Whole phase curvature-based particle positioning and size determination by digital holography.

We demonstrate the positioning and characterization of a transparent particle with a diameter of 60 µm in sparse particle fields. Particles appear elongated in optical setups with small numerical apertures that are used in digital holography; thus, an accurate method to position them is required. We propose a new optimization method using the whole phase curvature of a reconstructed wave along the optical axis to obtain not only the precise axial position but also the radius and refractive index of a particle. Experimental results show that the axial positions of particles can be detected with a standard deviation of 38.6 µm, corresponding to 66% of the average particle diameter. A radius of 29.3±0.4µ and a refractive index of 1.5910±0.0017 agree well with the manufacturer specifications of particles.