Nondestructive evaluation of transparent sheets using a full-field digital gradient sensor

A full-field, non-contact, optical inspection tool for transparent materials is demonstrated. The technique is sensitive to refractive index and thickness variations caused by inhomogeneities and defects in an otherwise uniform sheet stock. The technique utilizes a 2D digital image correlation method to visualize and quantify angular deflections of light rays in two orthogonal directions to assess the uniformity. The principle of the method and its feasibility is demonstrated by visualizing the heat affected zone in a uniform borosilicate sheet sample.