arXiv subjects

Sergey Kruk

Publications and source records attributed to Sergey Kruk.

At least 19 recordsLinked to original sources

arXiv2026

Asymmetric high-harmonic generation from subwavelength bianisotropic resonators

High-harmonic generation (HHG) enables attosecond light pulses and table-top sources of coherent extreme-ultraviolet and soft X-ray radiation. Although HHG has long been associated with gases and plasma, nanostructured solids are emerging as new alternative sources enabling both the enhancement and control of HHG. Here, we experimentally demonstrate and theoretically describe that a single dielectric subwavelength resonator can act as a direction-selective high-harmonic source, enabling control over multiple harmonic orders through the excitation and hybridization of Mie modes. The resonator's geometrical volume is $0.12 \lambda^3$, and its optical mode volume is $0.03 \lambda^3$ at its pump wavelength. Structural asymmetry of the resonator along the propagation direction translates into different mode coupling under opposite illumination directions, resulting in pronounced forward-backward asymmetry in the generation of the third, fifth, and seventh harmonics. These results establish bianisotropic subwavelength resonators as a platform for flexible asymmetric generation of high harmonics, expanding the toolbox for controlling strong-field light-matter interactions with Mie-resonant nanophotonics.

physics.optics↗

arXiv2025

Hopping of nanoparticles in optical tweezers governed by Mie resonances

Optical tweezers have become a standard tool for manipulating microscale and nanoscale particles and probing their local environments. However, complex particle dynamics under optical forces typically require structured light fields, multi-beam traps, or engineered environments. Here we achieve complex particle dynamics in a single Gaussian-beam optical tweezer. The effect originates from higher-order Mie resonances supported by wavelength-scale particles. In our optical tweezer, small particles in the regime of Rayleigh scattering or the lowest-order dipole-type Mie modes remain confined at the beam center. By contrast, particles within the range of sizes corresponding to quadrupole-type Mie modes exhibit more complex behavior. In a linearly polarized Gaussian beam, these particles are trapped in a potential with two off-axis equilibria. We observe thermally driven hopping between these equilibria, with the hopping frequency controlled by the laser power. In a circularly polarized Gaussian beam, the particles are confined to a stable orbit and exhibit circular motion driven by the spin (circular-polarization) degree of freedom of the beam, with angular velocity dependent on the laser power. These results reveal higher-order Mie resonances as an intrinsic mechanism behind complex optical forces. This establishes Mie-resonant nanophotonics as a flexible platform for inducing and controlling complex motion in optical tweezers for nanoparticle manipulation as well as sensing of local environments.

physics.optics↗

arXiv2025

Strong coupling and interfering resonances in isolated van der Waals nanoresonators

The study of strong light-matter interaction in van der Waals materials is at the forefront of current research in physics and chemistry, and it can be enhanced dramatically by employing resonances. Here we present the first observation of quasi-bound states in the continuum (qBICs) realized via polaritonic interfering resonances in isolated WS$_2$ nanodisks. We experimentally validate the existence of polaritonic qBICs driven by intrinsic coupling of Mie resonances and excitons. The system exhibits exceptionally strong light-matter interaction with a measured Rabi splitting exceeding 310 meV - the largest reported value among all transition metal dichalcogenide (TMDC) self-hybridized systems to date. The giant coupling strength stems from qBIC-induced in-plane field enhancement, which strongly interacts with in-plane excitonic dipoles while suppressing radiative losses. Polarization-controlled measurements further demonstrate selective excitation of qBIC through switching incident polarization to specific orthogonal configurations. The observed polarization-dependent coupling provides an additional degree of freedom to control over the hybrid states' spectral characteristics and spatial field distributions. Our demonstrations provide a pathway for engineering high-quality light-matter hybrid states in compact nanostructures, with potential applications in on-chip photonics, polaritonics, and quantum optics.

physics.optics↗

arXiv2025

Chiral high-harmonic generation in metasurfaces

High-harmonic generation (HHG) provides the only source of attosecond pulses -- currently the shortest accessible time intervals, and it is employed as the only table-top source of light in extreme UV and soft X-ray spectral regions. Chiral HHG can be employed as an efficient tool for studying the ultrafast response of chiral properties of matter, as well as for amplifying chiroptical effects. Traditionally, chiral high harmonics were associated with gases of enantiomer molecules or, more recently, solid surfaces with helicity in their crystalline structure. Here, we bring the concept of chiral high-harmonic generation to nanophotonics, specifically to metasurfaces consisting of arrays of nanoresonators. Our system is achiral at the material as well as at the level of individual nanoresonators. Chirality rises and falls in a controlled manner via an interplay of the nanoresonator symmetry and the symmetry of the metasurface lattice. Our calculations predict high contrast in harmonic brightness between the two orthogonal circular polarizations of the pump. Our findings, at the intersection of chiral nanophotonics and strong-field optics, pave the way for chiral attosecond physics and chiral extreme UV optics in nanostructured solids.

