Polarimetric observations of the Sun in He I 1083 nm line with LiNbO3 Fabry-Perot filtergraph and rotating waveplate

Le résumé fourni par la source

In order to derive solar magnetic fields, a 2D spectro-polarimeter working in the near-infrared wavelength range is under development. A voltage-wavelength-tunable lithium-niobate (LiNbO3) etalon filtergraph is used as the 2D spectrometer. A rotating waveplate for modulating the polarization is used, which has a nearly constant retardation of about 127 degrees over a wide wavelength range. The filtergraph consists of two etalons, 0.9 mm and 1.2 mm thick, optimized for ordinary ray transmission for both the He I 1083 nm chromospheric line and the photospheric magnetic-sensitive line of Fe I 1564 nm when used in tandem-etalon configuration. The etalons are Y-cut LiNbO3 wafers coated with reflective and conductive (ITO) layers. A linear polarizer between the rotating retarder and the filtergraph functions as a polarization analyzer and selects the ordinary ray transmission. We carried out polarization observations of solar active regions at several wavelength points in the He I 1083 nm line with a high-speed IR camera at Hida Observatory, Kyoto University. Some observational results together with the instrumental properties are presented.

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