Out-of-plane displacement measurement by using speckle fanning in a photorefractive BaTiO 3 crystal

Abstract

Summary We propose a method for the measurement of out-of-plane object displacement by a speckle technique utilizing the speckle fanning in a photorefractive barium titanate crystal. A portion of the converging incident beam has been used to illuminate the diffuser to generate speckles, while the remaining portion is allowed to fall directly on the crystal. Coupling of scattered beam with incident beam inside the crystal generates speckle fan of light after diffraction from the complex gratings formed in the volume of the crystal. Semi-circular speckle correlation fringes are formed due to the interference between reconstructed speckled fan beam recorded for an initial position of the diffuse surface, and directly transmitted speckled beam after introducing the out-of-plane displacement in the diffuser. Fringe diameter has been measured after ‘profiling’ operation on the fringes, for the calculation of out-of-plane displacement.