Holographic position measurement of nanoparticles trapped with optical tweezers

We demonstrate the holographic position measurement of a nanoparticle held in optical tweezers in water by using an in-line low-coherence digital holographic microscope with the pattern matching method and the three-dimensional sub-pixel estimation. The axial sub-pixel estimation allowed a step length in the diffraction calculation of a hologram to ~20 nm while keeping the axial resolution of a single nanometer order. This drastically decreased the computation cost of the diffraction calculation to less than 1/10.