Surface analysis by two-diode laser photorefractive holography

Shape measurement through holography using two diode lasers emitting in the red region and a sillenite Bi12TiO20 photorefractive crystal as a holographic medium is theoretically and experimentally studied. By properly aligning and tuning both lasers, a synthetic wavelength is obtained providing the contour fringes on the holographic image in single-exposure recordings. The influence of alignment and tuning of the lasers on the contour interval as well as the dependence of the interferogram visibility on the deviations from the Bragg regime was analysed. Contour intervals down to 150 Delta *mm where achieved and measurements of low-curvature and low-derivative surfaces were performed.