First observations with a new imaging polarimeter

We present first observations of solar polarization with a new imaging polarimetry system that simultaneously records three Stokes components, I , Q, V or I , U , V , in a single CCD. This instrument is an intermediate version on the way to ZIMPOL II (Zürich Imaging Stokes Polarimeter II), which will record all four Stokes parameters (Stenflo et al. 1992). The principle of operation is based on a piezoelastic polarization modulator in combination with a special CCD sensor equipped with a microlens array and a mask. This sensor is used as a synchronous demodulator. The theoretical performance of the instrument is discussed. Laboratory tests as well as initial solar observations at two different solar telescopes are presented and analysed to experimentally evaluate the performance. The polarimetric accuracy is better than 10−4, a noise level of 2×10−5 has been achieved; the polarimetric efficiency is in agreement with theory.