Search

Modern methods of nanophotonics allow creating miniature devices that change the direction of light propagation, modulate the phase front, and control the outcoming state of the polarization. One of the promising areas of research is the development of flat optics elements based on planar analogues of metamaterials—dielectric metasurfaces, which are two-dimensional arrays of subwavelength nanoparticles with a high refractive index and low absorption coefficient. However, the resonances of such nanoscatterers have usually a low quality factor. Symmetry breaking of particle can lead to the excitation of a high-Q quasi-bound states in the continuum. In this work, we numerically study infrared metasurfaces that support such resonances and are formed by dimers of germanium nanocuboids. The possibility of focusing radiation to a point and line by 300‑nm-thick spherical and cylindrical metalenses is shown.

We analyze the enhancement mechanisms of magneto-optical effects in all-dielectric metasurfaces caused by the bound state in the continuum resonance. In a structure under study, a square lattice of bismuth substituted yttrium iron garnet nanodisks with an air hole displaced away from the disk axis, magneto-optical polarization and intensity effects reach 0.7° and 22%, respectively.

The possibility of controlling the spectrum of the generated third harmonic for high quality-factor resonant metasurfaces is examined. The ultrafast dynamics for both fundamental wavelength and third harmonic generation is observed in all-dielectric metasurfaces with pump-probe technique.

The possibility of all-optical switching at both fundamental wavelength and third harmonic wavelength for high-Q resonant metasurfaces is examined. The ultrafast danymics is observed in all-dielectric metasurfaces with pump-probe technique.

Ultrafast modulation of optical response is realized in a multi-resonant magnetoplasmonic metasurface under resonant femtosecond pump. A saturation of resonant probe transient transmission is shown at dielectric quazi-waveguide mode.

Demonstration of magneto-optical effects enhancement in hybrid Ni/Si metasurfaces is reported. Our results show that the polarization plane rotation angle reaches the considerable value with a change of a sign in a very narrow spectral range in the vicinity of the optical magnetic dipole Mie - type resonance. The specific Faraday rotation is 160 degrees/μm, which is an outstanding effect for an ultra-thin magnetic material with a thickness of only 5 nm as used in this work. These results could be used for the creation of active nonreciprocal photonic nanostructures and metasurfaces.

The magnetooptical control of light implies different directions of polarization plane rotation, linear-to-circular and other polarization transformations. These opportunities can be opened using polarization-sensitive resonances, for example, Bloch surface waves (BSWs) and waveguide modes (WGMs) in magnetophotonic crystals (MPCs) [1]. Magneto-optical phenomena, such as Faraday effect, can be significantly increased near spectrally narrow optical resonances [2]. In this case, the Faraday rotation angle is determined both by the magnetic properties of the material and by the Q-factor of the resonances, which define their spectral width. The resonance of the BSW is shown to be extremely narrow. The proper choice of the MPC parameters gives the ways to observe the s-polarized BSW and p-polarized WGM of the MPC in the same spectral region. Here, we experimentally demonstrate how a fundamental property of magneto-optical effects to couple two linearly polarized modes allows one to control and modify the values of Faraday rotation angles. The interplay of the BSW and WGM results in an enhancement of the Faraday rotation angle, change of lineshape of Faraday rotation spectra and direction of the polarization rotation. Reflectance spectra of the one-dimensional magnetophotonic crystal and the corresponding Faraday rotation spectra were experimentally measured using the Kretschmann attenuated total internal reflection configuration and numerically calculated using the transfer matrix approach [3]. The studied magnetophotonic crystal sample consists of 15 alternating layers of fused quartz and Bi-substituted yttrium-iron-garnet on a sGGG substrate. The BSW excitation corresponds to a narrow resonance in the reflectance spectra of the s-polarized light. Wide dips in the reflectance spectra of p-polarized light correspond to the WGM resonances. As the incident angle increases, both the resonances shift to short wavelengths, but the WGM resonance shifts faster; thus, the spectral distance between the BSW and WGM resonances decreases. The spectral dependence of the Faraday rotation angle of s-polarized light has a feature coinciding in the BSW wavelength and caused by the BSW excitation. The feature in the Faraday rotation spectrum has a Fano resonance shape and changes from an asymmetric shape to a symmetric one, while the incident angle increases and the BSW and the WGM resonances approach each other. This behavior is observed both in the experiment and calculations. Thus, it can be argued that the spectral dependence of the Faraday rotation angle depends not only on the BSW resonance in the structure but also on the coupling of the BSW with the WGM mode that is not excited in the s-polarization of the incident light. Besides, the Faraday rotation changes direction while BSW and the WGM resonances spectral position approach each other that makes these resonance in MPCs promising for the future photonics devices. [1] M. N. Romodina, I. V. Soboleva, A. I. Musorin, Y. Nakamura, M. Inoue, A. A. [2] M. Inoue, M. Levy, A.V. Baryshev, Magnetophotonics: From Theory to Appli- cations, Springer Series in Materials Science, 2013. [3] D.W. Berreman, J. Opt. Soc. Am. 62, 502–510 (1972).

