Electric excitation of guided modes in integrated circuits is important for the development of compact optical signal processing components as well integrated bio- and chemical sensing applications. Surface plasmons in purely metallic nanostructures are typically excited by external illumination or high-energy electron beams. Low-energy inelastic electron tunnelling is an alternative way to excite surface plasmons in ambient environment with the advantages of high compactness and background free operation. Here we will discuss excitation of waveguided modes, light emission and hot-electrons in electrically-driven plasmonic nanorod metamaterials. The applications will be discussed in integrated photonics and gas sensing, including hydrogen and oxygen gases. Electrically-driven plasmonic nanorod metamaterials comprise a fertile platform merging photonics, electronics and chemistry, opening up opportunities for developing electron tunnelling-based nanoscale devices for light generation and modulation and chemical sensing.

Polar materials, i.e. those materials where it is possible to excite the collective oscillations of the lattice ions, along with derived phononic structures offer the possibility of manipulating and amplificating IR emissivity by the excitation of such surface modes. Since the oscillation frequencies of the crystalline lattice ions are typically lower, compared to the plasma frequencies, they fall in the infrared wavelength range. The asymmetric spectral emissivity in the infrared range of a metamateriale composed by subwavelength oriented air inclusions into a polar matrix was investigated. We show hoe the longitudinal phononic resonance can be excited and tuned as function of the inclusions content and orientation, within the application limit of the effective medium homogenization technique. Furthermore, our numerical result show that it is possible to enhance the emissivity in a given direction rather than in the opposite one by continuously grading the inclusions content along the matrix thickness. As a possible application we designed a graded air inclusion pattern into a silicon carbide layer, only few microns thick. A strongly asymmetry between forward and backward emission along the normal direction to the surface is obtained.

Terahertz (THz) technology has received considerable interest because of its potential in a wide variety of applications such as wireless communication, spectroscopy, imaging, and sensing. In the past several decades, cost-effective and compact THz sources and detectors have been intensively developed to use the THz wave in industrial applications. For more practical THz applications, various active and passive devices such as THz filters, modulators, phase shifters, switches, and mirrors must be developed. However, the development of THz devices is very deficient compared to microwave and light wave bands because the electromagnetic properties of most natural materials are not suitable to be used in the THz frequency range. To overcome the limitations of natural materials in the THz band, research on the utilization of metamaterials, which can artificially control electrical and magnetic properties, as devices in the THz band has attracted much attention. The controllable resonances of artificially engineered metamaterials can offer opportunities to realize novel THz devices for a wide variety of THz applications. Numerous research studies on the realization of tunable characteristics for THz metamaterials have been reported by using semiconductors, graphene, and tunable functional materials. Tunable metamaterials based on vanadium dioxide (VO2) present a promising approach to spatially manipulate the THz wave thanks to easy fabrication and high tunability. Several studies have researched tunable THz metamaterials based on the phase transition of VO2 by applying temperature, a THz field, or light. However, these methods require external devices such as a heater or a source of THz waves or light, and the external devices cause these THz tunable devices to be expensive and bulky. Thus, electrical control of the phase transition of VO2 is preferred for practical applications. The metamaterial that can be electrically controlled but has low Q-factor is limited in improving the performance when applied as a device. To improve the performance of THz devices using metamaterials, it is very important to increase the quality factor of the metamaterials. In this paper, we proposed an asymmetric split-loop resonator with an outer square loop (ASLR-OSL) based on vanadium dioxide thin film, which can actively control the transmission properties of a terahertz (THz) wave while maintaining a high quality factor of the asymmetric split-loop resonator (ASLR). The outer square loop was combined with the ASLR to be used as a microheater capable of controlling the temperature of the VO2 thin film through a directly applied bias voltage. Therefore, the transmission characteristics of the ASLR-OSL based on VO2 thin film were successfully controlled by directly applying a bias voltage. In addition, the ASLR-OSL could well maintain a high quality factor of the ASLR. The transmittance of the ASLR-OSL based on VO2 thin film was changed from 43.16% to 2.41% in mode 1 (0.7 THz) and 30.86% to 4.23% in mode 2 (1.1 THz). Based on these results, it is possible to impose active properties on a common metamaterial having a high quality factor by adding a simple loop structure that works as a microheater.

We propose a new approach of optical field management based on a local Hilbert transform, where the non-Hermitian potentials generating arbitrary vector fields of directionality, p→(r→), with desired shapes and topologies are designed. We derive a local Hilbert transform to build systematically such potentials, by modifying background potentials (being either regular or random, extended or localized). In particular, we explore particular directionality fields, for instance in the form of a focus to create sinks for probe fields, to generate vortices in the probe fields, and others. Physically, the proposed directionality fields provide a flexible new mechanism for dynamically shaping and precise control over probe fields leading to novel effects in wave dynamics.

