A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item HIGH THROUGHPUT STIMULATED BRILLOUIN SCATTERING SPECTROSCOPY(2024) Rosvold, Jake Robert; Scarcelli, Giuliano; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Brillouin light scattering arises from the coupled interaction between light and material acoustic phonons. The measurand of Brillouin scattering is the characteristic frequency difference between incident and scattered light which depends on the local longitudinal modulus of the material. Spontaneous Brillouin scattering has been used in combination with confocal microscopy to provide non-contact, label-free mapping at micron-scale resolution in biological media. To date, spontaneous Brillouin microscopy has reached the speed limit (~20-50ms per spectrum) as determined by the theoretical scattering efficiency. While a great deal of research has been directed to speeding up Brillouin microscopy acquisition times, spontaneous Brillouin scattering is fundamentally an inefficient process thus limiting the ability to study faster biological phenomena and rapid processes. To combat this limitation, its nonlinear counterpart, stimulated Brillouin scattering (SBS) has been proposed for microscopy applications. For decades, stimulated Brillouin scattering has been used in fiber sensing and all-optical pulse control and leverages a nonlinear interaction where two counterpropagating light beams stimulate a more efficient scattering relationship. However, the small interaction volumes and photodamage constraints presented in microscopy have hindered the translation of stimulated Brillouin scattering into the biological realm. Recently, continuous wave stimulated Brillouin microscopy has led to competitive acquisition times (~5ms per spectrum) when compared to the spontaneous alternative but has yet to be widely adopted. Due to a plethora of factors, such as an inefficient power balance between pump and probe beams, lack of proper commercial laser sources, and nonoptimal detection schemes, the complete picture of what SBS spectroscopy has to offer has yet to be revealed. As such, there is a need to customize light sources and detection schemes in order to fully take advantage of the enhanced Brillouin efficiency possible in SBS. Herein we introduce novel methodology to improve the acquisition speed of Brillouin microscopy by designing and developing proper laser sources and detection schemes for efficient SBS spectroscopy. First, we showcase the potential utility of our state-of-the-art continuous wave SBS technology in a flow cytometry application, highly suitable for the counterpropagating geometry of SBS where the laser position is fixed while the sample is being moved at high speeds. Additionally, we will present an optimized receiver design based on polarization detection which enables 100x faster spectral measurements in the low-gain regime relevant to biological materials. Finally, we demonstrate an optimal pulsed laser source specifically designed for SBS Brillouin microscopy.Item SPECTROSCOPY OF TWO LEVEL DEFECTS & QUASIPARTICLES IN SUPERCONDUCTING RESONATORS(2021) Kohler, Timothy; Osborn, Kevin D; Anlage, Steven; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Superconducting films are inherently limited by losses due to two-level system (TLS) defects within the amorphous oxide layers surrounding them and from quasiparticles in the film. In this thesis I will discuss novel theoretical and experimental methods toward understanding superconducting resonator loss from deleterious surface TLS defects as well as a loss transition from non-equilibrium quasiparticles in granular TiN. I will show using finite element solver software that a resonator with submicron linewidth and linespacing can be used to better characterize and simulate surface TLS as part of a circuit QED system. I have observed individual surface TLS and found coupling values in the range of g/2π =50 kHz -280 kHz with a maximum dipole moment pz-max = 4.5 Debye (.93 eÅ). I have found in in simulation of experiment that over 80% of the strongly coupled TLS reside within 50 nm of the corner between the Metal-Substrate (MS) and Substrate-Air (SA) interface. Additionally I have studied a loss transition from non-equilibrium quasiparticles in TiN films. These films exhibit an anomalous loss dependence on substrate treatment and film thickness. The films of interest are ones grown thin on oxidized substrates, which exhibit an order of magnitude decrease in internal quality factor (Qi) relative to either thicker ˝films or films grown without the oxidized substrate. These films additionally exhibit a grain size on average of 7.5 nm, a higher inhomogeneous gap, a transition to lower stress and a preference for the [111] crystal growth. The temperature dependence of the conductivity is fit and a factor of two difference in quasiparticle lifetime is found between the two films where the thinner film has a shorter lifetime. A two gap quasiparticle trapping model is fit to the temperature dependent loss data. The data is consistent with a model where non-equilibrium quasi-particles are trapped in low gapped grains on the inside of the films. From these works and others presented in my thesis the understanding of TLSs on surfaces and non-equilibrium quasiparticles in TiN has improved. This will help illuminate some of the most important absorption mechanisms plaguing superconducting qubits and resonators.Item TAILORING LOCALIZED SURFACE PLASMON RESONANCES IN METALLIC NANOANTENNAS(2020) Zhang, Kunyi; Rabin, Oded; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The strong localized electromagnetic field achievable with metallic nanoantennas provides new opportunities for harmonics generation and label-free chemical sensing. In this work, the localized surface plasmon resonances (LSPRs) of metallic nanoarcs on dielectric substrates have been systematically investigated with visible and infrared spectroscopy, with the goal of elucidating the relationship between the structural and material parameters of the nanoarcs and their resonances. The transmission spectra provide rich information regarding the fundamental and higher order LSPR modes. Experimental results and numerical simulations demonstrate that the LSPR wavelengths are governed by the mid-arc length of the nanoarcs, and the extinction cross-sections of the different order modes are controlled by the central angle of the nanoarc and the symmetry of the mode. The fundamental and second order LSPR wavelengths can be tuned independently through the design of a non-uniform arc-width profile. Several relationships between features of the LSPR modes and the geometric parameters of nanoarcs are also confirmed by transformation optics analysis. The newly found relationships are then utilized as guidelines for the realization of plasmonic nanoarc antennas exhibiting efficient second harmonic generation (SHG). In another application, strong coupling between LSPRs and molecular vibrations is evident in the IR spectra of plasmonic nanoarcs placed in contact with a thin film of polymer, a native oxide layer or a thiol monolayer, enhancing the vibrational mode signals. This observation suggests that by appropriately tuning the frequency of the LSPR modes, the localized electromagnetic field around nanoarcs can resonantly couple to another emitter to boost its far-field radiation, which could benefit applications requiring highly localized, sensitive and selective chemical detection.