Optical alignment-induced errors in holographic particle image velocimetry

A ray-tracing analysis of point-source imaging in the presence of optical misalignment is used to analyze relative image shift as a source of measurement error in holographic particle image velocimetry (HPIV). Although single-reference-beam HPIV is relatively insensitive to optical misalignment, dual-reference-beam systems may suffer substantial errors because of misalignments of the order of microradians. These systems are particularly sensitive to rotations of the hologram about an axis perpendicular to the film and to reconstruction beam misalignment. In a swirling flow experiment, a proposed error-compensation scheme was able to reduce uncertainty from 130% to 10% of the mean measured velocity.