High-precision & fast polarization measurements by SUNRISE-3/SCIP

Polarization measurements of the solar chromospheric lines at high precision is one of the key observations by future solar telescopes for understanding the magnetic field structures in the chromosphere. The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) for SUNRISE-3 is a slit-scanning spectropolarimeter that simultaneously observes multiple lines in the 770 nm band and the 850 nm band with a polarimetric precision of 0.03% (1σ). By combining polarization data in these two bands, we can obtain three-dimensional magnetic field structures in the photosphere - chromosphere. Polarization modulation is performed by a rotating wavelength plate in front of the slit, and two orthogonal polarizations are simultaneously measured by two polarization beam splitters placed in front of two CMOS cameras observing two wavelength bands. The retardation of the waveplate is almost constant in the wavelength bands of SCIP, and its variation in the range of the operational temperature (20 ° C. ± 10 ° C.) is small. The polarization beam splitter realizes the high extinction ratio (> 1:100) with a relatively simple and compact optics. The rotation mechanism that rotates the waveplate uniformly sends an exposure synchronization signal to SCIP electronics (SCIP-E). By using this signal SCIP-E performs the synchronous control among three CMOS cameras, on-board data processing, and a scan mirror mechanism. In the case of SCIP, 16 exposures are done by the cameras in one waveplate rotation of 0.5s, and the on-board demodulation and data compression are performed for 2k x 2k images. The fast polarization modulation and associated high-speed synchronous control are essential for the investigations of the magnetic fields of the dynamical chromospheric structures.