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Modified electronic speckle pattern shearing interferometry for simultaneous derivative map measurements

Electronic speckle pattern shearing interferometry (ESPSI) allows for the measurement of displacement derivative maps. To monitor the stress/strain state of an object surface and its material properties, it is necessary to measure more than one displacement derivative map. The conventional configuration of ESPSI has been modified by parallel adaptation of Michelson shearing interferometers and an optoelectronic/image processing head with the capability of simultaneous capturing of 2 images. The automatic analysis of speckle fields is performed by temporal phase stepping method with the separation of the information by orthogonal polarization states. In the paper the opto-mechanical and electronic configuration of the system is presented. The experimental results obtained in the modified ESPIS system, when applied to determination of shear strain in a tensile loaded aluminium specimen are also presented.