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The paper discusses the reasons for the decrease in the strength of the composite material in relation to the theoretical. A hypothesis is put forward according to which, along with the known reasons; in particular, the presence of internal interfaces, and together with them, the processes near the forming geometric features that arise during the structure formation of the binder paste can act as reasons for the decrease in strength. To simulate the occurrence of features in composite binder paste, the concept of the local formation of new growth on the nuclei of a new phase present in the binder paste ‒ layers of a hydrated binder on the surface of its grains ‒ is used. According to the proposed model, the growth of a new phase occurs according to the mechanism associated with the formation of a wave front. The wave front also undergoes metamorphosis, as a result of which its features are formed, near which structural defects are concentrated. Another type of geometric features is hidden interfaces, which are formed as a result of opposite growth of wave fronts and their contact. The proposed mechanism is confirmed by the data of a microscopic study of the processes of structure formation of a gypsum binder ‒ the formation of contact surfaces of the crystalline phase with different geometric and structural properties is observed on a model sample. As one of the main reasons for the occurrence of high concentrations of microcracks and other stress concentrators near hidden interfaces of the two types, the coexistence of solid phases with different structural characteristics in these regions is considered (there is a mismatch of the structural order parameters near the forming interfaces), as a result of which the strength decreases. This fact also explains the observed decrease in the ordering of the structure of the material in these areas. On the basis of the considered mechanisms of the formation of structural features leading to the destruction of the sample, methods are proposed for controlling the formation of the structure of the material, in particular, the targeted local introduction of solid phase nuclei into the binder paste.

The polarization plane rotators located outside the transmission line volume are presented. Their work is based on the excitation of special (‘dihedral') eigen-oscillations in a waveguide object fo...

The TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy) observatory is located in the Tunka valley (~50 km west from the southern shore of Lake Baikal) at an altitude of 675m a.s.l. The TAIGA observatory aims to address gamma-ray astronomy at energies from a few TeV to several PeV and CR physics from 100 TeV to several EeV. Its main feature is the complementary, hybrid approach to distinguish CR events from those of gamma rays. Currently TAIGA consists of ~80 wide-angle air Cherenkov detectors (HiSCORE stations), three ~4m diameter IACTs and several hundred surface and underground muon detectors, grouped in three jointly operating arrays. The exceptional feature of the TAIGA IACT array is it’s topology that allows one to aim for the optimal cost/performance by scanning the optimal inter-telescope distances from 300m up to 600m. The IACTs have alt-azimuth type mounts and 576-pixel imaging cameras in the foci, covering 9.6° aperture in the sky. The segmented reflectors of ~10m² area follow the Davis-Cotton design. The largest diameter of the hexagonal shape reflector is 4.3m and the focal length is 4.75m. The rigid telescope mount provides a maximum displacement of EAS image below 2mm (i.e. ≤ 0.024°) in the photodetector plane. The main parameters of IACTs are of a crucial importance for their efficient operation and is presented.

It is proposed to use the random field generation in the numerical simulation of the propagation of radiation through a random medium using method based on the Karhunen–Loeve expansion with various types of correlation operators to describe turbulence simulators. The properties of the calculated simulators of a random medium with a Gaussian correlation function were investigated in modeling the propagation of Laguerre-Gaussian vortex beams. The simulation results showed that an increase in the order of the optical vortex leads, as in the experiment, to lower stability of the phase singularity of the beams to random optical fluctuations. The similarity of the simulation results and the optical experiments indicates the promise of the proposed approach for the synthesis of random environment simulators.

The article deals with two concepts of phenomenon of singularity in philosophy. The first one is the idea of technological singularity as a final stage of the formation of the posthuman being. The other concept opposes human as a singularity phenomenon and opposes to idea of technological singularity.

