Abstract
Comparative digital speckle pattern interferometry can be used for direct optical comparison of two nominally identical objects (master and test) and to display the result of the comparison in the form of an interference pattern related to the difference in deformation, shape or refractive index change of the two objects. Reconstructed virtual images of the master object in its initial and final states are used as references in the comparison process. The master interferogram can be recorded by two reference beams and the virtual images can be reconstructed separately. On the other hand, if the master interferogram is recorded by a single reference beam, the wavefronts of the initial and final states of the master object are reconstructed simultaneously. The difference correlation fringes that coexist with the sum correlation fringes are recorded and analyzed using both computer-simulated speckle patterns and real experiments. Theoretical aspects of this technique are discussed.