Modelling and manufacture of an interference filter for narrow spectral selection

We made and investigated narrow spectral selection filter. The influence of the multilayer structure properties and parameters on the spectral characteristics of the optical filter was investigated. The possibility of applying such a filter for selecting a narrow range of wavelengths that can find various applications in the field of information transfer and medical devices was shown.This work was supported by the Federal Agency of Scientific Organizations (agreement No 007-ГЗ/ Ч3363/26) and Ministry of Education and Science and Russian Foundation for Basic Research grant No. 16-29-11744

Atomic structure of chlorine containing calcium silicate glasses by neutron diffraction and 29Si solid-state NMR

Bioactive glasses are of great importance for medical and dental applications. In order to understand, model, and predict the behavior of these materials, and ultimately improve their design, it is important to understand the structure of these glasses. Ion dissolution is known to be the crucial first step in bioactivity and is strongly dependent upon the atomic-scale structure and network connectivity. While significant progress has been made understanding the structure of oxide-based glasses, relatively little is known about the structure of bioactive glasses containing halides. Recently, a series of novel chloride-based bioactive glasses has been developed. Chlorapatite converts to hydroxyapatite in water and these glasses are therefore of interest for novel toothpastes. This study reports the first detailed structural investigation of these bioactive chloride glasses using neutron diffraction and solid-state NMR. Chlorine was found to bond to calcium within the glass, and no evidence of Si-Cl bonding was detected. Furthermore, the absence of a chemical shift in the 29Si NMR upon the addition of CaCl2 helped confirm the absence of detectable amounts of Si-Cl bonding. Given that chlorine does not disrupt the Si-O-Si network, widely used network connectivity models are therefore still valid in oxychloride glasses

Solid-state nuclear magnetic resonance spectroscopy of cements

Cement is the ubiquitous material upon which modern civilisation is built, providing long-term strength, impermeability and durability for housing and infrastructure. The fundamental chemical interactions which control the structure and performance of cements have been the subject of intense research for decades, but the complex, crystallographically disordered nature of the key phases which form in hardened cements has raised difficulty in obtaining detailed information about local structure, reaction mechanisms and kinetics. Solid-state nuclear magnetic resonance (SS NMR)spectroscopy can resolve key atomic structural details within these materials and has emerged as a crucial tool in characterising cement structure and properties. This review provides a comprehensive overview of the application of multinuclear SS NMR spectroscopy to understand composition–structure–property relationships in cements. This includes anhydrous and hydrated phases in Portland cement, calcium aluminate cements, calcium sulfoaluminate cements, magnesia-based cements, alkali-activated and geopolymer cements and synthetic model systems. Advanced and multidimensional experiments probe 1 H, 13 C, 17 O, 19 F, 23 Na, 25 Mg, 27 Al, 29 Si, 31 P, 33 S, 35 Cl, 39 K and 43 Ca nuclei, to study atomic structure, phase evolution, nanostructural development, reaction mechanisms and kinetics. Thus, the mechanisms controlling the physical properties of cements can now be resolved and understood at an unprecedented and essential level of detail

Three-layer diffraction structure for spatiotemporal differentiation of optical signals

Предложен оптический дифференциатор на основе трёхслойной дифракционной структуры, состоящей из узкого плоского диэлектрического волновода, окружённого с двух сторон слоями-обкладками. Дифференцирование оптического сигнала осуществляется при отражении за счет резонанса, связанного с возбуждением моды, локализованной в центральном слое. Добротность резонанса (ширина резонансного минимума) увеличивается с ростом толщины слоёв-обкладок. Теоретически обоснована и численно подтверждена возможность применения рассматриваемой структуры для выполнения операций дифференцирования первого и второго порядка огибающей падающего импульса (временное дифференцирование), профиля падающего пучка (дифференцирование по пространственной координате), а также так называемого пространственно-временного дифференцирования оптического сигнала (дифференцирование по направлению в пространстве (x,t)). Дифференцирование второго порядка выполняется системой из двух структур-дифференциаторов, расстояние между которыми выбирается в зависимости от угла падения оптического сигнала, его центральной частоты и фазы коэффициента пропускания на центральной частоте. Результаты численного моделирования методом фурье-мод демонстрируют высокую точность осуществляемого дифференцирования. Полученные результаты могут найти применение при разработке полностью оптических вычислительных устройств, более компактных и простых в изготовлении по сравнению с устройствами на основе метаповерхностей, представляющих собой массив нанорезонаторов. We propose an optical differentiator based on a three-layer structure composed of a parallel-plate dielectric wa-veguide surrounded by two identical cladding layers. The incident optical pulse is differentiated in reflection due to a resonance caused by excitation of a waveguide mode localized in the central (core) layer. The resonance quality factor (width of the resonance minimum) increases with the width of the cladding layers. We theoretically justify and numerically confirm that this structure can perform temporal differentiation (differentiation of an incident optical pulse envelope), spatial differentiation (differentiation of an optical beam profile) and the so-called "spatiotemporal differentiation" (differentiation of an optical signal envelope along a certain direction in the (x,t)-plane). Second order differentiation can be performed with a system of two differentiator elements separated with a homogenous layer the optical thickness of which is defined by the optical signal's angle of incidence, central frequency and the corresponding transmission coefficient phase. Simulation results obtained with RCWA confirm high accuracy of the performed operations. The proposed differentiator is more compact and easier to fabricate than metasurface-based devices incorporating periodically arranged nanoresonators and may find application in ultrafast analogue computing and signal processing systems.Работа выполнена за счёт гранта РНФ 14-19-00796