Purpose: Technical capabilities of the MARK-4B antenna system necessary for its further using as a 32-meter radiotelescope (RT-32) and making simultaneous spectral radioastronomical observations in the C and K frequency ranges, are investigated. Design/methodology/approach:The studies use the results of our own measurements made with the МАRK-4В antenna system, expert reviews, open information sources, technical documentation of the MARK-4B antenna system, radio astronomy and computer simulation methods and comparative analysis of this antenna main parameters with the corresponding parameters of the world’s best active radio telescopes. Combining different approaches allows us to determine the requirements for the receiving system, parameters of the spectrometer, calibration techniques and optimize the МАRK-4В antenna system modernization procedure. Findings: The radio telescope main parameters required for spectral observations in the C and K frequency ranges are determined. The antenna pointing system capabilities are specified. For the MARK-4B antenna system working frequency range, the main spectral lines of various molecules available for research have been considered. The transitions radiating the most intensive spectral lines are listed. The radio astronomical problems that can be solved using the MARK-4B in the mode of spectral observations are formulated. The required parameters of the spectrum analyzer and the receiver’s self-noise temperature are determined. Calibration techniques of the recorded signal are described, which are necessary for carrying out spectral observations. Conclusions: The here presented studies show that for making spectral observations based on the beam-waveguide MARK-4B antenna system, it is technically possible to create the RT-32 radio telescope with quality technical characteristics corresponding to the world-best analogs. Modernization of the beamwaveguide MARK-4B antenna system will allow at the first stage to create in Ukraine the dual-band radio-telescope permitting to make simultaneous spectral and/or continued observations in the C and K ranges. Henceforth, the amount of simultaneously working ranges can be increased.

The Tunka-133 Cherenkov complex for recording extensive air showers (EAS) collected data over seven winters from 2009 to 2017. The differential energy spectra of all particles was acquired in the 6 × 1015–3 × 1018 eV range of energies over 2175 h. The TAIGA-HiSCORE complex is continually being expanded and upgraded. Data acquired by 30 first-line stations over 35 days during the period 2017–2018 is analyzed in this work. As at the Tunka-133 setup, the primary particle energies above 1015 eV are measured using the density of the Cherenkov light flux at a distance of 200 m from a shower’s axis. Data on lower energies are collected by determining the energy of the light flux near a shower’s axis. This results in a spectrum of 2 × 1014–1017 eV. The combined spectrum for the two systems covers a range of 2 × 1014–2 × 1018 eV.

Work is currently under way in the Tunka Valley, 50 km from Lake Baikal, to create the TAIGA gamma observatory for studying gamma radiation and cosmic ray fluxes in the 1013–1018 eV range of energies. To detect gamma rays with energies above tens of TeV, a hybrid method of detecting showers is implemented. It is based on data obtained by the TAIGA Imaging Atmospheric Cherenkov Telescope (IACT) and the wide-angle TAIGA-HiSCORE array. The preliminary results from processing the telescope’s data for the low-energy region (>2–3 TeV) are presented. Joint events with energy more than 50 TeV are analyzed and compared to Monte Carlo calculations.

The TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma-ray Astronomy) experiment aims at observing gamma-rays in the energy range from 1 TeV to several 100 TeV. The operation of the observatory is based on a new hybrid approach that combines imaging air Cherenkov telescopes (IACTs) and wide-angle Cherenkov detectors (TAIGA-HiSCORE) for measuring times of extensive air shower (EAS) light front arrival. Monte Carlo simulations are compared to real data to determine the performance of the detector setup. Dedicated software and algorithms are described, model parameters are given, and an overview of the current status of model-based performance studies is presented.

We performed a comparative numerical study of the conservation of properties of individual Laguerre-Gauss beams and their superpositions in a random environment. The simulation is based on the extended Huygens-Fresnel principle. Studies have shown that increasing the number of rings of Laguerre-Gauss modes with the same vortex order allows one to increase the ratio of the energy of the minimum informative coefficient to the energy of the maximum parasitic coefficient, which is important when detecting information encoded in the coefficients. In addition, an increase in the number of rings partially compensates for the stronger effect of random fluctuations on beams with high topological charges. Such a positive impact can be explained by the structural redundancy of multi-ring distributions (the vortex phase structure of the beam is repeated in each ring). A similar result was obtained for beams corresponding to a two-mode superposition. The best result on information preservation was obtained for the superposition with duplication of information in complex conjugate coefficients, and the best ratio of informative energy to parasitic one was obtained for beams with the largest area.

