In this paper we propose the semiconductor sandwich heterostructure for the improving of the properties of domain generation. Within the numerical study of the collective dynamics of charge we demonstrate the possibility of a simultaneous increase in the frequency and power of the current oscillations, caused by the travelling domains, due to the synchronization of the domain dynamics in the different parts of the considered semiconductor sample.
Show AbstractThe optical Tamm states localized at both edges of a one–dimensional photonic crystal encloused by a nanocomposite are investigated. The nanocomposite consists of spherical nanoparticles with a dielectric core and a metal shell, which are dispersed in a transparent matrix. It is shown that the position of the spectral peaks is sensitive to the thickness of the outermost layer of the photonic crystal.
Show AbstractTheoretically studied propagation of a weak light pulse in electromagnetically induced grating (EIG) in the presence of an additional control field in four-level atoms of N-type. It is shown that one can effectively control the reflection and transmission of EIG. All–optical switching of the reflected and transmitted pulse is demonstrated.
Show AbstractThe example of a mechanical system which behaves like a double negative medium within a certain frequency band is suggested. The analytical expressions for the frequency dependence of its effective density and compressibility are derived. The results of numerical simulations in the two–dimensional case of an impulse propagating through the layer made of the considered medium are presented. The presence of negative refraction is shown while the causality principle is satisfied.
Show AbstractThe expression for the longitudinal part of the dielectric function non-degenerate electron gas in bilayer grapheme is obtained. In the calculations used low–energy approximation for the electron spectrum. The dispersion relation and the damping rate of the plasma waves in bilayer graphene is found.
Show AbstractWe propose a method of optical activity measurement based on the detection of the eigen polarization variations associated with the changes of optical activity of the analyzed medium.
Show AbstractProperties of surface plasmon–polaritons excited in two and three-layered structures containing topological insulators with axion effect were investigated. The plasmon polarization rotation was revealed and the conditions for the polarization effects enhancement were found.
Show AbstractIn this paper, we consider theoretically some examples of nonlinear photonics devices based on the coherent interaction of light with matter. The examples of these devices are lasers that generate extremely short single–cycle optical pulses based on so–called self–induced transparency coherent passive mode-locking (or coherent mode–locking), ultrafast laser beam deflector, and unipolar pulse generator. Such devices have several advantages compared to standard devices that operate in the regime when the interaction of light with matter is incoherent.
Show AbstractThe possibility of the diode laser far field radiation diagram quantitative analysis without carrying out time–consuming and expensive measurements of the intensity distribution in the near zone is shown.
Show AbstractThe radiation pattern and the degree of light polarization for high–power laser diodes in up–threshold mode have been measured. Time dependence of the radiations power and a degree of polarization have been investigated. The possibility of 2 W CW laser diode based on InGaAs/GaAs–heterostructures lifetime predicting by preliminary measurements of space-energy and polarization characteristics of radiation discusses.
Show AbstractThe method of determining the generation regime of the diode laser based the far field measurements at a fundamental mode considered. The implementation of the method for measurements of divergence angle in the two dimensional far field using the coordinates of the Gaussian function characteristic points discussed.
Show AbstractBehavioral features of two-dimensional few cycle optical pulses propagating in array of carbon nanotubes in the presence of external constant magnetic field, applied perpendicular to the axis of nanotubes, are analyzed and presented.
Show AbstractIn this paper the three dimensional theoretical model of holographic diffraction structures formation in photopolymer-liquid crystalline compositions is developed. The model takes into account the material optical properties anisotropy, amplitude and phase inhomogeneity of structure and nonlinearity of recording process. On the base of numerical simulations the complicated spatiotemporal dependence of amplitude profiles of higher spatial harmonics of refraction index is shown.
Show AbstractFormation of one-dimensional planar waveguides and couples of such waveguides within a bulk of undoped lithium niobate has been experimentally demonstarated. Waveguide structures with a channel size of 22 μm have been formed by the bright spatial solitons obtained at the compensation of the diffraction divergence of light beams in the crystal due to the contribution of the pyroelectric effect into the nonlinear response. The light wavelength was 532 nm and the optical power was ranged from 0.5mW to 1mW in experiments. The total compensation of the diffraction divergence at uniform heating of the crystal sample to the temperature from 75 ◦C.
