High speed analogue autocorrelation for PIV transparency analysis using a ferroelectric liquid crystal spatial light modulator

This paper describes a novel automated high-speed optical autocorrelation system for particle image velocimetry (PIV) analysis. In this system, a bistable ferroelectric optically addressed spatial light modulator (BOASLM) is used for real time optical autocorrelation. Input data from a PIV transparency is scanned into the system by utilising two scanning mirrors and the output autocorrelation signals are detected with a two-dimensional scanning tracking system implemented by two acousto-optic modulators. This data extraction system is equivalent to a random access camera, which is used to track the autocorrelation signals from region to region in order to retrieve velocity data at the full frame rate of the BOASLM. The factors that influence the processing capacity of the optical system are discussed in detail and a critical comparison is made with digital analysis systems. A working prototype of an optical PIV analysis system is described and the measurement of 1296 velocity vectors from a PIV transparency in approximately five seconds is demonstrated.