11 July 2006 Calibration strategies for instrumental polarization at the 10-5 level
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Abstract
Many current instrumental developments for both solar and nighttime telescopes are directed at measuring the polarization state of the incoming light in addition to determining its spatial, temporal and/or spectral properties. Such polarimeters need to be sensitive down to a polarization degree of the order of 10-5 e.g. to employ the full range of diagnostics to accurately measure solar magnetic fields or to enable direct imaging of extrasolar planetary systems. At the low polarization degree of these observations, it is crucial to accurately know the polarization properties of the instrument itself. Since instrumental polarization is inevitable for any telescopic configuration with oblique reflections or refractions, it is always necessary to cope with it by means of calibration in combination with (limited) forward modeling. I present general strategies based on discrete Fourier analysis for the calibration of instrumental polarization to enable astronomical (spectro-)polarimetry at the 10-5 level. The technique only assumes the presence of a freely rotatable polarizer and (quarter) wave plate to create known input polarization states. The Fourier components of the observed output polarization contain information about the full instrumental polarization, as well as about non-ideal effects in the calibration elements, polarized input to the calibration unit and non-linear response of the detector.
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Frans Snik, "Calibration strategies for instrumental polarization at the 10-5 level", Proc. SPIE 6269, Ground-based and Airborne Instrumentation for Astronomy, 62695P (11 July 2006); doi: 10.1117/12.671425; https://doi.org/10.1117/12.671425
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