Full characterization of the instrumental polarization effects of the spectropolarimetric mode of SCExAO/CHARIS

Joost G. J. 't Hart; Rob G. van Holstein; Steven P. Bos; Jasper Ruigrok; Frans Snik; Julien Lozi; Olivier Guyon; Tomoyuki Kudo; Jin Zhang; Nemanja Jovanovic; Barnaby Norris; Marc-Antoine Martinod; Tyler D. Groff; Jeffrey Chilcote; Thayne Currie; Motohide Tamura; Sébastien Vievard; Ananya Sahoo; Vincent Deo; Kyohoon Ahn; Frantz Martinache; Jeremy Kasdin

doi:10.1117/12.2602859

9 August 2021 Full characterization of the instrumental polarization effects of the spectropolarimetric mode of SCExAO/CHARIS

Joost G. J. 't Hart, Rob G. van Holstein, Steven P. Bos, Jasper Ruigrok, Frans Snik, Julien Lozi, Olivier Guyon, Tomoyuki Kudo, Jin Zhang, Nemanja Jovanovic, Barnaby Norris, Marc-Antoine Martinod, Tyler D. Groff, Jeffrey Chilcote, Thayne Currie, Motohide Tamura, Sébastien Vievard, Ananya Sahoo, Vincent Deo, Kyohoon Ahn, Frantz Martinache, Jeremy Kasdin

Author Affiliations +

Proceedings Volume 11833, Polarization Science and Remote Sensing X; 118330O (2021) https://doi.org/10.1117/12.2602859
Event: SPIE Optical Engineering + Applications, 2021, San Diego, California, United States

Abstract

SCExAO at the Subaru telescope is a visible and near-infrared high-contrast imaging instrument employing extreme adaptive optics and coronagraphy. The instrument feeds the near-infrared light (JHK) to the integralfield spectrograph CHARIS. The spectropolarimetric capability of CHARIS is enabled by a Wollaston prism and is unique among high-contrast imagers. We present a detailed Mueller matrix model describing the instrumental polarization effects of the complete optical path, thus the telescope and instrument. From measurements with the internal light source, we find that the image derotator (K-mirror) produces strongly wavelength-dependent crosstalk, in the worst case converting ∼95% of the incident linear polarization to circularly polarized light that cannot be measured. Observations of an unpolarized star show that the magnitude of the instrumental polarization of the telescope varies with wavelength between 0.5% and 1%, and that its angle is exactly equal to the altitude angle of the telescope. Using physical models of the fold mirror of the telescope, the half-wave plate, and the derotator, we simultaneously fit the instrumental polarization effects in the 22 wavelength bins. Over the full wavelength range, our model currently reaches a total polarimetric accuracy between 0.08% and 0.24% in the degree of linear polarization. We propose additional calibration measurements to improve the polarimetric accuracy to <0.1% and plan to integrate the complete Mueller matrix model into the existing CHARIS post-processing pipeline. Our calibrations of CHARIS’ spectropolarimetric mode will enable unique quantitative polarimetric studies of circumstellar disks and planetary and brown dwarf companions.

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Joost G. J. 't Hart, Rob G. van Holstein, Steven P. Bos, Jasper Ruigrok, Frans Snik, Julien Lozi, Olivier Guyon, Tomoyuki Kudo, Jin Zhang, Nemanja Jovanovic, Barnaby Norris, Marc-Antoine Martinod, Tyler D. Groff, Jeffrey Chilcote, Thayne Currie, Motohide Tamura, Sébastien Vievard, Ananya Sahoo, Vincent Deo, Kyohoon Ahn, Frantz Martinache, and Jeremy Kasdin "Full characterization of the instrumental polarization effects of the spectropolarimetric mode of SCExAO/CHARIS", Proc. SPIE 11833, Polarization Science and Remote Sensing X, 118330O (9 August 2021); https://doi.org/10.1117/12.2602859

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