Plasmonic nanostructures typically exhibit shifts in their resonant wavelength in response to changes in the refractive index of the surrounding medium. This limits their applications in scenarios requiring stable optical resonances. Here we present a metallic-dielectric hybrid metasurface that exhibits stable multi-wavelength resonance even if the refractive index of its surrounding varies. To quantitatively evaluate the stability of the optical response, we introduce a stability factor F_S=Δ n/Δλ . Here, Δ n and Δλ represent variation of refractive index and shift of the resonant wavelength, respectively. A larger factor indicates better stability. The factor reaches 5 RIU/μ m when silicon is employed as the central dielectric and increases to 33.3 RIU/μ m when Bi _2 Te _3 is utilized instead. The proposed innovative structure has potential applications in the development of substrates for in-vitro cell cultivation. Under broadband light illumination, it stably absorbs light at specific wavelengths, creating a consistent optical microenvironment leading to cell growth. It can find potential applications in precise control of various cellular processes, including metabolism and differentiation. It potentially brings a paradigm shift in the fields of cell based research and regenerative medicine, opening up new avenues for scientific exploration and therapeutic advancements.

The integration of elementary quantum objects (atoms, molecules, and quantum dots) with solid-state nanostructures lies at the forefront of nano-optics, nanophotonics, and quantum information science. However, the advancement of this field is hindered by the lack of a rigorous and feasible theoretical framework for describing atom-nanostructure interactions, which are inherently complex and multiparametric. In this work, we develop a theory of light transmission through a zero-mode waveguide (ZMW) containing a single atom. It is shown that the presence of a single atom inside the ZMW can lead to either a significant enhancement or suppression of light transmission, depending on the detuning of the excitation field frequency from the atomic resonance. This extraordinary transmission and blocking effect can be employed for studying the spatiotemporal dynamics of atoms in complex nanoscopic environments, probing quantum optical phenomena, and developing novel nano-optical devices.

Zero-mode waveguide (ZMW) nanowells confine light efficiently down to the nanometer scale and overcome the diffraction limit of single-molecule fluorescence analysis. However, the sticking of fluorescent molecules on ZMW surface can substantially hinder the interpretation of experiments. A regular quantitative method for the description of the fluorescence of molecules randomly moving in a ZMW with a functionalized surface is proposed. The autocorrelation functions of the single-molecule fluorescence fluctuations in a closed ZMW with different properties of its bottom and walls are found. It is shown that in the ZMW, where the diffusion coefficient at the bottom and/or walls is significantly smaller than the diffusion coefficient in the main volume, mode decoupling arises. A significant increase in the fluorescence correlation time appears, and quantitative estimates of this increase are found. The obtained results pave the way for the quantitative analysis of the properties of a ZMW with functionalized surfaces and expand the use of the ZMW to single-molecule fluorescence applications.

A regular method has been proposed to quantitatively describe the fluorescence of molecules randomly moving in a nanowell. Correlation functions of the fluorescence of single molecules depending on the geometry of the nanowell and the penetration depth of an exciting field into it have been determined. The obtained results can be used to quantitatively analyze the properties of molecules and to extract information on the parameters of the nanowell.

A method for estimating the spectral parameters of a polyharmonic process by the method of central finite differences of even order is considered for the case when the series of numerical observations is quite large and the number of harmonic components in the process under study is a priori unknown.

Fano’s resonance is not obviously that of a system parameter depending on the state energy or frequency. The spatial distribution of light intensity may experience this resonance if the continuum of eigenmodes interferes with a resonant mode. We found this spatial Fano resonance in the exact solution of a diffraction problem: a hollow Bessel impinges on a dielectric sphere with optically substantial but not very large radius. Tuning the frequency, one may engineer a very sharp Fano minimum in free space. This point at which the electromagnetic field vanishes may serve an optical trap for molecules and atoms. In accordance with our calculations, such the trap has no analogues in the available literature in what concerns its parameters and its ultimate simplicity.