physics.optics↗

arXiv2025

Nonreciprocal metasurfaces with epsilon-near-zero materials

Nonreciprocal optics enables asymmetric transmission of light when its sources and detectors are exchanged. A canonical example -- optical isolator -- enables light propagation in only one direction, similar to how electrical diodes enable unidirectional flow of electric current. Nonreciprocal optics today, unlike nonreciprocal electronics, remains bulky. Recently, nonlinear metasurfaces opened up a pathway to strong optical nonreciprocity at the nanoscale. However, demonstrations to date were based on optically slow nonlinearities involving thermal effects or phase transition materials. In this work, we demonstrate a nonreciprocal metasurface with an ultra-fast optical response based on indium tin oxide in its epsilon-near-zero regime. It operates in the spectral range of 1200-1300 nm with incident power densities of 40-70 GW/cm$^2$. Furthermore, the nonreciprocity of the metasurface extends to both amplitude and phase of the forward/backward transmission opening a pathway to nonreciprocal wavefront control at the nanoscale.

physics.optics↗

arXiv2024

Even-order optical harmonics generated from centrosymmetric-material metasurfaces

Generation of even-order optical harmonics requires noncentrosymmetric structures being conventionally observed in crystals lacking the center of inversion. In centrosymmetric systems, even-order harmonics may arise, e.g., at surfaces but such effects are usually very weak. Here we observe optical harmonics up to 4-th order generated under the normal incidence from centrosymmetric dielectric metasurfaces empowered by resonances. We design silicon metasurfaces supporting optical quasibound states in the continuum and guided-mode resonances, and demonstrate the enhancement of second-harmonic signals by over three orders of magnitude compared to nonresonant thin films. Under the optimal conditions, the brightness of the second harmonic approaches that of the third harmonic, and the 4th-order harmonic becomes detectable.

physics.optics↗

arXiv2024

Switchable optical trapping of Mie-resonant phase-change nanoparticles

Optical tweezers revolutionized the manipulation of nanoscale objects. Typically, tunable manipulations of optical tweezers rely on adjusting either the trapping laser beams or the optical environment surrounding the nanoparticles. We present a novel approach to achieve tunable and switchable trapping using nanoparticles made of a phase-change material (vanadium dioxide or VO$_2$). By varying the intensity of the trapping beam, we induce transitions of the VO$_2$ between monoclinic and rutile phases. Depending on the nanoparticles' sizes, they exhibit one of three behaviours: small nanoparticles (in our settings, radius $<0.12$ wavelength $\lambda$) remain always attracted by the laser beam in both material phases, large nanoparticles ($>0.22 \lambda$) remain always repelled. However, within the size range of $0.12$-$0.22 \lambda$, the phase transition of the VO$_2$ switches optical forces between attractive and repulsive, thereby pulling/pushing them towards/away from the beam centre. The effect is reversible, allowing the same particle to be attracted and repelled repeatedly. The phenomenon is governed by Mie resonances supported by the nanoparticle and their alterations during the phase transition of the VO$_2$. This work provides an alternative solution for dynamic optical tweezers and paves a way to new possibilities, including optical sorting, light-driven optomechanics and single-molecule biophysics.

physics.optics↗

arXiv2024

Wide-bandgap optical materials for high-harmonics generation at the nanoscale

High-order harmonics generation (HHG) is the only process that enables table-top-size sources of extreme-ultraviolet (XUV) light. The HHG process typically involves light interactions with gases or plasma-material phases that hinder wider adoption of such sources. This motivates the research in HHG from nanostructured solids. Here we investigate theoretically material platforms for HHG at the nanoscale using first-principle supercomputer simulations. We reveal that wide bandgap semiconductors, aluminium nitride AlN and silicon nitride SiN, are highly promising for XUV light generation when compared to one of the most common nonlinear nanophotonic material -- silicon. In our calculations we assume excitation with 100 fs pulse duration, 10^13 W/cm^2 peak power and 800 nm central wavelength. We demonstrate that in AlN material the interplay between the crystal symmetry and the incident light direction and polarization can enable the generation of both even and odd harmonics. Our results should advance the developments of high-harmonics generation of XUV light from nanostructured solids.

