Solar polarimetry with ZIMPOL Plans for the future

ZIMPOL (Zurich Imaging Polarimeter) has been developed since the early 1990s, and various versions at increasing levels of sophistication have been used with great success at di erent telescopes (IRSOL, McMath-Pierce, DST, SST, VTT). The main idea behind ZIMPOL is to overcome the problem of making fast polarization modulation com- patible with the slow read-out of large-scale CCD sensors. This is done by creating fast, hidden bu er storage areas within the CCD, and by shifting the photo charges at kHz rates between the illuminated and the bu er storage areas in synchrony with the modulation. ZIMPOL is not dependent on the type of modulator used. Although most observations have been done with piezo-elastic modulators, FLCs and Pockels cells have also been used. A version of the ZIMPOL sensor with an array of cylindrical microlenses to optimize the ef- ficiency has recently been implemented. An overview is given of the present status and the future plans with the ZIMPOL systems.