Direct determination of curvatures of bent plates using a double-glass-plate shearing interferometer

A single-exposure reflective moiré technique for the direct recording of curvature contours of laterally loaded plates is proposed. The specular reflection of a coherent, collimated beam of light by the loaded specimen is collected by a field lens and focussed onto a shearing interferometer. The shearing interferometer consists of two thin, identical plane-parallel glass plates, placed successively in the optical path near the focal plane and aligned at 45 deg to the optical axis. The two plates shear the narrow convergent beam from the lens twice optically, producing three sets of images—superposing one over the other—at the image plane. Curvature fringes result in the region overlapped by all three images.