# Design of a telescope-occulter system for THEIA

## TL;DR

This paper presents the design and optimization of occulters and coronagraphs for the THEIA space telescope mission, aiming to enhance direct imaging of terrestrial exoplanets with high starlight suppression.

## Contribution

It introduces two optimized occulter designs and evaluates hybrid occulter/coronagraph systems, advancing the technical feasibility for exoplanet imaging missions.

## Key findings

- Two optimized occulters achieve 10^-12 suppression over specified wavelength ranges.
- An AIC coronagraph can improve performance but requires precise manufacturing tolerances.
- Most other coronagraphs are infeasible due to non-plane wave residual starlight.

## Abstract

The Telescope for Habitable Exoplanets and Interstellar/Intergalactic Astronomy (THEIA) is a mission concept study for a flagship-class telescope-occulter system to search for terrestrial planets and perform general astrophysics with a space-based 4m telescope. A number of design options were considered for the occulter and telescope optical systems; in this paper we discuss the design of occulters and coronagraphs for THEIA and examine their merits. We present two optimized occulters: a 25.6m-radius occulter with 19m petals that achieves 10^-12 suppression from 250-1000nm with a 75mas inner working angle, and a 20.0m-radius occulter with 10m petals that achieves 10^-12 suppression from 250-700nm with a 75mas inner working angle. For more widely separated planets (IWA > 108mas), this second occulter is designed to operate at a second closer distance where it provides 10^-12 suppression from 700-1000nm. We have also explored occulter/coronagraph hybrid systems, and found that an AIC coronagraph that exploits the symmetry of the PSF at the occulter can improve performance; however, it requires very accurate tolerances on the occulter manufacturing of the telescope/occulter system as the AIC does not cancel asymmetric terms. Other coronagraphs proved infeasible, primarily due to the fact that the residual starlight from the occulter is not a plane wave, and so is poorly suppressed by the coronagraph.