Colloidal hydrodynamic coupling in concentric optical vortices

TL;DR

This paper investigates how colloidal particles move within concentric optical vortex traps, revealing how hydrodynamic interactions depend on circulation direction and enabling measurements of collective colloidal dynamics.

Contribution

It introduces a method to measure hydrodynamic coupling in concentric optical vortices, advancing understanding of colloidal behavior in optical trapping systems.

Findings

Hydrodynamic drag varies with circulation sense.

Concentric vortices form a microscopic Couette cell.

Measurements address hydrodynamic instabilities.

Abstract

Optical vortex traps created from helical modes of light can drive fluid-borne colloidal particles in circular trajectories. Concentric circulating rings of particles formed by coaxial optical vortices form a microscopic Couette cell, in which the amount of hydrodynamic drag experienced by the spheres depends on the relative sense of the rings' circulation. Tracking the particles' motions makes possible measurements of the hydrodynamic coupling between the circular particle trains and addresses recently proposed hydrodynamic instabilities for collective colloidal motions on optical vortices.