Examinando por Autor "Bolognini, Néstor"

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    Double exposure specklegrams obtained by using scaled aperture pupils
    (SPIE, 2001-08-14) Angel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    In speckle photography the pupil aperture is usually not modified between exposures. In our work, the change of the pupil aperture scale between exposures is analyzed on the basis of double-exposed image speckle, before and after a diffuse in-plane displacement is done. The apertures have the same shape but its scale is modified between exposures. Note that the relative position of the aperture is maintained. In particular, we analyze a simple case that uses a circular aperture whose diameter is modified for recording each image. The intensity in the image plane and the fringe visibility are evaluated, in terms of the geometric characteristics of the pupils. © (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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    Features on photorefractive registered speckles
    (SPIE, 1999-04-29) Ángel-Toro, Luciano; Bolognini, Néstor; Tebaldi, Myrian; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    The recording and read-out of a volume speckle pattern is investigated for transmission geometry. The modulation of the 3D speckle grains appears when the image of a coherently illuminated random diffusor is formed onto the crystal by an optical system whose pupil consists of two identical holes. The intensity distribution of the speckle pattern imaged onto the BSO crystal leads to a space-charge field by drift of photocarriers, resulting in a refractive index modulation. The main features of diffracted read-out light at the Fourier plane are discussed. © (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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    In-plane displacement measurement in vortex metrology
    (2013-10-09) Angel-Toro, Luciano; Sierra-Sosa, Daniel; Tebaldi, Myrian; Bolognini, Néstor; Angel-Toro, Luciano; Sierra-Sosa, Daniel; Tebaldi, Myrian; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    Recently we proposed an alternative method of displacement analysis in vortex metrology, based on the application of the Fourier optics techniques, that is suitable for an intermediate range of displacement measurements ranging below the resolution of speckle photography and above that of the conventional vortex metrology. However, for smaller displacements, we introduce an approach to perform the Fourier analysis from vortex networks. In this work, we present an enhanced method for measuring uniform in-plane displacements, taking advantage of the capability of determining the subpixel locations of vortices and having the ability to track the homologous vortices onto a plane. It is shown that high-quality fringe systems can be synthesized and analyzed to accurately measure in an extended range of displacements and for highly decorrelated speckle patterns. Experimental results supporting the validity of the method are presented and discussed. © 2013 Optical Society of America
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    Ítem
    Logic operations by using modulated speckle
    (SPIE, 2001-08-14) Tebaldi, Myrian; Ángel-Toro, Luciano; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    An alternative image multiplexing technique is proposed. In the arrangement implemented, the input is imaged by introducing a multiple aperture pupil in the imaging lens. Then, the speckle pattern is modulated by several system of fringes. The input images are sequentially encoded by using a different pupil during each exposure. The pupil arrangements implemented are selected to concentrate in each spot the spectral information corresponding to not more than two exposures. The spectral amplitude components for a pari of exposures are added into the common diffraction spots. All the diffraction spots contain information about a pair of inputs. Then, an image binary operation can be carried out in each spot. The technique is implemented by using as recording media photographic films and photorefractive crystals. The BSO crystal as recording medium is quite adequate in the applications proposed because it permits multiple storage in real time. However, due to its volume nature, each speckle grain exhibits angular selectivity in addition to those features observed in bidimensional media. © (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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    Multiple rotation assessment through isothetic fringes in speckle photography
    (OSA, 2007-04-20) Ángel-Toro, Luciano; Tebaldi, Myrian; Bolognini, Néstor; Ángel-Toro, Luciano; Tebaldi, Myrian; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    The use of different pupils for storing each speckled image in speckle photography is employed to determine multiple in-plane rotations. The method consists of recording a four exposure specklegram where the rotations are done between exposures. This specklegram is then optically processed in a whole field approach rendering isothetic fringes, which give detailed information about the multiple rotations. It is experimentally demonstrated that the proposed arrangement permits the depiction of six isothetics in order to measure either six different angles or three nonparallel components for two local general in-plane displacements. © 2007 Optical Society of America
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    New multiple aperture arrangements for speckle photography
    (Elsevier B.V, 2000-08-01) Angel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Angel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Angel-Toro, Luciano (langel@eafit.edu.co); Óptica Aplicada
    Abstract. We propose a multiple exposure specklegram by using an optical system whose multiple aperture pupil changes between exposures. In particular, we analyze experimentally two arrangements and we show that it is possible to store the required information by employing a minimum number of registers if an adequate selection of the pupil is done. We study the effect of the decorrelation (among the stored speckle pattern) introduced by changing the multiple aperture pupil arrangements between exposures. The fundamentals and the relative benefits of the new scheme proposed are discussed on the basis of a fringe visibility analysis.
