Examinando por Autor "Bolognini, N"

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    Double exposure specklegrams obtained by using scaled aperture pupils
    (SPIE-INT SOC OPTICAL ENGINEERING, 2001-01-01) Angel, L; Tebaldi, M; Trivi, M; Bolognini, N; 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 analysed on the basis of double-exposed image speckle, before and after a diffuser inplane 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 analyse a simple case that uses a circular aperture whose diameter is modified for recording each image. The intensities in the image plane and the fringe visibility are evaluated, in terms of the geometric characteristics of the pupils. © 2001 SPIE · 0277-786X/01/$15.00.
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    Fringe visibility analysis with different scale apertures in speckle photography
    (TAYLOR & FRANCIS LTD, 2001-09-15) Angel, L; Tebaldi, M; Trivi, M; Bolognini, N; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    The use of different scale aperture pupils for image recording in speckle photography is analysed. In particular a double-exposure specklegram is considered. The ensemble-average intensity in the Fourier plane is analytically derived and fringe visibility is investigated. The theoretical results are verified by in-plane displacement translation experiments.
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    New multiple aperture arrangements for speckle photography
    (ELSEVIER SCIENCE BV, 2000-08-01) Tebaldi, M; Toro, LA; Trivi, M; Bolognini, N; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    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. © 2000 Published by Elsevier Science B.V.
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    Properties of speckle patterns generated through multiaperture pupils
    (ELSEVIER SCIENCE BV, 2001-05-15) Angel, L; Tebaldi, M; Trivi, M; Bolognini, N; Universidad EAFIT. Departamento de Ciencias Básicas; 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. © 2001 Published by Elsevier Science B.V.
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    Speckle interferometric technique to assess soap films
    (ELSEVIER SCIENCE BV, 2004-01-02) Tebaldi, M; Angel, L; Bolognini, N; Trivi, M; Universidad EAFIT. Departamento de Ciencias Básicas; Óptica Aplicada
    An speckle interferometric technique to monitor the thinning process of vertical soap film before the film rupture is presented. The interferometric arrangement consists in a double aperture pupil optical system which images an input diffuser. In a first step, a reference specklegram is stored in the computer buffer memory. Afterwards, the soap film is located in front of one pupil aperture, an uniform displacement of the diffuser is produced and a new speckle pattern is stored. The soap film status is characterized in terms of the changes that this dynamic phase object introduces in the correlation fringes obtained by applying a FFT algorithm to the resulting summed specklegram. This procedure is done in real time as far as the soap film evolves in the successive status. It is experimentally demonstrated that the soap film during drawing acts as a variable wedge. The correlation fringes behavior becomes an important tool to establish the wedge shaped soap film angle and the thickness variations. © 2003 Elsevier B.V. All rights reserved.
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    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 Aplicada
    The 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.