We present a detection scheme for diffusing wave spectroscopy (DWS) based ona two cell geometry that allows efficient ensemble averaging. This is achievedby putting a fast rotating diffuser in the optical path between laser andsample. We show that the recorded (multi-speckle) correlation echoes provide anensemble averaged signal that does not require additional time averaging. Wefind the performance of our experimental scheme comparable or even superior tocamera based multi-speckle techniques that rely on direct spatial averaging.Furthermore, combined with traditional two-cell DWS, the full intensityautocorrelation function can be measured with a single experimental setupcovering more than 10 decades in correlation time.
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