Optical holography Holographic interferometry

It was in 1947 that Englishman Dennis Gabor came up with the idea of holography. But it wasn't until 1962, two years after the American Maiman had operated the first laser (a ruby laser, in this case), that holography really took off, with the recording of the first holograms of three-dimensional light-scattering objects by the Americans Leith and Upatnieks and the Russian Denisuyk, using the first continuous-emission gas lasers (helium-neon). These holograms, especially those by the Russian, have given rise to what is known as "image holography", known to the general public for its spectacular quality (striking full relief of giant holograms). A relatively well-developed application of image holography today is the special type of hologram used on bankcards, "cartes grises" and banknotes to make them tamper-proof.

The use of holograms as optical components (mirrors, lenses, separators, etc.) is undoubtedly another promising example of holography.

A few years later, in 1965, several laboratories were at the origin of holographic interferometry and the real start of holography in industry. Researchers realized that excessive movement of the object (or any other element of the set-up) during hologram recording resulted in the appearance of spurious dark and light interference bangs on the rendered image, which could completely alter it. To obtain a good quality hologram, it was therefore necessary to eliminate these parasitic bangs, ensuring sufficient stability of the object and the various elements of the montage during the exposure time. But, on the other hand, these parasitic interference bangs could be exploited to provide valuable quantitative information on the displacements that gave rise to them. A major shortcoming for an image hologram became very important for industrial applications.

Anything that deforms in nature is a priori susceptible to analysis by holographic interferometry: from the deformation of an eardrum under the effect of a supersonic airplane bang to the deformation of engine components in operation, via the growth of a crystal or variations in air density around an airplane wing profile.

Not only are major companies (Aérospatiale, Renault, PSA, SEP, Onera, Snecma, EDF, Thomson...) are increasingly using holography on a routine basis, but what's new is that SMEs and SMIs are turning to holography to solve specific problems [research into the origin of noise in structures, identification of defects in materials (particularly composites), modal analysis, measurement of dynamic deformations, control of brazing, identification of areas of weakness without having to carry out destructive fatigue tests, improvement or validation of a calculation code...] by turning to specialized organizations....