COHERENT MOIRE TECHNIQUE FOR OBTAINING SLOPE AND CURVATURE OF STRESS PATTERNS

A method for studying the stress-induced birefringence over the area o f a sample by simultaneous application of shearing interferometry and moire techniques is dealt with. This is a method by which one can have the fringe pattern for the first and second derivative of the birefri ngence distribution in the form of the slope and curvature of the test wavefront. There is, however, a method of obtaining the second deriva tive fringe system by using a four-exposure holographic technique in w hich the pattern is generated by shearing of two holograms of deformed surface. This is related to stress distribution in the structure unde r test. In the presented method, on the other hand, the test wavefront carries the information of stress distribution in terms of birefringe nce. The suggested experimental setup can provide the slope and curvat ure of the test wavefront in a single exposure.