УДК 520.272.2:621.396.677.494 PACS number: 95.55.-Jz Предмет и цель работы: Создание радиотелескопа на основе антенной системы МАRК-4В, которая была разработана для телекоммуникационных приложений, определение возможностей использования лучеводной антенной системы в широкополосном многодиапазонном режиме работы и оценка характеристик антенны с помощью радиоастрономических измерений. Методы и методология: Комплексный анализ всех систем МАRК-4В дает возможность выделить блоки и узлы, которые подлежат замене или модернизации. Анализ конструкции рефлектора и субрефлектора, лучевода, гофрированного рупора и волноводной системы позволяет определить возможные частотные диапазоны работы создаваемого радиотелескопа. Установка широкополосного приемника с предусмотренной возможностью калибровки по охлаждаемой и неохлаждаемой нагрузке позволяет определить температуру антенной системы. Наведение антенны на калибровочные источники и запись сканов за счет вращения Земли исключает систематические ошибки или погрешности системы наведения. Таким образом определяется ширина диаграммы направленности и эффективная площадь радиотелескопа. Результаты: Произведен анализ конструкции антенны и определены первоочередные этапы реконструкции антенной системы МАRК-4В. Демонтированы узкополосные передатчик и приемник диапазона С и установлен широкополосный приемник (диапазон 4.6÷5.1 ГГц ) с детектором и возможностью изменения времени интегрирования сигнала. По результатам наблюдений сделаны первоначальные оценки температуры шумов системы, которые позволяют надеяться на то, что радиотелескоп РТ-32 (г. Золочев, Львовская обл., Украина) совместно с охлаждаемым приемником будет обладать низкими собственными шумами. Рассчитана и установлена новая система наведения антенны, с помощью которой в С диапазоне проведены астрономические тесты ширины диаграммы направленности ( ≈ 7.2 ′ ) и уровня ее боковых лепестков (–12.5 дБ), эффективной площади ( ≈ 680 м 2 ) и коэффициента использования поверхности ( ≈ 0.84 ). Заключение: Выполненные измерения и расчеты показывают, что на базе антенной системы МАRК-4В возможно создать высокоэффективный радиоастрономический инструмент. Разработанные на данный момент системы приема и наведения для радиотелескопа РТ-32 свидетельствуют о высоком потенциале украинской науки. Дальнейшая кооперация научных исследований и высоких технологий приведет к созданию эффективного украинского радиотелескопа сантиметрового диапазона. Ключевые слова: антенна, излучатель, интерферометрия, поляризация, радиоастрономия, радиоисточник, радиотелескоп, сервер, стандарт частоты Статья поступила в редакцию 11.03.2019 Radio phys. radio astron. 2019, 24(2): 87-116 СПИСОК ЛИТЕРАТУРЫ 1. 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The possibility of using traditional (scalar) models of band-pass filters (BPF) of the millimeter range on "all-metal inserts" in design of three-dimensional modifications of such a BPF is estimated. The complication of the filter geometry is associated with the introduction of narrow grooves in each of the resonators, which provide a number of technological advantages in fabrication. It is proved that with all-metal inserts with a thickness of not more than λ/100, the results of the "vector" and "scalar" models completely coincide.

It is shown how the topology of the individual components of a two-layer 3D-chiral object affects the natural frequencies and the manifestation of the "artificial optical activity". Using the waveguide example, it is proved that the dihedral symmetry Dn with high n allows expanding the bandwidth of polarizer.

Numerical modeling data for the frequency selective surfaces whose elementary period contains one or two pairs of U-shaped slots are presented in the paper. A peculiarity of the numerical model implementation is discussed. In order to make the calculations rapid, a virtual waveguide is incorporated into the module that is responsible for the calculation of the scattering matrix of a plane junction of the Floquet channel and U-shaped waveguides. Numerical examples are given for a single-standing perforated screen and a two layer frequency selective surface. A possibility to generate a transmission response by the help of the resonant coupling via the first higher (not fundamental) mode of U-shaped slots is demonstrated.

