WALOP-South: a four-camera one-shot imaging polarimeter for PASIPHAE survey. Paper I—optical design

The Wide-Area Linear Optical Polarimeter (WALOP)-South instrument will be mounted on the 1-m South African Astronomical Observatory telescope in Africa as part of Polar-Areas Stellar Imaging Polarization High Accuracy Experiment (PASIPHAE) program to carry out a linear imaging polarization survey Galactic polar regions optical band. Designed achieve polarimetric sensitivity 0.05% across 35 × arc min field view (FOV), it capable measuring Stokes parameters I, q, and u single exposure R broadband narrowband filters between 0.5 0.7 μm. For each measurement, four images full corresponding angles 0 deg, 45 90 135 deg coordinate system created detectors from which can found using differential photometry. In designing system, major challenges included correcting for dispersion introduced by large split angle Wollaston prisms used analysers other aberrations entire obtain quality point spread function (PSF) at detector. We present design WALOP-South overcomes these delivers near seeing limited PSFs FOV.