Observation of Brownian motion of a micrometer-size bead in water by off-axis digital holographic microscopy

An effective volumetric measurement method for determination of the 3D position of a single particle based on off-axis digital holographic microscopy is presented in this paper. 3 μm polystyrene bead suspended water is used as a particle to be traced in our experiment. We have demonstrated the feasibility of our method by observing the bead undergoing Brownian motion in water by implemented setup. For fast determination, a series of transverse intensity images are numerically reconstructed from a single hologram of the bead, then centroid technique is applied to the reconstructed images for enhancing the position resolution. Nano-meter scale resolution with a frame rate of 30 is achieved in this experiment in both lateral and transverse direction.