The concept of the rapidly developing area of high-index resonant meta-optics is extended to the field of mag- netically active materials. We numerically analyze magneto-optical response of hybrid nickel-silicon (Ni/Si) nanoantennas in comparison with an all-dielectric analog based on the bismuth substituted iron yttrium garnet- silicon (Bi:YIG/Si) nanoantennas. The results demonstrate the multifold enhancement of the magneto-optical effects due to the Mie-type resonances excitation in the structure. To further optimize the magneto-optical re- sponse and achieve a significant enhancement of the effect, the metasurfaces composed of Ni/Si nanoantennas of the different shape and configuration are numerically simulated. The magneto-optical effects can be significantly enhanced by means of the specific design of these hybrid metasurfaces.

Planar magnetoplasmonic nanogratings composed of a two-dimensional square array of gold nanoparticles embedded into thin magnetic garnet films are proposed for enhancement of the transverse magneto-optical Kerr effect due to excitation of a quasi-waveguiding mode with light concentrated mostly inside the magnetic film. A proper optimisation of the size and periodicity of plasmonic nanoparticles as well as the thickness of magnetic dielectrics allows spectral tuning of the waveguiding mode leading to the sharp asymmetric resonance in the magneto-optical response in the desired spectral region.

We have observed the Fano-type Faraday rotation spectrum in a one-dimensional magnetophotonic crystal at the Bloch surface wave (BSW) resonance and found that it is a result of the coupling between the $s$-polarized BSW and the $p$-polarized waveguiding modes of the magnetophotonic crystal. The shape of the resonance is determined by the relative position and spectral splitting of the modes.

Control of light by an external magnetic field is one of the important methods for modulation of its intensity and polarization. Magneto-optical effects at the nanoscale are usually observed in nanostructured hybrid materials or magnetoplasmonic crystals. In this work, we combine the advantages of all-dielectric resonant nanostructures and magnetic materials for creating compact active magneto-optical metadevices. High-index nanostructures offer novel opportunities for controlling light at the nanoscale based on a strong localization of both electric and magnetic fields in such structures near the corresponding Mie resonance [1]. This fact makes them similar to plasmonic nanostructures with clear advantage that all-dielectric meta-optics structures composed of nanoparticles with high refractive index can overcome this limit and initiate a new platform for nanophotonic metadevices [2]. As the important next step in this field, we consider a control of optical properties by an applied magnetic field, known to be an effective tool for many plasmonic structures [3, 4].

Slow light is a phenomenon explained by low group velocity of the pulsed light. Faraday effect can be greatly enhanced in multilayered structures due to the artificial dispersion [1, 2]. Magnetophotonic crystals, as being layered nanostructures, can modulate electric filed amplitude and phase of a femtosecond pulse in time. For example, Faraday angle at the initial part of the pulse can differ from that at its tail, and from the steady-state value. In this work femtosecond dynamics of Faraday rotation is demonstrated experimentally in magnetophotonic crystals by polarization-sensitive correlation spectroscopy.

