Giant lateral optical forces on Rayleigh particles near hyperbolic and extremely anisotropic metasurfaces

Abstract

We report a dramatic enhancement of the lateral optical forces induced on electrically polarizable Rayleigh particles near hyperbolic and extremely anisotropic metasurfaces under simple plane wave illumination. Such enhancement is enabled by the interplay between the increased density of states provided by these structures and the out-of-plane polarization spin acquired by the particle. The resulting giant lateral forces appear over a broad frequency range and may openunprecedented venues for routing, trapping, and assembling nanoparticles. PACS: 32.10.Dk, 42.25.Fx, 73.20.Mf, 78.67.Wj Light-induced forces have led to many exciting applications in nanotechnology and bioengineering by trapping, pushing, pulling, binding and manipulating nanoparticles and biological samples [1][2][3][4][5][6][7][8]. Recently, the emergence of nano-optical plasmonic configurations has been exploited to boost the strength of optical forces at the nano-scale by exciting surface plasmon polaritons (SPPs) [9][10][11][12], which are confined electromagnetic waves traveling along dielectricmetal interfaces [13]. In fact, illuminating with light an electric, non-magnetic, Rayleigh particle (with radius r < λ 0 /20, being 0 the wavelength) located above a metallic surface like gold or

Optical forces from near-field directionalities in planar structures

“…(4) clearly shows the appearance of extra force terms which are not from the direct illumination. Several works do consider forces from the backscattered fields, and it has been shown that these forces can become very important to the motion of a particle close to a surface and so should not be neglected in general [33,35,[49][50][51][52][53]. We emphasize that any object that supports surface or guided modes can introduce non-trivial forces in this way due to a potentially directional dipole near-field.…”

Low-power Optical Traps Using Anisotropic Metasurfaces: Asymmetric Potential Barriers and Broadband Response

“…The direction and strength of this force mostly depends on the handedness of the particle polarization and the momentum of the excited plasmons, respectively [23]. Aiming to boost the strength of recoil forces, anisotropic and hyperbolic (HMTSs) metasurfaces have been proposed to substitute bulk plasmonic metals [31]. HMTSs [32][33][34][35][36][37][38][39] are ultrathin surfaces that exhibit a metallic or dielectric response as a function of the electric field polarization, possess a very large local density of states, and support ultra-confined SPPs over a broadband frequency range.…”

“…These structures can be constructed by appropriately patterning common plasmonic materials, such as silver [38], gold [39] or graphene [34,35]. It has been shown that the recoil force acting on nanoparticles located over anisotropic metasurfaces can be enhanced several orders of magnitude with respect to the one appearing over bulk, isotropic surfaces [31]. Such giant enhancement is enabled by the large momentum of the directional plasmons excited during the scattering process.…”

“…Such giant enhancement is enabled by the large momentum of the directional plasmons excited during the scattering process. Furthermore, the enhancement is broadband [31] in the sense that it appears when the particle is illuminated with light oscillating at any frequency within a very wide range defined by the anisotropic features of the structure.…”

Enhancement of recoil optical forces via high-k plasmons on thin metallic films

“…However, some works have theoretically proposed methods to greatly enhance this force. One approach has been to use hyperbolic metasurfaces, theoretically predicting an increase on the lateral force by roughly three orders of magnitude 24 . Hyperbolic metasurfaces are planar metamaterials which show an anisotropic surface conductivity [25][26][27][28] and were experimentally demonstrated using single-crystal silver nanostructures 29 , but such materials are challenging to fabricate in large areas useful for measurement and application of lateral optical forces, with no experimental demonstration yet produced of the enhanced force.…”