Back to the future: From speckle to holography

At present, speckle interferometry is a well-assessed experimental technique for investigating on deformations of specimen and real object in static and dynamic loading configurations. Its operating principle has made feasible the development of computer-aided methods for full-field non-contact measurements of in-plane and out-of-plane displacements or their (approximated) derivatives with interferometric sensitivity. Due to these facts, speckle interferometry comes up as a more versatile technique with respect to its ancestor, the holographic interferometry. Mainly devoted, at its early stage of development, to semi-quantitative non-destructive testing, the progress in electronic imaging and computer hardware and the use of novel techniques for phase measurement, boosted the performance of speckle interferometers which, when using appropriate software, can now straightforwardly produce accurate whole field phase maps by which the detected physical quantities can be obtained by an unwrapping procedure.