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Unipolar and quasi-unipolar half-cycle pulses having nonzero electric pulse area are a limit of pulse shortening in a given spectral range. In spite of the fact that existence of such pulses was considered by Jackson (1962), V.L. Ginzburg (1960-s), Bullough and Ahmad (1971) as well as Bessonov (1981), the possibility of their existence and propagation in space remained questionable for many years. Only within the past decades both the possibility of unipolar pulse existence and their propagation dynamics were shown and analyzed in detail theoretically and experimentally. So far such pulses became a subject of active research due to their potential in the ultra-fast optics and study of new regimes of light-matter interactions with subcycle resolution. Here, we show the possibility of the effective ultrafast control of the level populations in quantum well nanostructures by the half-cycle unipolar attosecond light pulses in comparison to the single-cycle ones. It is shown that the population dynamics can be determined by the electric pulse area divided to its characteristic "scale" determined by the quantum well width. The selective excitation of quantum states and the feasibility of the population inversion by the subcycle unipolar pulses is demonstrated.

Metamaterials based on regular two-dimensional arrays of thin wires have attracted renewed attention in light of a recently proposed strategy to search for dark matter axions. When placed in the external magnetic field, such metamaterials facilitate resonant conversion of axions into plasmons near their plasma frequency. Since the axion mass is not known a priori, a practical way to tune the plasma frequency of metamaterial is required. In this work, we have studied a system of two interpenetrating rectangular wire lattices where their relative position is varied. The plasma frequency as a function of their relative position in two dimensions has been mapped out experimentally, and compared with both a semi-analytic theory of wire-array metamaterials and numerical simulations. Theory and simulation yield essentially identical results, which in turn are in excellent agreement with experimental data. Over the range of translations studied, the plasma frequency can be tuned over a range of 16%.

The induced polarization oscillations in a one-dimensional rectangular quantum well are modeled by a numerical solution of the time-dependent Schroedinger equation. The finite-difference discretization over time is realized in the framework of the Crank-Nicolson algorithm, whereas over the spatial coordinate it is combined with the exterior complex-scaling technique. A formation of the harmonic oscillations of the dipole moment by an incident short unipolar pulse is shown. It is obtained that the frequency of oscillations is solely defined by the energy of the main resonant transition. Moreover, if two such short unipolar pulses are delayed by a half-period of the oscillation, then these oscillations can be abruptly induced and stopped. Thus, the so-called stopped polarization pulse is obtained. It is shown that both the amplitude and the duration of the incident unipolar pulse, contributing to the so-called electric pulse area, define the impact of the incident pulse on the quantum system., Comment: 11 pages; submitted to Micro and Nanostructures

Electromagnetic scattering bounds on subwavelength structures play an important role in estimating performances of antennas, RFID tags, and other wireless communication devices. An appealing approach to increase a scattering cross-section is accommodating several spectrally overlapping resonances within a structure. However, numerous fundamental and practical restrictions have been found and led to the formulation of Chu-Harrington, Geyi, and other limits, which provide an upper bound to scattering efficiencies. Here we introduce a 2D array of near-field coupled split-ring resonators and optimize its scattering performances with the aid of a genetic algorithm, operating in 19th-dimensional space. Experimental realization of the device is demonstrated to surpass the theoretical single-channel limit by a factor of >2, motivating the development of tighter bounds of scattering performances. A super-radiant criterion is suggested to compare maximal scattering cross-sections versus the single-channel dipolar limit multiplied by the number of elements within the array. This new empirical criterion, which aims on addressing performances of subwavelength arrays formed by near-field coupled elements, was found to be rather accurate in application to the superscatterer, reported here. Furthermore, the super-radiant bound was empirically verified with a Monte-Carlo simulation, collecting statistics on scattering cross sections of a large set of randomly distributed dipoles. The demonstrated flat superscatterer can find use as a passive electromagnetic beacon, making miniature airborne and terrestrial targets to be radar visible., 20 pages, 6 figures

additional material about a math, optical axis equation and full wave numerical simulation

The rapid development of chargeable devices has caused a great deal of interest in efficient and stable wireless power transfer (WPT) solutions. Most conventional WPT technologies exploit outdated electromagnetic field control methods proposed in the 20th century, wherein some essential parameters are sacrificed in favour of the other ones (efficiency vs. stability), making available WPT systems far from the optimal ones. Over the last few years, the development of novel approaches to electromagnetic field manipulation has enabled many up-and-coming technologies holding great promises for advanced WPT. Examples include coherent perfect absorption, exceptional points in non-Hermitian systems, non-radiating states and anapoles, advanced artificial materials and metastructures. This work overviews the recent achievements in novel physical effects and materials for advanced WPT. We provide a consistent analysis of existing technologies, their pros and cons, and attempt to envision possible perspectives.

