A hybrid optical/digital processing scheme for measuring phase distributions is described and demonstrated. It is intended to be an alternative to interferometric methods of measuring optical path length changes in flow diagnostics and can also be used as a flow visualization technique. The processing scheme enables one to make accurate measurements of phase at arbitrary points in the image plane. The system is based on a simple coherent optical Fourier processor but incorporates three separate measurements and postdetection digital processing to eliminate extraneous parts of the signal. The addition of a holographic filter to the system enables one to measure deformation or displacement of diffusely reflecting opaque objects. The technique is demonstrated by using it to visualize the flow of an expanding compressible gas jet and to measure the optical path length through a heated plume of air.

© 1983 Optical Society of America

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