The polarization plane rotators located outside the volume of a transmission line are presented. Their work is based on the excitation of special ("dihedral") eigen-oscillations in a waveguide object formed by two grooved flanges with rotational symmetry. When one of the flanges rotates relative to the other, the composite object becomes 3D-chiral and rotates the plane of polarization by a certain angle in the band of several percent with minimal reverse loss. In circular and coaxial waveguides, mechanical or electronic tuning of the polarization plane is possible by mutual rotation of the flanges or by placing the controlled elements (media) into the object cavity.

The possibility to design a tunable polarization plane (PP) rotator in waveguides with circular symmetry is proven. The appearance of artificial “optical activity” in the interaction of a pair of conjugated planar chiral irises by the fringing fields is used. The rotator can be reconfigured by rotating the irises relative to each other providing the rotation of the PP up to cross-one. Being relatively narrowband, the rotator has a longitudinal dimension $\lambda _{0}/50$ – $\lambda _{0}/10$ .

To analyze the ability of certain beams to maintain information stability under the influence of random fluctuations of the optical medium, numerical calculations are used with the help of turbulence simulators such as diffusers, scattering screens and turbulence cells. These turbulence simulators can be generated via the Karhunen-Loeve decomposition, which is the basis of the eigenfunctions of the correlation function. A random medium simulator formed for a Gaussian correlation function was used to study the ability of single-ring Laguerre-Gaussian vortex beams to retain their structure. The results showed that an increase in the order of the optical vortex leads to less beams phase singularity stability to random optical fluctuations.

To analyze the ability of certain beams to maintain information stability under the influence of random fluctuations of the optical medium, numerical calculations based on turbulence simulators such as diffusers, scattering screens and turbulence cells are used. These turbulence simulators can be generated via the Karhunen-Loeve expansion, which is a basis of the eigenfunctions of the correlation operator. In this paper, we consider an analytical calculation of the Karhunen-Loeve functions for a two-dimensional correlation function defined in the form of a Gaussian function, as well as numerical calculation for various four-dimensional correlation functions.

A new knee-like approximation of the lateral distribution function (LDF) of EAS Cherenkov light in the 30–3000 TeV energy range was proposed and tested with simulated showers in our earlier studies. This approximation fits the LDFs of individual showers accurately for all types of primary particles gamma-rays, protons, and nuclei) and is suitable for reconstructing the shower core, determining the energy, and separating gamma-induced showers from hadron-induced ones. In the present study, the knee-like fitting function is used to determine the parameters of real showers detected by TAIGA-HiSCORE. It is demonstrated that this approximation characterizes properly all types of individual LDFs of experimental events in the 300–1000 TeV range. The accuracy of fit is governed by fluctuations intrinsic to the process of measurement of the Cherenkov photon density. The probability density function of these fluctuations was reconstructed and introduced into simulations. Certain useful methodical applications of the knee-like approximation are con-sidered, and the possibility of shower sorting into nuclei groups is examined. The extensive statistical coverage and detailed LDF measurement data of HiSCORE have provided the first opportunity to examine in depth the LDF of Cherenkov radiation in the 300–1000 TeV range.

Three versions of two-layer polarization plane rotators in a circular waveguide based on the internal fringing field interaction are considered. They work on the excitation of unusual eigen-oscilla...

Over the past few years, the TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma-ray Astronomy) observatory has been being deployed in the Tunka Valley, Republic of Buryatia. It is designed for studying gamma rays of energy above 30 TeV and performing searches for sources of galactic cosmic rays with energies in the vicinity of 1 PeV, which is an energy region around the classic knee in the cosmic-ray energy spectrum. The first phase of the observatory will be situated at a distance of about 50 km from Lake Baikal at the site of the Tunka-133 array. The TAIGA gamma observatory will include a network of 500 wide-angle (0.6 sr) Cherenkov detectors (TAIGA-HiSCORE array) and up to 16 atmospheric Cherenkov telescopes (ACT) designed for analyzing the EAS images (imaging atmospheric Cherenkov telescopes, or IACT) and positioned within an area of 5 km2. The observatory will also include muon detectors of total area 2000 m2 distributed over an area of 1 km2. Within the next three years, it is planned to enhance the area of the TAIGA-HiSCORE array by a factor of four—from 0.25 km2 to 1 km2; to supplement the existing IACT with two new ones; and to deploy new muon detectors with a total coverage of 200 m2. The structure of the new observatory is described along with the data analysis techniques used. The most interesting physical results are presented, and the research program for the future is discussed.

