Holographic interferometry using photorefractive crystals: recent advances and applications

We present a real-time holographic interferometer using sillenite crystals for measurement of deformations of large diffusive objects. Two kind of optical heads have been investigated: a first system with a frontal crystal followed by a CCD camera with a short focal length objective, and a second system with imaging objective in front of the crystal, collecting light and imaging the object in its vicinity, the final image being observed with a second relay imagery. Both systems art compared with respect to their temporal behaviour and quality of interferograms. This interferometer is connected with quantitative phase-measurement systems. First, phase-shifting (PS) can be performed by translating a mirror in the reference beam, enabling acquisition of several interferograms subsequently processed leading to the object phase deformation. Nevertheless this requires stability of the object during the shifting process. Second, Fourier transform (FT) processing can be used on a single interferogram. This interferometer has been successively used in different applications: detection of defects in weakly disturbed structures using PS and monitoring of thermal deformation of an object with FT processing.