Analysis of coherent symmetrical illumination for electronic speckle pattern shearing interferometry

In an effort to find a non-contact technique capable of providing measurements of in-plane strain, the authors designed a speckle shearing interferometer using symmetrical coherent illumination. It is presented the analysis of the sensitivity to displacement and strain of this interferometer, together with the analysis of the phase-stepping of the resultant fringe patterns. A new notation is introduced alongside this analysis to define the interference components in speckle shearing interferometers using multiple illumination beams. Experimental results show the fringe patterns and the phase stepping, in support of the theoretical analysis.