An imaging polarimeter (IMPOL) for multi-wavelength observations

Abstract

Taking advantage of the advances in array detector technology, an imaging polarimeter (IMPOL) has been constructed for measuring linear polarization in the wavelength band from 400-800 nm. It makes use of a Wollaston prism as the analyzer to measure simultaneously the two orthogonal polarization components that define a Stoke's parameter. An achromatic half-wave plate is used to rotate the plane of polarization with respect to the axis of the analyzer so that the second Stoke's parameter also can be determined. With a field of view corresponding to about 30×30 mm² for a Ø20D 1.2 m, f/13 telescope, a sensitive, liquid-N₂ cooled CCD camera as the detector and a built-in acquisition and guidance unit, the instrument can be used for studying stellar fields or extended objects with an angular resolution of ~2''. The instrumental polarization is less than 0.05% and the accuracies of measurement are primarily limited by photon noise for typical observations.