Characterization of a half wave plate and a polarizer for accurate starlight polarimetry

Abstract In the process of developing a space-based imaging Stokes polarimeter for starlight polarization measurements, we established a procedure to characterize its two main optical components: the wave plate and the polarizer. We demonstrate that a simple optical bench setup combined with a custom calibration procedure can be used to measure the non-ideality parameters of both the polarizer and the wave plate. Using this approach, we characterized two high-quality components for the V-band. We set an upper limit for the cross-polarization of the polarizer, $$C_B \le 1 \times 10^{-4}$$ , and a limit of $$\Delta \le 2 \times 10^{-4}$$ for the transmission imbalance of the half-wave plate. We show that with these components the setup yields reproducible measurements at the level of $$0.001\%$$ for the polarization degree of a weakly polarized source, and $$3'$$ for the position angle. We also investigate the performance of the components under tilted incidence, up to $$6^o$$ off-axis, as required for a wide-field imaging version of a stellar polarimeter. We find that within this range, even without any off-axis bias correction, these components enable measurements of the polarization degree with an accuracy better than 0.005, and of the polarization angle with an accuracy better than $$1^o$$ .