Auxiliary nanostructures introduce additional flexibility into optomechanical manipulation schemes. Metamaterials and metasurfaces capable to control electromagnetic interactions at the near-field regions are especially beneficial for achieving improved spatial localization of particles, reducing laser powers required for trapping, and for tailoring directivity of optical forces. Here, optical forces acting on small particles situated next to anisotropic substrates, are investigated. A special class of hyperbolic metasurfaces is considered in details and is shown to be beneficial for achieving strong optical pulling forces in a broad spectral range. Spectral decomposition of Green's functions enables identifying contributions of different interaction channels and underlines the importance of the hyperbolic dispersion regime, which plays the key role in optomechanical interactions. Homogenised model of the hyperbolic metasurface is compared to its metal-dielectric multilayer realizations and is shown to predict the optomechanical behaviour under certain conditions related to composition of the top layer of the structure and its periodicity.Optomechanical metasurfaces open a venue for future fundamental investigations and a range of practical applications, where accurate control over mechanical motion of small objects is required.Control over mechanical motion of small particles with laser beams opened a venue for many fundamental investigations and practical applications. 1,2,3 Optical tweezers became one of the most frequently used tools in biophysical research, since they enable measuring dynamics of processes, control and monitor forces on pico-Newton level, e.g. 4,5 Classical optical tweezers, including the extension of the concept to holographic multi-trap configurations, 6 are based on diffractive optical elements, and can provide trapping stiffness at the expense of an increased overall optical power. This limitation also applies to trapping with structured and superoscilatory beams (e.g. 7 ). A promising solution for achieving improved localization and the highest possible stiffness within the trap is to introduce auxiliary nanophotonic or plasmonic structures that enable operation with nano-confined near fields. Plasmonic tweezers, for example, utilize localized resonances of noble metal nanoantennas and provide significant improvement in trap stiffness and spatial localization of trapped objects. 8 Optical manipulation with other auxiliary tools, e.g. endoscopic techniques, 9 nano-apertures, 10 nanoplate mirrors 11 and integrated photonic devices 12,13 was also demonstrated. A special attention was paid to particles trapping next to surfaces, since a typical experimental layout of a fluid cell may include substrates of different kinds, e.g. 14,15 and others. Furthermore, controllable transport over surfaces enables a range of particles sorting applications. 13 Here, additional advantages of carefully designed surfaces in application to optomechanical manipulations will be investigated.

Carefully designed nanostructures can inspire new type of optomechanical interactions and allow surpassing limitations set by classical diffractive optical elements. Apart from strong near-field localization, nanostructured environment allows controlling scattering channels and might tailor many-body interactions. Here we investigate an effect of optical binding, where several particles demonstrate a collective mechanical behaviour of bunching together in a light field. In contrary to classical binding, where separation distances between particles are diffraction limited, an auxiliary hyperbolic metasurface is shown here to break this barrier by introducing several controllable near-field interaction channels. Strong material dispersion of the hyperbolic metamaterial along with high spatial confinement of optical modes, which it supports, allow achieving superior tuning capabilities and efficient control over binding distances on the nanoscale. In addition, a careful choice of the metamaterial slab's thickness enables decreasing optical binding distances by orders of magnitude compared to free space scenarios due to the multiple reflections of volumetric modes from the substrate. Auxiliary tunable metamaterials, which allow controlling collective optomechanical interactions on the nanoscale, open a venue for new investigations including collective nanofluidic interactions, triggered bio-chemical reactions and many others.

Absorption of electromagnetic energy by a dissipative material is one of the most fundamental electromagnetic processes that underlies a plethora of applied problems, including sensing, radar detection, wireless power transfer, and photovoltaics. Common wisdom is that a finite dissipative object illuminated by a plane wave removes only a finite amount of the wave's energy flux, which is determined by the object's absorption cross‐section. Thus, it is of fundamental interest to see if any far‐field waveform can be perfectly absorbed by a finite object. Here, it is theoretically demonstrated that a precisely tailored light beam containing only far‐field components can be perfectly absorbed by a finite scatterer on a substrate. The self‐consistent scattering problem in the dipole approximation is analytically solved and finds a closed‐form expression for the spatial spectrum of the incident field and the required complex polarizability of the particle. All analytical predictions are confirmed with full‐wave simulations. The results introduce a qualitatively novel class of perfect absorption phenomena in electromagnetics and other wave processes.

Since surface plasmon polaritons (SPPs) are surface waves, they cannot be excited by an incident plane wave, because free-space photons do not possess a sufficient in-plane momentum. Phase matching between the incident light and SPP can be achieved using a high-refractive-index prism, grating, or nanoantennas. In this work, we found an expression for the amplitude of SPP excited by an arbitrary 3D current distribution placed near a metal interface. The developed method is based on the well-known technique used in waveguide theory that enables finding the amplitudes of waveguide modes excited by the external currents. It reduces the SPP excitation problem to the summation of the set of emitters. As a particular example, we considered a spherical dipole nanoantenna on a metal substrate illuminated by a normally incident plane wave. The analytical calculations were in good agreement with the full-wave numerical simulations.

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