Polarization offset through differential transmission in refractive CMB telescopes identified using a hybrid physical optics method

Abstract

We identify a polarization rotation systematic in the far field beams of refractive cosmic microwave background (CMB) telescopes caused by differential transmission in anti-reflection (AR) coatings of optical elements. This systematic was identified following the development of a hybrid physical optics method that incorporates full-wave electromagnetic simulations of AR coatings to model the full polarization response of refractive systems. Applying this method to a two-lens CMB telescope with non-ideal AR coating, we show that polarization-dependent transmission can produce a rotation of the far-field polarization angle that varies across the focal plane with a typical amplitude of 0.05-0.5 degrees. If ignored in analysis, this effect can produce temperature to polarization leakage and Stokes Q/U mixing.

Xiaodong Ren

Postdoc

Rustam Balafendiev

PhD Student

Rustam Balafendiev received the M.Sc. degree in radiophysics from the School of Physics and Engineering, ITMO University, Saint Petersburg, Russia, in 2021 and his first PhD degree at the same university in 2025. His current research interests include metamaterial applications in CMB instrumentation as well as the use of wire metamaterials in holography experiments.

Jón E. Guðmundsson

Professor

Professor of astrophysics at the University of Iceland and senior research scientist at Stockholm University.