Double shear speckle interlerometry for curvature measurement

A double shear speckle interferometer is presented that can provide information about the curvature, i.e., the second order derivative of the out of plane displacement of an object under study. Here, two shear interferometers are kept in sequence or tandem. The sheared images formed by the first interferometer are sheared once again by the second interferometer. The shears at the image plane can be adjusted for the required magnitude and orientation. A double exposure record is made on a photographic plate before and after the object deformation. When the processed plate is subjected to Fourier filtering, the curvature information is seen as a Moire of the two sheared slope fringe patterns. The results for a centrally loaded diaphragm are presented. The advantages of the present technique over the existing methods are discussed.