The article presents the relevance and advantages of the new gamma observatory TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy), which is being constructed in the Tunka Valley 50 km from Lake Baikal. Various detectors of the six TAIGA gamma observatory arrays register the Cherenkov and radio radiation, as well as the electron and muon components of EAS. The primary objective of the TAIGA gamma observatory is to study the high-energy part of the gamma-ray spectrum, in particular, in order to search for Galactic PeVatrons. The energy, direction, and position of the EAS axis are reconstructed in the observatory based on the data of the wide-angle Cherenkov detectors of the TAIGA-HiSCORE experiment. Taking into account this information, the gamma quanta are distinguished from the hadron background using the data obtained by the muon detectors and telescopes that register the EAS image in the Cherenkov light. In this hybrid mode of operation, the atmospheric Cherenkov telescopes can operate in the mono-mode, and the distance between them can be increased to 800–1000 m, which makes it possible to construct an array with an area of 5 km2 and more at relatively low cost and in a short time. By 2019, the first stage of the gamma observatory with an area of 1 km2 will be constructed; its expected integral sensitivity for detecting the gamma radiation with an energy of 100 TeV at observation of the source for 300 hours will be approximately $$2 \times 5$$ 10–13 TeV cm–2s–1.

This paper is devoted to theoretical analysis of optical signals passing through a double lens imaging system based on the double finite Hankel transform of vortex order m. The set of vortex eigenfunctions of such system was calculated, which permitted to analyze optical signal transmission distortion based on the approximation by this eigenfunctions. Analysis of various signals passing through a double lens system based on the approximation by calculated eigenfunctions demonstrated growing deviation when the order of vortex phase singularity in the original signal increases. This fact needs to be taken into account in such applications as optical communication when mode division multiplexing based on orbital angular momentum is used.

It is planned that new TAIGA-Muon detectors will complement the existing Tunka-GRANDE facility of scintillation detectors of the TAIGA gamma-observatory in the Tunka valley, Russia. The new design of scintillation detector with wavelength shifting bars and PMTs is developed. The first prototype of the counter was installed and tested using infrastructure of the Tunka-GRANDE installation in 2017. The mass production of counters has begun in 2018 at the Novosibirsk State University.

Subject and purpose. Open resonant system as the oscillating circuit of the solid-state oscillators and characteristics of the quasi-optical oscillators properly are the object of investigations. Purpose of article is review of works being fulfilled at the solid-state department over period 1979 and to the present day. The intent of the paper is to give the indication prerequisites of the creation of high-stabilized millimeter wave sources and way of this problem solution. Method and methodology. Theoretical and experimental methods of study of main parameters of open resonators with resonant and nonresonant inhomogeneities such as spectrum, field topology of open resonators are the waveguide model of resonator, decomposition method, generalized scattering matrix method, and experimental technique of the power, frequency, and spectrum measurements. Results. Results of study and development of quasi-optical solid-state oscillator are: the level of frequency noise is no more than –115…120 dB/Hz; power of generation at first harmonic is up to 130…150 mW at frequency of 40…50 GHz; at second harmonic – up to 10 mW at 60…90 GHz; generation power is no more than 3 mW at frequency of 150 GHz ; long-term frequency instability is 3×10–8 at active control temperature DТ ~ 0.1 °С. Conclusion. In the paper it is analyzed an application area of solid-state oscillators. They are local oscillators in receiving units and radiometers, refractometry, dielectro-metry, and fields where high stability and low level of frequency noise are needed. The promising lines are inquired, they are search of new physical properties for nonlinear element creating at Terahertz frequency band.

