Processing Techniques: Optical Correlators

Abstract

The Particle Image Velocimetry (PIV) is a technique which is utilized for measuring complete velocity vector fields in a few microseconds time. However, a lot of time is required during the evaluation. E.g., if employing the autocorrelation technique it is necessary to calculate a few thousand autocorrelation functions (ACFs) for each PIV recording. In this paper an evaluation system forphotographical PIV recordings will be described, which allows the determination of the ACFs of small sub areas of the recording completely analog optically. An optically addressable liquid crystal spatial light modulator was utilized to store the Young's fringes pattern appearing in the frequency plane at the output of a first optical Fourier processor and to provide them as the input for a second optical Fourier processor. Our analog optical autocorrelator offers a high processing speed and simultaneously a high resolution in the autocorrelation plane. The realized set up is compact and very easy to handle.