arXiv subjects

Pavel Belov

Publications and source records attributed to Pavel Belov.

At least 37 records · Page 2Linked to original sources

arXiv2018

Finite size scaling in the dimer and six-vertex model

We present results of the Monte-Carlo simulations for scaling of the free energy in dimers on the hexagonal lattice. The traditional Markov-chain Metropolis algorithm and more novel non-Markov Wang-Landau algorithm are applied. We compare the calculated results with the theoretical prediction for the equilateral hexagon and show that the latter algorithm gives more precise results for the dimer model. For a non-hexagonal domain the theoretical results are not available, so we present the numerical results for a certain geometry of the domain. We also study the two-point correlation function in simulations of dimers and the six-vertex model. The logarithmic dependence of the correlation function on the distance, which is in accordance with the Gaussian free field description of fluctuations, is obtained.

cond-mat.stat-mech↗

arXiv2018

Ultrahigh field MR-imaging: new frontiers and possibilities

Increasing the static magnetic field strength into the realm of ultrahigh fields (7 T and higher) is the central trend in modern magnetic resonance (MR) imaging. The use of ultrahigh fields in MR-imaging leads to numerous effects some of them raising the image quality, some degrading, some previously undetected in lower fields. This review aims to outline the main consequences of introducing ultrahigh fields in MR-imaging, including new challenges and the proposed solutions, as well as new scanning possibilities unattainable at lower field strengths (below 7 T).

physics.med-ph↗

arXiv2018

Hybrid Nanophotonics

Advances in the field of plasmonics, that is, nanophotonics based on optical properties of metal nanostructures, paved the way for the development of ultrasensitive biological sensors and other devices whose operating principles are based on localization of an electromagnetic field at the nanometer scale. However, high dissipative losses of metal nanostructures limit their performance in many modern areas, including metasurfaces, metamaterials, and optical interconnections, which required the development of new devices that combine them with high refractive index dielectric nanoparticles. Resulting metal-dielectric (hybrid) nanostructures demonstrated many superior properties from the point of view of practical application, including moderate dissipative losses, resonant optical magnetic response, strong nonlinear optical properties, which made the development in this field the vanguard of the modern light science. This review is devoted to the current state of theoretical and experimental studies of hybrid metal-dielectric nanoantennas and nanostructures based on them, capable of selective scattering light waves, amplifying and transmitting optical signals in the desired direction, controlling the propagation of such signals, and generating optical harmonics.

physics.app-ph↗

arXiv2017

All-dielectric nanophotonics: fundamentals, fabrication, and applications

In this Article, we review a novel, rapidly developing field of modern light science named all-dielectric nanophotonics. This branch of nanophotonics is based on the properties of high-index dielectric nanoparticles which allow for controlling both magnetic and electric responses of a nanostructured matter. Here, we discuss optical properties of high-index dielectric nanoparticles, methods of their fabrication, and recent advances in practical applications, including the quantum source emission engineering, Fano resonances in all-dielectric nanoclusters, surface enhanced spectroscopy and sensing, coupled-resonator optical waveguides, metamaterials and metasurfaces, and nonlinear nanophotonics.

physics.optics↗

arXiv2017

Boosting the Terahertz Photoconductive Antenna Performance with Optimized Plasmonic Nanostructures

Advanced nanophotonics penetrates into other areas of science and technology, ranging from applied physics to biology and resulting in many fascinating cross-disciplinary applications. It has been recently demonstrated that suitably engineered light-matter interactions at the nanoscale can overcome the limitations of today's terahertz (THz) photoconductive antennas, making them one step closer to many practical implications. Here we push forward this concept by comprehensive numerical optimization and experimental investigation of a log-periodic THz photoconductive antenna coupled to a silver nanoantenna array. We shed light on the operation principles of the resulting hybrid THz antenna, providing an approach to boost its performance. By tailoring the size of silver nanoantennas and the distance between them, we obtain an enhancement of optical-to-THz conversion efficiency 2-fold larger compared with previously reported results, and the strongest enhancement is around 1 THz, a frequency range barely achievable by other compact THz sources. Moreover, we propose a cost-effective fabrication procedure to realize such hybrid THz antennas with optimized plasmonic nanostructures via thermal dewetting process, which does not require any post processing and makes the proposed solution very attractive for applications.

physics.optics↗

arXiv2017

Mid-infrared directional surface waves on a high aspect ratio nano-trench platform

Optical surface waves, highly localized modes bound to the surface of media, enable manipulation of light at nanoscale, thus impacting a wide range of areas in nanoscience. By applying metamaterials, artificially designed optical materials, as contacting media at the interface, we can significantly ameliorate surface wave propagation and even generate new types of waves. Here, we demonstrate that high aspect ratio (1:20) grating structures with plasmonic lamellas in deep nanoscale trenches function as a versatile platform supporting both surface and volume infrared waves. The surface waves exhibit a unique combination of properties, such as directionality, broadband existence (from 4 μm to at least 14 μm and beyond) and high localization, making them an attractive tool for effective control of light in an extended range of infrared frequencies.

