Liquid Crystal Polarimeter for Solid-State Imaging of Solar Vector Magnetic Fields.

摘要

The Liquid Crystal Polarimeter (LCP) is a low-voltage complete Stokes polarimeter and spectral analyzer designed for measuring solar vector magnetic fields. The polarimeter consists of polarization and spectral analyzer sections each containing multiple commercially available nematic and ferro-electric liquid crystals that are modulated in phase at up to 31.5 kHz frequency. Used in conjunction with a Lyot birefringent filter and 2 CCDs, the system provides a complete polarization/spectral measurement for solid-state direct imaging of the vector magnetic flux, Doppler velocity, intensity, and line width in a spectral line. Simultaneous 2 CCD imaging gives reduced atmospheric seeing systematics, and automatic CCD gain and dark-current correction. The liquid-crystal design provides a considerable simplification to previous designs with greatly improved speed, sensitivity, reliability, and accuracy. The system is used with a universally tunable Lyot filter (of conventional rotating-element design) to provide sequential observations in a number of solar lines to permit calibration of field strength and measurements as a function of height in the solar atmosphere. An example vector magnetogram is shown as a proof of concept.