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Nonradiating sources of energy realized under a wave scattering on high-index dielectric nanoparticles have attracted a lot of attention in nano-optics and nanophotonics. They do not emit energy to the far-field, but simultaneously provides strong near-field energy confinement. Near-field wireless power transfer technologies suffer from low efficiency and short operation distance. The key factor to improve efficiency is to reduce the radiation loss of the resonators included in the transmitter and receiver. In this paper, we develop a wireless power transfer system based on nonradiating sources implemented using colossal permittivity dielectric disk resonator and a subwavelength metal loop. We demonstrate that this nonradiating nature is due to the hybrid anapole state originated by destructive interference of the fields generated by multipole moments of different parts of the nonradiating source, without a contribution of toroidal moments. We experimentally investigate a wireless power transfer system prototype and demonstrate that higher efficiency can be achieved when operating on the nonradiating hybrid anapole state compared to the systems operating on magnetic dipole and magnetic quadrupole modes due to the radiation loss suppression. © 2021 Esmaeel Zanganeh et al., published by De Gruyter, Berlin/Boston.

All-dielectric nanophotonics has become one of the most active fields of research in modern optics, largely due to the opportunities offered by the simultaneous resonant control of electric and magnetic components of light at the nanoscale. In this rapidly evolving scenario, the possibility to design artificial Huygens sources by overlapping electric and magnetic resonances has established a new paradigm in flat optics, bringing devices closer to efficient wavefront shaping with a direct phase engineering at the level of the individual meta-atoms. However, their efficiency is fundamentally limited by the near field coupling between the constituents of the metalattice. In this work, we challenge this well-conceived notion and propose an alternative concept to achieve phase control and full transmission in metasurfaces, based on the unusual properties of the nonradiating sources known as Hybrid Anapoles (HAs). We analyze theoretically an array of such sources and demonstrate that HAs are characterized by a negligible coupling with their neighbors. Therefore, in contrast to Huygens particles, the proposed sources can operate as individual meta-atoms even in highly compact designs, becoming robust against strong disorder and preserving its characteristics when deposited on dielectric substrates. Remarkably, the phase of the transmitted wave can be modulated with negligible reflection. To illustrate the capabilities of our platform, we also utilize a disordered HA array to implement a controlled phase modulation to an ultrafast gaussian pulse. The results of our study represent a departure from the currently established designs and open an avenue towards the realization of new devices for flat optics with unprecedented efficiency., 10 pages, 6 figures

Plasmonic nanoparticles can be employed as a promising integrated platform for lumped optical nanoelements with unprecedentedly high integration capacity and efficient nanoscale ultrafast nonlinear functionality. Further minimizing the size of plasmonic nanoelements will lead to a rich variety of nonlocal optical effects due to the nonlocal nature of electrons in plasmonic materials. In this work, we theoretically investigate the nonlinear chaotic dynamics of the plasmonic core-shell nanoparticle dimer consisting of a nonlocal plasmonic core and a Kerr-type nonlinear shell at nanometer scale. This kind of optical nanoantennae could provide novel switching functionality: tristable, astable multivibrators, and chaos generator. We give a qualitative analysis on the influence of nonlocality and aspect ratio of core-shell nanoparticles on the chaos regime as well as on the nonlinear dynamical processing. It is demonstrated that considering nonlocality is very important in the design of such nonlinear functional photonic nanoelements with ultra-small size. Compared to solid nanoparticles, core-shell nanoparticles provide an additional freedom to adjust their plasmonic property hence tuning the chaotic dynamic regime in the geometric parameter space. This kind of nanoscale nonlinear system could be the candidate for a nonlinear nanophotonic device with a tunable nonlinear dynamical response.