This article provides examples that illustrate the search for different two-layer metamaterials that provide rotation of the polarization plane (“optical activity”). Selected objects show a twenty-year history of the search for a new principle of creation of polarization rotators based on planar metamaterials that were implemented in the form of thin-layered periodic structures. The manifestation of optical activity, presence or absence of satisfactory or perfect matching, the possibility of a multiband phenomena, the role of high spatial harmonics in “electromagnetics” of this effect are explained by the features of the eigen-oscillations that are excited in the gap of the multilayer structure.

We have studied the possibility of designing compact polarization plane rotator electromagnetic waves on the basis of the structures with dihedral symmetry, and formed by 5-resonant slotted apertures with rectangular irises. The proposed structure allows to rotate polarization plane at angles being different from 90° and have an acceptable matching in a given frequency band.

The TAIGA experiment in the Tunka valley near Lake Baikal is planning an extension with new TAIGA-Muon scintillation detector stations. The main purpose of TAIGA is gamma-ray astronomy in the TeV to PeV energy range and cosmic ray physics. The purpose of the Taiga-Muon detectors is to measure the muon component of air showers for improving cosmic ray composition measurements as well as gamma–hadron separation above 100 TeV. Monte Carlo simulations of the experiment are done with the software packages CORSIKA and GEANT4. Extensive air showers of primary particles in the energy range 100–3000 TeV are created with CORSIKA. The trigger efficiency is calculated and used for optimization. The suppression factor of hadronic showers versus electromagnetic showers is studied, leading to an optimum depth of soil absorber (2 m), at the lowest energy range. Data on the identification efficiency for primary gamma-quanta and proton events are presented as well as the suppression factor.

One of the most informative methods of cosmic ray studies is the detection of Cherenkov light from extensive air showers (EAS). The primary energy reconstruction is possible by using the Earth’s atmosphere as a huge calorimeter . The EAS Cherenkov light array Tunka-133, with ∼ 3 km 2 geometrical area, is taking data since 2009. Tunka-133 is located in the Tunka Astrophysical Center at ∼ 50 km west of Lake Baikal. This array allows us to perform a detailed study of the energy spectrum and the mass composition in the energy range from 6 ⋅ 1 0 15 eV to 1 0 18 eV . Most of the ongoing efforts are focused on the construction of the first stage of the detector TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy). The latter is designed for the study of gamma rays and charged cosmic rays in the energy range of 1 0 13 eV – 1 0 18 eV . The TAIGA prototype will consist of ∼ 100 wide angle timing Cherenkov stations (TAIGA-HiSCORE) and three IACTs deployed over an area of ∼ 1 km 2 . The installation of the array is planned to be finished in 2019 while the data-taking can start already during the commissioning phase. The joint reconstruction of energy, direction, and core position of the imaging and non-imaging detectors will allow us to increase the distance between the IACTs up to 800 m, therefore providing a low-cost, highly sensitive detector. The relatively low cost together with the high sensitivity for energies ≥ 30–50 TeV make this pioneering technique very attractive for exploring galactic PeVatrons and cosmic rays. In addition to the Cherenkov light detectors we intend to deploy surface and underground muon detectors over an area of 1 km 2 with a total area of about 1000 m 2 . The results of the first season of coincident operation of the first ∼ 4 m diameter IACT with an aperture of ∼ 10°with 30 stations of TAIGA-HiSCORE will be presented.

Vortex light beams are used to compact data channels because they have orbital angular moments with an infinite number of possible quantum states. This allows the transmission of optical information in a single physical medium by encoding the data by different optical vortices. The aim of the paper is to modeling and analysis the state of orbital angular momentum of laser beams during propagation through free space and parabolic fiber in the presence of random fluctuations of the optical medium. The modeling results for Laguerre-Gauss beams showed that after the beams distortion by random noise, they self-regenerate with further propagation in an undisturbed medium, and it is possible to determine the initial state of the orbital angular momentum of the beam by means of binarization of the field expansion coefficients in angular harmonics.

