Method and apparatus for speckle-shearing interferometric deformation analysis

An apparatus for generating an interferogram for detection of subsurface voids, separations and nonuniformities of pneumatic tires comprising:

• (a) a means for generating a beam of coherent light to illuminate and reflect light off of said pneumatic tire;
• (b) a camera, including a photographic media and a converging lens comprising a double convex lens having one-half of one of its surfaces covered by a transparent plate having flat parallel sides oriented at a predetermined angular inclination with respect to an axis of the lens and an end contacting the surface of the double convex lens at its mid-point, said transparent plate adapted to displace laterally some of the light reflected from the pneumatic tire, and the converging lens adapted to receive light and focus it onto the photographic media to expose and record a focused image of interference fringes formed from two images of said tire, displaced with respect to one another and having a major portion of their areas overlapping;
• and
• (c) a means for viewing the focused image of the pneumatic tire with interference fringes comprising a white light adapted to pass through a collimating lens for illuminating a first surface of the developed photographic media, that was exposed in said camera, such that said interference fringes appear on an opposite surface of said photographic media when viewed from a vantage point that is offset from the central axis of the collimating lens.