Development of a Precise Polarization Modulator for UV Spectropolarimetry.

Ishikawa, S.; Shimizu, T.; Kano, R.; Bando, T.; Ishikawa, R.; Giono, G.; Tsuneta, S.; Nakayama, S.; Tajima, T.

We developed a polarization modulation unit (PMU) to rotate a waveplate continuously in order to observe solar magnetic fields by spectropolarimetry. The non-uniformity of the PMU rotation may cause errors in the measurement of the degree of linear polarization (scale error) and its angle (crosstalk between Stokes- $Q$ and - $U$), although it does not cause an artificial linear polarization signal (spurious polarization). We rotated a waveplate with the PMU to obtain a polarization modulation curve and estimated the scale error and crosstalk caused by the rotation non-uniformity. The estimated scale error and crosstalk were ${<}\, 0.01~\%$ for both. This PMU will be used as a waveplate motor for the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) rocket experiment. We confirm that the PMU performs and functions sufficiently well for CLASP.

ULTRAVIOLET spectrophotometry; ELECTRONIC modulators; LINEAR polarization; LAMB waves; CROSSTALK; SPECTROPOLARIMETERS

Solar Physics, 2015, Vol 290, Issue 10, p3081

0038-0938

Academic Journal

10.1007/s11207-015-0774-0