The review presents an analysis and generalization of classical and most modern approaches to the description and development of operation of open optical nanoresonators, that is, resonators all sizes of which are smaller than the resonant wavelength of radiation in a vacuum. Particular attention is paid to the physics of such phenomena as bound states in a continuum, anapole states, supercavity modes, and perfect nonradiating modes with extremely high quality factors and localizations of electromagnetic fields. An analysis of the optical properties of natural oscillations in nanoresonators made of metamaterials is also presented in the review. The effects considered in this review, besides being of fundamental import can also find applications in the development of optical nanoantennas, nanolasers, biosensors, photovoltaic devices, and nonlinear nanophotonics.

The natural oscillations of the electromagnetic field in a particle made from left-handed metamaterial, where both permittivity and permeability are negative, are considered. Based on the exact solution of the sourceless Maxwell equations, it is shown that due to the opposite directions of the phase and group velocities in the metamaterial, natural oscillations in such particles decay exponentially at infinity, that is, these natural oscillations can be considered as trapped modes with a finite energy. The manifestation of such modes in experiments with Bessel beams is also discussed.

A hypothesis of the existence of perfect nonradiating modes in dielectric nanoparticles of an arbitrary shape is put forward. It is strictly mathematically proved that such modes exist in axisymmetric dielectric nanoparticles and have unlimited radiation Q factors. With the smart tuning of the excitation beams, perfect modes appear as deep minima in the scattered radiation spectra (up to complete disappearance), but at the same time, they have a substantial amplification of the fields inside the particle. Such modes have no analogs and can be useful for the realization of nanosensors, low threshold nanolasers, and other strong nonlinear effects in nanoparticles.

In the diffraction of visible light by a dielectric microcylinder packages of evanescent waves always arise. However, a single-wave incidence corresponds to rather small impact of evanescent waves outside the cylinder. In this paper, we theoretically show that a symmetric pair of plane waves impinging a glass microcylinder corresponds to much higher impact of the evanescent waves. Namely, the interference of the evanescent waves with the propagating ones results in the suppression of the electromagnetic field in an area with very small cross section. This area is located in free space at a substantial distance from the {rear side of the microcylinder and along its axis}. It may serve a linear optical trap for cold atoms and ions.

The most important direction in the development of fundamental and applied physics is the study of the properties of optical systems at nanoscales for creating optical and quantum computers, biosensors, single-photon sources for quantum informatics, DNA sequencing devices, detectors of various fields, etc. In all these cases, nanosize light sources such as dye molecules, quantum dots (epitaxial or colloidal), color centers in crystals, and nanocontacts in metals are of utmost importance. In the nanoenvironment, the characteristics of these elementary quantum systems pumping rates, radiative and nonradiative decay rates, the local density of states, lifetimes, level shifts experience changes, which can be used to create nanosize light sources with the desired properties. Modern theoretical and experimental works on controlling the emission of elementary quantum systems with the help of plasmonic and dielectric nanostructures, metamaterials, and metamaterial nanoparticles are analyzed.

A generic model of two dissimilar antenna-type resonators coupled both via near-field and far-field and embedded in active gain and/or loss medium is considered. Conditions required for hitting the superscattering regime corresponding to the threshold of lasing emission operation are established. It is shown that modulation of the medium gain and losses level within realistic parameters is an efficient approach for implementation of tunability. This two-antenna setup can serve as an inspiration for the implementation of high-contrast tunable metasurfaces.

Generation of a photonic nanojet with a slightly subwavelength waist at the back side of a dielectric microsphere or microcylinder impinged by a plane wave has recently shown that the near-field effects may hold not only inside the dielectric microparticle, but also outside it. In this paper we explain how to drastically increase the external near-field effect. For it one has to replace a plane wave or a Gaussian beam by the fully symmetric diffraction-free beam. In this case we observe a deeply subwavelength focusing of the incident beam near the rear edge of the microcylinder. This effect is accompanied by a very strong enhancement of the local electric intensity. Microcylinders with slightly different parameters grant the significant enhancement of the intensity on the whole cylinder surface. These implications of the resonant scattering result from the destructive interference of the propagating spatial harmonics which vanish at the back side of the cylinder in favor of the evanescent ones.