We investigate the scattering properties of the finite periodic structure consisting of the PT dipoles represented by gain/loss cylinders arranged in a 2D honeycomb lattice. We found that the total scattered energy reveals series of sharp resonances at which the energy increases by two orders of magnitude and an incident wave with arbitrary frequency is scattered only in a few directions given by spatial symmetry of periodic structure. Both features can be qualitatively explained by analysis of the complex band structure associated with an infinite honeycomb array of the PT dipoles which supports the broken PT-symmetric phase at the symmetry points and along the ΓK and ΓM directions and provides the mechanisms leading to a significant enhancement of the radiated power and offers a plausible explanation to highly-directional scattering pattern. Specifically, we assigned the lowest resonance in the total scattering energy to the broken PT-symmetry mode formed by a doubly degenerate pair with complex conjugate eigenfrequencies corresponding to the K-point of the reciprocal lattice.

IV-VI compounds (PbTe, PbSe, PbS, SnTe, GeTe) and their alloys are narrow-gap semiconductors crystallizing in the rock-salt structure and known for very good thermoelectric and infrared optoelectronic properties exploited, e.g. in mid-infrared p-n junction lasers and detectors. Recently, these materials have been recognized as a new class of topological materials - topological crystalline insulators (TCI) [1]. The properties of TCI surface states will be discussed for bulk crystals, crystalline bulk nanocomposites, epitaxial multilayers and quantum dot heterostructures. The TCI surface states were discovered by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS) as well as observed in magneto-transport and magneto-optical studies [1,2]. These states constitute a new type of two-dimensional (2D) electron system with unique properties brought about by strong relativistic effects (spin-orbit interaction). Their electron structure exhibits metallic electronic structure with linear Dirac-like dispersion and spin–momentum locking. In Pb1-xSnxTe (x=0-1) and Pb1-xSnxSe (x=0-0.4) substitutional alloys the chemical composition, temperature and hydrostatic pressure induced band inversion is observed between conduction and valence bands. The terminal compounds SnTe and SnSe (in the rock-salt crystal structure) exhibit the inverted band ordering whereas in PbTe and PbSe the band ordering is topologically trivial. Particularly important technological path involves spontaneous formation of nanoscale two-phase coherent crystalline structures, e.g. in PbTe-SnTe-CdTe or PbSe-SnSe-CdSe semiconductor systems. It permits the growth of high crystalline quality composite thermoelectric or optoelectronic nanostrucutres. As the refractive index of IV-VI compounds is very high (typically n≈6) these materials show excellent optical contrast to other semiconductors as demonstrated, e.g. in very efficient Bragg-mirrors composed of just four layers of PbTe and CdTe. By designing the IV-VI topological/trivial heterostructures (superlattices) in the form of 2D multilayers, 1D nanowires or 0D quantum dots one can also exploit topological Dirac interface states in new class of infrared metamaterials [3-5]. [1] P. Dziawa, B.J. Kowalski, K. Dybko et al., Nature Materials 11, 1023 (2012). [2] P. Sessi, D. Di Sante, A. Szczerbakow et al., Science 354, 1269 (2016). [3] M. Szot, K. Dybko, P. Dziawa et al., Crystal Growth & Design 11, 4794 (2011). [4] G. Karczewski, M. Szot, S. Kret et al., Nanotechnology 26, 135601 (2015). [5] J. Sadowski, P. Dziawa, A. Kaleta et al., Nanoscale (2018) doi: 10.1039/c8nr06096g.

Topological insulators (TI) belong to category of phases which go beyond the theory of spontaneous symmetry breaking, well describing classical phases. TI are materials of strong spin-orbit interaction that leads to the inversed band structure. Thus, they belong to different topological class than surrounding “normal” world. Consequently, these materials behave as insulators in their volume while their surface hosts metallic states, that appear as a result of the need to meet boundary conditions. The metallic states have the unusual spin structure described by the Dirac-type Hamiltonian, with the electron spin locked to its momentum. They are protected by the time reversal symmetry, thus are resistant to non-magnetic disturbances. Introducing magnetic impurities breaks the time reversal symmetry, opening the energy gap at the Dirac point and eventually modifying spin texture. In research of magnetically doped TI there are still many challenges and open questions. Here, I will present results of our recent studies of three-dimensional TI from the Bi2-xSbxTe3-ySey family, doped with Mn ions. I will discuss possible locations of Mn impurity in the crystal host lattice, the influence of doping on the crystal structure and magnetic properties. Ferromagnetism was successfully obtained in Bi2Te3 and BiSbTe3 doped with 1.5-2 at. % of Mn, with the Curie temperature of the order of ~ 15 K. The role of free carriers in ferromagnetic interactions is not clear. Ferromagnetism is observed at diluted Mn concentrations suggesting a need for a medium mediating the long-range ferromagnetic order, but the Tc does not scale with the concentration of free carriers. We would like to acknowledge National Science Center, Poland, grant no 2016/21/B/ST3/02565.

