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Journal ArticleDOI

Speckle shearing interferometry: a new method

15 Aug 1982-Applied Optics (Optical Society of America)-Vol. 21, Iss: 16, pp 2865-2867
TL;DR: The main methods of speckle shear interferometry include Michelson's interferometric arrangement, two or multiple apertures in conjunction with a lens and defocusing, and use of parallel plates and wedges in front of the lens with or without aperture.
Abstract: The main methods of speckle shear interferometry include Michelson's interferometric arrangement, two or multiple apertures in conjunction with a lens and defocusing, and use of parallel plates and wedges in front of the lens with or without apertures. It has been our experience that the partial slope fringes are not localized at the plane of the specklegram in the case when defocusing is used for shear.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors proposed an original scheme for the systematic treatment of TVH and to review the existing techniques according to it, and split the measurement process into four highly independent stages (illumination and observation geometry, temporal treatment, secondary-correlogram generation and fringe-pattern analysis) and establish a common notation to formulate the corresponding techniques.
Abstract: Television holography (TVH) can be defined as `the family of optical measurement techniques based on the electronic recording and processing of holograms'. Image-plane TVH was introduced in the early 1970s with the name `electronic speckle-pattern interferometry' (ESPI). Since then, TVH has undergone an impressive development and become one of the most promising optical techniques for non-destructive testing and industrial inspection. The aim of this review is to propose an original scheme for the systematic treatment of TVH and to review the existing techniques according to it. In this approach we split the measurement process into four highly independent stages (illumination and observation geometry, temporal treatment, secondary-correlogram generation and fringe-pattern analysis) and establish a common notation to formulate the corresponding techniques. Such a strategy allows the free combination of the techniques proposed for each stage as building blocks to obtain every particular variant of the whole TVH measurement process, whether it has already been reported or not, and also the incorporation of new techniques while retaining compatibility with the existing variants of the previous and following stages.

90 citations

Book ChapterDOI
TL;DR: In this paper, a survey on the formation of the fringe patterns observed in these methods is presented, which helps in deriving dependences of their shape and visibility on object deformation parameters and optical systems by starting from the correlation properties of the light scattered from diffuse objects.
Abstract: Publisher Summary This chapter focuses fringe formations in deformation and vibration measurements using laser light. The chapter discusses a survey on the formation of the fringe patterns observed in these methods. The chapter helps in deriving dependences of their shape and visibility on object deformation parameters and optical systems by starting from the correlation properties of the light scattered from diffuse objects, and discuss the mutual relationships and features of each method by putting physical interpretations on derived mathematical relations. In holographic interferometry and speckle interferometry, the fringe shape represents the distribution of the phase change of the scattered light caused by object deformation, while the fringe visibility depends on the overlap of the corresponding speckle pair, therefore, on speckle displacement and speckle size. In speckle photography, on the other hand, the fringe shape represents the speckle displacement, while the fringe visibility is affected by the speckle decorrelation accompanying the displacement. In addition the relations derived in the present chapter would deliver a quantitative basis for selecting an adequate method of measurement and the optimum manner of signal processing in these modem interferometric techniques.

56 citations

Journal ArticleDOI
TL;DR: In this article, a method to measure the derivative of displacement using time variation changes in the object together with Fourier transform analysis in speckle shear interferometry is presented.
Abstract: A method to measure the derivative of displacement using time variation changes in the object together with Fourier transform analysis in speckle shear interferometry is presented. The concept of the method is that the object is deformed continuously and a large number of sheared images of the object motion are acquired using a high speed CCD camera. The derivative of the object deformation is then retrieved from this large set of data using Fourier transformation. The method is capable of obtaining information for object displacements over 500 µm, which is a very difficult task when using conventional electronic speckle pattern shearing interferometry. Theory as well as some of the experimental results with the new method are delineated.

52 citations

Journal ArticleDOI
TL;DR: A simple electronic speckle-shearing-pattern interferometer, in which the image of an object is focused and sheared with a split lens onto a diffuser, is described.
Abstract: A simple electronic speckle-shearing-pattern interferometer, in which the image of an object is focused and sheared with a split lens onto a diffuser, is described. The sheared images on the diffuser are focused by a television camera and then digitized and processed in a host computer. The results obtained for two basic types of shearing, lateral and radial, are presented.

