Polarization Modeling and Predictions for DKIST Part 2: Application of the Berreman Calculus to Spectral Polarization Fringes of Beamsplitters and Crystal Retarders

摘要

We outline polarization fringe predictions derived from a new application ofthe Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarderoptics. The DKIST retarder baseline design used 6 crystals, single-layeranti-reflection coatings, thick cover windows and oil between all opticalinterfaces. This new tool estimates polarization fringes and optic Muellermatrices as functions of all optical design choices. The amplitude and periodof polarized fringes under design changes, manufacturing errors, tolerances andseveral physical factors can now be estimated. This tool compares well withobservations of fringes for data collected with the SPINOR spectropolarimeterat the Dunn Solar Telescope using bi-crystalline achromatic retarders as wellas laboratory tests. With this new tool, we show impacts of design decisions onpolarization fringes as impacted by anti-reflection coatings, oil refractiveindices, cover window presence and part thicknesses. This tool helped DKISTdecide to remove retarder cover windows and also recommends reconsideration ofcoating strategies for DKIST. We anticipate this tool to be essential indesigning future retarders for mitigation of polarization and intensity fringeerrors in other high spectral resolution astronomical systems.