Measurement of Colloidal Interactions Using Holographic Microscopy and Multi-particle Scattering Theory

Holographic microscopy provides the ability to record particle information in three dimensions with rapid time resolution. Lorenz-Mie scattering theory has been used to interpret holographic images of single colloids and provide highest available resolution for imaging single colloids in three dimensions. This method, however, has yet to be employed to interpret images of multiple particles. We demonstrate the implementation of a multiple-particle generalization of Lorenz-Mie scattering solution to interpret holographic images of clusters of spherical colloids. Highly precise theoretical holograms of multiple spherical colloids are calculated using the multiple-particle scattering theory, and recorded holographic images of colloidal clusters are fit to those of the theoretical method. The parameters of the fitting routine are used to characterize colloids' sizes, indices of refraction and separation radii, amongst other properties.