35 citations

Journal ArticleDOI
TL;DR: Speckle and speckle-shearing interferometer geometries have been combined into a single setup by the use of a small ground glass reference diffuser on the lens pupil to obtain the moire curvature pattern.
Abstract: Speckle and speckle-shearing interferometer geometries have been combined into a single setup by the use of a small ground glass reference diffuser on the lens pupil. Sheared fields are obtained with a split lens arrangement. Judicious aperturing results in separated diffraction halos at the FT plane. Fringe patterns corresponding to out-of-plane displacement and slope are obtained by filtering via the appropriate halos. A four-aperture arrangement coupled with shearing elements extends the method to obtain the moire curvature pattern.

27 citations

References
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Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: A new image-shearing camera which focuses two laterally sheared images at the film plane and becomes a shearing interferometer, which directly measures the derivatives of the surface displacements.
Abstract: This paper describes a new image-shearing camera which focuses two laterally sheared images at the film plane. With coherent illumination, this camera becomes a shearing interferometer, which directly measures the derivatives of the surface displacements. This strain measuring tool enjoys several advantages over the conventional, holographic, and speckle interferometry, namely, (1) better fringe quality (than speckle interferometry); (2) does not require special vibration isolation; (3) very simple optical setup; (4) direct determination of strains; and (5) extended controllable range of sensitivity.

201 citations

Journal ArticleDOI
Donald E Duffy1
TL;DR: An easily implemented method of measuring in-plane surface displacement by photographing an object through two laterally displaced apertures is described and the experimental results are presented.
Abstract: An easily implemented method of measuring in-plane surface displacement by photographing an object through two laterally displaced apertures is described and the experimental results are presented. The displacement is displayed as a pattern of moire fringes over the image. No previously constructed grids or rulings are required as in normal moire devices. The method is noncontacting and requires no special surface preparation. The sensitivity is easily adjusted and is shown to be equivalent to that obtained using double-exposure holography or speckle pattern interferometry techniques. The method has potential application in mechanically unstable environments or where the conditions are such that grids or strain gauges cannot be attached to the object.

144 citations

Journal ArticleDOI
TL;DR: An improved speckle-shearing interferometric method is presented that allows simultaneous determination of derivatives of surface displacements of a structure with respect to four different directions and thus is adaptable to nonlaboratory environments.
Abstract: An improved speckle-shearing interferometric method is presented that allows simultaneous determination of derivatives of surface displacements of a structure with respect to four different directions. The technique relaxes several limitations associated with conventional interferometry and thus is adaptable to nonlaboratory environments. The relevant theory is presented, and the method demonstrated by determining spatial derivatives of in-plane and out-of-plane displacements of statically loaded and vibrated structures.

94 citations

Journal ArticleDOI
TL;DR: Speckle-shearing interferometry as discussed by the authors is an interferometric method for flexural deformation, which does not require the surface of the specimen must be of mirror quality.
Abstract: A specimen illuminated by coherent light is imaged by a camera through a shearing mechanism so that the speckle from one point on the surface can be made to interfere with the speckle from a neighboring point. The resultant speckle pattern is recorded. By mechanically interfering the recorded speckle pattern corresponding to deformed and undeformed states of the specimen, respectively, using double-exposure technique, a speckle-moire-fringe pattern is generated. These fringes which depict derivatives of deflections of the specimen are made visible by spatial-filtering technique. Speckle-moire fringes can also be obtained in real time. This method is a new interferometry and will be referred to as “speckle-shearing interferometry”. Speckle-shearing interferometry has the same function as Ligtenberg's technique. However, it does not have the sometimes inconvenient requirement of Ligtenberg's technique that the surface of the specimen must be of mirror quality. The new technique will be particularly useful in studies of flexural deformation such as flexed beams and plates. Although speckle-shearing interferometry is an interferometric method, it overcomes several of the limitations associated with holographic and speckle interferometries, namely: (1) the setup is simple and does not need laborious alignments of optical components, (2) it does not require stringent mechanical and ambient stabilities, (3) coherent requirement of light is greatly relaxed, and (4) the sensitivity is reduced that somehow fills the gap in sensitivity between moire techniques and holographic or speckle interferometry.

82 citations