Comparison of coronagraphs for high contrast imaging in the context of Extremely Large Telescopes

TL;DR

This paper compares various coronagraph designs for high contrast imaging on Extremely Large Telescopes, analyzing their robustness against errors and identifying the most promising options for exoplanet detection.

Contribution

It provides a comprehensive comparison of coronagraph concepts considering realistic error sources and proposes the Apodized Pupil Lyot Coronagraph as a suitable baseline for ELTs.

Findings

Amplitude-based coronagraphs generally perform better.

The Apodized Pupil Lyot Coronagraph is identified as a promising baseline.

Critical parameters for coronagraph performance are established.

Abstract

We compare coronagraph concepts and investigate their behavior and suitability for planet finder projects with Extremely Large Telescopes (ELTs, 30-42 meters class telescopes). For this task, we analyze the impact of major error sources that occur in a coronagraphic telescope (central obscuration, secondary support, low-order segment aberrations, segment reflectivity variations, pointing errors) for phase, amplitude and interferometric type coronagraphs. This analysis is performed at two different levels of the detection process: under residual phase left uncorrected by an eXtreme Adaptive Optics system (XAO) for a large range of Strehl ratio and after a general and simple model of speckle calibration, assuming common phase aberrations between the XAO and the coronagraph (static phase aberrations of the instrument) and non-common phase aberrations downstream of the coronagraph (differential aberrations provided by the calibration unit). We derive critical parameters that each concept will have to cope with by order of importance. We evidence three coronagraph categories as function of the accessible angular separation and proposed optimal one in each case. Most of the time amplitude concepts appear more favorable and specifically, the Apodized Pupil Lyot Coronagraph gathers the adequate characteristics to be a baseline design for ELTs.