Determination de rugosite par correlation des speckles dans l'image de la surface diffusante

Two speckle patterns are recorded on a photographic plate which lies in the image plane of a rough surface. The angle of incidence of the parallel beam illuminating the object is slightly varied between the two exposures. It is possible to localize and measure different roughness of the surface by observing suitably the photographic plate. We discuss the experimental setup and the effects of the optical system.     

Detection of small displacements of diffuse objects illuminated by a speckle pattern

The detection of axial displacements of an object imaged with a laser beam on to a photographic plate is not easy because the aperture of the imaging system is not generally large and the variation of its impulse response with the defect of focus is then relatively slow. We propose here a double-exposure method in which the object is illuminated under a large angle of incidence θ by a random beam which is generated by a laser-illuminated ground glass. After the first exposure, the object undergoes an axial translation ? and the photographic plate is laterally displaced. ? is small and we can assume that this axial translation results only in a lateral displacement ? tg θ of the incident amplitude from the ground glass. Under these conditions, the two intensity distributions recorded by the photographic plate are no more identical and the contrast of the Young's fringes observed in the Fourier plane of the photographic plate is a decreasing function of ?.     

The measurement of slope using shearography

This paper presents an optical method which is based on speckle-shearing interferometry for the measurement of the slope at any point of an object. The object under study is illuminated by an expanded laser beam and its image is recorded on a photographic plate placed at the image plane of an image-shearing camera. A second exposure on the photographic film is made after the light source is moved slightly. The resulting photograph yields a fringe pattern which represents lines of constant displacement gradients. Theory of the method as well as some experimental results are presented.     

Essay Review-Scholarly froth and engineering skeletons

Holography is a two-stage process of photography using coherent light from a laser to illuminate the scene. In the first stage a hologram is formed by combining the light scattered from the object and the direct laser beam on a photographic plate. In the second stage a three-dimensional image is reconstructed without the use of lenses, by directing the laser beam through the hologram. Applications of holography include information storage, recording of images in depth, the use of holograms as optical elements, and as a means of performing precise interferometric measurements on three-dimensional objects of any shape and surface finish.     

Vibration measurement by vibrating-plate holograms

If a hologram of a vibrating object is recorded on a photographic plate which vibrates synchronously with the object, the reconstructed image produces equi-amplitude fringes of the object vibration, the amplitude of which is reduced by a constant determined from the amplitude of the plate vibration. This phenomenon can be used as a method to extend the measurable range of vibration amplitudes, and some experimental results are shown.     

Utilisation des franges d'interference en lumiere diffuse pour l'etude de l'etat de surface d'un diffuseur

A diffuser, illuminated successively by light of two neighbouring wavelengths, produces on a photographic plate placed in a parallel plane two intensity distributions which are homothetic except for certain decorrelation terms. This homothecy (scale variation) can be compensated by a longitudinal displacement of the photographic plate between the two exposures and consequently, the decorrelation depends only on the structure of the diffuser. Under these conditions, if the photographic plate is given an additional displacement in its own plane between the two exposures, the contrast of Young's fringes obtained in the Fourier plane characterises the roughness of the diffuser.     

Production of binary amplitude gratings with arbitrary opening ratio and variable period

A simple double exposure technique is proposed for making binary amplitude gratings with preset opening ratio. Commercially available Ronchi type master ruling is imaged onto the photographic plate by a laser projection system. The controlled lateral displacement of the ruling or the photographic plate between two exposures results in the composite grating with the required opening ratio. A zoom-effect spherical beam projection system is suggested for producing binary gratings with continuously variable period.     

Double exposure, multiple-field particle image velocimetry for turbulent probability density

A particle image velocimeter method is described in which double exposed fields of particles moving in a two-dimensional slice of a steady turbulent flow are photographed repeatedly to build up a statistical ensemble of flow field realizations on a single photographic plate. Each interrogation spot on the plate contains a sample of the probability density function of the two components of velocity that lie in the photographic object plane, assuming paraxial photography. Theory is developed showing how this sample can be measured by two-dimensional spatial correlation analysis, followed by deconvolution to remove the effects of finite particle image size. The probability density measurements are biased inherently against large velocities, but these effects can be minimized and/or corrected.     

Observation of a phase object using carrier-frequency photography

A Ronch ruling is photographed through a phase object which produces deformations in the grating lines. The superposition of the straight rulings and the deformed ones on the photographic plate gives rise to a moiré pattern which characterises the phase variations of the object.     

