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Author

José A. Ferrari

Other affiliations: Simón Bolívar University
Bio: José A. Ferrari is an academic researcher from University of the Republic. The author has contributed to research in topics: Interferometry & Image processing. The author has an hindex of 19, co-authored 132 publications receiving 1297 citations. Previous affiliations of José A. Ferrari include Simón Bolívar University.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a fiber optic variable attenuator using a dichroic polarizer sheet illuminated by a heating beam is described, which allows one to control the amount of light to be coupled into an optical fiber.
Abstract: A fiber optic variable attenuator using a dichroic polarizer sheet illuminated by a heating beam is described. The light absorbed by the polarizer induces a thermal lens, which allows one to control the amount of light to be coupled into an optical fiber. Some experiments demonstrating the thermal lens action are presented.

2 citations

Proceedings ArticleDOI
TL;DR: For optical systems under severe defocus, a method to estimate the focus slices (i.e. in-focus region of each of the acquired images of a stack) from Fourier based all-in-focus reconstructed image is proposed.
Abstract: For optical systems under severe defocus, we propose a method to estimate the focus slices (i.e. in-focus region of each of the acquired images of a stack) from Fourier based all-in-focus reconstructed image. Experimental results are provided.

2 citations

Proceedings ArticleDOI
06 Jul 1999
TL;DR: In this paper, the authors present an overview of several active areas of research that include nonlinear optic spectroscopy, applied optics, and theoretical modeling of laser dynamics, and present some of the experimental and theoretical studies in lasers and optics that have currently been performed in our country.
Abstract: We present some of the experimental and theoretical studies in lasers and optics that have currently been performed in our country. We present an overview of several active areas of research that include nonlinear optic spectroscopy, applied optics, and theoretical modeling of laser dynamics.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

2 citations

Proceedings ArticleDOI
09 Sep 2019
TL;DR: A dual-sensitivity profilometry technique is presented, which is based on defocused projection of binary and sinusoidal fringe patterns with a high and low-frequency spatial carrier, respectively, to reduce the data acquisition time and maintain the quality of the unwrapped phase.
Abstract: In fringe projection profilometry, temporal phase unwrapping is an essential procedure to recover an unambiguous absolute phase even in the presence of large discontinuities or spatially isolated surfaces. In this work, a dual-sensitivity profilometry technique is presented, which is based on defocused projection of binary and sinusoidal fringe patterns with a high and low-frequency spatial carrier, respectively. The binary defocusing techniques (based on PWM or square-wave profile patterns, whose pitch is relatively narrow) have demonstrated successful for high-quality three-dimensional shape measurement when the projector presents a nonlinear response. But they suffer if pitch fringe is wide. On the other hand, using dual sensitivity profilometry, the quality of the unwrapped phase is determined by the high-frequency carrier. Thus, working with only one binary pattern, one can use a single defocusing level (low) in order to reduce the data acquisition time and maintain the quality of the unwrapped phase. Experimental results are presented to verify the success of the proposed method.

2 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a selfconsistent density functional method using standard norm-conserving pseudopotentials and a flexible, numerical linear combination of atomic orbitals basis set, which includes multiple-zeta and polarization orbitals, was developed and implemented.
Abstract: We have developed and implemented a selfconsistent density functional method using standard norm-conserving pseudopotentials and a flexible, numerical linear combination of atomic orbitals basis set, which includes multiple-zeta and polarization orbitals. Exchange and correlation are treated with the local spin density or generalized gradient approximations. The basis functions and the electron density are projected on a real-space grid, in order to calculate the Hartree and exchange-correlation potentials and matrix elements, with a number of operations that scales linearly with the size of the system. We use a modified energy functional, whose minimization produces orthogonal wavefunctions and the same energy and density as the Kohn-Sham energy functional, without the need for an explicit orthogonalization. Additionally, using localized Wannier-like electron wavefunctions allows the computation time and memory required to minimize the energy to also scale linearly with the size of the system. Forces and stresses are also calculated efficiently and accurately, thus allowing structural relaxation and molecular dynamics simulations.

8,723 citations

01 Feb 2009
TL;DR: This Secret History documentary follows experts as they pick through the evidence and reveal why the plague killed on such a scale, and what might be coming next.
Abstract: Secret History: Return of the Black Death Channel 4, 7-8pm In 1348 the Black Death swept through London, killing people within days of the appearance of their first symptoms. Exactly how many died, and why, has long been a mystery. This Secret History documentary follows experts as they pick through the evidence and reveal why the plague killed on such a scale. And they ask, what might be coming next?

5,234 citations

Journal Article
TL;DR: In this article, a fast Fourier transform method of topography and interferometry is proposed to discriminate between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour generation techniques.
Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

3,742 citations

Journal Article
TL;DR: In this article, a self-scanned 1024 element photodiode array and a minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100.
Abstract: A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

1,300 citations

Journal ArticleDOI
TL;DR: An overview of state-of-the-art phase shifting algorithms for implementing 3D surface profilometry is presented to provide a useful guide to the selection of the most appropriate phase shifting technique for a particular application.

611 citations