12 May 2015 Polarizers for a spectral range centered at 121.6 nm operating by reflectance or by transmittance
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Abstract
Polarimetry is a powerful tool to interpret how the coronal plasma is involved in the energy transfer processes from the Sun’s inner parts to the outer space. Space polarimetry in the far ultraviolet (FUV) provides essential information of processes governed by the Doppler and Hanle resonant electron scattering effects. Among the key FUV spectral lines to observe these processes, H I Lyman α (121.6 nm) is the most intense. Some developing or proposed solar physics missions, such as CLASP, SolmeX, and COMPASS, plan to perform polarimetry at 121.6 nm. Classical solutions, such as a parallel plate of a transparent material, either MgF2 or LiF, result in a modest efficiency of the passing polarization component. The development of more efficient linear polarizers at this wavelength will benefit future space instruments. A research has been conducted to develop polarizers based on (Al/MgF2)n multilayer coatings in a band containing 121.6 nm, to obtain a significant efficiency increase over plates. Coatings operating by reflectance resulted in a high efficiency after approximately one year of storage under nitrogen. In parallel, coating polarizers operating by transmittance have been prepared for the first time. Transmissive polarizers have the advantage that they involve no deviation of the beam. As a further benefit, the developed transmittance polarizers additionally incorporate filtering properties to help reject wavelengths both shortwards and longwards of a band containing 121.6 nm. Hence a polarizer combined with a filter is obtained with a single device. The combined polarizer-filter could enable a higher performance polarimeter for solar physics if the use of a separate filter to isolate Lyman α turns unnecessary.
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Juan I. Larruquert, Juan I. Larruquert, A. Marco Malvezzi, A. Marco Malvezzi, Angelo Giglia, Angelo Giglia, José A. Aznárez, José A. Aznárez, Luis Rodríguez-de Marcos, Luis Rodríguez-de Marcos, José A. Méndez, José A. Méndez, Paolo Miotti, Paolo Miotti, Fabio Frassetto, Fabio Frassetto, Giuseppe Massone, Giuseppe Massone, Gerardo Capobianco, Gerardo Capobianco, Silvano Fineschi, Silvano Fineschi, Stefano Nannarone, Stefano Nannarone, } "Polarizers for a spectral range centered at 121.6 nm operating by reflectance or by transmittance", Proc. SPIE 9510, EUV and X-ray Optics: Synergy between Laboratory and Space IV, 951008 (12 May 2015); doi: 10.1117/12.2179446; https://doi.org/10.1117/12.2179446
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