Optical EngineeringSpatial phase-shifting technique in large image-shearing electronic speckle pattern interferometry
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A technique for deformation measurement by carrier is presented, which is based on large image-shearing shearography. A reference object is fixed on the side of a test object. They are all illuminated by one expanded laser beam. When a large image-shearing Wollaston crystal is used in front of a charge-coupled device (CCD) camera, one image of the object is superposed by one image of the reference surface. The carrier can be introduced by tilting the reference surface at a small angle. When Fourier transform is used to demodulate the modulated fringe pattern, the phase of deformation can be calculated and the deformation can be measured accurately. The principle of spatial carrier frequency modulation in large-shearing electronic speckle pattern interferometry (ESPI) is discussed. A typical experiment using a centrally loaded clamped circular plate is completed. Some experimental results are presented. The experimental results prove that the method can modulate a speckle pattern very well and the displacement fields can be measured effectively.