The general concept of Fano resonance is considered so as to show the possibility of this resonance in space. Using a recently found solution for a Bessel wave beam impinging on a dielectric sphere, we analyze the electromagnetic fields near a microsphere with different optical sizes and permittivity values. We theoretically reveal spatial Fano resonance when a resonant mode of the sphere interferes with an amount of non-resonant modes. This resonance results in a giant jump of the electric field behind the sphere impinged on by the first-order Bessel beam. The local minimum of the electromagnetic field turns out to be noticeably distanced from the rear edge of the microsphere. However, this is a near-field effect, and we prove it. We also show that this effect can be utilized for engineering a submicrometer optical trap with unusual and useful properties.

In the framework of the dipole approximation, we have developed a model of optical properties of a meta-atom consisting of spherical nanoparticles located at the vertices of Platonic solids. Based on the model, we have found and analysed the dynamics of changes in the optical spectra with a change in the length of the edge of a polyhedron. We have observed strong hybridisation and splitting of initially degenerate modes of individual nanoparticles. The obtained results can be used as the basis for the development of an optical nanosensor, which can determine the change in the chemical and biological composition of the environment.

The exact analytical solution of Maxwell equations for a Bessel light beam scattered by a sphere is found. Scattered power, stored energy, and a generalized Q factor as a function of frequency, the sphere radius, permittivity, and the Bessel beam angle are found. On the basis of this solution, modes and pseudo-modes of a dielectric sphere are extracted by calculation of the generalized Q factor. It is shown that an appropriate choice of Bessel beam parameters can provide excitation of a single given mode and an unlimited value of the radiative Q factor of pseudo-modes.

It is shown in this letter related to the paper by M V Rybin and M F Limonov [Physics–Uspekhi 62 (8) (2019)] that in dielectric sub-wavelength resonators of equal volume but different shape no eigen-modes exist that would be qualitatively different from those in dielectric spheres. In particular, there are no ‘supercavity modes’ in dielectric cylinders whose Q-factor would exceed that of similar modes in dielectric spheres of the same volume.

The generic model of two coupled multimode plasmonic nanospheres with gain and loss forming a parity-time (PT) symmetric dimer is considered. Analytical solutions based on a quasistatic approximation are used to explore the behavior of the eigenmodes in such a coupled nanoantenna system as a function of their separation distances and their gain-loss level. It is shown that the introduction of the same amount of gain and loss modifies the composition of eigenmodes and breaks their orthogonality. The resulting entanglement of different spatial order and symmetry modes can be advantageously exploited to actively control the scattering properties of such multimode PT-symmetric nanoantennas.

Due to losses in metals, the propagation length of the surface plasmon-polariton (SPP) waves on metal surfaces is small. This severely limits development of numerous applications of the SPP optics: in the near-infrared spectral region propagation length of SPP waves is no longer than 200 μm as for plane SPP waves and for all types of SPP waveguides. In this work, we show that the focusing of SPPs allows for the first time realizing open-type waveguide for SPP waves characterized by long distance of SPP effective propagation length up to 1 mm at a wavelength of 780 nm. We show that focused SPP waves in such a waveguide can be effectively excited by a 16 fs laser as well as be amplitude modulated within a bandwidth about 3.5 THz. The fast dynamics of the focused SPP waves is limited by the SPP group velocity dispersion. The large effective propagation length of the SPPs and its ultra-high bandwidth open up new possibilities for using focused SPPs in different areas of plasmonics and photonics.

О существовании "суперрезонансных" состояний в субволновых диэлектрических резонаторах и их связи со связанными состояниями в континууме, Климов В.В.