Non-Hermitian photonic systems with loss and gain attract much attention due to their exceptional abilities in molding the flow of light. Introducing asymmetry to the $\mathcal{PT}$-symmetric system with perfectly balanced loss and gain, we reveal the mechanism of transition from the quasibound state in the continuum (quasi-BIC) to the simultaneous coherent perfect absorption (CPA) and lasing in a layered structure comprising epsilon-near-zero (ENZ) media. Two types of asymmetry (geometric and non-Hermitian) are analyzed with the scattering matrix technique. The effect of the CPA-lasing associated with the quasi-BIC is characterized with the unusual linear dependence of the quality factor on the inverse of asymmetry parameter. Moreover, the counter-intuitive loss-induced-lasing-like behavior is found at the CPA-lasing point under the non-Hermitian asymmetry. The reported features of non-Hermitian structures are perspective for sensing and lasing applications., 8 pages, 9 figures

The creation of single photon sources on a chip is a mid-term milestone on the road to chip-scale quantum computing. An in-depth understanding of the extended multipole decomposition of non-isolated sources of electromagnetic radiation is not only relevant for a microscopic description of fundamental phenomena, such as light propagation in a medium, but also for emerging applications such as single-photon sources. To design single photon emitters on a chip, we consider a ridge dielectric waveguide perturbed with a cylindrical inclusion. For this, we expanded classical multipole decomposition that allows simplifying and interpreting complex optical interactions in an intuitive manner to make it suitable for analyzing light-matter interactions with non-isolated objects that are parts of a larger network, e.g. individual components such as a single photon source of an optical chip. It is shown that our formalism can be used to design single photon sources on a chip.

In this Letter we further develop the proposed approach of optical manipulation based on the interactions of non-linear optical effects with nanoparticles. The interaction of the dissipative optical solitons with nanoparticles is studied numerically. It is shown that the attraction of the nanoparticles to the solitons can result in the formation of a stable bound state of the solitons and the nanoparticles. The collision of the solitons with different numbers of trapped particles is studied, and it is shown that the collision of the solitons can result in releasing or redistributing the nanoparticles between the solitons. It is demonstrated that the particle mediated interaction between the solitons can affect their dynamics significantly. The reported effects can be successfully used for optical manipulation of nanoparticles and pave a way for efficient control over their dynamics on nanoscale.

We propose and verify experimentally a novel mechanism for achieving superscattering from subwavelength dielectric resonators empowered by the physics of bound states in the continuum.

Modern nanophotonics has witnessed the rise of "electric anapoles" (EDAs), destructive interferences of electric and toroidal electric dipoles, actively exploited to resonantly decrease radiation from nanoresonators. However, the inherent duality in Maxwell equations suggests the intriguing possibility of "magnetic anapoles," involving a nonradiating composition of a magnetic dipole and a magnetic toroidal dipole. Here, a hybrid anapole (HA) of mixed electric and magnetic character is predicted and observed experimentally via dark field spectroscopy, with all the dominant multipoles being suppressed by the toroidal terms in a nanocylinder. Breaking the spherical symmetry allows to overlap up to four anapoles stemming from different multipoles with just two tuning parameters. This effect is due to a symmetry-allowed connection between the resonator multipolar response and its eigenstates. The authors delve into the physics of such current configurations in the stationary and transient regimes and explore new ultrafast phenomena arising at sub-picosecond timescales, associated with the HA dynamics. The theoretical results allow the design of non-Huygens metasurfaces featuring a dual functionality: perfect transparency in the stationary regime and controllable ultrashort pulse beatings in the transient. Besides offering significant advantages with respect to EDAs, HAs can play an essential role in developing the emerging field of ultrafast resonant phenomena.

Bound states in the continuum (BICs) enable unique features in tailoring light-matter interaction on nanoscale. These radiationless localized states drive theoretically infinite quality factors and lifetimes for modern nanophotonics, making room for a variety of emerging applications. Here we use the peculiar properties possessed by the so-called $\mathcal{PT}$ symmetric optical structures to propose the novel mechanism for the quasi-BIC manifestation governed by the $\mathcal{PT}$ symmetry breaking. In particular, we study regularities of the spontaneous $\mathcal{PT}$ symmetry breaking in trilayer structures with the outer loss and gain layers consisting of materials with permittivity close to zero. We reveal singular points on the curves separating $\mathcal{PT}$ symmetric and broken-$\mathcal{PT}$ symmetry states in the parametric space of the light frequency and the angle of incidence. These singularities remarkably coincide with the BIC positions at the frequency of volume plasmon excitation, where the dielectric permittivity vanishes. The loss and gain value acts as an asymmetry parameter that disturbs conditions of the ideal BIC inducing the quasi-BIC. Fascinating properties of these quasi-BICs having ultrahigh quality factors and almost perfect transmission can be utilized in sensing, nonlinear optics, and other applications.

