Minimizing instrumental polarization in the Multiangle SpectroPolarimetricImager (MSPI) using diattenuation balancing between the three mirror coatings

摘要

Special enhanced silver mirror coatings were designed and fabricated to minimize the polarization introduced by a three-mirror off-axis high-accuracy telescope. A system diattenuation of approximately 1% in the VIS-NIR was achieved byboth reducing the diattenuation from each mirror individually and by balancing the diattenuations introduced by thethree mirrors over the spectral range. This process of low-polarization engineering involves minimizing systempolarization introduced by surface geometry, thin film coatings and birefringent elements, and measuring the system. Inthis report we will outline a methodology to minimize instrumental polarization aberrations, with an emphasis onachieving low diattenuation in the MSPI camera, given its off-axis geometry and coating design constraints imposed bythe space-based application. This polarization balancing technique for mirror coatings can be applied to astrophysicsapplications.