High-Contrast Coronagraphy

Imaging terrestrial exoplanets around nearby stars is a formidable technical challenge, requiring the development of coronagraphs to suppress the stellar halo of diffracted light at the location of the planet. In this review, we discuss the science requirements for high-contrast imaging, present an overview of diffraction theory and the Lyot coronagraph, and define the parameters used in our optimization. We discuss the working principles of coronagraphs both in the laboratory and on-sky with current high-contrast instruments, and we describe the required algorithms and processes necessary for terrestrial planet imaging with extremely large telescopes and proposed space telescope missions: ▪ Imaging terrestrial planets around nearby stars is possible with a combination of coronagraphs and active wavefront control using feedback from wavefront sensors. ▪ Ground-based 8–40 m class telescopes can target the habitable zone around nearby M-dwarf stars with contrasts of 10 −7 , and space telescopes can search around solar-type stars with contrasts of 10 −10 . ▪ Focal plane wavefront sensing, hybrid coronagraph designs, and multiple closed loops providing active correction are required to reach the highest sensitivities. ▪ Polarization effects need to be mitigated in order to reach 10 −10 contrasts while keeping exoplanet yields as high as possible. ▪ Recent technological developments, including photonics and microwave kinetic inductance detectors, will be folded into high-contrast instruments.