Volumetric reconstruction of Brownian motion of a micrometer-size bead in water

An effective volumetric measurement and reconstruction scheme for imaging three-dimensional phase objects based on off-axis digital holography is presented. We have experimentally demonstrated the feasibility of our method by observing the Brownian motion of a 3 μm diameter polystyrene bead in water. From a single off-axis hologram of a diffracted field by a sample, a series of transverse intensity images for various axial positions were numerically generated. The center position of the bead sample was pinpointed with a nanometer-scale resolution in 3D space and updated with a frame rate of 30 frames/s. Detailed procedures for elimination of virtual images in an off-axis hologram, reduction of background DC noise, and extraction of exact electric fields in an off-axis hologram are described as advantages of our proposed method over conventional in-line holographic 3D measurement schemes.