Three-dimensional rigid body motion measurement using speckle fanning in a photorefractive BaTiO3 crystal
A simple speckle technique, utilizing speckle fanning in a BaTiO3 crystal, is demonstrated for the measurement of rigid body displacement in an arbitrary direction. Collimated laser beam illuminates a diffuser to generate speckles, which are then recorded inside a photorefractive barium titanate crystal thus producing speckle fan. Speckle correlation fringes are formed due to interference between the reconstructed speckle fans corresponding respectively to the initial- and final positions of the diffuser. Displacements occurring in a direction making small angles with the optical axis have been measured by profiling the fringes. The measurement of displacement in a direction making large angle with the optical axis is possible only by taking the Fourier transform of the fringes. This facilitates the separation of transverse and axial correlation peaks giving the transverse and axial components of the motion.