Optical forces from near-field directionalities in planar structures

Abstract

Matter manipulation with optical forces has become commonplace in a wide range of research fields and is epitomized by the optical trap. Calculations of optical forces on small illuminated particles typically neglect multiple scattering on nearby structures. However, this scattering can result in large recoil forces, particularly when the scattering includes directional near-field excitations. Nearfield recoil forces have been studied in the case of electric, magnetic and circularly polarized dipoles, but they exist for any type of directional near-field excitation. We use the force angular spectrum as a concise and intuitive analytical expression for the force on any dipole near planar surfaces, which allows us to clearly distinguish the effect due to the dipole, and due to the surface. We relate this directly to the coupling efficiency of surface or guided modes via Fermi's golden rule. To exemplify this, a near-field force transverse to the illumination is computationally calculated for a Huygens dipole near a metallic waveguide. We believe this formalism will prove insightful for various nanomanipulation systems within areas such as nanofluidics, sensing, biotechnology and nano-assembly of nanostructures. arXiv:1811.05237v3 [physics.optics]

Laser-Driven Aggregation in Dextran–Graft–PNIPAM/Silver Nanoparticles Hybrid Nanosystem: Plasmonic Effects

“…Second, besides the thermal action, the excitation of SPR in metal NPs by the laser illumination leads to the mechanical action on them. Light can induce the appearance of significant optical forces acting between the metal NPs [42][43][44][45][46][47][48]. When two metallic NPs are in a close proximity, and the pair is illuminated by the laser radiation, there is a laserinduced attractive force between them.…”

Optical magnetic dipole levitation using a plasmonic surface

“…The time-averaged optical force on a time-harmonic magnetic dipole in free space near a surface is given by [51,52]…”

“…The reflected fields of a dipole can be expressed in the angular representation [50,52,53] as an integral over the The quasistatic limit of the force, given by Eq. ( 3), used to model Fz near a realistic metal.…”

“…( 2) are checked with an independent force calculation method, provided by the Maxwell stress tensor (MST) method and the reflected fields of the dipole. These fields are calculated directly with the semianalytical Green's function approach that we discuss in [48] and comes from literature [50,52,53]. The quasistatic limit of Eq.…”

“…The magnetic repulsion has a quasistatic behavior so in order to observe an appreciable force, the particle has to be at a height h < 0.2λ above the surface [52]. In this example, we place the particle at d = 50 nm so that it strongly interacts with its reflected near fields.…”