Holographic interferometry using photorefractive crystals for quantitative phase measurement on large objects

We recently have presented a real-time holographic interferometer using sillenite crystals connected with phase-shifting for quantitative measurement of diffuse objects deformations. In our basic set-up, the crystal, sandwiched between two polarizers, is set in front of the optical head and followed by a CCD camera with an imaging objective. With this system, for conventional objects and using 2.2 Watts of Ar3+ laser power @ 514 nm, interferograms can be observed on object fields of about 30 cm*20 cm (crystal size 1 cm*1 cm and 26 mm objective focal length). In this paper we present investigations to increase the observed field in the existing system and to be able to use lower power lasers. Since setting the object at larger distances should lead to an insufficient luminous level for hologram recording, we have proceeded by different ways. First, we use shorter focal length objectives, giving a larger field-of-view, and larger crystals have to be used in this case to avoid vignetting. Second, we use a large aperture frontal objective in order to collect more light and that images the object on the crystal, the final image being observed through relay imagery.