Non-invasive Mechanical Measurement for Transparent Objects by Digital Holographic Interferometry Based on Iterative Least-Squares Phase Unwrapping

A non-invasive measurement method for transparent objects using digital holographic interferometry based on iterative least-squares phase unwrapping is presented. Holograms are captured and processed by digital method. The phase reconstructed from holograms is wrapped. Continual and real phase is obtained by phase unwrapping. In this paper iterative unwrapping of phase difference is combined with least-squares unwrapping to eliminate errors. The relations between the phase variation of object wave and the thickness deformation and stress of transparent object are given. A polymethyl methacrylate (PMMA) specimen with a hole under uniform tensile force is tested by this method. The experimental results are in accordance with the theoretical ones. That means the method is correct.