Slope measurement by two-wavelength electronic shearography

A technique is presented for the slope measurement of objects using an electronic shearography system. To detect the gradients of an object shape, a laser diode is modulated to produce two wavelengths on successive image frames. These two frames are then subtracted to generate correlation fringes which depict slope variations of the object surface. The theory of this technique is described and measurements of conical, cylindrical, and spherical test objects are presented. Comparisons of experimental results with theoretical data are demonstrated to be in good agreement. The implementation of fringe analysis using phase stepping techniques is also discussed. (C) 1997 Elsevier Science Ltd.