Direct particle depth displacement measurement in DHPTV using spatial correlation of focus metric curves

A method to accurately measure the particle depth displacement between a hologram pair is presented. A simple theoretical model formulates that the focus metric curves of a particle in a hologram pair are strongly spatially correlated, and that the particle's depth displacement is essentially encoded in the shift between the focus metric curves. The particle depth displacement can be directly evaluated from the cross correlation of the focus metric curves, rather than prior locating the particle's depth positions. Both simulation and experimental hologram pairs with depth displacement ranging from 10μm to 1000μm are tested, and results show that the depth displacement can be accurately obtained with the proposed method. This method has great potential in accurate 3D velocity computation in DHPTV.