Examinando por Materia "Optics"
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Ítem Analysis of vibrations in a plate using interferometric methods(SPIE, 2004-10-21) Ángel-Toro, Luciano; Prieto, Daniel Velasquez; Rueda Muñóz, Edgar Alberto; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaIn this work some frequencies and modes of vibration of a thin plate were determined using interferometric methods like: real-time holographic interferometry, time-average holographic interferometry, digital speckle pattern interferometry DSPI. And the results obtained are compared with those obtained with the program of finite elements COSMOS.Ítem Contrast inversion in the Lau phenomena implemented with a photorefractive grating(SPIE, 1999-07-06) Ángel Toro, Luciano; Tebaldi, Myrian Cristina; Bolognini, Néstor Alberto; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaIt was implemented the Lau effect with a grating registered in a BSO crystal. Two different arrangement were analyzed. In both cases, it is possible to control the visibility and to produce the contrast inversion of fringes, by properly setting the pass plane orientation of an analyzer located at the crystal output.Ítem Design of a control system for interferometric fringe stabilization system with remote access(SPIE-INT SOC OPTICAL ENGINEERING, 2013-01-01) Espitia-Gomez, Javier; Angel-Toro, Luciano; Velasquez, Daniel; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaStability in a fringe pattern is a necessary condition in interferometric processes, such as holography, and not always is enough the use of passive stabilization systems, like holographic tables, in particular, when perturbations are caused by thermal or acoustic variations. For these cases, active systems are required. In this work it is presented the implementation of a control system for interferometric fringes stabilization. The interferometric arrangement characteristics are also discussed, which permits to act independently over each of the interferometer's arms by means of two piezoelectric actuators that change the length of the optical path of light that goes through, in order to perturb the system and simultaneously compensate this perturbation in real time. It is also shown that the proposed system allows evaluating the control system's performance subjected to diverse perturbations, and it is shown how remote access was given to the implemented platform. © 2013 SPIE.Ítem Effect of the internal modulation of speckles in displacement measurements in optical vortex metrology(SPIE-INT SOC OPTICAL ENGINEERING, 2013-01-01) Gomez-Tejada, Daniel; Sierra-Sosa, Daniel; Castaneda, Roman; Angel-Toro, Luciano; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaThe Optical Vortex Metrology is based on the possibility of characterizing, through topological and morphological parameters, each one of the vortices existing in the phase of the optical field, or in a pseudo-phase obtained by means of the Hibert, Reisz or Laguerre-Gauss transforms. On this basis, it is possible tracking and pairing the homologous vortices. Then, the locations and relative displacements between the homologous vortices are determined with sub-pixel precision. Because of the statistical nature of the measurements, their quality is determined, among other factors, by the amount of available vortices per unit area. In this work, it is proposed to use the internal modulation of the speckles to generate a significant increase in the vortex density, which can be achieved by employing a double aperture pupil optical system. Simulations of the speckle distributions are presented to analyze the increase of the vortex density as a function of the distance between the apertures, and to evaluate the influence of the increment of this density in the quality of uniform in-plane displacements measurements. The results corresponding to modulated speckles are compared with those obtained with a single aperture. © 2013 SPIE.Ítem ¿Es real todo lo que percibimos con nuestros ojos?(2012) Velásquez Prieto, Daniel Ignacio; Abad Restrepo, Ana Cristina; Daniel Velásquez (dvelas@eafit.edu.co); Ana Cristina Abad (abad@eafit.edu.co)Ítem Holopixel: estudio de la factibilidad de implementar la tecnología para el registro de hologramas de matriz de puntos(Universidad EAFIT, 2016) González Villegas, Alejandro; Velásquez Prieto, Daniel IgnacioEn este trabajo se presenta la investigación realizada con el objeto de determinar la factibilidad tecnológica para el registro de los hologramas de matriz de punto utilizados ampliamente en la industria de las artes gráficas como elementos de seguridad en la lucha contra la piratería y la falsificación de productos -- Para ello se estudian y presentan los fundamentos ópticos de las rejillas de difracción que los conforman, derivando los métodos que permiten el cálculo a partir de condiciones establecidas de iluminación y reconstrucción -- A partir de dichos métodos se desarrollan y se ponen en funcionamiento sistemas y arreglos experimentales completos, que involucran el software para el control de los dispositivos mecánicos, para el manejo y diseño de las imágenes, y adicionalmente la óptica propiamente dicha -- Los sistemas de esta forma implementados, que permiten la generación y registro de las rejillas, son puestos a prueba y se presentan los resultados tomando como parámetro la medición de los espectros generados por difracción -- Finalmente se presentan y evalúan varios ejemplos típicos de la aplicación de los hologramas de seguridad generados en el sistema desarrolladoÍtem Reduction of speckle noise in digital holography(SPIE, 2004-10-21) Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Castañeda Sepúlveda, Román; Herrera Ramírez, Jorge Alexis; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaA fundamental problem in holography, as well optical as digital, is the presence of speckle noise in the reconstruction process -- Many approaches have been carried out in order overcome such a problem, ranging from altering the spatial coherence (optical techniques) of the illumination to imaging processing techniques (digital techniques) -- This work shows the merged use of digital i maging techniques in order t o reduce the speckle noise in digital reconstruction of optically recorded Fresnel's holograms -- The proposed filtering techniques are illustrated with experimental results --Ítem Reduction of speckle noise in digital holography by using digital image processing(ELSEVIER GMBH, URBAN & FISCHER VERLAG, 2005-01-01) Garcia-Sucerquia, J; Ramirez, JAH; Prieto, DV; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaA fundamental problem in optical and digital holography is the presence of speckle noise in the reconstruction process. Many approaches have been carried out in order to overcome such a problem ranging from modifying the spatial coherence of the illumination (optical techniques) to image processing techniques (digital techniques). This work shows the merged use of digital image processing techniques in order to reduce the speckle noise in digital reconstruction of optically recorded Fresnel's holograms. The proposed filtering techniques are illustrated with experimental results. © 2005 Elsevier GmbH. All rights reserved.