We propose implementations of the Haldane and Kane-Mele models in both electronic and photonic “artificial-graphene” type systems. We first suggest an electronic realization of the Haldane model in a patterned two-dimensional electron gas with broken inversion and time-reversal symmetries. Then, based on an analogy between the two-dimensional Schrodinger and Maxwell equations, we propose a photonic analogue based on a photonic crystal made of air cylinders with honeycomb symmetry embedded in a metallic background with a spatially variable pseudo-Tellegen response. The anisotropic pseudo-Tellegen coupling emulates a periodic effective magnetic field for photons. In a second step, it is demonstrated that by enforcing matched electric and magnetic responses one obtains a precise analogue of the Kane-Mele model in the same nonreciprocal photonic platform. Remarkably it is shown that by applying a duality transformation, the Kane-Mele model can be implemented using matched anisotropic dielectrics with identical permittivity and permeability, without requiring any form of bianisotropic couplings. These findings evidence the possibility to observe bidirectional topologically protected edges-state propagation in a fully reciprocal all-dielectric and non-uniform anisotropic metamaterial.

Within oscillation electron model the superconducting crystal A2B3 is considered consisting of two subsystems A2B3=A2+1.5 B2. Free electrons couple to lower system energy. For this purpose it is necessary, that squared electron binding energy in a local phase Φ₁₂² was essentially much less, than one Φ₁², Φ₂² in an initial phase where Φ₁₂² is squared electron interaction energy in an initial phase, Φ₁², Φ₂² are squared electron interaction energy in the local again formed phase, Tc is superconducting phase transition temperature, q = Φ² [Bι2Se3]/ΣΦ² is interaction parameter. It is necessary to satisfy condition, Φ₁² ≥ Φ₁₂², 1.5•Φ₂² ≥ Φ₁₂². For component A paired electrons are produced only at T=Tc, for component B paired electrons are formed at T<Tc. The superconducting phase transition is performed with the full formation of paired electrons. Correlated paired electrons are formed below Tc the superconducting phase transition temperature. At T=0 all electrons are dependent on each other – coherent or correlated. In high-temperature superconductors spontaneous division into two phases: superconducting and isolating was revealed. The phase superconducting transition of bismuth selenide is close to 0 K. The equation of the phase transition curve for superconductors is Tc = 40.05687q^2-234.44056q + 191.51842, Tc = 0, q = 0.981522371. Φ² [Bι2Se3] = 271.821169, Φ² [Bι] = 194.6025, Φ² [Se] = 303.177744 eV². With the introduction of impurities or with high pressure, the crystals of bismuth selenide and telluride go into the superconducting state in accordance with the balance of square plasma energy. The crystals of bismuth selenide and telluride are superconductors at Tc → 0K. It are inhomogeneous systems and are characterized by phase separation below Tc = 195 K.

Recent theoretical predictions confirmed by experimental observations provided evidence that there exist materials which behave as insulators in the bulk but possess gapless, spin-momentum-locked, linearly dispersed states on the surface. They are called topological insulators (TI). The conducting surface states of TIs are immune to localization as long as the disorder potential does not violate time reversal symmetry. One way to break the time reversal symmetry is to introduce magnetic dopants into the TIs that can induce ferromagnetism and open the surface energy gap. Opening a gap at the topological surface may result in exotic quantum phenomena including magnetoelectric effect and quantized anomalous Hall effect. In this work, we studied magnetic and electrical properties of the bismuth telluride doped with 2 % of Mn atoms. Ferromagnetic resonance (FMR) measurements show two resonance lines with different spin relaxation times, which we assigned to Mn2+ ions located at different lattice sites. Hall resistance measurements reveal that below 15 K the curve becomes hysteretic that is typical for ferromagnetic conductors. Hall as well as FMR demonstrate that the Curie temperature of the studied sample is between 10 and 15 K. Furthermore, the electric transport measurements reveal n-type conductivity indicating that Mn atoms may occupy interstitial position in van der Waals gaps. Magnetoresistance data show weak localization effect which may be one of the signature of the gap opening on the topological surface, other possible explanations related to the crystal structure will be also discussed. We would like to acknowledge National Science Center, Poland, grant no 2016/21/B/ST3/02565.

