HIGH-SPEED ANALOG AUTOCORRELATION FOR PIV TRANSPARENCY ANALYSIS USINGA FERROELECTRIC LIQUID-CRYSTAL SPATIAL LIGHT-MODULATOR

This paper describes a novel automated high-speed optical autocorrelat ion system for particle image velocimetry (PIV) analysis. In this syst em, a bistable ferroelectric optically addressed spatial light modulat or (BOASLM) is used for real time optical autocorrelation. Input data from a PIV transparency is scanned into the system by utilising two sc anning mirrors and the output autocorrelation signals are detected wit h a two-dimensional scanning tracking system implemented by two acoust o-optic modulators. This data extraction system is equivalent to a ran dom access camera, which is used to track the autocorrelation signals from region to region in order to retrieve velocity data at the full f rame rate of the BOASLM. The factors that influence the processing cap acity of the optical system are discussed in detail and a critical com parison is made with digital analysis systems. A working prototype of an optical PIV analysis system is described and the measurement of 129 6 velocity vectors from a PIV transparency in approximately five secon ds is demonstrated.