Abstract of Junho Shin's Paper
A Universal Polarimeter Using Liquid Variable Crystal Retarders
at the Norikura Solar Observatory
Kazuya Shinoda, Kiyoshi Ichimoto, Takeo Fukuda and Junho Shin
National Astronomical Observatory, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
ABSTRACT
A universal Stokes polarimeter was developed for the 25-cm coronagraph of the
Norikura Solar Observatory. The polarimeter utilizes two liquid crystal variable
retarders (LCVR) as the polarization modulator and a Savart plate as the
polarization analyser. By controlling the voltages applied to LCVRs, modulations
of the polarization states are achieved more flexibly and efficiently in a
wavelength range of 450-1,600 nm. The polarimeter is installed at the primary
focus of the coronagraph to minimize the instrumental polarization caused by
optics. Two orthogonal polarization states are measured simultaneously to minimize
the effect of guiding errors and seeing effects. Combined with the coronagraph
and the high resolution spectrograph at the coude focus, the polarimeter enables
us not only observations of photospheric Zeeman effect but also various types of
diagnostics of the solar atmosphere, including coronal Zeeman effect, Hanle effect,
impact polarization, and Stark effect.