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    Wavefront Control Techniques for the Direct Imaging of Exoplanets

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    Author
    Rodack, Alexander Thomas
    Issue Date
    2022
    Keywords
    Adaptive Optics
    High Contrast Imaging
    Wavefront Control
    Advisor
    Males, Jared R.
    
    Metadata
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Embargo
    Release after 11/03/2022
    Abstract
    Over two decades ago, the first planet around a star other than the Sun was discovered. With each passing year, more and more such exoplanets are discovered as new technologies and methods of discovery are developed and enhanced. As these techniques continue to mature, humanity gets closer to finally being able to answer the question: are we alone in the universe? Improvements to Adaptive Optics (AO) have enabled ground-based observation to expand to including high-contrast imaging instruments called coronagraphs that are meant to make the direct imaging of exoplanet light possible.Direct imaging is a method of observation that gives astronomers the ability to determine if a planet exhibits signatures of life via spectroscopic analysis for biomarkers. This is a difficult task for three major reasons: the planet orbits very close to its host star if it is located in the so-called habitable zone, the planet light is up to 10^-10 times fainter than the host star light, and static and quasi-static aberration being present during the observation degrades both coronagraph performance and post-processing technique efficacy. In this dissertation, I explore two methods for estimating non-common path aberration (NCPA) in the science instrument of AO enabled, ground-based telescopes. The first is a method called the Differential Optical Transfer Function (dOTF), which is a simple, non-iterative, non-interferometric technique to estimate the complex amplitude field in the exit pupil of an optical system exploiting the properties of the functional derivative of the Optical Transfer Function. dOTF is demonstrated in both simulation and lab based experiments, showing several possible applications, including AO system self calibration, segment cophasing, and estimating systematic NCPA using an off-axis light source. The second method is known as Frazin's algorithm, which is a statistical regression framework that uses wavefront sensor (WFS) and science camera (SC) telemetry with advanced computational models of optical systems to estimate any NCPA and any present exoplanet signals. I develop the history of the method starting from its inception in 2013 and its extension to potential real-time use in 2018, followed by the conception of an improved version that is fully realizable. Three separate estimators are presented within the framework, and then are demonstrated via comprehensive end-to-end simulation of an AO system running at 1kHz frame rate with a Lyot Coronagraph in the science arm. Finally, preliminary future extensions of the work done on Frazin's algorithm are presented to guide future steps to evolve the method to improve the current limits of ground-based direct imaging of exoplanets.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Optical Sciences
    Degree Grantor
    University of Arizona
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