Absorption loss influence on optical characteristics of multilayer distributed Bragg reflector: wavelength-scale analysis by the method of single expression

Electrodynamical model of a classical distributed Bragg reflector (DBR) consisting of alternating quarter-wave layers of high and low permittivity is considered at the plane wave normal incidence. Reflective characteristics of DBR possessing absorption loss in constituting layers are analysed via correct wavelength-scale boundary problem solution by the method of single expression (MSE). Analysis of optical field and power flow density distributions within the lossy DBR structures explained the peculiarities of their reflective characteristics. Optimal configurations of lossless and lossy DBRs are revealed. Specific DBR structures possessing full transparency at definite number of layers are also analysed.     

Synthesis of 3,4‐Dialkyl‐5‐(1‐oxo‐ethyl)‐3H‐thiazole‐2‐thiones Derivatives and Their Pesticidal Activity

By interaction of N‐methyl(ethyl)‐dithiocarbamate sodium salt with 3‐chloro‐pentane‐2,4‐dion the 1‐(3‐alkyl‐4‐methyl‐2‐thioxo‐2,3‐dihydro‐thiazol‐5‐yl)‐ethanones 1 , 2 and corresponding oximes 7 , 8 were synthesized. On the basis of the mentioned compounds hydrazono ( 3 , 4 ), ureayl and thioureayl ( 5 , 6 ) derivatives, substituted oximes ( 9 , 10 ) and azinyl oximes ( 11 , 12 ) were obtained. The structures of synthesized compounds were confirmed by proton nuclear magnetic resonance spectroscopy and elemental analysis. The pesticidal activities of synthesized compounds were studied. Some of the synthesized compounds simultaneously have shown growth stimulant and fungicidal activity.     

Simulation of amplifying phase-shifted fiber Bragg gratings by the method of single expression

An advanced method of single expression (MSE) is used for simulation of uniform and phase-shifted amplifying fiber Bragg gratings (FBGs) as potential narrowband transmission filters-amplifiers. In MSE the solution of Helmholtz's equation is represented in a special form of a single expression, which enables the exact solution of the corresponding boundary problem by means of numerical integration. Spectral dependences of amplifying uniform and π phase-shifted FBG are obtained. The electric field and power flow density distributions within and outside of amplifying FBGs permit to understand electrodynamically the process of amplification in modulated media. Amplification at transparency points of spectral dependences of uniform and π phase-shifted FBGs indicates essential gain accumulation against other parts of the spectrum. Amplification turns over uniform FBG from the stop-band filter to the narrow pass-band filter-amplifier with two sharp peaks at both edges of the stop-band region of corresponding FBG without gain. In amplifying π phase-shifted FBGs only one amplified narrow transmission peak appears at the center of the spectral dependences that is more acceptable for contemporary DWDM systems.     

Modification of the MgO–Al2O3–TiO2–SiO2 Glass by Silver Diffusion for the Formation of Luminescent Molecular Clusters

Doklady Chemistry - The capabilities of diffusion treatment of alkali-free MgO–Al2O3–TiO2–SiO2 glass using Ag-containing salt melts or special pastes for the formation of...     

Modelling of linearly chirped fiber Bragg gratings by the method of single expression

To model chirped fiber Bragg gratings (FBGs) for dispersion compensation in optical fibers a novel method of single expression (MSE) is used. The reformulation of Helmholtz's equation in the MSE to the full set of first-order differential equations leads to dealing with the electric field amplitude, its derivative, power flow density and phase distributions in any aperiodic media. The phase derivative obtained numerically permits to compute the dispersion slope in the time delay of investigated chirped gratings. Reflective and time delay spectra of linearly chirped gratings of different lengths and chirp coefficients are computed. A self-similarity law for the gratings of the same strength but different lengths and chirp coefficients is revealed. The apodization of gratings is applied to reduce sidelobes in gratings' reflection spectra and eliminate oscillations in the time delay characteristics.     

