Orbital rotation of spheroidal Mie particles driven by counter-propagating circularly-polarized beams

TL;DR

This paper theoretically investigates the orbital and proper rotation of spheroidal submicron particles driven by counter-propagating circularly polarized beams, revealing two dynamic regimes and potential applications in nano-gyroscopes and particle sorting.

Contribution

It derives equations linking optical forces and torques to particle motion, identifying two distinct rotational regimes and confirming findings with numerical simulations.

Findings

Orbital and proper rotations can occur simultaneously or separately.

The orbital rotation direction can match or oppose the electric vector rotation.

Rapid proper rotation can be an order of magnitude faster than orbital rotation.

Abstract

We theoretically consider orbital rotation of a spheroidal submicron particle in the field of two counter-propagating circularly polarized Gaussian beams. We derived equations connecting the parameters of the circular orbits centered on the beams axis to the optical force and torque. The equations show that, besides orbital rotation, the spheroidal particle simultaneously rotates around its equatorial axis. We found that two distinct dynamic regimes are possible. The orbital motion can be accompanied by a rapid proper rotation with angular velocity an order of magnitude larger than the angular velocity of the orbital rotation. Alternatively, the orbital and proper rotations can be synchronized. The direction of orbital rotation can either coincide with or be opposite to the direction of rotation of the electric vector. The findings are confirmed by direct numerical simulations. The results can be of use in development of nano-scale gyroscopes as well in shape-selective sorting of submicron particles.