In-plane deformation measurement using ESPI carrier fringes

We present a technique to evaluate in-plane ESPI fringe patterns by the Fourier Transform Method (FTM). The spatial carrier is introduced, as in some contouring techniques, by symmetrically shifting the illumination beams. We present a three-dimensional theoretical model for the generation of the carrier fringes. The technique is demonstrated for a metallic plate which undergoes in-plane deformations under static conditions. Experimental results obtained with a cw laser are presented. We propose this technique for transient analysis. We describe an optical set-up without moving parts nor electro-optical devices and a twin-cavity Nd:YAG laser as illumination source. We have previously demonstrated this approach for both out-of-plane and shearing arrangements.