Resonant propulsion of a microparticle by a surface wave

A. V. Maslov, V. N. Astratov, M. I. Bakunov

We investigate the electromagnetic force experienced by a microparticle supporting high-quality whispering gallery modes that are excited by a surface wave. Our theoretical approach is based on an analytical representation of the solution of the scattering problem with a subsequent numerical treatment. It accounts rigorously for the interaction of the microparticle with the waveguiding surface and allows us to establish the balances of electromagnetic power and momentum flow for the system. We show that the resonant excitation of the whispering gallery modes and suppression of the transmitted surface wave lead to an almost complete transformation of the momentum flow of the initial surface wave into the propelling force on the microparticle. The validation of the momentum balance justifies the definition of the momentum flow of the surface wave as the ratio of carried power and phase velocity. A simple approximate relation between the propelling force and the power of the transmitted surface wave is also introduced. The transverse force can be either attractive or repulsive depending on the particle-to-surface distance, particle size, and operating frequencies, and it can significantly exceed the value of the propelling force. A comparison with a microparticle excited by a plane wave is also included.
DOI