Plasmonic trapping and antitrapping of nanoparticles

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.