Polarization aberration modeling of black silicon apodizer masks

Diffraction artifacts from aperture segmentation will degrade contrast well above the 10^-10 requirement of the Habitable Worlds Observatory coronagraph instruments. Shaped pupil coronagraphs can theoretically meet this contrast by extinguishing select pupil regions while passing the rest. JPL developed reflective aluminum-coated silicon masks cryo-etched to produce black silicon, a highly absorptive metamaterial. The Roman Space Telescope will flight-qualify these masks at ~10^-8 contrast. Achieving 10^-10 contrast may require mask features only a few wavelengths wide, where mask optical behavior becomes anisotropic and polarization aberrations at reflective–absorptive boundaries cause leakage. We use FDTD simulations to characterize polarization aberrations induced by black silicon masks. We then estimate the resulting contrast degradation, establishing a lower limit on feature size and beam diameter, and explore geometry-tuning strategies to minimize polarization-induced leakage.