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Application of photorefractive crystals for holographic interferometry of vibrating diffuse specimens

Real-time interferometry of vibrating specimens is achieved using two-wave mixing in Bi12SiO20 (BSO). By using anisotropic self-diffraction in the photorefractive crystal, despite the small diffraction efficiency of the photorefractive grating, good fringe visibility and good singal to noise ratio are achieved by synchronizing the illumination with the CCD camera. In addition, the application of an external electric field is used to enhance the diffraction efficiency of the photorefractive grating. This greater efficiency makes possible the visualization of large diffusely scattering specimens. It is shown that the good SNR of the resulting holographic interferograms enables phase unwrapping which allows for quantitative deformation analysis. The performance of the photorefractive interferoemeter is compared with the performance of an electronic speckle pattern interferometer.