Development of a High-Contrast Adaptive Optics Phasing Testbed for the Giant Magellan Telescope

Abstract

Our galaxy hosts ∼ 300 billion stars. Ever since the first exoplanet was discovered in 1992, over 5,000 more exoplanet discoveries have been confirmed, and the number is still counting. As each new exoplanet is discovered, the case seems more and more likely that each star in our Milky Way galaxy must have at least one exoplanet orbiting around it. Many of these exoplanets also fall into the potentially habitable, terrestrial size category, meaning there could be billions of earth like planets waiting to be discovered. If we hope to discover life outside of our solar system, it has been shown that directly imaging these potentially habitable exoplanets in visible light reflected from its host star is optimal. This is very possible, however difficult, since this requires Extremely Large Telescopes (ELTs; ∼30m in diameter) to achieve high angular resolutions and contrasts, extreme adaptive optics (ExAO) to suppress the effects of atmospheric seeing, and coronagraphy to block the starlight. These three technologies could coexist once the 25.4-m Giant Magellan Telescope (GMT) is completed in 2029. With the combined power of ExAO and the future GMT, the discovery of life outside of our solar system may become a reality. However, the GMT’s unique seven segmented primary mirror design raises a challenge to keep the telescope segments co-phased—a task which is critical for direct imaging of exo-earths and any other diffraction-limited science with the GMT. This dissertation addresses the challenge of co-phasing a giant segmented telescope for exoplanet imaging and describes the development of a High-Contrast Adaptive optics phasing Testbed (HCAT) for the GMT. The testbed simulates the GMT with real optics in a lab environment with six piston, tip, and tilt actuators and tests a working concept for a “parallel deformable mirror” to optically redistribute the GMT pupil onto seven commercially available 3,000 actuator deformable mirrors. HCAT also leverages an existing ExAO system called MagAO-X to test and demonstrate segment phase sensing and AO-control with a real ExAO system. I will first introduce the GMT and the “piston problem.” Then, I will give an introduction to adaptive optics and discuss the design and build of MagAO-X. I will then discuss the development of an early stage GMT proto-testbed which was a simple GMT simulator that provided insight into co-phasing a segmented telescope. This early stage GMT proto-testbed evolved into the official prototype version of HCAT (p-HCAT), which led to the development of a new phasing method for co-phasing the GMT using a novel optic called the “Holographic Dispersed Fringe Sensor” (HDFS). The success of the demonstrations performed with p-HCAT and the novel HDFS are discussed. These results have influenced the GMT to adapt this phasing method as their official designated phase sensor for GMT exoplanet imaging. Finally, the design and build of the full-scale HCAT testbed will be described with a demonstration of the “parallel DM” working in the lab.