Coherence concepts in holographic particle image velocimetry

A special holographic configuration has been introduced for the sheet-wise reconstruction of sample areas in a particle image field that is reconstruc ted for particle image velocimetry analysis. A distinct feature is the supp ression of light from most of the out-of-focus region of the flow volume. T his is realised by light-in-flight holography, where the illuminating laser light of short coherence length allows the discrimination of depth regions by selection of the position of the reconstruction aperture on the hologra m. The basic features of the method are outlined, and results are given for flow visualisation in a free nozzle stream and for velocimetry in a wind t unnel vortex street and free nozzle jets. The method is supplemented by ele ctro-optic switching for separate images and cross-correlation evaluation.