Carefully designed nanostructures can inspire a new type of optomechanical interactions and allow surpassing limitations set by classical diffractive optical elements. Apart from strong near-field ...

Unique and flexible properties of non-Hermitian photonic systems attract ever-increasing attention via delivering a whole bunch of novel optical effects and allowing for efficient tuning light-matter interactions on nano- and microscales. Together with an increasing demand for the fast and spatially compact methods of light governing, this peculiar approach paves a broad avenue to novel optical applications. Here, unifying the approaches of disordered metamaterials and non-Hermitian photonics, we propose a conceptually new and simple architecture driven by disordered loss-gain multilayers and, therefore, providing a powerful tool to control both the passage time and the wave-front shape of incident light with different switching times. For the first time we show the possibility to switch on and off kink formation by changing the level of disorder in the case of adiabatically raising wave fronts. At the same time, we deliver flexible tuning of the output intensity by using the nonlinear effect of loss and gain saturation. Since the disorder strength in our system can be conveniently controlled with the power of the external pump, our approach can be considered as a basis for different active photonic devices.

Versatile manipulation of nano- and microobjects underlies the optomechanics and a variety of its applications in biology, medicine, and lab-on-a-chip platforms. For flexible tailoring optical forces, as well as for extraordinary optomechanical effects, additional degrees of freedom should be introduced into the system. Here, we demonstrate that photonic crystals provide a flexible platform for nanoparticles optical manipulation due to both Bloch surface waves (BSWs) and the complex character of the reflection coefficient paving a way for complex optomechanical interactions control. We demonstrate that appearance of enhanced pulling and pushing transversal optical forces acting on a single bead placed above a one-dimensional photonic crystal due to directional excitation of Bloch surface wave at the photonic crystal interface. Our theoretical results, which are supported with numerical simulations, demonstrate angle or wavelength assisted switching between BSW-induced optical pulling and pushing forces. Easy-to-fabricate for any desired spectral range photonic crystals are shown to be prospective for precise optical sorting of nanoparticles, especially for core-shell nanoparticles, which are difficult to sort with conventional optomechanical methods. Our approach opens opportunities for novel optical manipulation schemes and platforms and enhanced light-matter interaction in optical trapping setups.

Focused laser beams allow controlling the mechanical motion of objects and can serve as a tool for assembling micro and nanostructures in space. While small particles mainly experience attractive gradient forces and repulsive radiation pressure, introducing additional flexibility suggests approaching new capabilities. Herein, optical forces acting on a high refractive index sphere in a focused Gaussian beam are analyzed and new regimes are revealed. Multipolar analysis allows separating an optical force into interception and recoil components, resulting in different mechanical actions. In particular, interplaying interception radial forces and multipolar resonances within a particle can lead to either trapping or antitrapping, depending on the system parameters. At the same time, the recoil force generates a significant azimuthal component along with an angulardependent radial force. Those contributions enable enhancing either trapping or antitrapping and also introduce bending reactions. These effects are linked to the far-field multipole interference and, specifically, to asymmetric scattering patterns. The latter approach is extremely useful, as it allows assessing the nature of optomechanical motion by observing far-fields. Multipolar engineering of optical forces, being quite a general approach, is not necessarily linked to simple spherical shapes and paves a way to new possibilities in microfluidic applications, including sorting and microassembly

Dielectric nanophotonics became a hot topic during the last decade. Particularly, a lot of relevant studies were devoted to metasurfaces and their optical properties. Here we propose and numerically study the quadrumerbased silicon metasurface supporting magnetic octupole response. Specific meta-atoms allow to excite magnetic octupole moment in optical range without going beyond the diffraction limit. Comparing to a metasurface based on solid blocks of similar size, the quadrumer-based metasurface feature significant absorption enchantment and strong change of a reflection spectrum. Obtained results can be exploited in development of novel sensors, optical elements and energy harvesting devices.

Bound states in the continuum (BIC) attracted great attention in the photonics community. The existence of such states has led to numerous applications, including optical sensors and filters. Here we report on the approach to externally tune a magnitude and spectral position of high-Q resonances, associated with not symmetry-protected BIC state in silicon nitride (Si3N4) photonic crystals. We show that BIC properties can be controlled by the external thermal impact. These results can be used to construct compact and thermally stable optical sensors immune to harsh environmental conditions.

