Holographic interferometry is an extension of interferometric measurement techniques in which at least one of the waves that interfere is reconstructed by a hologram.

The unique capabilities of holographic interferometry are due to the fact that holography permits storing a wavefront for reconstruction at a later time. Wavefronts which were originally separated in time or space or even wavefronts of different wavelengths can be compared by holographic interferometry. As a result, changes in the shape of objects with rough surfaces can be studied with interferometric precision.

One of the most important applications of holographic interferometry is in nondestructive testing (see Erf [1974], Vest [1981], and Rastogi [1994]). It can be used wherever the presence of a structural weakness results in a localized deformation of the surface when the specimen is stressed, either by the application of a load or by a change in pressure or temperature. Crack detection and the location of areas of poor bonding in composite structures are fields where holographic interferometry has been found very useful. An allied area of applications has been in medical and dental research, where it has been used to study the deformations of anatomical structures under stress, as well as for nondestructive tests on prostheses [Greguss, 1975, 1976; von Bally, 1979]; see also, Podbielska [1991, 1992].

Holographic interferometry has also proved its utility in aerodynamics, heat transfer, and plasma diagnostics.