Alexander S. Shalin

Surface plasmon polariton assisted optical pulling force

We demonstrate both analytically and numerically the existence of optical pulling forces acting on particles located near plasmonic interfaces. Two main factors contribute to the appearance of this negative recoil force. The interference between the incident and reflected waves induces a rotating dipole with an asymmetric scattering pattern, while the directional excitation of surface plasmon polaritons (SPPs) enhances the linear momentum of scattered light. The strongly asymmetric SPP excitation is determined by spin–orbit coupling of the rotating dipole and surface plasmon polariton. As a result of the total momentum conservation, the force acting on the particle points in a direction opposite to the incident wave propagation. We derive analytical expressions for the force acting on dipolar particles placed in the proximity of plasmonic surfaces. Analytical expressions for this pulling force are derived within the dipole approximation and are in excellent agreement with results of electromagnetic numerical calculations. The forces acting on larger particles are analyzed numerically, beyond the dipole approximation.

Purcell effect in hyperbolic metamaterial resonators

The radiation dynamics of optical emitters can be manipulated by properly designed material structures modifyinglocaldensityofphotonicstates,aphenomenonoftenreferredtoasthePurcelleffect.Plasmonicnanorod metamaterials with hyperbolic dispersion of electromagnetic modes are believed to deliver a significant Purcell enhancement with both broadband and nonresonant nature. Here, we have investigated finite-size resonators formed by nanorod metamaterials and shown that the main mechanism of the Purcell effect in such resonators originates from the supported hyperbolic modes, which stem from the interacting cylindrical surface plasmon modes of the finite number of nanorods forming the resonator. The Purcell factors delivered by these resonator modes reach several hundreds, which is up to 5 times larger than those in the e-near-zero regime. It is shown �

Plasmonic Nanostructures as Accelerators for Nanoparticles: Optical Nanocannon

We suggest a model of an optical structure that allows to accelerate nanoparticles to velocities on the order of tens of centimeters per second using low-intensity external optical fields. The nano-accelerator system employs metallic V-grooves which concentrate the electric field in the vicinity of their bottoms and creates large optical gradient forces for the nanoparticles in that groove. The conditions are found when this optical force tends to eject particles away from the groove.

Optical properties of nanostructured layers on the surface of an underlying medium

An analytical approach to the description of the optical characteristics of layers consisting of interacting nanoclusters is developed based on the integral equation method. Expressions for the fields inside and outside the system are obtained, the effective parameters of the structure elements are studied taking into account the mutual polarizing effect of nanoclusters and underlying medium, and the applicability conditions of the model proposed are determined. The possibility of controllable the tuning of the spectral properties of the system by changing its structural parameters is considered; it is shown that the reflection from the substrate surface can be decreased by depositing a nanostructured coating. Good agreement is obtained between the analytical calculation and the exact numerical solution of Maxwell’s equations.

Enhancement of artificial magnetism via resonant bianisotropy.

All-dielectric “magnetic light” nanophotonics based on high refractive index nanoparticles allows controlling magnetic component of light at nanoscale without having high dissipative losses. The artificial magnetic optical response of such nanoparticles originates from circular displacement currents excited inside those structures and strongly depends on geometry and dispersion of optical materials. Here an approach for enhancing of magnetic response via resonant bianisotropy effect is proposed and analyzed. The key mechanism of enhancement is based on electric-magnetic interaction between two electrically and magnetically resonant nanoparticles of all-dielectric dimer. It was shown that proper geometrical arrangement of the dimer in respect to the incident illumination direction allows flexible control over all vectorial components of the magnetic moment, tailoring the latter in the dynamical range of 100% and delivering enhancement up to 36% relative to performances of standalone spherical particles. The proposed approach provides pathways for designs of all-dielectric metamaterials and metasurfaces with strong magnetic responses.