Supplement 1-6 for the main text

The spatial resolution and signal-to-noise ratio (SNR) attainable in magnetic resonance microscopy (MRM) are limited by intrinsic probe losses and probe–sample interactions. In this work, the possibility to exceed the SNR of a standard solenoid coil by more than a factor-of-two is demonstrated theoretically and experimentally. This improvement is achieved by exciting the first transverse electric mode of a low-loss ceramic resonator instead of using the quasi-static field of the metal-wire solenoid coil. Based on theoretical considerations, a new probe for microscopy at 17 T is developed as a dielectric ring resonator made of ferroelectric/dielectric low-loss composite ceramics precisely tunable via temperature control. Besides the twofold increase in SNR, compared with the solenoid probe, the proposed ceramic probe does not cause static-field inhomogeneity and related image distortion.

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.

Optically generated electron-hole plasma in high-index dielectric nanostructures was demonstrated as a means of tuning of their optical properties. However, until now an ultrafast operation regime of such plasma driven nanostructures has not been attained. Here, we perform pump-probe experiments with resonant silicon nanoparticles and report on dense optical plasma generation near the magnetic dipole resonance with ultrafast (about 2.5 ps) relaxation rate. Basing on experimental results, we develop an analytical model describing transient response of a nanocrystalline silicon nanoparticle to an intense laser pulse and show theoretically that plasma induced optical nonlinearity leads to ultrafast reconfiguration of the scattering power pattern. We demonstrate 100 fs switching to unidirectional scattering regime upon irradiation of the nanoparticle by an intense femtosecond pulse. Our work lays the foundation for developing ultracompact and ultrafast all-optical signal processing devices.

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.

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.

Hybrid nanophotonics based on metal-dielectric nanostructures unifies the advantages of plasmonics and all-dielectric nanophotonics providing strong localization of light, magnetic optical response and specifically designed scattering properties. Here we demonstrate a novel approach for fabrication of ordered hybrid nanostructures via femtosecond laser melting of asymmetrical metal-dielectric (Au-Si) nanoparticles created by lithographical methods. The approach allows selective reshaping of the metal components of the hybrid nanoparticles without affecting dielectric ones. We apply the developed approach for tuning of the hybrid nanostructures scattering properties in the visible range. The experimental results are supported by molecular dynamics simulation and numerical solving of Maxwell equations., Comment: Published in Advanced Materials

We review a new, rapidly developing field of all-dielectric nanophotonics which allows to control both magnetic and electric response of structured matter by engineering the Mie resonances in high-index dielectric nanoparticles. We discuss optical properties of such dielectric nanoparticles, methods of their fabrication, and also recent advances in all-dielectric metadevices including couple-resonator dielectric waveguides, nanoantennas, and metasurfaces.

A novel method for single-step, lithography-free, and large-scale laser writing of nanoparticle-based plasmonic structures has been developed. Changing energy of femtosecond laser pulses and thickness of irradiated gold film it is possible to vary diameter of the gold nanoparticles, while the distance between them can be varied by laser scanning parameters. This method has an advantage over the most previously demonstrated methods in its simplicity and versatility, while the quality of the structures is good enough for many applications. In particular, resonant light absorbtion/scattering and surface-enhanced Raman scattering have been demonstrated on the fabricated nanostructures.

We study numerically, analytically and experimentally the resonant transmission of light in a waveguide formed by a periodic array of high-index dielectric nanoparticles with a side-coupled resonator. We demonstrate that a resonator with high enough Q-factor provides the conditions for the Fano-type interference allowing to control the resonant transmission of light. We suggest a practical realization of this resonant effect based on the quadrupole resonance of a dielectric particle and demonstrate it experimentally for ceramic spheres at microwaves.

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.

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., Comment: 5 pages, 3 figures

We propose a new type of highly efficient Yagi-Uda nanoantenna and introduced a novel concept of superdirective nanoantennas based on silicon nanoparticles. In addition to the electric response, this silicon nanoantennas exhibit very strong magnetic resonances at the nanoscale. Both types of nanoantennas are studied analytically, numerically and experimentally. For superdirective nanoantennas we also predict the effect of the beam steering at the nanoscale characterized by a subwavelength sensitivity of the beam radiation direction to the source position.

We propose a novel approach to facilitate a readout processes of isolated negatively charged nitrogen-vacancy (NV) centers based on the concept of all-dielectric nanoantennas. We reveal that all-dielectric nanoantenna can significantly enhance both the emission rate and emission extraction efficiency of a photoluminescence signal from a single NV center in a diamond nanoparticle placed on a dielectric substrate. We prove that the proposed approach provides high directivity, large Purcell factor, and efficient beam steering, thus allowing an efficient far-field initialization and readout of several NV centers separated by subwavelength distances.

We study dispersion properties of layered metal-dielectric media having different layers thicknesses ratios. Plotting dispersion diagrams and isofrequency contours, we find that strong nonlocality is inherent property of such periodic structures. We introduce different level of losses and analyze complex modes of the metamaterial demonstrating that it operates in a regime with infinite numbers of eigenmodes, with nonlocality slightly affected by losses.