Ítem Remote access to an interferometric fringes stabilization active system via RENATA(SPIE-INT SOC OPTICAL ENGINEERING, 2013-01-01) Espitia-Gomez, Javier; Angel-Toro, Luciano; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaThe Advanced Technology National Network (RENATA, for its acronym in Spanish) is a Colombian, collaborative work tool, linked to other networks worldwide, in which take participation researchers, teachers and students, by sharing laboratory resources located in different universities, institutes and research centers throughout the country. In the Universidad EAFIT (Medellín, Colombia) it has been designed an interferometric fringes stabilization active system, which can be accessed remotely via the RENATA network. A Mach-Zehnder interferometer was implemented, with independent piezoelectric actuators in each arm, with which the lengths of optical path of light that goes over in each of them can be modified. Using these actuators, one can simultaneously perturb the system and compensate the phase differences caused by that perturbation. This allows us to experiment with different disturbs, and analyze the system response to each one of them. This can be made from any location worldwide, and especially from those regions in which optical and optoelectronic components required for the implementation of the interferometer or for the stabilization system are not available. The device can also be used as a platform in order to conduct diverse experiments, involving optical and controlling aspects, constituting with this in a pedagogic tool. For the future, it can be predicted that remote access to available applications would be possible, as well as modifications of the implemented code in labVIEWTM, so that researchers and teachers can adapt and improve their functionalities or develop new applications, based on the collaborative work. © 2013 SPIE.Ítem Shack - Hartmann spot dislocation map determination using an optical flow method(OSA, 2014-01-14) Vargas, Javier; Restrepo Gómez, René; Belenguer, Tomás; Vargas, Javier; Restrepo Gómez, René; Belenguer, Tomás; 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].Ítem Speckle photography with different pupils in a multiple-exposure scheme(OPTICAL SOC AMER, 2000-01-01) Angel, L; Tebaldi, M; Bolognini, N; Trivi, M; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaThe use of different multiple-aperture pupils for recording each image in speckle photography is proposed. The introduction of suitable spatial frequency carriers, by internally modulating imaged speckles, allows one to selectively isolate or combine the spectral content of different images into spatially separated regions in the Fourier plane. Theoretical and experimental results extend the speckle photography technique to the depiction of several specklegrams of multiple uniform in-plane displacements. In this case, because different pupils are considered for recording, the cross-correlation functions for the amplitudes and intensities in the image plane are calculated on the basis of the statistical properties of the object. Also, the ensemble-average intensity in the Fourier plane is analytically derived, and fringe visibility is investigated. © 2000 Optical Society of America.Ítem Three-dimensional contouring with digital holography(Sociedad Colombiana De Física, 2005-04-28) Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Universidad EAFIT. Departamento de Ciencias Básicas; dvelas@eafit.edu.co; Óptica AplicadaWe report on a technique to determine the 3D contour of objects with dimensions of at least four orders of magnitude larger than the illumination optical wavelength. Our proposal is based on the numerical reconstruction of the object optical wave field of digitally recorded holograms. The re-quired 2π-module phase map in any contouring process is obtained by means of the direct subtraction of two phase-contrast images (phase-difference image) of a still object under different illumination angles. Obtaining phase difference images is only possible by using the capability of numerical reconstruction of the complex optical field provided by the digital holography. This unique characteristic leads us to a robust, reliable, and fast procedure that only requires of two images. We support our proposal with the theoretical means of numerical and experimental results.Ítem Three-dimensional surface contouring of macroscopic objects by means of phase-difference images(OSA, 2006-04-16) García Sucerquia, Jorge Iván; Velásquez Prieto, Daniel Ignacio; García Sucerquia, Jorge Iván; Velásquez Prieto, Daniel Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; dvelas@eafit.edu.co; Óptica AplicadaWe report a technique to determine the 3D contour of objects with dimensions of at least 4 orders of magnitude larger than the illumination optical wavelength. Our proposal is based on the numerical reconstruction of the optical wave field of digitally recorded holograms. The required modulo 2 phase map in any contouring process is obtained by means of the direct subtraction of two phase-contrast images under different illumination angles to create a phase-difference image of a still object. Obtaining the phase-difference images is only possible by using the capability of numerical reconstruction of the complex optical field provided by digital holography. This unique characteristic leads us to a robust, reliable, and fast procedure that requires only two images. A theoretical analysis of the contouring system is shown, with verification by means of numerical and experimental results. © 2006 Optical Society of America