Examinando por Autor "Alvarez-Herrero, A."

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    Imaging polarimeters based on liquid crystal variable retarders: An emergent technology for space instrumentation
    (SPIE-INT SOC OPTICAL ENGINEERING, 2011-01-01) Alvarez-Herrero, A.; Uribe-Patarroyo, N.; García Parejo, P.; Vargas, J.; Heredero, R.L.; Restrepo, R.; Martínez-Pillet, V.; Del Toro Iniesta, J.C.; López, A.; Fineschi, S.; Capobianco, G.; Georges, M.; López, M.; Boer, G.; Manolis, I.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    The use of Liquid Crystal Variable Retarders (LCVRs) as polarization modulators are envisaged as a promising novel technique for space instrumentation due to the inherent advantage of eliminating the need for conventional rotary polarizing optics hence the need of mechanisms. LCVRs is a mature technology for ground applications; they are wellknow, already used in polarimeters, and during the last ten years have undergone an important development, driven by the fast expansion of commercial Liquid Crystal Displays. In this work a brief review of the state of the art of imaging polarimeters based on LCVRs is presented. All of them are ground instruments, except the solar magnetograph IMaX which flew in 2009 onboard of a stratospheric balloon as part of the SUNRISE mission payload, since we have no knowledge about other spaceborne polarimeters using liquid crystal up to now. Also the main results of the activity, which was recently completed, with the objective to validate the LCVRs technology for the Solar Orbiter space mission are described. In the aforementioned mission, LCVRs will be utilized in the polarisation modulation package of the instruments SO/PHI (Polarimetric and Helioseismic Imager for Solar Orbiter) and METIS/COR (Multi Element Telescope for Imaging and Spectroscopy, Coronagraph). © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
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    Space-qualified liquid-crystal variable retarders for wide-field-of-view coronagraphs
    (SPIE-INT SOC OPTICAL ENGINEERING, 2011-01-01) Uribe-Patarroyo, N.; Alvarez-Herrero, A.; García Parejo, P.; Vargas, J.; Heredero, R.L.; Restrepo, R.; Martínez Pillet, V.; Del Toro Iniesta, J.C.; López, A.; Fineschi, S.; Capobianco, G.; Georges, M.; López, M.; Boer, G.; Manolis, I.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    Liquid-crystal variable retarders (LCVRs) are an emergent technology for space-based polarimeters, following its success as polarization modulators in ground-based polarimeters and ellipsometers. Wide-field double nematic LCVRs address the high angular sensitivity of nematic LCVRs at some voltage regimes. We present a work in which wide-field LCVRs were designed and built, which are suitable for wide-field-of-view instruments such as polarimetric coronagraphs. A detailed model of their angular acceptance was made, and we validated this technology for space environmental conditions, including a campaign studying the effects of gamma, proton irradiation, vibration and shock, thermo-vacuum and ultraviolet radiation. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).