Examinando por Autor "Vargas, J."
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Ítem High dynamic range imaging method for interferometry(ELSEVIER SCIENCE BV, 2011-01-01) Vargas, J.; Restrepo, R.; Quiroga, J.A.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe demonstrate a method to easily and quickly extend the dynamic range imaging capabilities of the camera in a typical interferometric approach. The camera dynamic range is usually low and limited to 256 gray levels. Also, it is well known that one may have over or under-exposed regions in the interferogram (due to non-uniform illumination) which makes these image regions not reliable. In our proposed method it is not necessary to obtain or use the non-linear camera response curve in order to extend the camera dynamic range. We obtain a sequence of differently exposed interferograms, typically five or six; after that, we compute the corresponding normalized fringe patterns and modulation maps using a typical normalization method. These normalized patterns are combined through a temporal weighted average using as weights the corresponding modulation maps. We show a set of experimental results that prove the effectiveness of the proposed method. © 2011 Elsevier B.V. All rights reserved.Ítem 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 AplicadaThe 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).Ítem Inspection of an extended surface by an active 3D multiresolution technique(Springer-Verlag Berlin Heidelberg, 2009-01-01) Vargas, J.; Restrepo, R.; Quiroga, J.A.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaReliable inspection of large surfaces with low depth recovery error is needed in a wide variety of industrial applications, for example in deformation measurement or defect inspection of extended surfaces as communication antennas. Active triangulation measurement systems present a compromise between the depth recovery error and the measured area. For an optimized active three-dimensional measuring system the expected ratio between the depth resolution and the inspected area is in the rage of 10-4. Therefore, if we want to scan a large object with a high level of detail we need multiresolution techniques. In this work we demonstrate the application of an active triangulation multiresolution method for the inspection of communication antennas. The technique is based on a standard camera-projector system. The result is a global measurement formed by a set of superposed local measurement with high depth resolution. © 2009 Springer-Verlag Berlin Heidelberg.Ítem Shack-Hartmann centroid detection using the spiral phase transform(OSA - The Optical Society of America, 2012-01-01) Vargas, J.; Restrepo, R.; Estrada, J.C.; Sorzano, C.O.S.; Du, Y.-Z.; Carazo, J.M.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe present a Shack-Hartmann (SH) centroid detection algorithm capable to measure in presence of strong noise, background illumination and spot modulating signals, which are typical limiting factors of traditional centroid detection algorithms. The proposed method is based on performing a normalization of the SH pattern using the spiral phase transform method and Fourier filtering. The spot centroids are then obtained using global thresholding and weighted average methods. We have tested the algorithm with simulations and experimental data obtaining satisfactory results. A complete MATLAB package that can reproduce all the results can be downloaded from [http://goo.gl/o2JhD]. © 2012 Optical Society of America.Ítem Shack-Hartmann spot dislocation map determination using an optical flow method(OPTICAL SOC AMER, 2014-01-27) Vargas, J.; Restrepo, R.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe present a robust, dense, and accurate Shack-Hartmann spot dislocation map determination method based on a regularized optical flow algorithm that does not require obtaining the spot centroids. The method is capable to measure in presence of strong noise, background illumination and spot modulating signals, which are typical limiting factors of traditional centroid detection algorithms. Moreover, the proposed approach is able to face cases where some of the reference beam spots have not a corresponding one in the distorted Hartmann diagram, and it can expand the dynamic range of the Shack-Hartmann sensor unwrapping the obtained dense dislocation maps. We have tested the algorithm with both simulations and experimental data obtaining satisfactory results. A complete MATLAB package that can reproduce all the results can be downloaded from [http://goo.gl/XbZVOr]. © 2014 Optical Society of America.Ítem 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 AplicadaLiquid-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).