Three dimensional particle tracking is useful technology to characterize live cell or surrounding environment by tracing
small particles such as fluorescence beads or polystyrene beads which adhered to objective samples. In microscopy
imaging system, the longitudinal(z axis) tracking of the particle is essential for implementation of three-dimensional
particle tracking, however it's been still a challenging topic to find the exact position of the particle in z axis with high
In this study, we present that a novel technique to find the longitudinal position of the particle, as well as the transverse
position(x,y axis) by applying the numerical reconstruction and focusing with digital holographic microscope.
Transmission type off-axis digital holographic microscope is implemented for this experiment, based on Mach-Zehnder
interferometer and 632.8nm HeNe laser is used as a coherent light source of the microscope and high-speed CMOS
camera is utilized for acquiring the hologram. Digital holographic microscope makes it possible to record and reconstruct
the phase and amplitude image of the sample. In order to find the position of the particle in z axis, we apply the
numerical focusing algorithm, which enables the translation of the imaging focus without actual longitudinal movement
of the sample. To demonstrate the presented method, Brownian movement of 3μm polystyrene sphere suspended in
water is investigated in this experiment.