2018/03/23 by David M. Harrington, Stacey R. Sueoka, Harrington, David M. +1
Physics and Astronomy · #Astronomy and Astrophysical Research #FOS: Physical sciences #Instrumentation and Methods for Astrophysics (astro-ph.IM) #Solar and Space Plasma Dynamics #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.1803.08987
openalex publication_date 2018/03/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Data products from high spectral resolution astronomical polarimeters are\noften limited by fringes. Fringes can skew derived magnetic field properties\nfrom spectropolarimetric data. Fringe removal algorithms can also corrupt the\ndata if the fringes and object signals are too similar. For some narrow-band\nimaging polarimeters, fringes change the calibration retarder properties, and\ndominate the calibration errors. Systems-level engineering tools for\npolarimetric instrumentation require accurate predictions of fringe amplitudes,\nperiods for transmission, diattenuation and retardance. The relevant\ninstabilities caused by environmental, thermal and optical properties can be\nmodeled and mitigation tools developed. We create spectral polarization fringe\namplitude and temporal instability predictions by applying the Berreman\ncalculus and simple interferrometric calculations to optics in beams of varying\nF/ number. We then apply the formalism to super-achromatic six crystal\nretarders in converging beams under beam thermal loading in outdoor\nenvironmental conditions for two of the worlds largest observatories: the 10m\nKeck telescope and the Daniel K. Inouye Solar Telescope (DKIST). DKIST will\nproduce a 300 Watt optical beam which has imposed stringent requirements on the\nlarge diameter six-crystal retarders, dichroic beamsplitters and internal\noptics. DKIST retarders are used in a converging beams with F/ ratios between 8\nand 62. The fringe spectral periods, amplitudes and thermal models of retarder\nbehavior assisted DKIST optical designs and calibration plans with future\napplication to many astronomical spectropolarimeters. The Low Resolution\nImaging Spectrograph with polarimetry (LRISp) instrument at Keck also uses\nsix-crystal retarders in a converging F/ 13 beam in a Cassegrain focus exposed\nto summit environmental conditions providing observational verification of our\npredictions.\n