Directed refraction and strong dispersion, which are characteristic properties of hyperbolic metamaterials, make such materials suitable for performing spatial-spectral transformation. This transformation involves encoding of spatial information with resolution beyond the diffraction limit in the scattering spectrum, which may be collected with standard optics in the far-field. This gives rise to potential applications in compressive super-resolution microscopy in which compressive sensing algorithms are used for reconstruction of super-resolved images from a broadband measurement of an objects spectrum illuminated through the hyperbolic metamaterial. For such imaging to be successful, light, which carries subwavelength information, needs to be coupled to high-k modes of a hyperbolic metamaterial. This is required to observe wavelength-dependent directional propagation, which is necessary for the spatial-spectral transformation. Although it is possible to exploit diffraction on nanoholes in a Cr mask to provide additional momentum, this approach suffers from low transmittance which is especially detrimental for compressive imaging applications. In this paper we analyze dielectric spherical nanoparticle arrays as an alternative broadband coupling method with increased efficiency. Light transmittance and concentration are enhanced through photonic nanojets, localized enhanced _elds with low beam divergence. The finite-element method study of the structure is performed to find wavelength-dependent coupling efficiency as a function of nanoparticle size, material as well as array period and configuration. The analysis with effective hyperbolic dispersion relation is further refined to include a metal-dielectric multilayer.

Metamaterials are a highly topical field of modern physics that has created new exciting technological opportunities in many areas, including medical imaging and sensor developments. Managing near-field light-matter interactions at a subwavelength scale provides new avenues to develop efficient antennas and detectors.

Metamaterials have been proposed as a potential solution to control emission or conversion of light for more than a decade. The Near Zero Index metamaterials have been proposed to design directive emitters. More recently so-called hyperbolic metamaterials have been intensively studied. These structures possess effective permeability or permittivity tensors components such that one principal component is opposite to the two others.

With the example of coils for Ultra-High field magnetic resonance imaging and positron emission tomography we will show how medical imaging could benefit from such control of the electromagnetic waves.

In modern optic and photonic applications, tunability of the asymmetric transmission has become important due to its adjustable unidirectional transmission. In this study, we design a three-dimensional trapezoidal metallic nano structure on a stretchable substrate. It shows broadband tunable asymmetric light transmission in the visible spectrum. The proposed structure is made of a periodic nano array of a trapezoidal shaped aluminum on a stretchable substrate. The transmission properties of the proposed structure with respect to the geometric parameters were systematically investigated employing finite-difference time-domain computations. It was shown that the intensity and the bandwidth of the asymmetric light transmission between 400 nm and 800 nm wavelengths change when the flexible substrate is stretched. The period of the designed structure varies depending on the stretch of the substrate. For example, when the substrate is stretched, the period of the structure is 450 nm and when it is unstretched, the period is 350 nm. This increase in the period causes a red shift in the wavelength range of the asymmetric transmission. While the asymmetric transmission under unstretched case starts at 350 nm and stops at 514.5 nm, under stretched case it starts at 450 nm and stops at 661.5 nm. In addition, the performance of our structure is insensitive the polarization of the incoming radiation in both forward and backward illumination directions. This study provides a path toward the realization of tunable optical devices for the applications which require dynamic tunability.

