Optical "Bernoulli" forces

TL;DR

This paper demonstrates that a rotating dielectric cylinder in an electromagnetic wave experiences a lateral force analogous to Bernoulli's principle, with the force's direction depending on the material's electric susceptibility.

Contribution

It introduces the concept of optical Bernoulli forces, showing that rotating dielectric objects in light fields experience measurable lateral forces based on material properties.

Findings

Dielectric cylinders experience lateral forces in electromagnetic waves.

Force direction depends on the sign of electric susceptibility.

Mie-resonance enhances the lateral force.

Abstract

By Bernoulli's law, an increase in the relative speed of a fluid around a body is accompanies by a decrease in the pressure. Therefore, a rotating body in a fluid stream experiences a force perpendicular to the motion of the fluid because of the unequal relative speed of the fluid across its surface. It is well known that light has a constant speed irrespective of the relative motion. Does a rotating body immersed in a stream of photons experience a Bernoulli-like force? We show that, indeed, a rotating dielectric cylinder experiences such a lateral force from an electromagnetic wave. In fact, the sign of the lateral force is the same as that of the fluid-mechanical analogue as long as the electric susceptibility is positive (\epsilon>\epsilon_{0}), but for negative-susceptibility materials (e.g. metals) we show that the lateral force is in the opposite direction. Because these results are derived from a classical electromagnetic scattering problem, Mie-resonance enhancements that occur in other scattering phenomena also enhance the lateral force.