We are developing a high sensitivity and fast readout near-infrared (NIR) detector and an integral field unit (IFU) for making spectro-polarimetric observations of rapidly varying chromospheric spectrum lines, such as He I 1083 nm and Ca II 854 nm, in the next space-based solar mission SOLAR-C. We made tests of a 1.7 μm cutoﬀ H2RG detector with the SIDECAR ASIC for the application in SOLAR-C. It’s important to verify its perfor- mance in the temperature condition around -100 °C, which is hotter than the typical temperature environment used for a NIR detector. We built a system for testing the detector between -70 °C and -140 °C. We verified linearity, read-out noise, and dark current in both the slow and fast readout modes. We found the detector has to be cooled down lower than -100 °C because of significant increase of the number of hot pixels in the hotter environment. The compact and polarization maintenance IFU was designed using fiber-optic ribbons consisting of rectangular cores which exhibit good polarization maintenance. A Silicone adhesive DC-SE9187L was used to hold the fragile fiber-optic ribbons in a metal housing. Polarization maintenance property was confirmed though polarization calibration as well as temperature control are required to suppress polarization crosstalk and to achieve the polarization accuracy in SOLAR-C.
We developed a new universal spectropolarimeter on the Domeless Solar Telescope at Hida Observatory to realize
precise spectropolarimetric observations in a wide range of wavelength in visible and near infrared. The
system aims to open a new window of plasma diagnostics by using Zeeman effect, Hanle effect, Stark effect, and
impact polarization to measure the external magnetic field, electric field, and anisotropies in atomic excitation
in solar atmosphere. The polarimeter consists of a 60 cm aperture vacuum telescope, a high dispersion vacuum
spectrograph, polarization modulator and analyser composed of a continuously rotating waveplate whose
retardation is constant in 400 - 1100 nm and Wallaston prisms located closely behind the focus of the telescope,
and a fast and high sensitive CCD camera or a infrared camera. The duration for this polarimeter's achieving
photometric accuracy of 10-3 is 30 - 60 s. Instrumental polarization of the telescope is calibrated by using a
remotely controllable turret accommodating linear polarizer attached at the entrance window of the telescope to
induce well known polarized light into the telescope. Thus a Mueller matrix model of the telescope is established
to compensate the instrumental polarization included in observed data within the required accuracy.