Magnetophotonic crystals (MPCs) support Bloch surface waves (BSWs) and waveguided modes (WGMs) propagation. The influence of the BSW on the Faraday effect in the one-dimensional MPCs is studied. The technique of measuring the angle of Faraday rotation in the MPCs in attenuated total internal reflection scheme in Kretschmann configuration is discussed. The spectra of Faraday rotation demonstrate a Fano-shaped resonance near the spectral-angular position of the BSW resonance both for s- and p-polarized incident light. The presence of the feature in the spectrum of p-polarized light can be explained by the Faraday rotation effect and subsequent BSW excitation mutually enhancing each other.

The advantages of gyrotopic materials are combined with the field of high-index metamaterials. The enhancement of the magneto-optical response in the spectral vicinity of the magnetic dipole resonance of a dielectric silicon nanodisks is numerically shown.

We study numerically the possibility of controlling light properties by means of an external magnetic field. Considerable changes in the shape, value, and spectral position of the magneto-optical response are demonstrated in Voigt geometry for the transmitted light depending on the parameters of the magnetophotonic metasurface made up of nickel/silicon nanoparticles. The spectral overlapping of the fundamental magnetic and electric dipole Mie resonances leads to interference with a strong modification of phase relations, which manifests itself through an enhanced magneto-optical signal.

Control of light by an external magnetic field is one of the important methods for modulation of its intensity and polarisation. Magneto-optical effects at the nanoscale are usually observed in magnetophotonic crystals, nanostructured hybrid materials or magnetoplasmonic crystals. An indirect action of an external magnetic field (e.g. through the Faraday effect) is explained by the fact that natural materials exhibit negligible magnetism at optical frequencies. However, the concept of metamaterials overcome this limitation imposed by nature by designing artificial subwavelength meta-atoms that support a strong magnetic response, usually termed as optical magnetism, even when they are made of nonmagnetic materials. The fundamental question is what would be the effect of the interaction between an external magnetic field and an optically-induced magnetic response of metamaterial structures. Here we make the first step toward answering this fundamental question and demonstrate the multifold enhancement of the magneto-optical response of nanoantenna lattices due to the optical magnetism., Comment: 7 pages, 5 figures

Femtosecond dynamics of the Faraday effect is experimentally studied in thin magnetic films by polarization-sensitive correlation spectroscopy.

The spectrally controllable enhancement of the transverse magneto-optical Kerr effect is realized in 2D hybrid metal-dielectric magnetoplasmonic metasurfaces. The light diffracted at different interfaces allows one to manipulate light phase in the condition of plasmonic and waveguiding resonance excitation controllable via the azimuthal angle. The multimodal nature of the system provides the flexible tunability of its magneto-optical response.The spectrally controllable enhancement of the transverse magneto-optical Kerr effect is realized in 2D hybrid metal-dielectric magnetoplasmonic metasurfaces. The light diffracted at different interfaces allows one to manipulate light phase in the condition of plasmonic and waveguiding resonance excitation controllable via the azimuthal angle. The multimodal nature of the system provides the flexible tunability of its magneto-optical response.

The multifold enhancement of the Faraday effect induced by magnetic dipole and Voigt effect amplification due to electric dipole Mie resonances of the magnetophotonic metasurface is demonstrated. The values of the magneto-optical responses up to 0.8° and 0.5% are experimentally observed for the metasurface with an ultrathin ferromagnetic layer. The results can be used for the development of novel active magnetophotonic metadevices.

The speed of light is medium-dependent, and when the properties of the medium can be chosen---as in a photonic crystal---light can be slowed to the point where it can be ``stored'' or handily manipulated. The authors use a $m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c$ crystal to harness the Faraday effect, and realize $t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}e-r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}d$ rotation of the polarization of a single femtosecond laser pulse. This achievement bodes well for photonic applications such as spatial light modulators, and holographic memory for optical computing.