physics.optics↗

arXiv2024

Coherent Control of Relativistic Electron Dynamics in Plasma Nanophotonics

Intense femtosecond laser pulses interacting with solids can drive electrons to relativistic energies, enabling miniaturized particle accelerators and bright extreme-ultraviolet light sources. In-situ space-time control of these electrons is crucial for developing next-generation laser-based accelerators but remains extremely challenging. We present a novel approach to achieve such control by manipulating the local fields driving these electrons using a nanoengineered dielectric nanopillar target. We demonstrate via experiments and simulations that this sub-femtosecond and nanometer-scale control enables enhanced electron acceleration and control of the directionality of relativistic electrons over a wide angular range and predicts the coherent formation of sub-femtosecond electron bunches from the nanopillars. This research bridges nanophotonics and strong-field plasma physics, offering new opportunities for in-situ control of high-energy particles and advancements in plasma technology.

physics.plasm-ph↗

arXiv2023

Spectral tuning of high-harmonic generation with resonance-gradient metasurfaces

High-index dielectric subwavelength structures and metasurfaces are capable of enhancing light-matter interaction by orders of magnitude via geometry-dependent optical resonances. This enhancement, however, comes with a fundamental limitation of a narrow spectral range of operation in the vicinity of one or few resonant frequencies. Here we tackle this limitation and introduce an innovative and practical approach to achieve spectrally tunable enhancement of light-matter interaction with resonant metasurfaces. We design and fabricate {\it resonance-gradient metasurfaces} with varying geometrical parameters that translate into resonant frequencies dependence on one of the coordinates of the metasurface. The metasurfaces are composed of bone-like nanoresonators which are made of germanium, and they support high-$Q$ optical resonances in the mid-IR spectral range. We apply this general concept to observe the resonant enhancement of the $3^{\text{rd}}$ and $5^{\text{th}}$ harmonics generated from the gradient metasurfaces being used in conjunction with a tunable excitation laser to provide a wide spectral coverage of resonantly-enhanced tunable generation of multiple optical harmonics.

physics.optics↗

arXiv2023

High harmonic generation from a subwavelength dielectric resonator

Higher-order optical harmonics entered the realm of nanostructured solids being observed recently in optical gratings and metasurfaces with a subwavelength thickness. Structuring materials at the subwavelength scale allows for resonant enhancing of the efficiency of nonlinear processes and reducing the size of high-harmonic sources. Here we report the observation of up to a seventh harmonic generated from a single subwavelength resonator made of AlGaAs material. This process is enabled by careful engineering of the resonator geometry for supporting optical modes associated with a quasi-bound state in the continuum in the mid-infrared spectral range at around λ=3.7 μm pump wavelength. The resonator volume measures ~ 0.1 λ^3. The resonant modes are excited with an azimuthally polarized tightly focused beam. We evaluate the contributions of perturbative and non-perturbative nonlinearities to the harmonic generation process. Our work proves the possibility to miniaturize solid-state sources of high harmonics to the subwavelength volumes.

physics.optics↗

arXiv2022

Asymmetric parametric generation of images with nonlinear dielectric metasurfaces

Subwavelength dielectric resonators assembled into metasurfaces have become a versatile tool for miniaturising optical components approaching the nanoscale. An important class of metasurface functionalities is associated with asymmetry in both generation and transmission of light with respect to reversals of the positions of emitters and receivers. Nonlinear light-matter interaction in metasurfaces offers a promising pathway towards miniaturisation of the asymmetric control of light. Here we demonstrate asymmetric parametric generation of light in nonlinear metasurfaces. We assemble dissimilar nonlinear dielectric resonators into translucent metasurfaces that produce images in the visible spectral range being illuminated by infrared radiation. By design, the metasurfaces produce different and completely independent images for the reversed direction of illumination, that is when the positions of the infrared emitter and the visible light receiver are exchanged. Nonlinearity-enabled asymmetric control of light by subwavelength resonators paves the way towards novel nanophotonic components via dense integration of large quantities of nonlinear resonators into compact metasurface designs.

physics.optics↗

arXiv2022

Nonlinear imaging of nanoscale topological corner states

Topological states of light represent counterintuitive optical modes localized at boundaries of finite-size optical structures that originate from the properties of the bulk. Being defined by bulk properties, such boundary states are insensitive to certain types of perturbations, thus naturally enhancing robustness of photonic circuitries. Conventionally, the N-dimensional bulk modes correspond to (N-1)-dimensional boundary states. The higher-order bulk-boundary correspondence relates N-dimensional bulk to boundary states with dimensionality reduced by more than 1. A special interest lies in miniaturization of such higher-order topological states to the nanoscale. Here, we realize nanoscale topological corner states in metasurfaces with C6-symmetric honeycomb lattices. We directly observe nanoscale topology-empowered edge and corner localizations of light and enhancement of light-matter interactions via a nonlinear imaging technique. Control of light at the nanoscale empowered by topology may facilitate miniaturization and on-chip integration of classical and quantum photonic devices.

