Figure 2.

Optical force acting on a particle (ε=3, radius R=15 nm, z=15 nm) touching the substrate and illuminated by the Gaussian beam focused above (f=100 μm, a) or below (f=−100 μm, b) the substrate interface. Blue solid lines correspond to the silver substrate; red dashed lines correspond to the model without plasmon contribution; gray solid lines correspond to the glass substrate; and dotted lines correspond to the force calculated via approximate Equation (3). (c) F_x and (d) F_z at f=−100 μm as a function of particle position. (e) Comparison of the dipole model and the numerical simulation for f=−130 μm; the particle is suspended above the substrate. The beam waist diameter w=10λ at the wavelength λ=342 nm and the permittivities ε₂=−1.25+0.32i, ε₁=1 are used for all plots.