In this Letter we study the interactions of the dissipative domain walls with dielectric particles. It is shown that particles can be steadily trapped by the moving domain walls. The influence of the ratchet effect on particle trapping is considered. It is demonstrated, that the ratchet effect allows to obtain high accuracy in particle manipulation.

We uncover a novel mechanism of superscattering from subwavelength resonators linked to the physics of bound states in the continuum (BICs). Enhanced scattering occurs due to constructive interference within the Friedrich-Wintgen mechanism of interfering resonances. Through this process, the scattering cross section of a single resonance can exceed the currently established limit. We develop a general non-Hermitian model to describe interfering resonances of quasi-normal modes, and study subwavelength dielectric nonspherical resonators exhibiting avoided crossing resonances and quasi-BIC states. Our results reveal novel physics of non-Hermitian systems suggesting important applications for metadevices.

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. Homogenized model of the hyperbolic metasurface is compared to its metal-dielectric multilayer realizations and is shown to pr...

Specialized electromagnetic fields can be used for nanoparticle manipulation along a specific path, allowing enhanced transport and control over the particle’s motion. In this paper, we investigate the optical forces produced by a curved photonic jet, otherwise known as the “photonic hook”, created using an asymmetric cuboid. In our case, this cuboid is formed by appending a triangular prism to one side of a cube. A gold nanoparticle immersed in the cuboid’s transmitted field moves in a curved trajectory. This result could be used for moving nanoparticles around obstacles; hence we also consider the changes in the photonic hook’s forces when relatively large glass and gold obstacles are introduced at the region where the curved photonic jet is created. We show, that despite the obstacles, perturbing the field distribution, a particle can move around glass obstacles of a certain thickness. For larger glass slabs, the particle will be trapped stably near it. Moreover, we noticed that a partial obstruction of the photonic jet’s field using the gold obstacle results in a complete disruption of the particle’s trajectory.

A recently introduced femtosecond laser printing technique was further developed for the fabrication of crystalline single Ge and SiGe nanoparticles (NPs). Amorphous Ge and SiGe thin films deposited by e-beam evaporation on a transparent substrate were used as donors. The developed approach is based on a laser-induced forward transfer process, which provides an opportunity for NP-controlled positioning on different types of receiver substrates. The size of the generated nanoparticles can be varied from about 100 to 300 nm depending on the laser pulse energy and wavelength. The crystallinity and composition of nanoparticles are both confirmed by the Raman spectroscopy measurements. The experimental visible scattering spectra of single nanoparticles are found to be well coincident with theoretical simulations performed on the basis of Mie theory. It is demonstrated that Ge and SiGe nanoparticles are characterized by electric and magnetic dipole resonances in the visible and near-infrared spectral ranges, wh...

Light-matter interaction processes are significantly affected by surrounding electromagnetic environment. Dielectric materials are usually introduced into an interaction picture via their classical properties, e.g. permittivity, appearing in constitutive relations. While this approach was proven to be applicable in many occasions, it might face limitations when an emitter is situated very close to a material boundary. In this case nonlocal extend of a quantum wave function of an emitter becomes comparable with a distance to a boundary and a lattice constant of a material. Here a semi-classical model, taking into account material's granularity, is developed. In particular, spontaneous emission process in the vicinity of flat boundaries is considered. The material boundary is divided into a pair areas - far zone is modeled as a continuous phase, while the near zone next to a nonlocal emitter is represented with a discrete array of polarizable particles. This array resembles optical properties of the continuous phase under the standard homogenization procedure. Local field effects were shown to lead orders of magnitude corrections to spontaneous emission rates in the case of sub-nanometer emitter-surface separation distances. The developed mesoscopic model enables addressing few aspects of local field corrections in quite complex scenarios, where quantum ab initio techniques yet face challenges owing to involved computational complexity. The developed method could be utilized for designs of quantum sources and networks, enhanced with structured electromagnetic environment., 15 pages, 5 figures

In recent years, the ability to manipulate both electric and magnetic components of light along with strongly reduced heat losses in comparison with plasmonics, has rendered all-dielectric nanophotonics as one of the hottest research fields in the photonics community. A plethora of exciting effects have been discovered and are currently in the process of being implemented in real-world applications. Among them, one of the most interesting are the so-called anapole states, allowing to minimize scattering from an object while keeping enhanced near fields. Here, we exploit the quasi-normal mode (QNM) formalism to discuss the origin of a novel regime, where the hybridization of four anapole states takes place in the visible region. We rigorously show that the effect is formed due to the interference of a Mie-like mode and a Fabry- Perot-like mode with the incident wave.

