High-accuracy measurement of depth-displacement using a focus function and its cross- correlation in holographic PTV

We propose a method using a focus function and its cross-correlation to measure depth-position and precise depth-displacement. The focus function provides acceptable results in the determination of depth-position of a transparent particle, an opaque particle, and a red blood cell. However, positional errors and a short time interval can cause unreliable results in identifying depth-displacement (Δz) and depth-directional velocity in digital holographic particle tracking velocimetry (DHPTV). To minimize the errors in Δz, we propose a method that directly obtains depth displacement from the cross-correlation of focus values between consecutive holograms. The feasibility of this method is demonstrated by quantitatively visualizing a 3D flow using HPTV.