Showing papers by "José A. Ferrari published in 1999"

Diffracted field by an arbitrary aperture

Abstract: Diffraction patterns of apertures on screens uniformly illuminated are standard calculations in undergraduate optics and acoustics courses. These calculations imply two-dimensional (2-D) integrations which are often performed in the far zone, at moderate angles of diffraction, i.e., using Fresnel and Fraunhofer approximations. In this note, the 2-D integration is reduced to a 1-D parametric integration over the perimeter of the aperture—resembling the Rubinowicz’s representation of the Kirchhoff diffraction integral—which allows numerical evaluation with few computational resources. The proposed formula allows mathematically exact calculation of the near-field, in the context of scalar wave theory. Explicit calculations for circular and elliptical apertures are shown.

Fast Hankel transform of nth order

Abstract: An analytical form that provides a computationally efficient algorithm for numerical evaluation of the Hankel transform of nth order by fast-Fourier-transform techniques is presented and tested with some well-known functions.

Robust one-beam interferometer with phase-delay control.

Abstract: A robust one-beam interferometer with external phase-delay control is described. The device resembles a Mach-Zehnder interferometer in which the two arms are together in one collimated beam. However, the proposed device is not an amplitude-division interferometer but a wave-front division one. The phase-delay control occurs at the interferometer output with the help of two polarizing beam splitters, a quarter-wave plate, a Faraday rotator, and a polarizer. An additional phase delay is introduced by application of an electrical current to the Faraday rotator or by rotation of the polarizer (the latter is of topological origin), which permits the use of techniques of phase-stepping interferometry.

Current sensor using heterodyne detection

Abstract: Based on the Faraday effect for measuring ac current, we describe a fiber-optic sensor that uses laser-diode intensity modulation to perform heterodyne signal detection. The sensor output at the carrier frequency is used as a reference signal to normalize the results. The sensing element consists of a few coils low-birefringence fibers between polarizers. We built the current sensor described above and tested its performance—sensitivity and noise—as functions of the angle between polarizers.

Space integrating joint transform correlator using a moving grating

Abstract: A new one-step joint transform correlator (JTC) is presented, in which the joint transform of the images to be correlated is filtered by a moving Ronchi ruling. An alternative JTC architecture without moving parts using two Ronchi rulings is also suggested. A lens produces the spatial integral of the product of the joint transform image and the trans- mission factor of the Ronchi ruling, and a single element detector is used to capture the integral. The amplitude of the light modulation on the detector gives the cross-correlation function of the input images at coor- dinates (0,0) without major processing. Therefore, in principle this tech- nique significantly reduces the time required to evaluate the cross- correlation function, compared to that for usual JTCs. Experimental validation of the proposed one-step architecture is presented. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01807-3)

Laser and optics in Uruguay

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.

Pancharatnam phase-shifting interferometry: Spatial and temporal applications

Abstract: where (x,y) are spatial coordinates, t is the time, I0 is the average intensity, V is the visibility, φ is the phase to be reconstructed and δn (n = 1,2,) is the shift induced in the reference phase At least three interferograms are required for wavefront reconstruction, because there are three variables in (1) When I0, V and φ are time independent, the reference phase is usually varied by translating one of the interferometer mirrors with a piezoelectric transducer This procedure is not applicable in a time dependent situation, eg in an interferometric vibration sensor We have described a new PSI method in which phase-shifts are produced by changing the so-called Pancharatnam's phase With the proposed method, arbitrary phase-delays between the reference and test waves can be induced without varying the length of the optical paths Suppose that the waves traveling through both interferometer arms are linear polarized orthogonal to each other, and that they pass through a λ/4-waveplate (QW) with its fast axis at 45° respect to the polarization directions (Figure la) After QW there are two waves of opposite helicities According to Pancharatnam's theorem, when these waves pass through a polarizer (P) they acquire an extra phase delay (δ) given by δ = Ω/2, where Ω is the area enclosed by the trajectory of polarization states on the Poincare sphere (the "lune" RALPR in Figure lb) It is easy to see that δ = 2θ, where θ is the angle between the transmission direction of P and the fast axis of QW This method of phase shifting can be applied with different interferometric configurations The polarizer can be mechanically rotated or, alternatively, the waves of opposite helicities could be delayed with a Faraday rotator The method can be used for vibration sensing by projecting the waves of opposite helicities simultaneously on a series of polarizers with different orientations