Resonant optical forces associated with the excitation of whispering gallery modes in microparticles

The resonant excitation of whispering gallery modes (WGMs) in microparticles can give rise to the appearance of large and highly selective optical forces. The forces can also be viewed as a result of the significant change of the electromagnetic momentum in the system. We compare the forces and their relation to the electromagnetic momentum of the incident radiation in several geometries. The considered geometries include the excitation by a plane wave, focused beam, surface wave, guided mode of a parallel plate waveguide, and by the backward wave of a thin plasma layer.