Approaches to revising the documentation regulating the safety of decommissioning power-generating units of nuclear power plants are examined. It is proposed that the concept of planning decommissioning for operating and newly designed power-generating units of nuclear power plants at all stages of their lifecycle be introduced into the analysis. It is shown that the sections concerning the decommissioning of the power-generating units of nuclear power plants be revised in documents validating operation and decommissioning.

Femtosecond Faraday rotation evolution and a propagation of a femtosecond pulse through a thin magnetic films is calculated and measured.

The AIRM system, which uses the 16N activity in the VVER-1000 reactor at the Kalinin nuclear power plant to measure the thermal power of the reactor and the coolant flow rate, and similar systems used in nuclear power plants with PWR reactors are described.

Measurements of the primary coolant flow rate and reactor thermal power were compared in a VVER type reactor for two measurement systems. Monthly measurements taken for a year by the automated radiation system (AIRM) and the standard SVRK system were compared. The systems showed an error of 1 to 2% in measuring the coolant flow rate through the reactor. When the units operate on two or three loops in the backward coolant flow regime, the SVRK system overestimated the coolant flow by approximately 8000 cubic meters per hour. 3 refs., 2 tabs.

The present paper discusses the results of measurements of the coolant flow rate in all six of the main circulating loops (ML) and the thermal power of the first unit of the Armenian Power Plant. The coolant flow rate was measured by a method based on the registration of the decay of leN activity with coolant circulating in the ML; the method used to measure the thermal power was based on registration of the neutron flux density under the reactor vessel. For practical implementation of these methods we developed and set up in the first unit of the power plant a flowmeter in the form of a system of 12 experimental channels above the pipes of the primary circuit with sensors installed in them and a power meter was set up under the reactor (Fig. 1). Measuring the Flow Rate of Coolant in the Primary Circuit. High-stability SI-3BG Geiger-Miiller counters were used as sensors. The sensors were installed above the primary-circuit pipes in special collimators to isolate a definite, strictly specified volume of coolant. The first sensor records the intensity of the 16N ~/ rays of the primary-circuit coolant in the segment of the ML at the outlet from the reactor (first detection point DP-1); the second sensor, after the coolant has passed through the steam generator at the inlet of the ML to the reactor (second detection point DP-2). The coolant flow rate G in each ML was found from the ratio of the counting rates N 1 and N 2 of the sensors

An important factor in providing safe operation in a nuclear power station unit is to determine the thermal power of the reactor with an error of 1-2%. Operational methods have been proposed for measuring the thermal power by statistical computer calculations. Elsewhere, operational correlation dispersion methods were considered for determining the thermal power by means of radiation meters, these meters operating with the neutrons leaking from the reactor containment (power meters -PM) or on the radiation from /sup 16/N in the coolant (loop detector-LD). The data entering these meters are used in determining discrete quantities of statistical nature, and this enables one to obtain given errors in the readings of the PM (N /sub PM/ ) and LD (N /sub II/ ). Also, a major feature of a radiation meter is that N /sub PM/ and N /sub LD/ are strictly proportional to the thermal power of the reactor. In view of this, the authors perform a combined statistical analysis of the data obtained by these methods and those provided by the standard thermal detectors in order to define the reactor thermal power more accurately and to determine the errors.

This article describes a radiation-based monitoring system for the WWER-1000 reactor which consists of three functionally independent automated subsystems: a power meter, installed under the reactor vessel, based on recording neutrons arriving from the side wall of the vessel and proceeding through the annular gap between the vessel and the concrete shield; loop sensors which measure the thermal output by recording the N 16 gamma radiation from the coolant of the primary circuit; and a flow meter which monitors primary circuit coolant flow rate by recording the N 16 disintegration as the coolant passes into the main circulation loop. The architecture of the computerized system is diagramed and performance characteristics are given.

This paper addresses the problem of monitoring and control of the energy distribution in regard to the size and power of reactors. The authors attempt to obtain the integrated characteristics of the energy distribution from the readings of detectors set up outside the reactors. Results of this study show that in most cases the dependence of the readings of extrareactor detectors on the height of the energy distribution can be represented as a linear dependence, while the estimate of the power can be represented as a linear combinati n of the detector readings.