Beyond the speckles: New horizons in high-contrast imaging for exoplanet science
Date
2025
Authors
Johnson, Adam B.
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Abstract
Direct imaging of exoplanets offers a uniquely powerful way of characterizing planetary atmospheres, surface conditions, and potential biological markers beyond our solar system. However, the extreme contrast and small angular separations involved present significant observational challenges that demand continual innovation in instrumentation and observing strategies. This dissertation addresses these challenges through a coordinated set of developments in instrumentation for focal plane wavefront sensing, post-processing, calibration systems, and atmospheric tomography.
The first contribution presents the design, implementation, and deployment of the SPIDERS instrument for the Subaru Telescope. This compact, modular platform integrates the fast atmospheric self-coherent camera technique (FAST), a Lyot-based low-order wavefront sensor (LLOWFS), and an imaging Fourier transform spectrometer (IFTS) to validate advanced wavefront control, spectral retrieval, and post-processing techniques. A custom ultra-low speed optical chopper (ULSOC) enables stable fringe modulation at subhertz frequencies, supporting focal plane wavefront sensing and coherent differential imaging (CDI). A dedicated motion control system further supports full-field broadband spectral acquisition through the IFTS.
The second major contribution focuses on the CAL 2.0 upgrade for the Gemini Planet Imager (GPI). The system incorporates adapted versions of the focal plane mask (FPM) wheel and polarization modulator (PolMod) from the original CAL architecture, along with a facility-class ULSOC, enabling real-time focal plane wavefront correction and enhanced post-processing. Informed by lessons from SPIDERS, these upgrades are expected to improve contrast by up to two orders of magnitude beyond current state-of-the-art systems for bright stars at small angular separations.
Finally, the dissertation introduces STARLITE, a mission concept for satellite-aided atmospheric tomography. STARLITE proposes a constellation of small satellites carrying laser beacons in highly elliptical orbits, periodically aligning with ground-based observatories to enable tomographic reconstruction of atmospheric turbulence. A feasibility study is presented, evaluating orbital mechanics, optical performance, and reconstruction fidelity, demonstrating STARLITE’s potential to support diffraction-limited, high-contrast imaging for small separation targets.
Together, these contributions advance the capabilities of direct imaging systems and establish a technical foundation for future instruments to probe terrestrial exoplanets and explore their potential for life with unprecedented precision.
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Keywords
Exoplanet direct imaging and spectroscopy, High-contrast imaging, Adaptive optics (AO), Coronagraphy, Focal plane wavefront sensing, Self-coherent camera (SCC), Imaging Fourier transform spectrometer (IFTS), Fast Atmospheric Self-Coherent Camera technique (FAST), Atmospheric tomography, Subaru Pathfinder Instrument for Detecting Exoplanets & Retrieving Spectra (SPIDERS), Gemini Planet Imager Calibration Unit 2.0 (GPI CAL 2.0), Superluminous Tomographic Atmospheric Reconstruction with Laser-beacons for Imaging Terrestrial Exoplanets (STARLITE)