Holographic Three-Dimensional Measurement of an Optically Trapped Nanoparticle

Three-dimensional (3D) measurement of a nanometer-sized particle (nanoparticle) held in optical tweezers in water using a low-coherence, in-line digital holographic microscope with a pattern matching processing was demonstrated here. Suppressing the movement of the nanoparticle using optical tweezers enabled us to detect its 3D position. The spatial resolutions of the microscope were 3.2 nm in the transverse direction and 3.4 nm in the axial direction from the standard deviation of measurements of the 200 nm polystyrene particle fixed on glass. Changes in the Brownian motion of a 200 nm polystyrene particle in response to a change in the trapping laser power were measured. The 3D position measurement of a gold nanoparticle with 60 nm diameter was also demonstrated.