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 published on a yearly basis
Papers
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06 Jan 1994
TL;DR: In this paper, an optical fiber is illuminated at a point (V) by a collimated laser beam forming an angle (theta) with the fiber axis, and a light cone (divergence 2(theta), vertex V, axis coincident with the optical fiber) is generated.
Abstract: An optical fiber is illuminated at a point (V) by a collimated laser beam forming an angle ((theta) ) with the fiber axis. A light cone (divergence 2(theta) , vertex V, axis coincident with the fiber) is thus generated. The 3D curve (C) resulting from intersection of the light cone with a given opaque surface is recorded by a CCD camera coaxial with the optical fiber. Numerical processing of the curve image allows determination of the polar coordinates (with origin at point V) of each point of curve (C). This device allows internal topographic inspection of concave surfaces. So it may be considered as the counterpart in polar coordinates of classic methods using lateral projection of a light plane to determine contour lines of convex surfaces in cartesian orthogonal coordinates. Applications of this method to inspection of the human bucal cavity shows strong influence of laser light diffusion within human tissue in the resolution of resulting images.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
2 citations
TL;DR: Tay et al. as discussed by the authors proposed a phase extraction method from a single fringe pattern based on a couple of assumptions on the behavior of the fringe pattern, which are closely related to the well-known Fourier transform technique.
2 citations
TL;DR: An optical implementation of the circle Hough transform with an electrical lens with variable focal length and annular pupil is presented, suitable for real-time applications.
Abstract: We present an optical implementation of the circle Hough transform with an electrical lens with variable focal length and annular pupil. The system works under incoherent light and it is suitable for real-time applications. Validation experimental results are provided.
2 citations
TL;DR: In this paper, the authors proposed a method for orientation-selective enhancement of the first derivatives of a pure phase object based on the transport-of-intensity equation (TIE), which contains a term proportional to the scalar product of the phase gradient and an intensity gradient, which plays the role of amplifying factor of first derivatives.
2 citations
TL;DR: The characteristic features of the proposed interferometer, i.e. one-beam single-element scheme combined with external phase-shift control without moving parts, make a highly vibration insensitive device.
Abstract: We describe a robust interferometer with external phase-shift control that does not require moving parts. The optical architecture resembles a common-path device in which the interfering waves propagate together in one collimated beam passing through the test sample. The collimated beam is incident on a calcite plate, which produces a polarization selective lateral translation and superposition of the reference and test waves. The characteristic features of the proposed interferometer, i.e. one-beam single-element scheme combined with external phase-shift control without moving parts, make a highly vibration insensitive device. Validation experiments are presented.
2 citations
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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
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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
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