A differential-imaging polarimeter for high-contrast exoplanet imaging

Abstract

Starlight is generally unpolarized, but the light reflected from the planet is linearly polarized as the result of the Rayleigh scattering. For ground-based exoplanet imaging, atmospheres turbulence is changing from time to time, which induces speckle noise and hampers the high-contrast imaging of the faint exoplanets. In this paper, we propose a differential-imaging polarimeter dedicated for exoplanet high-contrast imaging. The system contains a zero-order half-wave plate (HWP) located on the optical pupil plane, which can rotate to modulate the incoming light, and a Wollaston prism (WP) is used to generate two polarized images, which is used for simultaneously polarization differential imaging and thus our system is fundamentally immune to the atmospheric turbulence induced temporally-variable wavefront aberration. Our polarimeter can be inserted near the telescope image focal plane, and provide an extra contrast for the exoplanet high-contrast imaging. To achieve best differential-imaging performance, dedicated algorithm is developed, which can effectively correct the distortion and the intensity unbalance between the two differential images. The system successfully achieves an extra contrast of ~30~50 times, which can be used with current adaptive optics and coronagraph system for directly imaging of giant Jupiter-like exoplanets.