Metasurfaces for polarization aberration correction for the Habitable Worlds Observatory

Abstract

Polarization aberrations can limit coronagraphic contrast and can influence engineering choices made for large space telescopes such as the Habitable Worlds Observatory. These engineering choices include primary-secondary mirror distance, splitting of polarization channels, focal plane mask type, and mirror coatings. These choices have major impacts on the telescope’s throughput and cost, directly affecting exoplanet discovery yield. In this paper, we show the capability to directly compensate for polarization aberrations using a reflective metasurface in a bench-top Michelson interferometer with a polarization camera. The metasurface consists of a thin nanopatterned layer of SiO2 on aluminum. Specifically, we show a reduction of the rms linear retardance in an optical beam from 1.31 nm to 0.59 nm at a 500 nm wavelength. We note that this performance in the initial demonstration is likely limited by the engineering of the testbed, rather than the capability of the metasurface technology. We show that the metasurface itself only causes a <2% loss of light and show the potential for broadband performance over a ≥20% bandwidth.