Real-time photorefractive recording and optical processing for speckle velocimetry

A photorefractive crystal (Bi(12)GeO(20)) is used to record double-exposure speckle patterns produced by Q-switched laser pulses in real-time speckle metrology and velocimetry applications. The speckle pattern displacements are immediately measured with an optical processor of the type used for measuring speckle displacements recorded on photographic film. Operation of the optical processor is described and compared with the case of film recording. Observed spatial and temporal recording properties of the crystal in this imaging configuration are discussed and compared with published results for single-frequency grating recording in photorefractives. The system is applied to measuring velocities of a moving solid object.