Physics Theses

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This collection is made up of doctoral and master theses by research, which have been received in accordance with university regulations.

For more information, please visit the UCD Library Theses Information guide.

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Now showing 1 - 5 of 31
  • Publication
    Hardware and Embedded Firmware Development of a Gamma-Ray Burst Detector for a 2U CubeSat
    (University College Dublin. School of Physics, 2022)
    Gamma-ray bursts (GRBs) are among the most extreme energetic events in the universe and represent the death knell of massive stars and compact objects. In one scenario, a massive and ancient star has burnt through its fuel reserve resulting in a core collapse event, a supernova. In the other, massive compact binary objects, like black hole - black hole (BH-BH), neutron star - black hole (NS-BH) and NS-NS pairs coalesce through merger events caused by the radiation of gravitational energy. In both cases a GRB may be observed. If the object is orientated just right, a beamed emission directed towards Earth may be detectable as a sudden, intense but brief flash of gamma-ray photons with a later afterglow emission observable in longer wavelengths for days to weeks after the initial event. The advent of gravitational wave astronomy as a multi-messenger for high-energy astrophysical phenomena, along side recent advancements towards the miniaturisation of detector technology, have made it possible for CubeSat missions to perform cost-effective and fruitful science. Furthermore, widely accessible commercial-off-the-shelf hardware allows small non-agency institutions and universities to build robust missions with custom payloads for technology demonstrations and to contribute to the aims of the scientific community alongside traditional flagship missions. The Gamma-Ray Module (GMOD) is a CubeSat compatible, scintillation based gamma-ray detecting instrument, with dimensions <1U (less than 10 cm x 10 cm x 10 cm). GMOD has been developed primarily for the detection of GRBs and other high-energy electromagnetic phenomena from Earth orbit. This thesis will introduce GMOD through its origin, development and testing, its mission objectives and future outlook, all with respect to the astrophysical context of current high-energy astronomy and instrumentation. During its mission, GMOD will experience the mechanical stresses induced during its launch, deployment and the sustained thermal and radiation effects of the harsh space environment. Furthermore, the instrument firmware will be expected to perform over long durations, often operating continuously for weeks on end. The instrument must be capable of performing effectively and to operate continually without disruption to the handling of science data. To achieve this, several tests have been conducted including a high altitude balloon flight, SiPM irradiation testing, subsystem thermal vacuum and vibration testing and a full benchmarking of the firmware performance and response to simulated GRB events. The GMOD hardware has been fully tested in accordance with European Space Agency standards and the firmware has been rigorously assessed, while the methodology has been subject to peer-review. GMOD has been accepted for flight and will be flown in 2023 onboard EIRSAT-1, Ireland’s first satellite, with an expected detection yield of ~11–14 GRB triggers at 10σ significance. Once in operation, GMOD will contribute to the high-energy astronomy community and will be a demonstrator for future GRB detecting instruments.
      11
  • Publication
    Angle-resolved studies of tin laser plasma extreme ultraviolet sources
    (University College Dublin. School of Physics, 2008)
    The work presented in this thesis is primarily concerned with the radiation and ions emitted by laser produced plasmas (LPPs) containing tin. If the semiconductor manufacturing industry is to meet Moore’s law (a doubling in the number of transistors per square inch on integrated circuits every two years), new lithographic techniques are required. EUV lithography (EUVL) shows the most promise, requiring a bright source of radiation in the 2% band centered at 13.5 nm, known as in-band radiation. This is due to the high reflectivity of molybdenum/silicon multilayer mirrors at these wavelengths. Tin-based LPPs have been shown to emit strongly in the in-band region. Chapter 2 presents a unique optical system with the ability to present a range of observing angles to a fixed detector, while maintaining normal incidence for the laser onto a planar solid target. This allows the system to be rotated, with respect to a fixed detector, while maintaining spatially stable plasma formation. Chapter 3 presents absolute intensity measurements of in-band radiation, emitted from pure tin laser produced plasmas, for a range of angles. Also measured is the angular distribution of intensities from 10 to 18 nm. Light, from outside the 2% band at 13.5 nm in this region, will result in flare at the resist in extreme ultraviolet lithography, thus limiting the feature resolution attainable. Two of the main problems facing next generation lithography are thermal and debris mitigation. Sn-based LPPs are highly emissive in the region of 100 to 3000 nm, where the multilayer optics can be highly reflective. This out-of-band (OOB) radiation can cause flare, heat the wafer and create overlay issues. It is necessary to quantify the levels of OOB radiation, over a range of wavelength regions, to facilitate the development of suitable optical components that will reduce the OOB radiation at the wafer plane to acceptable levels. Chapter 4 presents the angular distributions of OOB radiation for a range of wavelength regions between 200 and 1000 nm. Also, ions that are emitted from these LPPs may cause significant damage to the components in a real world projection lithography system. Fast ions, impinging on multilayer optics, can lead to the sputtering of mirror layers and debris deposited on multilayer optics and can degrade in-band reflectivity. In order to effectively mitigate this damage it is necessary to know the speed and direction of the emitted ions. The angular distribution of the total number of ions, from Sn1+ to Sn9+, emitted from a Snbased LPP, is investigated in Chapter 5. The charge state, energy and relative number of these ions have also been determined. In order to facilitate comparison between EUV, OOB and ion data in chapters 3, 4 and 5, the measurements in these chapters were performed at approximately equal plasma conditions. This comparison is explored and detailed in Chapter 6.
      30
  • Publication
    Time-resolved studies of colliding laser-produced plasmas
    (University College Dublin. School of Physics and Czech Technical University in Prague, 2018)