Purcell effect refers to the case when a quantum emitter couples to a resonant ambient (scatterer, cavity, antenna, antenna array, etc.). Therefore, the surface-enhanced Raman scattering (SERS) -- enhancement of the Raman emission by a patterned/textured plasmonic surface – is, in fact, essentially the same effect. In this talk, we compare the Purcell effect in SERS with that observed in the plasmon-enhanced fluorescence (PEF). In PEF the Purcell effect is a commonplace, whereas in SERS it is not yet recognized by the majority of experts. The reason why it is so is simple: In PEF the Purcell factor is a measurable decrease of the fluorescence lifetime. Meanwhile, in SERS, the enhanced power of the Raman signal is also measurable, however, how the decay rate of the excited Raman states is enhanced in SERS is not directly observed. Moreover, in PEF, the spectrum of the pumping radiation is far from the plasmon resonance band, whereas, in SERS, the pumping radiation resonates with the surface plasmon. Therefore, in PEF, the gain in the fluorescence is solely due to the radiative Purcell factor (RPF), whereas, in SERS, the Purcell effect is accompanied by the local field intensity enhancement (LFIE) of the source wave. This combination of the two seemingly different effects created a mess in the literature on the electromagnetic gain in SERS. This situation becomes apparent when one discusses the equivalence of the LFIE and the RPF. In the approximate model of SERS (this model reduces the action of the plasmonic substrate to a quasistatic action of an ellipsoidal plasmonic protrusion on which the reference molecule is located), the equivalence between LFIE and RPF can be analytically proved by averaging of both LFIE and RPF over all possible positions of a molecule on the protrusion surface. In the analytical model developed by M. Stockman, this equivalence is absent and these two effects appear different, although both factors are expressed through the same dyadic Green function. In the present work, we prove the fundamental equivalence between LFIE and RPF for arbitrary molecule locations in any electromagnetically reciprocal environments. The identity of these two factors (and the effects) was not evident from the theory of M. Stockman, because he did not average the LFIE and RPF factors over all possible directions of the molecule dipole moment and the source local field vector. After this averaging (which is a commonplace in SERS), these factors match exactly, because, basically, they refer to the same underlying physics. Such identity explains the huge values of the Raman gain in the advanced SERS schemes and opens new doors in the enhancement of both photo-fluorescence and luminescence. It is important for all applications where the Purcell effect potentially combines with the local field enhancement.

Dielectric structures with high refractive indices give rise to Mie-type resonances with a remarkably high localization of electric and magnetic fields inside the dielectric structures due to excitation of selective multipolar modes. It is known that the specific geometries like rings give rise to magnetic responses comparable to the electric modes in metallic structures. In the present work, we study the resonant characteristics of high refractive index circular and square dielectric rings using full-wave electromagnetic simulations. Effect of geometry, thickness of the structures and refractive index on the electromagnetic response is studied in the sub-wavelength regime. Square rings are observed to exhibit sharper resonances at lower frequencies compared to the circular rings as a consequence of enhanced field localization within the dielectric structures. It is observed that the thickness plays a major role in the excitation of various resonant modes. Electric modes are predominantly sustained in the thinner rings (thickness lesser compared to the lattice constant) while thicker rings support magnetic modes predominantly. When such rings are placed in birefringent liquid crystal medium orientation of the liquid crystal molecules are observed to enhance certain modes over the other giving rise to tunable metasurfaces. Further, novel modes such as electric dipole+electric quadrupole and toroidal modes are observed, hitherto not observed in air.

All-dielectric metasurfaces are unique component to control optical wavefront with high transmission or reflection coefficient. Recently, accelerating beam, which propagates along curved arbitrary trajectories, has been realized with conventional diffractive optical elements (DOE). However, DOE suffer from low sampling ratio of rapid phase gradients and its diffraction efficiency drops quickly when the wavelength is switched to another wavelength which is different than the designed wavelength.. In this study, we show accelerating beam which is generated by highly efficient and polarization insensitive all-dielectric metasurfaces in the visible wavelength. The acceleration beam is numerically generated with the proposed metasurfaces which are composed of TiO₂ nanopillars residing on glass substrate using finite difference time-domain computational method. It is shown that this beam has the ability to propagate curved trajectories in air medium. Transmission efficiency of the proposed structure is above 65% and desired arbitrary trajectories have been achieved. Generating highly efficient accelerating beam can be used in photonic applications in optical imaging, spectroscopy, optical micromanipulation and nonlinear optics.

We propose liquid-crystal-based reconfigurable chiral metasurface absorbers and numerically investigate their chiro-optical properties. The chiral metasurface absorber is based on a metal-insulator-metal structure on the substrate, which can strongly absorb a circularly polarized wave of one spin state and reflects that of the opposite spin, resulting a strong circular dichroism. A birefringent liquid crystal (LC) is exploited to serve as the insulator layer in the metal-insulator-metal structure. We could then vary the circular state of the incident light by controlling the alignment of the LC molecules, hence inversing the circular dichroism. The simulation results show that the sign of the circular dichroism can be effectively changed by externally controlling the alignment of the LC molecules in between the homogenous and homeotropic states. The absorption efficiency for the specific circularly polarized wave can be larger than 80% and the CD is nearly 70%. The simple and compact design of our proposed chiral metasurface absorber is especially favorable for integration, and such reconfigurable chiral metasurface absorber could find many potential applications in biological detection/sensing, polarimetric imaging, and optical communications.

