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arXiv · 2610.29628

Optimization of Petal-Shaped Occulters for Exo-Earth Observation

Simon Prunet·Céline Theys·Claude Aime
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Abstract

Petal-shaped occulters are giant, formation-flying optical devices designed for use in space astronomy. Their primary function is to block the intense starlight to enable the direct observation of exoplanets, a process challenged by the extreme contrast ratio (lower than 1e-10 for an exo-Earth). This study focuses on optimizing the shape of the occulter in order to significantly reduce Fresnel diffraction. For a circular occulter, the diffraction pattern shows the bright Arago spot. Nevertheless, we construct an apodized occulter as the weighted sum of circular occulters of various diameters, owing to the fact that their diffraction are complex amplitudes which can, with adequate weighting, interfere with each other in such a way as to form a resulting diffraction pattern with a very dark central area. This basis of circular occulters allows the use of a simple analytical form for their Fresnel diffraction. First, occulter diameters are fixed on a regularly sampled linear scale, and the weights are obtained by minimizing a quadratic criterion. An improvement is then obtained using a combined optimization over the weights and the diameters sizes. Eventually, the apodized profile is used to design the petal-shaped occulter for physical imple- mentation constraints. The resulting rejection rates are comparable to the results obtained using SISTER ( http://sister.caltech.edu ), which uses a completely different non-parametric approach.

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Simon Prunet, Céline Theys, Claude Aime. 2026-10-21. Optimization of Petal-Shaped Occulters for Exo-Earth Observation. https://doi.org/10.1117/12.3101753

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