Show AbstractThe optical induction of waveguide and diffraction elements in lithium niobate samples with surface doping by photorefractive impurities is experimentally investigated in the research. The spatial distribution of refractive index inhomogeneities in the exposed areas of crystal wafer surface has been visualized using the light diffraction method. Channel waveguide elements are formed by point-by-point exposure of sample’s surface method. And the one-dimensional diffraction gratings are created by the sample surface exposure with laser radiation through the amplitude mask.
Show AbstractThe system of the equations describing dynamics of parameters of the super-Gaussian pulse propagating in isotropic dielectric as in the field of normal, and abnormal dispersion of group speed is received.
Show AbstractThe second optical harmonic generation in quadratic nonlinear crystal structure is theoretically investigated. The structure consists of regularly modulated inhomogeneous layers that are divided by homogeneous layers of random thickness. The dependence of the process efficiency on the layer number and dispersion of the layer thickness is determined.
Show AbstractIt is considered a method optimizing parameters of MRI scanning pulse sequence of gradient echo type, based on calculating a spin system response in different variants of its selective excitation.
Show AbstractAn acousto–optic spectral imaging device is designed to obtain stereoscopic images on arbitrary wavelengths within the visible range. Spectrometer is based on the simultaneous spectral filtration of two light beams carrying the image of the object from two different angles. The layout of spectrometer is manufactured. Examples of stereo images are presented.
Show AbstractBy exciting different parts of $^{19}$F–NMR–spectrum of Perftoranum $^{R}$ and experimentally the spectral range, which gives the maximum NMR–signal, was determined. It was shown that the preferable scanning method is pulse sequence RARE.
Show AbstractProblem of automated EEG signal analysis and extraction of normal and proepilptic activity was studied. Method based on wavelet analysis and empirical mode decomposition was proposed. Analysis of experimental EEG signals was performed, proposed method allows to detect and distinguish basic types of patterns.
Show AbstractMagnetic resonance imaging and local NMR spectroscopy with adjusting on Larmor frequencies of nuclei different from protons namely deuterium, fluorine, carbon, phosphorus, sodium, chlorine are considered.
Show AbstractMethods using data of surface waves are very effective for study of structure of the upper strata of the Earth, which is the most non-uniform. There are a number of such methods, originally developed for use on land, among which we should highlight microseismic sounding method (MSM) and ambient noise tomography (ANT). Unlike other methods of depth sounding MSM and ANT are easier to practical implementation, cheaper and could be performed with minimal restrictions on the environmental side of the experiment, because they don’t have harmful effects on the environment. However, these techniques were used mainly on land before. In this paper, a comparison of these two approaches based on experimental data from a network of bottom seismic stations located in the area of the Hawaiian Islands. The results of microseismic sounding derived according to the bottom stations, as well as a comparative analysis of those results with tomographic estimates of parameters of the medium obtained in the present work for the first time. These results indicate that the methods of Earth sounding based on an analysis of the characteristics of surface waves can lead to satisfactory results, not only when they are used on land, but even in marine conditions.
Show AbstractThe kinetics of peroxodisulfate anions electroreduction on the mechanically updated silver electrode was investigated by the impedance method. It is established, that impedance diagrams of the negative charged area on the metal surface could be successfully replaced by equivalent circuit which consists from the solution resistance and reaction resistance in parallel connection with constant phase shift element replacing the capacity of double electrical layer. The experimental data analysis, carried out within the framework of represented equivalent circuit, let us conclude, that kinetics of anions S$_2$O$_8^{2−}$ reduction reaction on the researched electrode is adequately described in terms of the phenomenological theory of slow discharge.
Show AbstractWe measured fluorescence trails of the thin films of CdSe quantum dots grown in a liquid crystal matrix of cadmium octanoate at high temperature. Blinking nature of the luminescence suggests that there are single quantum emitters on the surface of the film.
Show AbstractEssential difficulties arising in organization of anisotropic regulated illumination for an investigated object in correlation thermoacoustic tomography schemes with a ring antenna array are discussed. However, the illumination of such a type is really created in schemes with focusing structural elements. Output signal-to-interference relation is estimated for the focusing schemes.