We develop a new approach for creating photonic metasurfaces based on nematic liquid crystal material. The periodical modulation of the LC director field is imposed by nanoscale change of the alignment properties of polyimide thin layer by means of focused ion beam treatment. The resulted spatially periodic modulation with a period determined by that of the pattern at the substrate provides distinct photonic properties of LC layer. A part of transmitted light is redistributed into a few first diffraction orders. The diffraction is switchable by electric field with millisecond switching times.

In recent years, much effort has been expended upon managing and tuning the radiative properties of structures and material surfaces in the infrared (IR) wavelength range for several applications, such as thermal radiation control as well as IR sensing. Metamaterials are artificial electromagnetic materials, composed by periodically or randomly arranged, subwavelength elements. Since the typical dimensions of the constitutive elements of a metamaterials are smaller than the interaction wavelengths, they behave as an effective medium and may give rise to peculiar electromagnetic properties, such as negative refraction, superlensing and cloaking, to name some. In the present work we review the use of metamaterials composed by dispersed nanowires systems into a dielectric matrix, for managing and tuning of the infrared emission. The main homogenization techniques effective medium approach are presented and discussed, along with several parameters such as filling factor, inclusions orientations and shape. We finally show some examples with different materials (metallic or polar nanowires) and many configurations in order to get spectral and/or spatial modulation of the resulting infrared emissivity. Taming and tuning the infrared radiation of a metamaterial allows the design of versatile optical elements as basic elements for further developments of infrared filters, thermal diodes and thermal logic gates.

Diffraction of light of a visible spectral range by subwavelength metal gratings is investigated theoretically and experimentally. The diffraction efficiencies of the gratings made of various metals (Ni, Ag, Al, etc.) with different depths of the profile are calculated and measurements are carried out. It is demonstrated that under certain conditions an effect of plasmon resonance occurs, at which a complete absorption of the incident light takes place. It is demonstrated, that the influence of the incident beam width on the diffraction efficiency and the electric field profile of the reflected beam is significant for the incident angles, at which the plasmon resonance occurs. It is shown that the incident beam width must be larger than the propagation distance of the surface plasmon in order to couple energy effectively into the plasmon mode.

In this paper, we present recent developments in our modal expansion technique for electromagnetic structures with highly dispersive media and its application for unbounded geometries. The expansion formula, based on a simple version of Keldys’s theorem, make use of Dispersive Quasi-Normal Modes (DQNMs), also known as natural modes of photonic structures, obtained by solving spectral problems associated to the Maxwell's equations. Such structures can be defined very generally by their geometry (bounded or unbounded), and the electromagnetic properties of various media (permeability and permittivity can be dispersive, anisotropic, and even possibly non reciprocal). As an example, a dispersive benchmark case, a diffraction grating, made of a periodic slit array etched in a free-standing silver membrane, is presented.

The most common approach in standard nanoplasmonics for the analysis of the resonant behavior of light interaction with these nanostructures has been the application of the local-response approximation (LRA), using – depending on the structure complexity and relation between a characteristic dimension and the interacting wavelength – either (quasi)analytic or numerical approaches. Recently, however, as the characteristic dimensions of such structures have scaled down, it has turned out that more complex models based on the nonlocal response (NOR), or even quantum interaction are required for explaining novel effects, e.g. blue spectral shifts, etc. This fact has lately started a rapid increase of interest in developing appropriate nonlocal models. In particular, in our studies, we have concentrated on understanding the interaction and developing a simple model capable of predicting the longitudinal nonlocal response based on the linearized hydrodynamic model, generalizing the standard Abajo’s nonlocal model. Our model is applicable to simple structures, such as a spherical nanoparticle. Within our model, we have also shown and compared several alternatives within the approach, with respect to inclusion of the current “damping”. As the most promising approach, we have found the approach incorporating both radiative and viscosive damping. Here, we have considered the Landau damping, too. We have demonstrated the applicability of our extended model on comparing the extinction cross section predictions of both gold and silver spherical nanoparticles. Using this model, we have systematically studied the relevant components of the electric fields and electric current densities, with respect to nanoparticles immersed in dielectric surrounding media (such as air or water). In parallel, we have also looked at the multilayer system with a general combination of local and nonlocal layers, in terms of overall transmission and reflective properties. Our results of the analysis will be also shown. Next, as an alternative (and more general) approach, based on our previous rich experience with Fourier modal methods, we have considered and developed the extension of the rigorous coupled wave analysis technique capable of treating nonlocal response numerically, for more general structures. Also, moving to even smaller characteristic dimensions of studied nanostructures, we have also adopted within our numerical techniques the Quantum corrected model, to estimate the corrections on spectral cross-section dependences, due to quantum electron tunneling effects.

