Abstract

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 ${29.3}\;{\pm}\;{0.4}\;\unicode{x00B5}{\rm m}$ and a refractive index of ${1.5910}\;{\pm}\;{0.0017}$ agree well with the manufacturer specifications of particles.

© 2020 Optical Society of America

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