Design and performance characterization of the fast solar polarimeter

IGLESIAS, F. A; FELLER, A.; NAGARAJU, K.; SOLANKI, S.K.

Otro; ASTRONOMICAL INSTRUMENTATION IN THE 21ST CENTURY; 2014

HEIDELBERG UNIVERSITY AND ESO

Due to the differential and non-simultaneous nature of polarization measurements, the errors introduced by seeing induced crosstalk (SIC) can easily counterbalance the benefits of ground based polarimetry. When a temporal modulation scheme is adopted, it has been shown that in spite of partial seeing correction by an adaptive optics system, only higher modulation frequencies can considerably reduce the SIC [1]. Following this line, and considering the success of pre-existing high-precision imaging polarimeters like ZIMPOL, we are developing the Fast Solar Polarimeter (FSP) [2]. The working prototype of FSP is a full-Stokes, single-beam imaging polarimeter with a modulator based on Ferroelectric Liquid Crystals (FLC) and a 264x264 pixels pnCCD sensor capable of recording up to 800 frames/s while keeping noise levels and systematic errors low enough to reach an intended polarimetric accuracy of 0.01%. The modulator, based on the successful SOLIS design, reaches total polarimetric efficiencies between ~0.79 and ~0.91 in the 400 nm to 860 nm range. Here we present the FSP main components, a numerical frame transfer correction technique, which allows the pnCCD camera to work without a shutter at a very high duty cycle of 95%, and the results of the first observing campaigns of the instrument.