Multidimensional optical fractionation with holographic verification

TL;DR

This study experimentally verifies how colloidal particles' trajectories in holographic optical landscapes depend on their size and refractive index, enabling precise multi-parameter optical sorting.

Contribution

It provides the first experimental validation of theoretical predictions on kinetically locked-in transport and demonstrates high-resolution multi-parameter optical fractionation.

Findings

Confirmed predictions of kinetically locked-in transport thresholds

Achieved part-per-thousand resolution in sorting by size and refractive index

Demonstrated simultaneous multi-parameter colloidal sorting

Abstract

The trajectories of colloidal particles driven through a periodic potential energy landscape can become kinetically locked in to directions dictated by the landscape's symmetries. When the landscape is realized with forces exerted by a structured light field, the path a given particle follows has been predicted to depend exquisitely sensitively on such properties as the particle's size and refractive index These predictions, however, have not been tested experimentally. Here, we describe measurements of colloidal silica spheres' transport through arrays of holographic optical traps that use holographic video microscopy to track individual spheres' motions in three dimensions and simultaneously to measure each sphere's radius and refractive index with part-per-thousand resolution. These measurements confirm previously untested predictions for the threshold of kinetically locked-in transport, and demonstrate the ability of optical fractionation to sort colloidal spheres with part-per-thousand resolution on multiple characteristics simultaneously.