We suggest a broadband optical unidirectional arrayed nanoantenna consisting of equally spaced nanorods of gradually varying length. Each nanorod can be driven by near-field quantum emitters radiating at different frequencies or, according to the reciprocity principle, by an incident light at the same frequency. Broadband unidirectional emission and reception characteristics of the nano-antenna open up novel opportunities for subwavelength light manipulation and quantum communication, as well as for enhancing the performance of photoactive devices such as photovoltaic detectors, light-emitting diodes, and solar cells., Comment: 3 pages, 3 figures

This is a comment on "Guiding, Focusing, and Sensing on the Subwavelength Scale Using Metallic Wire Arrays" by G. Shvets, S. Trendafilov, J. B. Pendry and A. Sarychev published in Phys. Rev. Lett. 99, 053903 (2007), which demonstrates that the endoscope proposed in the letter does not demonstrate satisfactory subwavelength imaging performance., Comment: 2 pages, an updated version with results of numerical simulations confirming our statements

The letter contains an important message regarding the numerical modeling of left-handed media (LHM) using the finite-difference time-domain (FDTD) method which remains at the moment one of the main techniques used in studies of these exotic materials. It is shown that conventional implementation of the dispersive FDTD method leads to inaccurate description of evanescent waves in the LHM. This defect can be corrected using the spatial averaging at the interfaces. However, a number of results obtained using conventional FDTD method has to be reconsidered. For instance, the accurate simulation of sub-wavelength imaging by the finite-sized slabs of left-handed media does not reveal the cavity effect reported in [Phys. Rev. Lett. 92, 107404 (2004)]. Hence the finite transverse dimension of LHM slabs does not have significant effects on the sub-wavelength image quality, in contrary to previous assertions., Comment: 4 pages, 3 figures, submitted to PRL

In this letter we experimentally demonstrate a possibility to achieve significant sub-wavelength resolution of a near-field image channeled through a layer of an electromagnetic crystal. An image having radius of $\lambda/10$ has been realized using an electrically dense lattice of capacitively loaded wires. The loading allows to reduce the lattice period dramatically so that it is only a small fraction of the free-space wavelength. It is shown that losses in the structure only decrease the total amplitude of the image, but do not influence the resolution., Comment: 4 pages, 7 figures, submitted to PRL

Original realization of a lens capable to transmit images with sub-wavelength resolution is proposed. The lens is formed by parallel conducting wires and effectively operates as a telegraph: it captures image at the front interface and the transmit it to the back interface without distortion. This regime of operation is called canalization and is inherent in flat lenses formed by electromagnetic crystals. The theoretical estimations are supported by numerical simulations and experimental verification. Sub-wavelength resolution of $\lambda/15$ and 18% bandwidth of operation are demonstrated at gigahertz frequencies. The proposed lens is capable to transport sub-wavelength images without distortion to nearly unlimited distances since the influence of losses to the lens operation is negligibly small., Comment: 4 pages, 4 figures, submitted to PRL

The restrictions on the resolution of transmission devices formed by wire media (arrays of conductive cylinders) recently proposed in [Phys. Rev. B, 71, 193105 (2005)] and experimentally tested in [Phys. Rev. B, 73, 033108 (2006)] are studied in this paper using both analytical and numerical modeling. It is demonstrated that such transmission devices have sub-wavelength resolution that can in principle be made as fine as required by a specific application by controlling the lattice constant of the wire medium. This confirms that slabs of the wire medium are unique imaging devices at the microwave frequency range, and are capable of transmitting distributions of TM-polarized electric fields with nearly unlimited sub-wavelength resolution to practically arbitrary distances., Comment: 10 pages, 12 figures, submitted to PRE

Imaging with sub-wavelength resolution using a lens formed by periodic metal-dielectric layered structure is demonstrated. The lens operates in canalization regime as a transmission device and it does not involve negative refraction and amplification of evanescent modes. The thickness of the lens have to be an integer number of half-wavelengths and can be made as large as required for ceratin applications, in contrast to the other sub-wavelength lenses formed by metallic slabs which have to be much smaller than the wavelength. Resolution of $\lambda/20$ at 600 nm wavelength is confirmed by numerical simulation for a 300 nm thick structure formed by a periodic stack of 10 nm layers of glass with $\epsilon=2$ and 5 nm layers of metal-dielectric composite with $\epsilon=-1$. Resolution of $\lambda/60$ is predicted for a structure with same thickness, period and operating frequency, but formed by 7.76 nm layers of silicon with $\epsilon=15$ and 7.24 nm layers of silver with $\epsilon=-14$., Comment: 4 pages, 4 figures, submitted to PRL

We perform multipolar analysis of second-harmonic generation (SHG) from gallium arsenide (GaAs) nanoantennas grown along different crystallographic directions and discuss their specifics. In particular, analysis of the nonlinear response of nanoantennas grown along the (110) axis based on the Lorentz lemma shows that such nanoantennas generate multipoles with only odd azimuthal index m. This feature of (110)-GaAs nanoantennas provides the best forward/backward directivity as compared to their (100) and (111) counterparts. Using numerical modeling we determine parameters of the cylindrical nanoantenna to achieve optical switching in the nonlinear regime by rotating the pump polarization. We then experimentally demonstrate the nonlinear switching between forward and backward SHG emissions from (110)-grown GaAs nanodisks. ISSN:0094-243X ISSN:1551-7616