The optical properties of spherical nanoparticles are described by Mie theory which yields their multipole electric and magnetic resonances. Their characteristics (and presence) depend on nanoparticle size and material. For sufficiently small metallic nanoparticles the response is determined by the electric dipolar polarizability in the small particle limit. However, as the size increases, higher order electric multipoles have to be accounted for. Although, not particularly strong, the magnetic response of metallic nanoparticles can also lead to significant optical effects when the nanoparticle is placed in an array. It is, however, significantly stronger in dielectric nanoparticles due to circular displacement current of the electric field. The orientation of the induced magnetic dipole is perpendicular to that of the corresponding electric dipole. As in the case of metallic nanoparticles higher order multipoles have to be considered. This work focuses on amorphous arrays of nanoparticles in which the nanoparticles are placed randomly using a random sequential adsorption algorithm (RSA) with the condition that a minimum center-to-center distance (lcc) between the nanoparticles is present, lcc=CCxD, where D is the nanoparticle diameter and CC is a dimensionless parameter. For simplicity it is assumed that all the nanoparticles have the same diameter. Building upon previous work, we develop a framework in which a localized optical mode of an amorphous array of discrete nanoparticles is self-consistently calculated by assuming that, on average, the nanoparticle is excited by the same field consisting of the incident field and the average scattered field from all the other particles in the system. In this work, this approach is extended to include higher order modes as well as those of the magnetic character. First, the extinction cross-section spectra for dielectric spherical nanoparticles are analyzed as a function of size in terms of contributions from various multipoles. Then, the effective medium description of amorphous arrays of nanoparticles is presented and supported by numerical calculations with T-Matrix method.

The plasmonic properties of a gold nanorod array surface can be tuned through modification of the surface parameters. To experimentally fabricate and investigate would be both resource and time expensive. This work utilises a finite element method (FEM) model to investigate the effect of varying parameters on the optical properties of the surface. Near-field coupling effects are considered within the nanorod array and between the array and gold underlayer. Increased coupling and blue-shifted resonance peaks occur for reduced array spacing and increased underlayer thicknesses red-shift resonance positions and increase overall extinction values. Nanorod geometry simulations show that larger diameters significantly blue-shift resonance peaks and increase local field enhancements throughout the array; whereas increasing height increases the extinction spectra and causes red-shift of resonance peaks. The results obtained for these investigations aid understanding of the electromagnetic interactions associated with the nanorod array which will benefit practical applications of the surface. Current experimental nanorod array geometries were investigated for plasmon-enhanced fluorescence (PEF) applications, with the maximum plasmonic signal and field enhancements occurring for 25x200nm array with 60nm spacing at fluorescent absorption and emission wavelengths. However, these significant field enhancements are localised to the surface of the nanorods rather than throughout the array so fluorescent molecules would have to be in contact with the surface to experience these enhancements.

The use of plasmonic inclusions in heterojunction solar cells promises increase of solar-to-electric energy conversion efficiency. Recently, solar cells with ZnO nanorods attracted a lot of attention due to improved efficiency provided by highly scattering ZnO nanostructures on silicon or perovskite. N-type ZnO nanorods are grown on p-Si monocrystalline 180 μm thick substrates among others by means of a hydrothermal technique which requires prior seeding by deposition of thin film of ZnO or noble metals. In the latter case, naturally formed metal islands can also act as plasmonic nanoparticles (NPs). Excitation of plasmonic resonance on the NPs leads to directional scattering of light towards Si layer and electromagnetic field enhancement at their vicinity, close to the ZnO-Si junction, what results in improved energy absorption in the semiconductor layer and thus energy conversion efficiency. In this study, we investigate optimal conditions at which plasmonic phenomenon further improves light trapping in the Si-ZnO solar cells. In simulations performed by means of 3D FDTD method, we calculate light absorption enhancement in the system due to plasmonic NPs used as a seed layer at the ZnO/Si. In the calculations Ag, and Al NPs of different size and geometry close to that achievable in the experiment are analyzed. Finally, numerical results taking into account the granulometry of metal NPs achieved in the experiment are compared with the efficiency of fabricated cells.

Photons produced in the SPDC process typically propagate through optical elements such as waveguides, lenses and beam splitters. We aim to exploit unconventional optical elements, whose fabrication has recently become possible due to the rapid development of nanotechnologies. Such miniaturized devices are typically integrated on microchips that may later become parts of larger quantum circuits. An example is provided by metamaterials, which are periodic arrays of metallic nanoparticles. These nanoparticles support surface plasmon polaritons - hybrid excitations that combine electromagnetic fields with coherent oscillations of valence-electron plasma. Here we experimentally characterize in free space a nanostructural beam splitter, which was designed to feature 25 % of reflection and transmission, and 50 % of absorption. Furthermore we experimentally show quantum interference in that device.