We analyze the physical meaning of exceptional points (EPs), which are the spectral degeneracies of the non-Hermitian optical systems. The situation is complicated by the existence of two definitions of the scattering matrix giving different positions for the EPs. Taking a PT-symmetric multilayer structure as a specific example, we give the unambiguous formulation of the scattering matrix and find the “true” EPs where the symmetry breaking occurs. However, the EPs given by another definition of the scattering matrix are not totally meaningless being associated with coherent perfect absorption and lasing.

In this work, we consider resonant anapole state of an electric dipole in a dielectric spherical particle. The analytical expression that describes the minimum size parameter of a resonant state at a given refractive index of the scatterer was shown. Using Cartesian multipole decomposition, we reveal the resonant anapole state does consist of the basic electric dipole and a minimum contribution of 7 resonant toroidal moments. It was shown that the presence of vortex- like configurations indicates the appearance of toroidal moments in the scattering spectra. Interestingly, with the correct description of electric dipole anapole state, increasing number of singularities in the near-field region that is associated with the increase of refractive index doesn’t change the minimum set of toroidal moments.

In this work, we demonstrate poloidal current configuration produced by an ideal toroidal source simulated numerically in the COMSOL Multiphysics software. The Cartesian multipole decomposition with the implicit contribution of two first toroidal moments is used to demonstrate that the impact of the basic electric dipole to the radiation power is negligible.

High index dielectric particles proved superior in performing many exotics photonics effects and has become a subject to an extensive studies towards functional devices. Enhancing and controlling light scattering is a strongly sought after characteristic of antennas as an essential component of various technologies such as bio-sensing. We study an effect where particle mainly scatterers the incident power to the side-directions rather than to the forwards or backward. This type of scattering on symmetric scatterer requires at least the contribution of two orders of multipoles to enable simultaneous forward and back-scattering suppression, or the so-called transverse scattering. We explore helicity enhancement in the nearfield when illuminating the nanocube by an optimally-chiral beam that generates parallel induced electric and magnetic dipole and quadrupoles moments that satisfy the transverse Kerker condition. These moments generate an optimally-chiral scattered field preserving the handedness of the incident field.

$\mathcal{PT}$ symmetry is a unique platform for light manipulation and versatile use in unidirectional invisibility, lasing, sensing, etc. Broken and unbroken $\mathcal{PT}$-symmetric states in non-Hermitian open systems are described by scattering matrices. A multilayer structure, as a simplest example of the open system, has no certain definition of the scattering matrix, since the output ports can be permuted. The uncertainty in definition of the exceptional points bordering $\mathcal{PT}$-symmetric and $\mathcal{PT}$-symmetry-broken states poses an important problem, because the exceptional points are indispensable in applications as sensing and mode discrimination. Here we derive the proper scattering matrix from the unambiguous relation between the $\mathcal{PT}$-symmetric Hamiltonian and scattering matrix. We reveal that the exceptional points of the scattering matrix with permuted output ports are not related to the $\mathcal{PT}$ symmetry breaking. Nevertheless, they can be employed for finding a lasing onset as demonstrated in our time-domain calculations and scattering-matrix pole analysis. Our results are important for various applications of the non-Hermitian systems including encircling exceptional points, coherent perfect absorption, $\mathcal{PT}$-symmetric plasmonics, etc., 7 pages, 5 figures

We study analytically the effect of a substrate on the optical response of an arbitrarily-shape particle. We describe the substrate-induced bianisotropic interaction between electric and magnetic modes of any order. This results in a specific feature of the radiation pattern, that can be exploited in an experiment to determine the interactions between multipoles for various reasoning including metasurfaces.