physics.optics↗

arXiv2017

Giant field enhancement in high-index dielectric subwavelength particles

Besides purely academic interest, giant field enhancement within subwavelength particles at light scattering of a plane electromagnetic wave is important for numerous applications ranging from telecommunications to medicine and biology. In this paper, we experimentally demonstrate the enhancement of the intensity of the magnetic field in a high-index dielectric cylinder at the proximity of the dipolar Mie resonances by more than two orders of magnitude for both the TE and TM polarizations of the incident wave. We present a complete theoretical explanation of the effect and show that the phenomenon is very general - it should be observed for any high-index particles. The results explain the huge enhancement of nonlinear effects observed recently in optics, suggesting a new landscape for all-dielectric nonlinear nanoscale photonics.

physics.optics↗

arXiv2017

Electron spin contrast of Purcell-enhanced nitrogen-vacancy ensembles in nanodiamonds

Nitrogen-vacancy centers in diamond allow for coherent spin state manipulation at room temperature, which could bring dramatic advances to nanoscale sensing and quantum information technology. We introduce a novel method for the optical measurement of the spin contrast in dense nitrogen-vacancy (NV) ensembles. This method brings a new insight into the interplay between the spin contrast and fluorescence lifetime. We show that for improving the spin readout sensitivity in NV ensembles, one should aim at modifying the far field radiation pattern rather than enhancing the emission rate.

cond-mat.mes-hall↗

arXiv2017

Reflection compensation mediated by electric and magnetic resonances of all-dielectric metasurfaces

All-dielectric nanostructures have recently emerged as a promising alternative to plasmonic devices, as they also possess pronounced electric and magnetic resonances and allow effective light manipulation. In this work, we study optical properties of a composite structure that consists of a silicon nanoparticle array (metasurface) and high-index substrate aiming at clarifying the role of substrate on reflective properties of the nanoparticles. We develop a simple semi-analytical model that describes interference of separate contributions from nanoparticle array and the bare substrate to the total reflection. Applying this model, we show that matching the magnitudes and setting the π-phase difference of the electric and magnetic dipole moments induced in nanoparticles, one can obtain a suppression of reflection from the substrate coated with metasurface. We perform numerical simulations of sphere and disk nanoparticle arrays for different permittivities of the substrate. We find full agreement with the semi-analytical results, which means that the uncoupled-element model adequately describes nanostructure reflective properties, despite the effects of induced bi-anisotropy. The model explains the features of the reflectance spectrum, such as a number of dips and their spectral positions, and show why it may not coincide with the spectral positions of Mie resonances of the single nanoparticles forming the system. We also address practical aspects of the antireflective device engineering: we show that the uncoupled-element model is applicable to the structures on top of silicon substrates, including lithographically defined nanopillars. The reflectance suppression from nanoparticle array on top of the silicon substrate can be achieved in a broad spectral range with disordered nanoparticle array and for a wide range of incidence angles.

physics.optics↗

arXiv2016

Tuning of Hybrid Oligomers via Nanoscale fs-Laser Reshaping

Various clusters of metallic or dielectric nanoparticles can exhibit sharp Fano resonances originating from at least two modes interference of different spectral width. However, for practical applications such as biosensing or nonlinear nanophotonics, the fine-tuning of the Fano resonances is generally required. Here, we propose and demonstrate a novel type of hybrid oligomers consisting of asymmetric metal-dielectric (Au/Si) nanoparticles with a sharp Fano resonance in visible range, which has a predominantly magnetic origin. We demonstrate both, numerically and experimentally, that such hybrid nanoparticle oligomers allow fine-tuning of the Fano resonance via fs-laser induced melting of Au nanoparticles at the nanometer scale. We show that the Fano resonance wavelength can be changed by fs-laser reshaping very precisely (within 15~nm) being accompanied by a reconfiguration of its profile.

physics.optics↗

arXiv2016

Flexible and compact hybrid metasurfaces for enhanced ultra high field in vivo magnetic resonance imaging

Developments in metamaterials and related structures such as metasurfaces have opened up new possibilities in designing materials and devices with unique properties. The main progress related to electromagnetic waves applications was done in optical and microwave spectra. Here we report about a new hybrid metasurface structure, comprising a two-dimensional metamaterial surface and a very high permittivity dielectric substrate that was designed to enhance the performance of an ultra-high field MRI scanner. This new flexible and compact resonant structure is the first one which can be integrated into a multi-element close-fitting receive coil array used for all clinical MRI. We successfully demonstrated the operation of the metasurface in acquiring vivo human brain images and spectra with enhanced local sensitivity on a commercial 7 Tesla system. These experimental findings prove the feasibility of real clinical applications of metasurfaces in MRI.

physics.med-ph↗

arXiv2016

Approach to tune near- and far-field properties of hybrid dimer nanoantennas via laser melting at the nanoscale

