A novel approach to time-lapse interferometry and contouring is introduced that uses television rather than photographic techniques. A first interferogram is stored on a video storage device such as a magnetic disk. After a change in the stress of the object, a second interferogram is electronically compared to the stored pattern to form a signal representative of the fringe pattern caused by the deformation. This signal may be directly displayed on a cathode-ray tube or employed by some automatic inspection device.
A. Macovski, S. D. Ramsey, and L. F. Schaefer, "Time-Lapse Interferometry and Contouring Using Television Systems," Appl. Opt. 10, 2722-2727 (1971)