Abstract
A technique is proposed for the real-time measurement of in-plane displacement utilizing objective speckles and two-beam coupling in a photorefractive BaTiO 3 crystal. Speckles generated by a diffuse object in free-space geometry are used as the signal in two-beam coupling. The set-up is such that the phase shift between the refractive index grating and the interference grating is + π 2 (amplification mode). Due to the in-plane displacement, Young's fringes are obtained with a bright speckle background as a result of the signal amplification and beam fanning. The slow process of two-beam coupling amplification in a BaTiO 3 crystal is exploited for recording multiple exposures. This method of recording multiple exposures provides a simple and convenient way of analyzing the rigid body motions with enhanced accuracy by sharpening the fringes and with acceptable contrast. Theory has been developed to obtain the intensity distribution in the fringes formed in real time at the observation plane. Experiments have been conducted to show the validity of the theoretical results. Good agreement is established between the theory and the experiments.
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