Asymmetric metal-dielectric nanostructures are demonstrated superior optical properties arise from the combination of strong enhancement of their near fields and controllable scattering characteristics which originate from plasmonic and high-index dielectric components. Here, being inspired by the recent experimental work [Dmitry~Zuev, \textit{et al.}, Adv. Mater. \textbf{28}, 3087 (2016)] on a new technique for fabrication of asymmetric hybrid nanoparticles via femtosecond laser melting at the nanoscale, we suggest and study numerically a novel type of hybrid dimer nanoantennas. The nanoantennas consist of asymmetric metal-dielectric (Au/Si) nanoparticles and can allow tuning of the near- and far-field properties via laser melting of the metal part. We demonstrate a modification of scattering properties, near electric field distribution, normalized local density of states, and power patters of radiation of the nanoantennas upon laser reshaping. The parameters used to investigate these effects correspond to experimentally demonstrated values in the recent work.

physics.optics↗

arXiv2016

Demonstration of the enhanced Purcell factor in all-dielectric structures

The Purcell effect is usually described as a modification of the spontaneous decay rate in the presence of a resonator. In plasmonics, this effect is commonly associated with a large local-field enhancement in "hot spots" due to the excitation of surface plasmons. However, high-index dielectric nanostructures, which become the basis of all-dielectric nanophotonics, can not provide high values of the local-field enhancement due to larger radiation losses. Here, we demonstrate how to achieve a strong Purcell effect in all-dielectric nanostructures, and show theoretically that the Purcell factor can be increased by two orders of magnitude in a finite chain of silicon nanoparticles. Using the eigenmode analysis for an infinite chain, we demonstrate that the high Purcell factor regime is associated with a Van Hove singularity. We perform a proof-of-concept experiment for microwave frequencies and observe the 65-fold enhancement of the Purcell factor in a chain of 10 dielectric particles.

physics.optics↗

arXiv2015

Core-shell multilayered nanoparticles: giant photonic density of states coupled to the far-field

We present a quantum theoretical treatment of light-matter coupling in the system consisting of a quantum dot and a spherical core-shell metal-dielectric multilayer nanoparticle. It is shown that both weak and strong coupling regimes can be realized in the set-up. Specifically, we demonstrate a strong coupling regime between a quantum dot and a nanoparticle, when the quantum dot resonance is tuned to the frequency at which normal component of effective nanoparticle permittivity is crossing zero. Moreover, we demonstrate the regime at which the quantum dot decays much faster than in vacuum (due to the large Purcell factor) and at the same time radiates more power to the far field. This findings pave the way towards more efficient control over radiation properties of quantum emitters.

physics.optics↗

arXiv2015

All-dielectric nanoantennas for unidirectional excitation of electromagnetic guided modes

Engineering of intensity and direction of radiation from a single quantum emitter by means of structuring of their environment at the nanoscale is at the cornerstone of modern nanophotonics. Recently discovered systems exhibiting spin--orbit coupling of light are of particular interest in this context. In this Letter, we have demonstrated that asymmetrical excitation of a high-index subwavelength dielectric nanoparticle by a point dipole source located in a notch at its surface results in formation of a chiral near field, which is similar to that of a circularly polarized dipole or quadrupole. Using numerical simulations, we have shown that this effect is the result of a higher multipole (quadrupole and octupole) modes excitation within the nanoparticle. We have applied this effect for unidirectional excitation of dielectric waveguide and surface plasmon-polariton modes. We have achieved the value of front--to--back ratio up to 5.5 for dielectric waveguide and to 7.5 for the plasmonic one. Our results are important for the integrated nanophotonics and quantum information processing systems.

physics.optics↗

arXiv2015

Tuning of magnetic optical response in a dielectric nanoparticle by ultrafast photo-injection of dense electron-hole plasma

We propose a novel approach for efficient tuning of optical properties of a high refractive index subwavelength nanoparticle with a magnetic Mie-type resonance by means of femtosecond laser irradiation. This concept is based on ultrafast photo-injection of dense (>10^20 cm^-3) electron-hole plasma within such nanoparticle, drastically changing its transient dielectric permittivity. This allows to manipulate by both electric and magnetic nanoparticle responses, resulting in dramatic changes of its scattering diagram and scattering cross section. We experimentally demonstrate 20 % tuning of reflectance of a single silicon nanoparticle by femtosecond laser pulses with wavelength in the vicinity of the magnetic dipole resonance. Such single-particle nanodevice enables to design fast and ultracompact optical switchers and modulators.

physics.optics↗

arXiv2015

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 a new approach for increasing 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 nanoantenna. 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 magnetic polarizability, tailoring the later in the dynamical range of 100 % and 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 response.

physics.optics↗

arXiv2015

Large Purcell enhancement without strong field localization

The Purcell effect is defined as the modification of spontaneous decay in the presence of a resonator, and in plasmonics it is usually associated with the large local-field enhancement in "hot spots" due to surface plasmon polaritons. Here we propose a novel strategy for enhancing the Purcell effect through engineering the radiation directivity without a strict requirement of the local field enhancement. Employing this approach, we demonstrate how to enhance the Purcell effect by two orders of magnitude in all-dielectric nanostructures recently suggested as building blocks of low-loss nanophotonics and metamaterials. We support our concept by proof-of-principle microwave experiments with arrays of high-index dielectric resonators.

physics.optics↗