Variations of the optical detection path-length in image correlation based flow-field measurements result in strong errors in position allocation and thus lead to a strong enhancement of the measurement uncertainty of the velocity. In this contribution we use digital holography to measure the wavefront distortion induced by fluctuating phase boundary, employing spatially extended guide stars. The measured phase information is used to correct the influence of the phase boundary in the detection path employing a spatial light modulator. We analyze the potential of guide stars that are reflected by the phase boundary, i.e. the Fresnel reflex, and transmitted. Our results show, that the usage of wavefront shaping enables to strongly reduce the measurement uncertainty and to strongly improve the quality of image correlation based flow-field measurements. The approaches presented here are not limited to application in flow measurement, but could be useful for a variety of applications.
Jürgen W. Czarske, Nektarios Koukourakis, Bob Fregin, Jörg König, and Lars Büttner, "Adaptive flow-field measurements using digital holography," Proc. SPIE 10074, Quantitative Phase Imaging III, 100740F (Presented at SPIE BiOS: January 30, 2017; Published: 21 February 2017); https://doi.org/10.1117/12.2252084.
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