A system is described which uses a diode array TV camera to view the real-time fringes and digital electronics to measure and store the irradiance levels at a 100 × 100 array of points. A microcomputer calculates the phase at each point from the irradiance values obtained from three successive scans of the array made with the phase of the reference beam shifted in steps of 120° by means of a mirror mounted on a piezoelectric translator. The optical system permits four holograms to be recorded in quick succession, using a photothermoplastic camera, with the object illuminated from four different directions. Phase data from these holograms are processed in a microcomputer to determine the components of the vector displacement at each of these points; these figures can then be transferred to a fast computer for further processing to evaluate the stress distribution.
P. Hariharan, B. F. Oreb, and N. Brown, "Real-time holographic interferometry: a microcomputer system for the measurement of vector displacements," Appl. Opt. 22, 876-880 (1983)