Author
J A Leendertz
Bio: J A Leendertz is an academic researcher from Loughborough University. The author has contributed to research in topics: Speckle pattern & Interferometry. The author has an hindex of 3, co-authored 3 publications receiving 772 citations.
Papers
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TL;DR: In this article, the distribution of intensity in the resultant pattern depends on the relative phases of the component patterns, and by measuring the correlation between the resultant patterns at two different times a change of relative phase is detected.
Abstract: When a surface is illuminated with laser light it has a speckled appearance due to random interference. If two speckle patterns are superimposed the distribution of intensity in the resultant pattern depends on the relative phases of the component patterns. By measuring the correlation between the resultant patterns at two different times a change of relative phase is detected. This leads to a versatile method of measuring either the normal or in-plane components of displacement over the whole of a surface at one time.
485 citations
TL;DR: In this paper, a fringe system is obtained showing contours of constant slope resolved in the direction of image displacement, which is a comparison with result obtained by holographic interferometry.
Abstract: The surface to be studied is illuminated with laser light and two images are formed, displaced relative to one another in the image. Speckle pattern interferometry is used to measure phase changes between the two images resulting from deformation of the surface. A fringe system is obtained showing contours of constant slope resolved in the direction of image displacement. A comparison is made with result obtained by holographic interferometry.
298 citations
TL;DR: In this paper, the theoretical interpretation of speckle pattern interference fringes produced by small surface displacements is considered, and a new arrangement for a specke pattern interferometer is described, which can be employed to determine the components of plane strain tensors.
Abstract: The theoretical interpretation of speckle pattern interference fringes produced by small surface displacements is considered. New arrangements for a speckle pattern interferometer are described. Firstly the object is illuminated by plane wavefronts propagating at the same angle to orthogonal axes in the plane of the object. Secondly a 'composite speckle interferogram' is obtained when adjacent regions in the object are illuminated by different configurations of wavefront. Part of the object is illuminated as previously described, the remainder is illuminated by two wavefronts propagated at equal angles to a single axis in the surface. Interferograms made using this system can be employed to determine the components of plane strain tensors. A method for the measurement of elastic constants is experimentally verified and white light projection of frozen speckle pattern interference fringes is briefly discussed.
21 citations
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2,002 citations
TL;DR: In this paper, a theoretical and experimental study of speckle as applied to ultrasonic imaging is presented, and several techniques for generating independent speckles patterns for use in image summation schemes are proposed.
332 citations
TL;DR: In this article, the authors measured local displacements in the plane of an object surface illuminated by coherent light by recording double-exposure photographs of it and using the optical transform of the negative image.
Abstract: Local displacements in the plane of an object surface illuminated by coherent light may be measured by recording double-exposure photographs of it. When the surface is illuminated symmetrically by two oblique beams, ‘speckle correlation fringes’ appear in the doubly exposed negative, due to the non-linear nature of the photographic recording. Factors affecting the visibility of these fringes and the range of displacement which can be measured are discussed. The fringe visibility falls to zero for displacements larger than a speckle width, but measurements can then be performed upon the optical transform of the negative image. With uni-directional object illumination, the in-plane displacement can be measured on a point-by-point basis in magnitude and in direction from Young's fringes observed. With two symmetrical oblique illuminating beams the effect of a small surface strain is displayed, even if large lateral displacement has occurred, by using spatial filtering when viewing the photographic image.
302 citations
TL;DR: In this paper, a fringe system is obtained showing contours of constant slope resolved in the direction of image displacement, which is a comparison with result obtained by holographic interferometry.
Abstract: The surface to be studied is illuminated with laser light and two images are formed, displaced relative to one another in the image. Speckle pattern interferometry is used to measure phase changes between the two images resulting from deformation of the surface. A fringe system is obtained showing contours of constant slope resolved in the direction of image displacement. A comparison is made with result obtained by holographic interferometry.
298 citations
TL;DR: In this paper, surface displacement can be measured by recording a double-exposure photograph of the laser-illuminated object, followed by optical processing of the recorded speckle-pattern image.
Abstract: Surface displacement can be measured by recording a double-exposure photograph of the laser-illuminated object, followed by optical processing of the recorded speckle-pattern image. The analysis can either be on a point-by-point basis, or by a spatial filtering technique which resolves the motion in any desired direction orthogonal to the line of sight. The limits within which the technique may be used to measure lateral translations and rotations of the surface are examined theoretically and experimentally, and the effect of lens aberrations and surface scattering properties are discussed. Surface tilt may also be measured by recording a defocused double exposure image and analysing its optical transform. The photographic techniques described can be extended to measuring surface vibration, by recording a single ‘time-averaged’ exposure and examining the modified optical transform fringe pattern.
294 citations