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    Optical processing by fringed speckles registered in a BSO crystal
    (SPIE, 2000-07-28) Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Ángel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Ángel-Toro, Luciano; Universidad EAFIT. Departamento de Ciencias Básicas; langel@eafit.edu.co; Óptica Aplicada
    An alternative image multiplexing technique, employing a multiple-aperture pupil for each exposure, is presented. The aperture arrangement of the pupil is modified between exposures. A thick photorefractive BSO crystal is used as recording material. The technique allows concentrating the spectral components of a pair of images selectively into isolated spots in the Fourier plane. Two applications are proposed, in image processing and optical metrology. © 2000 Society of Photo-Optical Instrumentation Engineers. © 2000 Society of Photo-Optical Instrumentation Engineers
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    Phase-object detection by use of double-exposure fringe-modulated speckle patterns
    (OSA, 2003-01) Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Angel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Angel-Toro, Luciano; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    We study the properties of a double-exposure image specklegram of a diffuse object obtained by use of a doubleaperture pupil. A phase object is placed in front of one aperture during the first or the second exposure. Also, it is assumed that a uniform displacement of the diffuser between exposures is produced. The recorded specklegram is coherently illuminated and analyzed by Fourier transform operations. The average intensity distribution and the interference fringe visibility in the Fourier plane are investigated. On this basis, an alternative interference technique to detect phase objects is proposed.
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    Propierties of speckle patterns generated through multiaperture pupils
    (Elsevier, 2001-05-15) Ángel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Ángel-Toro, Luciano; Tebaldi, Myrian; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Ángel-Toro, Luciano (langel@eafit.edu.co); Óptica Aplicada
    The characteristics of the image speckles obtained through multiple aperture pupils are theoretically analyzed in terms of the parameters defining the pupils. The possibility of interpreting and synthesizing the image speckle distribution in terms of rather elementary structures is considered, based on the Fourier optics analysis. Then, first and second order statistical properties of the speckle patterns are studied by evaluating both the mutual intensity and the auto-correlation intensity of speckle distributions obtained by means of pupils consisting of identical apertures. Experimental results are presented to confirm the analysis.
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    Soap film analysis by speckle interferometer
    (SPIE, 2003-11-18) Tebaldi, Myrian; Ángel-Toro, Luciano; Trivi, Marcelo; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    In this paper a soap film is characterized by using a speckle interferometer. The arrangement consists of a double-exposure specklegram obtained through a double-aperture system, by introducing a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and the changes experimented by the interferometric fringe visibility in the Fourier plane due to the introduction of a soap film in each exposure are analyzed.
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    Vortex metrology using Fourier analysis techniques: vortex networks correlation fringes
    (OSA, 2012-10-19) Ángel Toro, Luciano; Sierra Sosa, Daniel; Tebaldy, Myrian; Bolognini, Néstor; Ángel Toro, Luciano; Sierra Sosa, Daniel; Tebaldy, Myrian; Bolognini, Néstor; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    In this work, we introduce an alternativemethod of analysis in vortexmetrology based on the application of the Fourier optics techniques. The first part of the procedure is conducted as is usual in vortexmetrology for uniformin-plane displacement determination. On the basis of two recorded intensity speckled distributions, corresponding to two states of a diffuser coherently illuminated, we numerically generate an analytical signal fromeach recorded intensity pattern by using a version of the Riesz integral transform. Then, fromeach analytical signal, a two-dimensional pseudophase map is generated in which the vortices are located and characterized in terms of their topological charges and their core’s structural properties. The second part of the procedure allows obtaining Young’s interference fringes when Fourier transforming the light passing through a diffracting mask with multiple apertures at the locations of the homologous vortices. In fact, we use the Fourier transformas amathematical operation to compute the far-field diffraction intensity pattern corresponding to themultiaperture set. Each aperture fromthe set is associatedwith a rectangular hole that coincides both in shape and size with a pixel from recorded images.We show that the fringe analysis can be conducted as in speckle photography in an extended range of displacement measurements. Effects related with speckled decorrelation are also considered. Our experimental results agree with those of speckle photography in the range in which both techniques are applicable. © 2012 Optical Society of America OCIS codes: 050.4865, 030.6140.