In this study, we propose a new approach for controlling reflection of light by using highly efficient and polarization insensitive all-dielectric metasurfaces. Moreover, we applied our model on the planar silicon solar cell to manage light trapping. For the inital design, TiO2 nano-pillars with single diameter is arranged on the silicon substrate. However, single diameter nano pillars is not enough to reducereflection covering all solar spectrum. To induce reflection reduction over the entire visible spectrum, we include different pillars with varying diameters.. The reflection of final structure with three rods is lower than 17% at 400-1000 nm. Numerical results show that the short circuit current and solar cell efficiency has been enhanced by factors of 1.66 and 1.62 compared to planar basic solar cell. The presented method allows to improve absorbing efficiency of solar cell via reducing reflection and enhancing light trapping.

A large number of scientific papers are currently devoted to the investigation of metasurfaces, based on the subwavelength gratings. Such subwavelength gratings are anisotropic – TE- and TM-polarized waves propagated through them have a different phase. Based on this effect it is possible to create analogues of the classical half-wave plates, which rotate the direction of polarization. In this work we proposed a spiral metalens, which simultaneously converts linearly polarized light into an azimuthally polarized vortex beam and focuses it. This metalens is a combination of a spiral zone plate with a topological charge m = 1 (focal length f = 633 nm) and a sector subwavelength grating (period of 220 nm, relief depth of 120 nm, illumination wavelength of λ = 633 nm). The metalens was fabricated using electron beam lithography and ion etching in 130-nm thick amorphous silicon film. Using FDTD-method it was numerically shown that the metalens illuminated by a plane wave with linear polarization forms a circular focal spot with dimensions smaller than the scalar diffraction limit: FWHMx = 0.435λ and FWHMy = 0.457λ. The focusing by the fabricated metalens was investigated experimentally using scanning near-field optical microscope (Ntegra Spectra, NTMDT).

In this work, we investigated the optical properties and surface chemistry of gold nanoparticles modified by 4,4'- dimercaptostilbene. Dimercaptostilbene was chosen as the molecule which is able to impart the new functional properties to the metasurface constructed based on assembled plasmonic nanoparticles. The influence of dimercaptostilbene concentration on the nanoparticles aggregation was investigated by X-ray photoelectron spectroscopy, UV-vis spectroscopy, transmission electron microscopy and surface enhanced Raman scattering. The interaction of dimercaptostilbene with the gold surface through a sulfur atom as well as the presence of free mercapto groups on the surface were revealed based on obtained experimental data. The effects of pH and halide anions on the Raman response of modified nanoparticles were also checked out showed their good stability in strong acidic medium as well as at high chloride background.

Organic nanoclusters, so-called J-aggregates, composed of cyanine dyes possess properties different from constituting molecules. There is a growing interest in the study of organic dyes conjugates with metal nanoparticles. The combination of unique properties of J-aggregates and plasmonic nanoparticles allow novel effects to be observed in such systems. The optical properties of molecular layer of cyanine dyes and its J-aggregates, coated on the island films in the form of a heterogeneous ensemble of silver or gold nanoparticles, were studied by absorption and fluorescent spectroscopy, as well as AFM. The original method for obtaining cyanine J-aggregates on metallic films without use of salt and water was developed. The molecular nanoclusters obtained on silver island film were stable for a week, while aggregation of cyanine molecules was much smaller on gold island films. The absorption spectrum of the organometallic film is not a simple sum of the spectra of its components. The absorption of dye molecules increases several times in the presence of silver nanoparticles in comparison with gold island film. Besides, the induced transparency is observed at the absorption maximum of J-aggregates, which can indicate the interaction between the plasmons of metal nanoparticles and the excitons of the J-aggregate.

In this work, the tight focusing of high-order cylindrical vector beams was investigated. Our analysis relies upon the Richard-Wolf equations, which have been extensively utilized when studying tightly focused laser beams with due regard for the vector properties of light fields. The FDTD method implemented in FullWave software was used to verify the results obtained with the Richards-Wolf integrals. It was shown that in the focus, there are areas with the direction of the Poynting vector opposite to the direction of propagation of the beam and the negative values are comparable in absolute value with positive values. If the order of the beam is equal to two, then the region with negative values is located in the center of the focal spot. In contrast to previous papers, where the inverse energy flow was propagated along a spiral, in this work we investigate a non-vortex inverse flow with a laminar propagation of light.