HOLOGRAPHIC INSPECTION SYSTEM WITH INTEGRAL STRESS INDUCER

An apparatus for remote inspection of a surface such as a drilled fastener hole of the type used in the aerospace industry includes a borescope having an integral stress inducer at one end for inducing stress directly in the surface to be evaluated. A holographic image of the surface is captured by directing a coherent radiation beam off the surface and shearing and recombining the reflected beam in a shearing interferometer. Inducement of stress and capture of the holographic images is synchronized by capturing the images at a frequency which is synchronized with the frequency of the induced stress wave in the surface, thus permitting overlapping of maximally stressed and unstressed images, and thereby eliminating the blurring which previously limited the application of holographic interferometry techniques in this context. The probe is rotatable to permit scanning of the surface and preferably includes a minimal number of optical elements in order to ensure maximum reliability, minimum cost, and the most effective space utilization.