REAL-TIME VELOCITY-MEASUREMENT BY THE USE OF A SPECKLE-PATTERN CORRELATION SYSTEM THAT INCORPORATES A FERROELECTRIC LIQUID-CRYSTAL SPATIAL LIGHT-MODULATOR

We describe a technique for noncontact velocity measurement by using d ouble-exposure speckle-pattern techniques with optical signal processi ng. The two speckle patterns are recorded on a ferroelectric liquid-cr ystal (FLC) spatial light modulator (SLM), which is a bistable optical ly addressed SLM, and the composite pattern is then analyzed by an opt ical system similar to a joint transform correlator, in which another FLC-SLM and a position-sensitive detector are used. We show that the p erformance of the system can be significantly improved by adjusting th e time between exposures using a real-time feedback system that is bas ed on the position of the correlation spot in the output plane.