    This thesis presents work done on investigating colliding laser-produced plasmas with time-resolved, UV-visible spectroscopy and time-resolved visible imaging. A nanosecond Nd:YAG laser pulse was split with a wedge prism and the two laser pulses created were focused onto the target surface, with power densities of ϕ = 1:6 x 10^12 W/cm2. The separation between the two plasmas was 2.6 mm and in between them a stagnation layer was formed. Plasmas of silicon (Si, Z=14), tin (Sn, Z=50) and lead (Pb, Z=82) were investigated. Time-resolved spectroscopy was used to determine the expansion velocities for different ion stages of Si and Pb, for both single plasmas as well as in the case where two plasmas collided to yield stagnation layers. Time-resolved visible imaging was used to obtain the expansion velocities of both seed plasmas and stagnation layers plasma-plume front. Colliding plasmas of different elements, Pb and Si, were studied and expansion velocities of different ion stages were compared with those obtained for colliding two identical plasmas. Acceleration of ions due to an electric potential difference is observed in the stagnation layer. Obtaining information about expansion velocities of different ion species provides great insight into the dynamics of laser-produced plasma expansion. Charge and time resolved dynamics have not been used before to study stagnation layers.
      20
  • Publication
    Observations of Circumstellar Interaction in Diverse CCSNe
    (University College Dublin. School of Physics, 2022) ;
    0000-0002-1178-2859
    In this thesis, I investigate the observational properties of two supernovae displaying strong signatures of interaction with circumstellar material, and how they contribute to furthering our understanding of their respective subtypes. The first part of this thesis concerns the photometric and spectroscopic analysis of SN 2018zd. I coordinated the follow-up campaign for this object on behalf of the NUTS collaboration, acquiring hours of observations in the UV through NIR bands. I determine that this transient event is the result of the Fe core collapse of a 8-10M¿ red supergiant. The high ionisation lines observed in the early epochs of spectra are the observational signature of delayed shock breakout through circumstellar material detached from the progenitor envelope. Finally, I compare SN 2018zd to the sample of objects known as LLEV’s, luminous low expansion velocity transients; these objects have an enhanced plateau magnitude relative to their expansion velocities due to the extra photon source provided by early time interaction with circumstellar material. This enhanced plateau luminosity affects the inclusion of these objects in samples used to derive correlations from “normal” Type II SN characteristics. One such relationship we investigate is the Standard Candle Method, which can be used to estimate distances to Type IIP SNe where spectra are lacking, and we show that SN 2018zd breaks this correlation. I propose that a caveat should be attached to the Standard Candle Method, and other similar photometric distance estimate methods for Type IIP SNe, that in the absence of early spectral observations to rule out interaction with circumstellar material, strict cuts should be applied to the light curves of these transients before they are included in such samples. The second half of this thesis concerns the analysis of an archival dataset for SN 2015G, comprising of one of the highest cadence and lengthy follow-up campaigns of a Type Ibn SNe to date. SN 2015G was one of the closest observed Type Ibn’s at a distance of ~20.9 Mpc, allowing for prolonged observations of the tail phase, up to approximately six and a half months after discovery. We observed undulations in the light curve, and determine that these are the result of prolonged interaction with circumstellar material ejected shortly prior to the SN explosion. This excludes production of the circumstellar material via smooth progenitor winds, and we conclude that the material was most likely stripped by a binary companion. The results presented in this thesis span nearly the full range of possible circumstellar interaction scenarios, from the very brief, early interaction of SN 2018zd, to the interaction observed in SN 2015G which endured for the entire follow-up campaign. Both studies further our understanding of how interaction affects the evolution of transients; they bolster the broad diversity possible even within well established subtypes of SNe, and act as an all important reminder that our understanding of these subtypes is still limited by the cadences, duration, and wavelength coverage of our observational follow-up capabilities.
      82
  • Publication
    Observational constraints on Supernovae and Supernova Impostors
    (University College Dublin. School of Physics, 2022) ;
    0000-0003-1325-6235
    This thesis focuses on the observational campaign for the interacting transient AT 2016jbu, and the development and workings of a novel automated photometry code, AutoPhOT. We provide an overview of the current stellar evolutionary theory and transient astronomy, including a brief section on photometry, in Chapter 1. Chapter 2 covers the Automated Photometry Of Transients (AutoPhOT) photometric pipeline. This software package was designed to provide a fast, precise, and accurate means for the modern astronomer to measure the magnitude of astronomical point sources. We demonstrate the modern photometric techniques implemented in the code, and its capabilities to produce publication ready data with little human interaction. Chapters 3 and 4 cover the observational campaign for the interacting transient, AT 2016jbu. This transient was observed almost a decade before it exploded, allowing for strong constraints on the progenitor. Comparing to the current stellar evolutionary theory, this star is not expected to explode as a core collapse supernova, and one must question whether we are observing the death of a star at all. We present the multi-chromatic dataset for AT 2016jbu in Chapter 3 and compare with similar transients. Chapter 4 focuses on modelling the progenitor for AT 2016jbu and using a high quality, high cadence dataset, we attempt to model the transient, producing a self-consistent explosion model, that may be applied to similar transients. In Chapter 5, we present observations from the Hubble Space Telescope almost 5 years after its apparent demise. The goal of these measurements was to address whether the progenitor may have survived the 2016 events, and is now enshrouded by massive amounts of dust formed in the ejecta of AT 2016jbu. We find a unrealistic amount of dust (for a non-terminal explosion) is needed to hide the progenitor. We conclude that AT 2016jbu is indeed a genuine, albeit strange, terminal explosion and further investigate a possible explosion scenario, focusing on massive stars within a binary system. Chapter 6 provides a general overview of the most salient findings found during this thesis and comments on future work.
      121