physics.optics↗

arXiv2022

Topological membrane devices for terahertz on-chip photonics

Terahertz waves offer a profound platform for next-generation sensing, imaging, and information communications. However, all conventional terahertz components and systems suffer from a bulky design, sensitivity to imperfections, and transmission losses. Here, we propose and experimentally demonstrate on-chip integration and miniaturization of topological devices which may address many existing drawbacks of the terahertz technology. We design and fabricate topological devices based on valley-Hall photonic structures that can be employed for various integrated components of on-chip terahertz systems. More specifically, we demonstrate the valley-locked asymmetric energy flow and mode conversion with topological straight waveguide, multi-port couplers, wave division, and whispering gallery mode resonators. Our devices are based on topological membrane metasurfaces which are of great importance for developing on-chip photonics and bringing many novel features into terahertz devices.

physics.optics↗

arXiv2020

Topological nanophotonics for photoluminescence control

Rare-earth doped nanocrystals are emerging light sources used for many applications in nanotechnology enabled by human ability to control their various optical properties with chemistry and material science. However, one important optical problem -- polarisation of photoluminescence -- remains largely out of control by chemistry methods. Control over photoluminescence polarisation can be gained via coupling of emitters to resonant nanostructures such as optical antennas and metasurfaces. However, the resulting polarization is typically sensitive to position disorder of emitters, which is difficult to mitigate. Recently, new classes of disorder-immune optical systems have been explored within the framework of topological photonics. Here we explore disorder-robust topological arrays of Mie-resonant nanoparticles for polarisation control of photoluminescence of nanocrystals. We demonstrate polarized emission from rare-earth-doped nanocrystals governed by photonic topological edge states supported by zigzag arrays of dielectric resonators. We verify the topological origin of polarised photoluminescence by comparing emission from nanoparticles coupled to topologically trivial and nontrivial arrays of nanoresonators.

physics.optics↗

arXiv2020

High-harmonic generation from metasurfaces empowered by bound states in the continuum

The concept of optical bound states in the continuum (BICs) underpins the existence of strongly localized waves embedded into the radiation spectrum that can enhance the electromagnetic fields in subwavelength photonic structures. Early studies of optical BICs in waveguides and photonic crystals uncovered their topological properties, and the concept of quasi-BIC metasurfaces facilitated applications of strong light-matter interactions to biosensing, lasing, and low-order nonlinear processes. Here we employ BIC-empowered dielectric metasurfaces to generate efficiently high optical harmonics up to the 11th order. We optimize a BIC mode for the first few harmonics and observe a transition between perturbative and nonperturbative nonlinear regimes. We also suggest a general strategy for designing subwavelength structures with strong resonances and nonperturbative nonlinearities. Our work bridges the fields of perturbative and nonperturbative nonlinear optics on the subwavelength scale.

physics.optics↗

arXiv2020

Topological states in disordered arrays of dielectric nanoparticles

We study the interplay between disorder and topology for the localized edge states of light in topological zigzag arrays of resonant dielectric nanoparticles. We characterize topological properties by the winding number that depends on both zigzag angle and spacing between nanoparticles in the array. For equal-spacing arrays, the system may have two values of the winding number $ν=0$ or $1$, and it demonstrates localization at the edges even in the presence of disorder, being consistent with experimental observations for finite-length nanodisk structures. For staggered-spacing arrays, the system possesses richer topological phases characterized by the winding numbers $ν=0$, $1$ or $2$, which depend on the averaged zigzag angle and disorder strength. In a sharp contrast to the equal-spacing zigzag arrays, staggered-spacing arrays reveal two types of topological phase transitions induced by the angle disorder, (i) $ν= 0 \leftrightarrow ν= 1$ and (ii) $ν= 1 \leftrightarrow ν= 2$. More importantly, the spectrum of staggered-spacing arrays may remain gapped even in the case of a strong disorder.

cond-mat.mes-hall↗

arXiv2020

Nonlinear imaging with all-dielectric metasurfaces

Nonlinear metasurfaces incorporate many of the functionalities of their linear counterparts such as wavefront shaping but simultaneously they perform nonlinear optical transformations. This dual functionality leads to a rather unintuitive physical behavior which is still widely unexplored for many photonic applications. The nonlinear processes render some basic principles governing the functionality of linear metasurfaces not directly applicable, such as the superposition principle and the geometric optics approximation. On the other hand, nonlinear metasurfaces facilitate new phenomena that are not possible in the linear regime. Here, we study the imaging of objects through a dielectric nonlinear metalens. We illuminate objects by infrared light and record their generated images at the visible third-harmonic wavelengths. We revisit the classical lens theory and suggest a generalized Gaussian lens equation for nonlinear imaging, verified both experimentally and analytically. We also demonstrate experimentally higher-order spatial correlations facilitated by the nonlinear metalens, resulting in additional image features.

physics.optics↗