Removal of periodic artifacts in polarimetric data. The sample CRISP Fe I 6302 Å, −210 mÅ from line core. Data were collected on 2019 May 10 at 09:07 UT with AR 2741 in the FOV. The image shown is 53″ squared. (a) Stokes U component, sunspot saturated to emphasize artifacts in the lower left corner. (b) The polarization calibration image on which the Fourier filter is based. (c) Fourier filtered U component without the artifacts.