Examinando por Autor "Uribe-Patarroyo, N."
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Ítem Electronic speckle pattern interferometry technique for the measurement of complex mechanical structures for aero-spatial applications(SPIE-INT SOC OPTICAL ENGINEERING, 2010-01-01) Restrepo, R.; Uribe-Patarroyo, N.; Garranzo, D.; Pintado, J.M.; Frovel, M.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaUsing the electronic speckle pattern interferometry (ESPI) technique in the in-plane arrangement, the coefficient of thermal expansion (CTE) of a composite material that will be used in a passive focusing mechanism of an aerospace mission was measured. This measurement with ESPI was compared with another interferometric method (Differential Interferometer), whose principal characteristic is its high accuracy, but the measurement is only local. As a final step, the results have been used to provide feedback with the finite element analysis (FEA). Before the composite material measurements, a quality assessment of the technique was carried out measuring the CTE of Aluminum 6061-T6. Both techniques were compared with the datasheet delivered by the supplier. A review of the basic concepts was done, especially with regards to ESPI, and the considerations to predict the quality in the fringes formation were explained. Also, a review of the basic concepts for the mechanical calculation in composite materials was done. The CTE of the composite material found was 4.69X10-6 ± 3X10-6K-1. The most important advantage between ESPI and differential interferometry is that ESPI provides more information due to its intrinsic extended area, surface deformation reconstruction, in comparison with the strictly local measurement of differential interferometry. © 2010 Copyright SPIE - The International Society for Optical Engineering.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 Improvement of the signal-to-noise ratio in interferometry using multi-frame high-dynamic-range and normalization algorithms(ELSEVIER SCIENCE BV, 2012-01-01) Restrepo, R.; Uribe-Patarroyo, N.; Belenguer, T.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaUsing both high dynamic range (HDR) and normalization methodologies, we show a method to improve the fringe pattern contrast in interferometric measurements normally used for phase recovering. In a simulated interferogram that mimics the main effects that can be found in an interferometric process (stray-light, photon noise, electronic noise, scattering phenomena, etc.) it was possible to improve the contrast of the fringes and to decrease the root mean square error by more than 35%. The method proposed is applied to experimental interferograms to measure wavefront error and retardance changes on liquid crystal (LC) devices. It is done by using a Mach-Zehnder set-up in which we used different polarization areas. The proposed method increases the quality of the phase recovered and decreases the root mean square error by 50%. © 2011 Elsevier B.V. All rights reserved.Ítem Improving on-axis optical vortex generation by transmissive spatial light modulator using coherent phase diversity(OSA - The Optical Society, 2016-01-01) Cuartas-Vélez, C.; Restrepo, R.; Echeverri-Chacón, S.; Uribe-Patarroyo, N.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe present a modification of numerical optimization coherent phase diversity in order to detect and correct undesired effects of non-linear and incomplete phase modulation of transmissive spatial light modulators for on-axis optical vortices. © OSA 2016.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).Ítem Volumetric non-local-means based speckle reduction for optical coherence tomography(OSA - The Optical Society, 2018-07-01) Cuartas-Vélez, C.; Restrepo, R.; Bouma, B.E.; Uribe-Patarroyo, N.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe present a novel tomographic non-local-means based despeckling technique, TNode, for optical coherence tomography. TNode is built upon a weighting similarity criterion derived for speckle in a three-dimensional similarity window. We present an implementation using a two-dimensional search window, enabling the despeckling of volumes in the presence of motion artifacts, and an implementation using a three-dimensional window with improved performance in motion-free volumes. We show that our technique provides effective speckle reduction, comparable with B-scan compounding or out-of-plane averaging, while preserving isotropic resolution, even to the level of speckle-sized structures. We demonstrate its superior despeckling performance in a phantom data set, and in an ophthalmic data set we show that small, speckle-sized retinal vessels are clearly preserved in intensity images en-face and in two orthogonal, cross-sectional views. TNode does not rely on dictionaries or segmentation and therefore can readily be applied to arbitrary optical coherence tomography volumes. We show that despeckled esophageal volumes exhibit improved image quality and detail, even in the presence of significant motion artifacts. © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.Ítem Vortex-enhanced coherent-illumination phase diversity for phase retrieval in coherent imaging systems(OSA - The Optical Society, 2016-04-15) Echeverri-Chacón, S.; Restrepo, R.; Cuartas-Vélez, C.; Uribe-Patarroyo, N.; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaWe propose a phase-retrieval method based on the numerical optimization of a new objective function using coherent phase-diversity images as inputs for the characterization of aberrations in coherent imaging systems. By employing a spatial light modulator to generate multiple-order spiral phase masks as diversities, we obtain an increase in the accuracy of the retrieved phase compared with similar state-of-the-art phase-retrieval techniques that use the same number of input images. We present simulations that show a consistent advantage of our technique, and experimental validation where our implementation is used to characterize a highly aberrated 4F optical system. (C) 2016 Optical Society of America