Twofold increase in sensitivity with a dual-beam illumination arrangement for electronic speckle pattern interferometry

A modification of a dual-beam illumination arrangement for electronic speckle pattern interferometry (ESPI) that leads to a twofold increase in the sensitivity to in-plane displacements is described. For each of the two illumination beams, the scattered light is observed along the direction of illumination, and these two components of the scattered light are then combined. The error in perspective caused by oblique observation can be almost corrected for by using two right-angle prisms in front of the object being studied. Experimental results including phasestepping are presented and compared with the results predicted by theory.