Structured environment controls dynamics of light-matter interaction processes via modified local density of electromagnetic states. In typical scenarios, where nanosecond-scale fluorescent processes are involved, mechanical conformational changes of the environment during the interaction processes can be safely neglected. However, slow decaying phosphorescent complexes (e.g. lanthanides) can efficiently probe micro- and millisecond scale motion via near-field interactions with nearby structures. As the result, lifetime statistics can inherit information about nano-scale mechanical motion. Here we study light-matter interaction dynamics of phosphorescent dyes, diffusing in a proximity of a plasmonic nanoantenna. The interplay between time-varying Purcell enhancement and stochastic motion of molecules is considered via a modified diffusion equation, and collective decay phenomena is analyzed. Fluid properties, such as local temperature and diffusivity, are mapped on phosphorescent lifetime distribution and then extracted with the help of inverse Laplace transformation. The presented photonic platform enables performing contactless all-optical thermometry and diffusion measurements, paving a way for a range of possible applications. In particular, detailed studies of nanofluidic processes in lab-on-a-chip devices, challenging for analysis with other optical methods, can be performed with time-dependent phosphorescence.

Tuning electric and magnetic response of dielectric structures at the nanoscale is a very important task nowadays. Multipole decomposition is a useful instrument to analyze and then control an opical response. Here we show the way to excite magnetic octupole moment by nanostructuring dielectric scatterer in near-IR spectral range. This response leads to magnetic hot-spots generations and a eresonant peak in scattering cross-section. Our results can be widely used to design novel metasurfaces avoiding diffraction limit, for particle trapping and imaging applications.

Nanoparticles made from dielectric materials with a high refractive index have caused a surge of interest and have been proposed for various all-dielectric nanophotonic applications. In this regard, the development of optical manipulation technology for such nanoparticles becomes an important task. High-index nanoparticles support electric and magnetic multipole responses in the visible wavelength range, and interference between such modes can manifest itself in optical forces. Here, we present a study of the optical forces acting on silicon nanoparticles in a Gaussian beam, calculated analytically using the Mie theory, as well as the numerical simulations results based on the Maxwell stress tensor. We have shown that the interaction of а laser beam electromagnetic field with electric and magnetic dipoles in a nanoparticle can lead to a possible anti-trapping effect. This behavior of the particle is not typical for optical tweezers, where the particle is usually attracted to the beam axis.

In this work, using the numerical simulation in the COMSOL Multiphysic package, we studied the optical properties of the hybrid anapole state in silicon nanocylinders and their metasurfaces. Our investigations show the possibility of creating invisible metasurfaces consisting of silicon cylinders based on the novel state. These results can be used in various fields of nanophotonics and may have important outcome in the development of various sensors and other photonic devices.

Here we study light-induced interaction of several dielectric particles above a hyperbolic metamaterial. It is shown, that both surface and volumetric modes of the substrate define distances between interacting particles, beyond the diffraction limit. Moreover, by varying the thickness of the metamaterial substrate it is possible to tune magnitude of the optical force and distances between the particles.

Multipole decomposition is a powerful tool for analysis of electromagnetic systems. This work considers high order irreducible Cartesian multipole moments in approximation of electric 32-pole and magnetic 16-pole. The explicit contributions to scattering of high order toroidal moments up to toroidal electric octupole and toroidal magnetic quadrupole are demonstrated for a dielectric high refractive index scatterer.

Optomechanics is a promising technique for a wide range of applications and an intensively studied branch of nanophotonics. The flexibility of optical manipulation can be increased with the help of auxiliary substrates providing additional degrees of freedom. In this paper, we consider optical force acting on a particle near a one-dimensional photonic crystal. The excitation of bulk and surface modes of the crystal occurs due to the near fields of the particle and does not require additional mechanisms. Oblique incidence of a plane wave can lead to the directional excitation of the substrate modes, and therefore, an optical pulling force arises.

In this work we considered lateral optical forces acting on high refractive index nanoparticles. It is shown that the tightly focused Gaussian beam exerts pulling or pushing forces on a spherical nanoparticle depending on the type and the order of an excited multipole resonance. The nanoparticle's refractive index thermal nonlinearity is used to demonstrate switching between multipole resonances and as a consequence the lateral force pushing/pulling regimes.