Calibration of Liquid Crystal Visible-light Polarimeter for Metis/Solar Orbiter Coronagraph

Casti, M.;Fineschi, S.;Capobianco, G.;Landini, F.;Romoli, M.;Antonucci, E.;Andretta, V.;Naletto, G.;Nicolini, G.;Spadaro, D.;Alvarez-Herrero, A.;Garcia-Parejo, P.;Marmonti, M. 2018. Calibration of Liquid Crystal Visible-light Polarimeter for Metis/Solar Orbiter Coronagraph. Conference on Space Telescopes and Instrumentation – Optical, Infrared, and Millimeter Wave, 10698, DOI: 10.1117/12.2325075

Metis is the solar coronagraph selected for the payload of the ESA Solar Orbiter mission. Metis will acquire simultaneous imaging in linearly polarized, broadband visible light (580-640 nm) and in the narrow-band HI Ly-alpha line (121.6 nm). The METIS visible light path includes a polarimeter, designed to observe and analyse the K-corona linearly polarized by Thomson scattering. The polarimeter comprises a liquid crystal Polarization Modulation Package (PMP) together with a quarter-wave retarder and a linear polarizer. The Metis PMP consists of two Anti-Parallel Nematic Liquid Crystal Variable Retarders (LCVRs) with their fast axis parallel with respect to each other and a pre-tilted angle of the molecules in opposite direction. The LCVRs provide an electro-optical modulation of the input polarized light by applying an electric field to the liquid crystal molecules inside the cells. A given optical retardance can be induced in the LCVRs by selecting a suitable voltage value. This presentation will report the polarimetric characterization of the Flight Model of the Metis polarimeter and the voltage-to-retardance calibration.

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