Imaging Multiple Colloidal Particles by Fitting Electromagnetic Scattering Solutions to Digital Holograms

TL;DR

This paper advances digital holographic microscopy by developing new electromagnetic scattering fitting techniques, enabling precise 3D imaging of multiple colloidal particles and clusters with improved computational efficiency.

Contribution

It introduces an exact multisphere superposition method and an approximate Mie superposition approach for fitting holograms of multiple colloidal spheres, extending the system's applicability.

Findings

Exact multisphere superposition fits clusters of up to six spheres.

Mie superposition provides a computationally simpler fit for well-separated spheres.

Quantitative criteria for the validity of the approximate method.

Abstract

Digital holographic microscopy is a fast three-dimensional (3D) imaging tool with many applications in soft matter physics. Recent studies have shown that electromagnetic scattering solutions can be fit to digital holograms to obtain the 3D positions of isolated colloidal spheres with nanometer precision and millisecond temporal resolution. Here we describe the results of new techniques that extend the range of systems that can be studied with fitting. We show that an exact multisphere superposition scattering solution can be used to fit holograms of colloidal clusters containing up to six spheres. We also introduce an approximate and computationally simpler solution, Mie superposition, that is valid for multiple spheres spaced several wavelengths or more from one another. We show that this method can be used to fit holograms of several spheres on an emulsion droplet, and we give a quantitative criterion for assessing its validity.