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Tomography has been a highly active research field for the last 20 years and great progress has been made in numerical reconstruction methods. This paper deals with a new method of tomographic reconstruction based on optical processing. We first present a system of acquisition by ultrasound and then the backprojection procedure which is performed by optical methods. The projections are coded by an opto-acoustic modulator and deflector into a laser beam and the image is obtained by integrating the resulting pattern over one revolution by a CCD camera. This procedure, which is entirely analogical, allows the real time reconstruction of images, the only delay being the time required for the aquisition (approximatively 1 sec.). Echotomographies obtained by this method are presented

The photorefractive effect allows the optical generation in electro-optic and photoconductive materials of index variations, with very low energy levels. Described twenty years ago, the effect recently gain interest due to its use for optical processing and optical phase conjugation. In the case of sillenite crystals, we presently summarize the physics involved in the photorefractive effect under both quasi-continuous and short pulse illuminations. Caracterizations of the samples are derived and specific applications are proposed Mecanisme de l'effet photorefractif, caracteristiques en regime d'excitation quasi continue puis nanoseconde. Applications liees aux proprietes specifiques de l'effet photorefractif