Optical forces on cylinders near subwavelength slits: effects of extraordinary transmission and excitation of Mie resonances

Abstract

We study the optical forces on particles, either dielectric or metallic, in or out their Mie resonances, near a subwavelength slit in extraordinary transmission regime. Calculations are two-dimensional, so that those particles are infinite cylinders. Illumination is with p-polarization. We show that the presence of the slit enhances by two orders of magnitude the transversal forces of optical tweezers from a beam alone. In addition, a drastically different effect of these particle resonances on the optical forces that they experience; namely, we demonstrate an enhancement of these forces, also of binding nature, at plasmon resonance wavelengths on metallic nanocylinders, whereas dielectric cylinders experience optical forces that decrease at wavelengths exciting their whispering gallery modes. Particles located at the entrance of the slit are easily bound to apertures due to the coincidence in the forward direction of scattering and gradient forces, but those particles at the exit of the slit suffer a competition between forward scattering force components and backward gradient forces which make more complex the bonding or antibonding nature of the resulting mechanical action.