Examinando por Autor "Velásquez-Prieto, Daniel"
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Ítem DC term filtering techniques in digital holography(SPIE, 2004-10-21) Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Herrera Ramírez, Jorge Alexis; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaIn numerical hologram reconstruction like in optical holography, there exist different diffraction orders, which many times produce difficulties for the image visualizations. In numerical reconstruction, the filtering of the DC term, or zero order diffraction, provides an improved utilization of the dynamic range of the visualization systems, which is needed for the right displaying purposes of reconstructed images. In the case of the in-line set-ups, the zero diffraction order has even more devastating effects because it does not allow reconstructing the images itself as in Gabor's holograms, so it is necessary to attempt a filtering of this DC term. In this work is shown a qualitative assessment of different techniques of DC term filtering applied to numerical reconstruction of Fresnel's holograms recorded by means of off-line set-ups.Ítem Improvement of the signal-to-noise ratio in digital holography(Sociedad Mexicana de Física, 2005-02) Velásquez-Prieto, Daniel; Herrera Ramírez, Jorge Alexis; García Sucerquia, Jorge Iván; Velásquez-Prieto, Daniel; Herrera Ramírez, Jorge Alexis; García Sucerquia, Jorge Iván; Universidad EAFIT. Departamento de Ciencias Básicas; dvelas@eafit.edu.co; Óptica AplicadaA fundamental problem in optical and digital holography is the presence of speckle noise in the reconstruction process, which essentially diminishes the signal to noise ratio (SNR). For many applications, that reduction of the SNR makes the digital holography impractical, so great number of approaches have been carried out in order to overcome such a problem. They range from modifying the spatial coherence of the illumination to the application of image processing techniques. In this paper we propose the merged use of digital image processing techniques in order to increase this SNR by reducing the speckle noise in the digital reconstruction of optically recorded Fresnel’s holograms. The proposed techniques are illustrated with experimental results.Ítem Phase-difference images by digital holography applied to 3D surface contouring(Academia Colombiana de Ciencias Exactas Físicas y Naturales, 2005-06) Velásquez-Prieto, Daniel; García Sucerquia, Jorge Iván; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica AplicadaThe problem to determine the 3D-contour of objects with all sizes and shapes is a hot topic in diverse fields of optical research and engineering. Through the use of the numerical reconstruction of digital recorded holograms, we propose a technique to evaluate the 3D contour of objects at least four orders of magnitude larger than the optical wavelength. The required 2π-module phase map in any contouring process is obtained by means of phase-difference image of two digital reconstructed holograms. These holograms are interferometric recordings from a still object under different angle illumination. Our proposal is supported on the theoretical analysis of the contouring system, verified by means of numerical results.Ítem 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 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.