A technique to improve the sensitivity of in-plane deformation measurements on transparent and reflective specimens under tension or compression is described. The principle of this technique is that of moiré fringe multiplication. Experiments with 20-cycle/mm gratings yielded results having eighteen times the sensitivity of the conventional moiré technique. One fringe shift of each moiré fringe corresponded to an in-plane deformation of 2.7 µm.
Kazuya Matsumoto and Matsuo Takashima, "Improvement on Moiré Technique for In-Plane Deformation Measurements," Appl. Opt. 12, 858-864 (1973)