Black silicon characterization for coronagraphs

The Habitable Worlds Observatory (HWO) flagship mission plans to image and spectrally characterize earth-like exoplanets at 10⁻¹⁰ planet-to-star contrast with a coronagraph instrument. HWO’s 6-meter primary mirror will mostly likely be segmented for launch-related mass and packaging constraints. To suppress the extra diffraction from the primary mirror segmentation, a pupil apodizer mask could be used as part of several coronagraphic architectures. Reflective amplitude apodizers using cryogenic black silicon have already been flight qualified to 4 × 10⁻⁹ contrast for the Roman Space Telescope. In this paper, we detail our laboratory experiments and numerical simulations to characterize the amount of stray light from black silicon at levels relevant to HWO’s contrast budget.