Optical forces in nanorod metamaterial

Optomechanical manipulation of micro and nano-scale objects with laser beams finds use in a large span of multidisciplinary applications. Auxiliary nanostructuring could substantially improve performances of classical optical tweezers by means of spatial localization of objects and intensity required for trapping. Here we investigate a three-dimensional nanorod metamaterial platform, serving as an auxiliary tool for the optical manipulation, able to support and control near-field interactions and generate both steep and flat optical potential profiles. It was shown that the ‘topological transition’ from the elliptic to hyperbolic dispersion regime of the metamaterial, usually having a significant impact on various light-matter interaction processes, does not strongly affect the distribution of optical forces in the metamaterial. This effect is explained by the predominant near-fields contributions of the nanostructure to optomechanical interactions. Semi-analytical model, approximating the finite size nanoparticle by a point dipole and neglecting the mutual re-scattering between the particle and nanorod array, was found to be in a good agreement with full-wave numerical simulation. In-plane (perpendicular to the rods) trapping regime, saddle equilibrium points and optical puling forces (directed along the rods towards the light source), acting on a particle situated inside or at the nearby the metamaterial, were found.

Scattering suppression from arbitrary objects in spatially dispersive layered metamaterials

Concealing objects by making them invisible to an external electromagnetic probe is coined by the term cloaking. Cloaking devices, having numerous potential applications, are still face challenges in realization, especially in the visible spectral range. In particular, inherent losses and extreme parameters of metamaterials required for the cloak implementation are the limiting factors. Here, we numerically demonstrate nearly perfect suppression of scattering from arbitrary shaped objects in spatially dispersive metamaterial acting as an alignment-free concealing cover. We consider a realization of a metamaterial as a metal-dielectric multilayer and demonstrate suppression of scattering from an arbitrary object in forward and backward directions with perfectly preserved wavefronts and less than 10% absolute intensity change, despite spatial dispersion effects present in the composite metamaterial. Beyond the usual scattering suppression applications, the proposed configuration may serve as a simple realisation of scattering-free detectors and sensors.

Photovoltaic absorption enhancement in thin-film solar cells by non-resonant beam collimation by submicron dielectric particles

We propose the enhancement of the photovoltaic absorption in thin-film solar cells using densely packed arrays (not obviously regular) of non-absorbing submicron or micron-sized dielectric spheres located on top of the cell. The spheres can decrease reflection forming an effective blooming layer. Simultaneously, they can suppress the transmission through the photovoltaic layer transforming the incident radiation into a set of collimated beams. The focusing of the light inside the photovoltaic layer allows enhanced absorption in it leading to the increase of the photovoltaic current. Every sphere focuses the incident wave separately—this mechanism does not require collective effects or resonances and therefore takes place in a wide spectral range. Since the fabrication of such the coating is easy, our light-trapping structure may be cheaper than previously known light-trapping ones and perhaps even than flat anti-reflecting coatings.

Resonant forward scattering of light by high-refractive-index dielectric nanoparticles with toroidal dipole contribution

In this Letter, we demonstrate and investigate the Kerker-type effect in high-index dielectric nanoparticles for which the third-order multipoles give a considerable contribution to the light scattering process. It is shown that the Kerker-type effect (strong suppression of the backward light scattering and, simultaneously, resonant forward light scattering) can be associated with the resonant excitation of a toroidal dipole moment in the system. This effect is realized due to the interference of the scattered waves generated by electric, magnetic, and toroidal dipole moments of high-index nanoparticles.

Plasmon-assisted optical trapping and anti-trapping

The ability to manipulate small objects with focused laser beams has opened a venue for investigating dynamical phenomena relevant to both fundamental and applied science. Nanophotonic and plasmonic structures enable superior performance in optical trapping via highly confined near-fields. In this case, the interplay between the excitation field, re-scattered fields and the eigenmodes of a structure can lead to remarkable effects; one such effect, as reported here, is particle trapping by laser light in a vicinity of metal surface. Surface plasmon excitation at the metal substrate plays a key role in tailoring the optical forces acting on a nearby particle. Depending on whether the illuminating Gaussian beam is focused above or below the metal-dielectric interface, an order-of-magnitude enhancement or reduction of the trap stiffness is achieved compared with that of standard glass substrates. Furthermore, a novel plasmon-assisted anti-trapping effect (particle repulsion from the beam axis) is predicted and studied. A highly accurate particle sorting scheme based on the new anti-trapping effect is analyzed. The ability to distinguish and configure various electromagnetic channels through the developed analytical theory provides guidelines for designing auxiliary nanostructures and achieving ultimate control over mechanical motion at the micro- and nano-scales.