Tagged-weak <Emphasis Type="Italic">π</Emphasis> method

A new “tagged-weak π method” is proposed for determination of electromagnetic transition probabilities B(E2) and B(M1) of the hypernuclear states with lifetimes of ∼10⁻¹⁰ s. With this method, we are planning to measure B(E2) and B(M1) for light hypernuclei at JLab. The results of Monte Carlo simulations for the case of E2(5/2⁺, 3/2⁺ → 1/2⁺) transitions in _Λ⁷He hypernuclei are presented.     

Problem of plane EM wave self-action in multilayer structure: an exact solution

To solve exactly the problem of plane EM wave interaction with multilayer nonlinear structures a non-traditional theoretical method is applied. Wave equation's solution in each layer of a structure is presented in the special form of a single expression. This form of field presentation does not require the fulfillment of superposition principle, contrary to the traditional approach. Multilayer structures of threefold quarter-wavelength bilayers with alternate linear and nonlinear indices are investigated. Multistable dependences of reflection coefficients on incident electric field amplitude are obtained for negative and positive nonlinearity. The results of investigation not only permits to deeply understand the phenomena of intense electromagnetic wave interaction with multilayer structures but also will be very useful for elaboration of nonlinear devices.     

Heavy-nucleus multifragmentation induced by coherent bremsstrahlung photons with endpoint energy <Emphasis Type="Italic">E</Emphasis><Stack><Subscript>γ</Subscript><Superscript>max</Superscript></Stack>=4.1 GeV

New experimental data are presented that were obtained by studying the multifragmentation of ¹⁹⁷Au, ²⁰⁹Bi, ²³⁸U, and ²⁴³Am nuclei in a coherent bremsstrahlung-photon beam with an endpoint energy of 4.1 GeV from the Erevan Synchrotron. For the first time, four or more fragments are observed. For all the nuclei studied here, the respective production cross sections are about (1–3)×10^?3 of the total inelastic photon-nucleus cross section. The fragment yields are isotropic.     

Synthesis of Novel 2‐Amino‐(2‐thioxo‐3‐alkyl‐4‐methyl‐3H‐thiazol‐5‐yl)‐[1,3,4]thiadiazole Derivatives and Their Growth Stimulant Activity

On the base of synthesized 2‐amino and 2‐ethylamino‐(2‐thioxo‐3‐alkyl‐4‐methyl‐3H‐thiazol‐5‐yl)‐[1,3,4]thiadiazoles, their alkyl, acetyl, and alkylacetylamino derivatives are obtained. The alkylation of 2‐ethylamino derivatives can occur at both exo and endo nitrogen atoms of amidine group, and the acetylation takes place exclusively at the exocyclic nitrogen atom. At acetylation of 2‐amino‐[1,3,4]thiadiazoles, only exo substitution is observed. At the further alkylation of these products, a mixture of exo‐ and endo‐substituted forms is obtained. At preliminary screening, the synthesized compounds have shown expressed growth stimulant properties. The activity of the most active derivatives was in the range of 65–100%, compared with that of heteroauxin.     

Modelling of strongly nonlinear sinusoidal Bragg gratings by the Method of Single Expression

The one-dimensional problem of plane EM wave interaction with strongly nonlinear sinusoidal Bragg gratings is exactly solved using the new Method of Single Expression (MSE). The basic point of the method is the presentation of the electrical field in the modulated medium (Bragg grating) in the form of a single expression, contrary to the traditional counter-propagating waves approach. The spectral characteristics of linear Bragg gratings of different length are presented. The influence of loss or gain on the spectral characteristics of Bragg gratings is considered. The electrical field amplitude distributions along a grating at the wavelengths corresponding to the minima and maxima of reflectivity in the vicinity of the Bragg resonance are illustrated. Bistable and multistable dependences of reflectivity on the incident electrical field amplitude are obtained for negative and positive nonlinearities.