy necessitates its usage such that reducing energy usage is not possible leaving transitioning to renewable energy technologies as the only sustainable option. Currently, the largest barrier to large scale incorporation of renewable energy sources (e.g., solar, wind) is the high cost of energy storage technologies. Electrochemical energy storage technologies (e.g., lithium-ion batteries and supercapacitors) have been identified as a key approach for enabling the transition to renewable energy technologies.
\r\n\r\nGraphene is a material with exceptional properties that is receiving much attention for application in various energy storage technologies and could help reduce the cost of energy storage technologies. This thesis describes a novel fabrication procedure for low-cost and efficient synthesis of high-quality graphene nanostripes (GNSPs) and their application in lithium-ion battery and supercapacitor electrodes.
\r\n\r\nThis thesis is structured as follows. Chapter 1 outlines the motivation and technical background of this research. Chapter 2 describes the instrumentation and procedures for fabricating GNSPs. Chapter 3 describes in situ exfoliation of GNSPs as electrodes in supercapacitors to increase the capacitance. Chapter 4 describes synthesis and application of pyridinic-type nitrogen-doped GNSPs as a lithium-ion battery anode. Chapter 5 describes the synthesis and application of silicon-, germanium-, and tin-doped GNSPs and their application in lithium-ion battery anodes. Chapter 6 concludes and synthesizes the findings of the thesis holistically. Additionally, future outlook and potential research objectives are presented.
", "doi": "10.7907/hfdw-fs13", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14018", "collection": "thesis", "collection_id": "14018", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12072020-235133438", "type": "thesis", "title": "Chirped Pulse Microwave and Single-Shot Terahertz Spectroscopy Studies of Intermolecular Interactions", "author": [ { "family_name": "Mead", "given_name": "Griffin John", "orcid": "0000-0003-0067-4219", "clpid": "Mead-Griffin-John" } ], "thesis_advisor": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "thesis_committee": [ { "family_name": "Miller", "given_name": "Thomas F.", "orcid": "0000-0002-1882-5380", "clpid": "Miller-T-F" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "While the glow of a sodium vapor lamp or the crisp reds in autumn leaves are eye-catching examples of transitions between atomic and molecular energy levels (hv ~2-3 eV), it is arguably the much lower energy, thermally populated intermolecular \"bath\" states (hv ~10\u207b\u2075-10\u207b\u00b2 eV) that contribute most directly to the physical properties of matter. Although invisible to the human eye, in this thesis we study fundamentals of these low-energy interactions with two complementary techniques: chirped pulse microwave spectroscopy and nonlinear single-shot terahertz (THz) Kerr effect spectroscopy.
\r\n \r\nIn the first section, we apply chirped pulse-Fourier transform microwave (CP-FTMW) spectroscopy from 8-16 GHz to study fundamental hydrogen bonding motifs in gas phase alcohol water dimers. Hydrogen bonding is ubiquitous in nature and directly contributes to a range of phenomena from phase transitions in water to solvation of ions to enzymatic activity. Our focus on gas phase dimers reduces the spectral ambiguity arising in condensed phase samples, where inhomogeneous and homogeneous broadening can hamper observation of conserved intermolecular interaction motifs. The hydrogen bonding conformation of two alcohol-water dimers, n-propanol-water and isopropanol-water, were characterized. Both were found to adopt a shared water donor-alcohol acceptor conformation.
\r\n \r\nThe following sections use nonlinear THz spectroscopy from 0.1-10 THz to investigate molecular dynamics in the condensed phase. We focus on halogenated methane liquids, whose intense intramolecular vibrational modes are commensurate in energy to the intermolecular bath states. One central goal of this section was developing a technique to more rapidly collect nonlinear, multi-dimensional data from liquid systems. To that end, we developed a single-shot measurement approach using a reflective nickel echelon mirror and a high frame rate camera. With this new device we achieved an order of magnitude reduction in experimental integration times. High resolution, nonlinear multi-dimensional THz studies of several halogenated methane liquids and materials were produced as a result. From these data, we identified important spectral contributions from the experimental instrument response function.
