Simultaneous measurement of slope and curvature with a three-aperture speckle shearing interferometer

A simple three-aperture speckle shearing arrangement is proposed for simultaneous measurement of slope and curvature of the specimen. The double exposed shearogram of the laser-illuminated specimen yields five distinct diffraction halos when subjected to Fourier filtering. The first-order halos on either side of the central halo give slope fringes of the specimen, together with relatively broad low-visibility curvature fringes. The second-order halos provide pure slope fringes with a sensitivity double that of the slope fringes obtained from the first-order halo.