A full-field reflection-mode digital gradient sensing method for measuring orthogonal slopes and curvatures of thin structures

A full-field optical technique capable of measuring angular deflections of light rays reflected off specularly reflective planar surfaces is developed. The method is aided by 2D digital image correlation to measure angular deflection of light rays. The principle of the method is described and the governing equations that relate light ray deflections to surface slopes are presented. The method is demonstrated by measuring the orthogonal surface slopes of a circumferentially clamped silicon wafer subjected to a central load and are shown to be in good agreement with the analytical solutions. The curvature fields are also computed by taking advantage of differentiation schemes integral to digital image correlation algorithms. The method is utilized to successfully quantify relatively small surface slopes of the order of 10 −5 rad caused by a curing layer of spin-coated epoxy on a thin (100 μm) silicon wafer. (Some figures may appear in colour only in the online journal)