The solution of the problem of overcoming the diffraction limit based on the representation of an optical signal in the form of a superposition of communication modes matched with the vortex eigenfunctions of a bounded (in the object and spectral regions) nonparaxial propagation operator in free space is considered. Nonparaxial propagation of laser beams is described using an expansion in terms of conic waves based on the m-th order Fourier-Hankel transform. The eigenfunctions of such an operator, which have near-unity eigenvalues, determine the number of degrees of freedom and characteristics of an optical signal transmitted without distortion over a given distance. Based on the considered approach, a parametric method was developed for solving the inverse diffraction problem, including overcoming the diffraction limit.

The propagation of Laguerre-Gauss vortex beams through a random phase distorting medium is numerically and experimentally investigated. The influence of the order of the mode on the degree of conservation of vortices of different orders in a random environment is analyzed. An increase in the stability of the detection of a vortex in a beam with a small defocusing of the output Fourier cascade of the optical correlator is shown experimentally.

Two compound circular hole screens, which possess rotation symmetry and are conjugately stacked in such a way that the whole structure has ${D_4}$ dihedral symmetry, are considered to rotate polarization plane of a normally incident wave. The eigenmodes responsible for the polarization plane rotation are analytically investigated on the base of the representation theory of groups and illustrated by numerical results.

The work concerns the development of aerogel radiators for RICH detectors. Aerogel tiles with a refractive index of 1.05 were tested with a RICH prototype on the electron beam on the VEPP-4M collider. It has been shown that polishing with silk tissue yields good surface quality, the amount of light loss at this surface being about 5–7%. The Cherenkov angle resolution was measured for a tile in two conditions: with a clean exit face and with a polished exit face. The number of photons detected was 13.3 and 12.7 for the clean and polished surfaces, respectively. The Cherenkov angle resolution for the polished surface is 55% worse, which can be explained with the forward scattering on the polished surface. A tile with a crack inside was also tested. The experimental data show that the Cherenkov angle resolution is the same for tracks crossing the crack area and in a crack-free area.

In this paper, we consider using a binary curved fork grating not only for the simultaneous formation of several Bessel vortex beams but also for detecting the presence of angular harmonics (optical vortices) in an analyzed beam outside the focal plane. In this case, we use the effect of a longitudinal shift of focus (or correlation peak) when the lens is supplemented with an axicon. The combination of a lens and an axicon provides, in the focal plane, the generation of narrow light rings whose radii do not depend on the vortex phase component. Thus, the detection of an optical vortex cannot be carried out in the focal plane, but only at a certain distance from it, which provides additional security for information transmission. In addition, the use of these gratings makes it possible to simultaneously manipulate microparticles in various planes, and they can be used for fabricating complex three-dimensional metastructures as well as the single-shot pulse laser processing of transparent materials or polymers.

In this paper, we propose a simple design of a planar-chiral screen based polarization plane rotator that enables a polarization conversion at two assigned frequency bands simultaneously. The rotator is composed of a pair of conjugated double periodic perforated screens separated by a short distance. Two groups of four rectangular slots are cut along a perimeter of the screen periodical cell. Polarization rotation frequencies are controlled by choosing appropriated dimensions and placements of the slots' groups. At the same time, we report that even a rotator with equal slots belonging to different (outer or internal) quadruples enables a dual-frequency operation as well.

Vortex laser beams possessing an integer orbital angular momentum are promising for compaction of communication channels in the transmission of information by means of free-space optics. We consider vortex beams representing a superposition of the Laguerre-Gaussian modes with different indices, so they have a fractional orbital angular momentum. Such beams enhance the capabilities and improve the security of information transfer. We consider the propagation of vortex laser beams in a random medium based on the extended Huygens-Fresnel principle. To determine the modal composition of the considered beams under the conditions of random distortions we propose to use multichannel diffractive optical elements (DOE) matched with optical vortices.