Ultrasonic absorption constant in liquids by an improved optical method

The optical diffraction set up as originally employed byDebye andSears andLucas andBiqdard has been used with various modifications to estimate the intensity of sound fields at two or more points along the axis of an ultrasonic beam travelling in a liquid and thereby to determine the absorption coefficient of the liquid medium. Almost all these methods involve a two step operation with the attendant possibility of errors due to variation in the conditions under which the two observations are made. In the method here reported two axially parallel beams of parallel monochromatic light are made to traverse the liquid normally to the direction of propagation of the sound beam and the resulting diffraction spectra are brought to focus on a common photographic plate. Sound intensities at two points separated by a known distance are thus measured simultaneously under identical conditions. Absorption coefficients calculated for half a dozen liquids by this method are reported. The values compare very favourably with those obtained by other precision methods.     

An optical topographic technique to study the dissolution kinetics at dislocation sites in sodium chloride crystals

A technique has been developed to study the dissolution kinetics at dislocation sites in sodium chloride single crystals. A parallel beam of light is allowed to fall upon the silvered etched surface of the crystals and the reflected beam is received back on a photographic film. The pattern thus obtained on the photographic film gives information about (i) the structure of the etched surface (ii) the nature of the surface forming the pit and (iii) the slope of the pit at the source of dissolution.     

Detection of small displacements with the help of an auxiliary diffuser

We propose here a method of detection of small displacements, in which the speckled image of the object is modulated by an additional speckle. Due to this additional speckle, the Fourier transform fringes of the doubly-exposed photographic plate undergo a diminution of contrast when the object suffers a displacement.     

Speckle photography by birefringent plates

This paper describes a birefringent system with which it is possible to record three laterally shifted speckle images of an object, on a photographic plate. The recording is made with only two exposures. The exposure times and relative positions of the images are adjusted automatically by the birefringent plates.     

分束量可调的等光程平行分束技术

基于厚波片平行分束特性,提出了一种分束量可调的等光程平行分束技术,给出透射式和反射式两种平行分束光路.透射式平行分束光路由厚波片和1/2波片组成,反射式平行分束光路由分束镜、厚波片、1/4波片和反射镜组成.通过旋转厚波片可实现分束量的调节.实验结果和理论值相吻合,验证了该技术的有效性.     

分束量可调的等光程平行分束技术

基于厚波片平行分束特性,提出了一种分束量可调的等光程平行分束技术,给出透射式和反射式两种平行分束光路.透射式平行分束光路由厚波片和1/2波片组成,反射式平行分束光路由分束镜、厚波片、1/4波片和反射镜组成.通过旋转厚波片可实现分束量的调节.实验结果和理论值相吻合,验证了该技术的有效性.     

Multiplexing with an extended broad-band source

Carrier-frequency photography in incoherent light can be employed for storing a number of real amplitude objects on a single photographic plate. The objects are placed, successively in contact with a grid and a frequency-plane mask selects two different spectral orders for each object. Different intensity distributions modulate different fringe systems in the image plane and can be retrieved with appropriate filters.     

Correlation of light beams scattered at different angles by a ground glass

A quantitative study of the contrast of Young's fringes obtained with a fully scattering element by double exposure technique as a function of the inclination of the incident beam and the effect of varying the scatterer- photographic plate distance upon the γ - θ curve have been presented.     

Visualization of isoclinics and isochromatics in a birefringent slice optically singled out in a three-dimensional model

The speckle patterns scattered from the boundary surfaces of a birefringent slice are imaged on a photographic plate. The method consists in taking account of the variations of the statistical properties of the two superimposed speckle patterns. The results are similar to those obtained by observing this thin slice in a classical parallel or crossed polariscope. This method does not need the slicing of the model.     

Speckle-pattern interferometry applied to the study of phase objects

If a speckle pattern is photographed through a phase object, the individual speckles are displaced over varying distances depending upon the phase irregularities in the object. A double exposure is made, the object being present during one of the two exposures only. When the processed photographic plate is observed through an aperture stop in the Fourier transform plane, interference fringes representing contours of the optical path gradient are obtained. The sensitivity of the method and the direction along which the gradient is measured can be varied by modifying, respectively, the distance of the Fourier-plane aperture from the optical axis and its azimuth.     

Measurement of an arbitrary parallel displacement of a rigid body by using polychromatic speckle patterns

A novel speckle method for measuring the parallel displacement of a rigid body in an arbitrary direction is presented. The amount of displacement as well as its angle made with the optical axis is to be measured from the Fourier transform patterns of a doubly exposed photographic plate.