This paper deals with the application of a speckle interferometer, which works on the new operating principle of double-focusing presented by the authors in recent studies, to the field of non-destructive testing (NDT). Using this interferometer, the components of displacement given by holographic interferometry can be measured, but with no need for an external reference beam. The implementation of this interferometry can be indifferently carried out by adopting a Michelson or a Mach-Zender configuration. In the paper a double-focus interferometer based on the Michelson design and sensitive to out-of-plane displacements was implemented and applied to a metallic specimen which simulates the deformations of a typical debonding.
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