International audience; Emerging part of condensed matter science, which deals with the systems of extreme two-dimensionality, renews the interest in natural 2D objects such as planar stacking faults (SFs) in semiconductor crystals. We report on the observation of an excitonic state localized at the 1D intersection of the SF with a high quality ZnSe quantum well (QW). The micro-photoluminescence measurements are performed in a specimen used for preceding transmission electron microscopy studies. We demonstrate that the observed narrow lines are polarized along SFs and their linewidths depend on the SFs length. For short SFs, the linewidth can be as low as 0.15 meV. Using the combination of the effective mass approach and the density functional theory calculations we show that the exciton localization is due to the intrinsic electric field inside the SF, which also leads to a spatial separation of electron and hole in the exciton. The 1D intersection of perfect natural and artificial 2D objects can serve as a promising playground for the study of subtle excitonic effects in single defects.

A compact waveguide polarization rotator, able to turn the polarization plane by an arbitrary angle, is proposed. Its operational principle is based on a strong electromagnetic coupling between two conjugated quadruple-slot planar-chiral irises in a square waveguide by the below cutoff modes. The physical interpretation for the observed phenomenon is provided based on the analysis of the eigenoscillations of such a ${ D}_{4}$ symmetrical object considered as an open waveguide resonator. It is demonstrated that there exist two perfect matching points controlled by the iris geometry and width of the narrow gap between two planar chiral components. The reported unit has a bandwidth of several percent with return loss better than 20–30 dB. The conclusions of this work are fully applicable to double-periodical two-layer screens or metasurfaces having such square cells.

International audience; The physical mechanisms behind the formation of shaped-beam radiation patterns by flat horns (i. e., open ended waveguide feeds with finite-size corrugated flanges) are studied in a rigorous manner using the singular integral equation (SIE) approach. The problem is considered for TM polarization in the two-dimensional (2-D) formulation. First, dispersion curves of periodic grating are presented and used to analyze the modes supported by the waveguide flanges. This includes the surface wave, stopband, and leaky-wave regimes. The modes corresponding to the poles on the bottom "nonphysical" Riemann sheets are also considered. Finally, various types of radiation patterns produced by flat horns with gratings operating in different regimes are illustrated with an emphasis on generating sectoral beams being of interest for many practical applications. The results are validated via comparison with full-wave three-dimensional (3-D) analysis.

The polarization plane rotation generally occurs in structures having optical activity, Faraday effect or in liquid crystals. Recently, investigations aimed at creation of artificial environments (metamaterials) with similar properties have been actively carried out. The paper shows that the double screen system with circular holes can rotate polarization plane of incident plane wave, if its periodic cells have the special spatial symmetry. Theoretical and experimental results for fishnet metamaterial based on it are presented. Explanation of the phenomenon is carried out using the method of generalized scattering matrices and taking into account characteristics of the eigenfield spatial distributions, which are specified by the screen system symmetry. It is shown that there are several spatial types of the eigenoscillations, which are responsible for polarization plane rotation under plane wave excitation. Numerical experiments show that the polarization plane rotation can be controlled by changing the structure of the periodic cell, and the polarization plane rotation through specified angles can be achieved even at small distances between screens.

A number of proposed experiments aimed at dark matter studies are based on detection of luminescence in liquid argon at 128 nm. Existing solid-state photomultipliers do not have the capability to detect emission at 128 nm in the photon counting mode. Spectral properties of a new silicon photomultiplier prototype for vacuum ultraviolet registration are presented. The prototype demonstrates the photon detection efficiency about 1% in 112–182 nm range.

The physics motivations and advantages of the new TAIGA (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy) detector are presented. TAIGA aims at gamma-ray astronomy at energies from a few TeV to several PeV, as well as cosmic ray physics from 100 TeV to several EeV. For the energy range 30 – 200 TeV the sensitivity of 10 km2 area TAIGA array for the detection of local sources is expected to be 5 × 10-14 erg cm-2 sec-1 for 300 h of observations. Reconstruction of the given EAS energy, incoming direction and its core position, based on the timing TAIGA-HiSCORE data, allows one to increase a distance between the IACTs up to 600-1000 m. The low investments together with the high sensitivity for energies ≥ 30-50 TeV make this pioneering technique very attractive for exploring the galactic PeVatrons and cosmic rays. At present the TAIGA first stage has been constructed in Tunka valley, 50 km West from the Lake Baikal. The first experimental results of the TAIGA first stage are presented.