", "doi": "10.7907/7wzt-ak58", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:11809", "collection": "thesis", "collection_id": "11809", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10072019-141728052", "primary_object_url": { "basename": "Davis_HunterC_2019_final.pdf", "content": "final", "filesize": 4540297, "license": "other", "mime_type": "application/pdf", "url": "/11809/1/Davis_HunterC_2019_final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Mechanistic Insights for Magnetic Imaging and Control of Cellular Function", "author": [ { "family_name": "Davis", "given_name": "Hunter Cole Davis", "orcid": "0000-0003-1655-692X", "clpid": "Davis-Hunter-Cole-Davis" } ], "thesis_advisor": [ { "family_name": "Shapiro", "given_name": "Mikhail G.", "orcid": "0000-0002-0291-4215", "clpid": "Shapiro-M-G" } ], "thesis_committee": [ { "family_name": "Miller", "given_name": "Thomas F.", "orcid": "0000-0002-1882-5380", "clpid": "Miller-T-F" }, { "family_name": "Meister", "given_name": "Markus", "orcid": "0000-0003-2136-6506", "clpid": "Meister-M" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Shapiro", "given_name": "Mikhail G.", "orcid": "0000-0002-0291-4215", "clpid": "Shapiro-M-G" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The vast biomolecular toolkit for optical imaging and control of cellular function has revolutionized the study of in vitro samples and superficial tissues in living organisms but leaves deep tissue unexplored. To look deeper in tissue and observe system-level biological function in large organisms requires a modality that exploits a more penetrant form of energy than visible light. Magnetic imaging with MRI reveals the previously unseen, with endogenous tissue contrast and practically infinite penetration depth. While these clear advantages have made MRI a cornerstone of modern medical imaging, the sparse library of molecular agents for MRI have severely limited its utility for studies of cellular function in vivo. The development of new molecular agents for MRI has suffered from a lack of tools to study the connection between changes in the microscale cellular environment and the corresponding millimeter-scale MRI contrast. Bridging this gap requires revisiting the mechanistic underpinnings of MRI contrast, casting aside some of the simplifications that smooth over sub-voxel heterogeneity that is rich with information pertinent to the underlying cell state.
\r\n\r\nHere, we will demonstrate theoretical, computational, and experimental connections between subtle changes in microscale cellular environment and resultant MRI contrast. After reviewing some foundational principles of MRI physics in the first chapter, the second chapter of the thesis will explore computational models that have significantly enhanced the development of genetically encoded agents for MRI, including the first genetically encoded contrast agent for diffusion weighted imaging. By improving the efficacy of these genetically encoded agents, we unlock MRI reporter genes for in vivo studies of cellular dynamics much in the same way that the engineering of Green Fluorescent Protein has dramatically improved in vitro studies of cellular function.
\r\n\r\nIn the third chapter, we introduce our study that maps microscale magnetic fields in cells and tissues and connects those magnetic fields to MRI contrast. Such a connection has previously been experimentally intractable due to the lack of methods to resolve small magnetic perturbations with microscale resolution. To overcome this challenge, we leverage nitrogen vacancy diamond magnetometry to optically probe magnetic fields in cells with sub-micron resolution and nanotesla sensitivity, together with iterative localization of field sources and Monte Carlo simulation of nuclear spins to predict the corresponding MRI contrast. We demonstrate the utility of this technology in an in vitro model of macrophage iron uptake and histological samples from a mouse model of hepatic iron overload. In addition, we show that this technique can follow dynamic changes in the magnetic field occurring during contrast agent endocytosis by living cells. This approach bridges a fundamental gap between an MRI voxel and its microscopic constituents and provides a new capability for noninvasive imaging of opaque tissues.
\r\n\r\nIn the fourth chapter, we focus on the use of magnetic fields to perturb, rather than image, biological function. Recent suggestions of nanoscale heat confinement on the surface of synthetic and biogenic magnetic nanoparticles during heating by radiofrequency alternating magnetic fields have generated intense interest due to the potential utility of this phenomenon in non-invasive control of biomolecular and cellular function. However, such confinement would represent a significant departure from classical heat transfer theory. We present an experimental investigation of nanoscale heat confinement on the surface of several types of iron oxide nanoparticles commonly used in biological research, using an all-optical method devoid of potential artifacts present in previous studies. By simultaneously measuring the fluorescence of distinct thermochromic dyes attached to the particle surface or dissolved in the surrounding fluid during radiofrequency magnetic stimulation, we found no measurable difference between the nanoparticle surface temperature and that of the surrounding fluid for three distinct nanoparticle types. Furthermore, the metalloprotein ferritin produced no temperature increase on the protein surface, nor in the surrounding fluid. Experiments mimicking the designs of previous studies revealed potential sources of artifacts. These findings inform the use of magnetic nanoparticle hyperthermia in engineered cellular and molecular systems and can help direct future resources towards tractable avenues of magnetic control of cellular function.
", "doi": "10.7907/9QEJ-6H55", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" } ]