Numerical and analytical models for calculating optical forces near auxiliary plasmonic substrates

Abstract

The optical force acting on a nanoparticle near a planar substrate is governed by incident light and excitation of surface and volume modes of the substrate. The realization of negative optical forces ("tractor beams") via propagating plasmon-polaritones and volume modes will be shown and considered in detail on the basis of the described analytical and numerical models for certain types of anisotropic substrates. In addition, optical tweezers performance is investigated when the Gaussian beam is focused on the metal substrate with nanoparticle. When the beam is focused above the substrate optical force increases about an order of magnitude due to evanescent field of surface plasmon. Novel effect of repulsion from Gaussian beam ("anti-trapping") is obtained when the beam waist is moved below the substrate which is confirmed by both the analytical approach and finite element simulation.