Polygonal micro-whirlpools induced in ferrofluids

TL;DR

This paper reports the creation and control of polygonal micro-whirlpools in ferrofluids using laser beams with optical vortices and magnetic fields, revealing new micro-scale fluid structures.

Contribution

It introduces a novel method to generate and manipulate polygonal whirlpools in ferrofluids at micro-scale using holographic optical tweezers and magnetic fields.

Findings

Polygonal whirlpools can be induced in ferrofluids with laser vortex beams.

The shape of whirlpools can be tuned by magnetic field strength.

Whirlpool diameter is less than 20 micrometers.

Abstract

We report on the observation of the polygonal whirlpools in the thin layer of ferrofluid under illumination with a laser beam carrying optical vortex and in the presence of a vertical magnetic field. This kind of structures have attracted attention after discovering a hexagonal storm in Saturns atmosphere. Our polygonal whirlpools were created in a closed system (no free surfaces) in micro scale (whirlpool diameter less than 20 micrometers) by the use of holographic optical tweezers. The polygonal shape was changed by varying the magnetic field strength or value of the optical vortex topological charge.