Show AbstractAlgorithm of estimating the geometrical and phase corrections for receiving–transmitting transducers of ring antenna array of ultrasound tomograph is discussed. These corrections should be taken into account during reconstruction of spatial distributions of sound velocity and absorption of an investigated object, in order to avoid a deterioration of tomogram quality.
Show AbstractOptical coefficients of copper and gold films with thicknesses 0.5 to 10 nm are studied at the frequency of 10GHz. The vector network analyzer R&S ZVA 24 and waveguide resonator are used in measuring circuit. It is shown that the experimental results for transmission coefficient of the copper films correspond to the calculated values when equivalent thickness reduced on the 6 nm is introduced. The measured value of conductivity of the copper film is almost an order of magnitude less than the bulk conductivity of copper.
Show AbstractAn experimental prototype of the near-field microscope based on the coaxial microwave resonator and a vector network analyzer R&S ZVA 24 is described. The results of test measurements of the shift of the resonance frequency and the quality factor of the resonance curve with the use of bulk conductors made of metals of different conductivity are presented. It is shown qualitatively that the resonant frequency and the quality factor decreases as the probe approaches the surface of the conductor. Q–value is minimal when using a conductor with the lowest conductivity.
Show AbstractThe influence of various factors on the characteristics of generation of multibeam vircator (the distance between the beams, beams mismatch currents) is investigated numerically. Maps of regimes on the main planes of the control parameters of multipath vircator are created. The effect of synchronization of the virtual cathodes in the model of a relativistic multibeam vircator is revealed.
Show AbstractWave propagation in a drifting low-voltage electron beam has been studied. The causes of such a flow instabilities and features of its interaction with the electromagnetic wave have been discussed. The effect of beam cross–sectional velocity variation on the starting conditions BWO has been considered.
Show AbstractIn the study a model of a rectenna array is analyzed. Possibilities of applying rectenna arrays for converting solar power into electric energy are discussed. Potential options for manufacturing such structures and carrying out experiments are laid down.
Show AbstractMethods of computer simulation were used for investigating of the electron beam dynamics in the multi-wave Cherenkov generator. The possibility of the formation of a flow of charged particles moving toward the cathode part of device was demonstrated. Basic characteristics of backward moving electron flow were studied.
Show AbstractThe study of influence of external harmonic signal on generation in low-voltage vircator with magnetron-injection gun as source of electron beam in squeezed state are carried out. The classical phenomenon of synchronization in the distributed electron-wave system are observed. The possibility of vircator output signal power increasing with the frequency of external signal changing are shown.
Show AbstractIn the present work we have studied the novel nonlinear phenomenon of plasma physics — beam–plasma instability in a charged plasma in the absence of ions. We have shown the possibility of the instability development and analyzed the characteristics of physical processes taking place during the beam-plasma interaction.
Show AbstractThe paper deals with the effect of the degeneration of asymmetric hybrid waves in a circular periodic waveguide near the frequency of $\pi$–type the symmetric mode E$_{01}$. This effect greatly intensifies on competition modes in the Cherenkov electronic devices on overmoded waveguides.
Show AbstractUse of OFDM signals with central frequency sweep in radars offers some advantages over conventional radiolocation systems based on chirp signals or short impulses, including increased time-domain resolution and dynamic range. The implementation of such system is described in the article. The results of measurements demonstrating obtained range resolution of 10 cm are presented.
Show AbstractThe application of piezo quartz resonators (PQR) in liquid media has found a strong dependence of changes in their oscillation frequency from liquid media permittivity. The present work shows theoretical calculation of edge effect for circular plane capacitor and experimental research of influence of resonator’s geometrical parameters and permittivity of liquid media on frequency shift of PQR. The effect of sensor’s capacity with different geometrical parameters of capacitor and various permittivity coefficients of liquid media was experimentally determined.
Show AbstractThe theory of orotron of common design, which utilizes two interacting electron beams, is presented here. The cases of a field of constant amplitude and a Gaussian distribution of the field in the resonator are analyzed.
Show AbstractIn this paper is considering dynamics of electron beam in coaxial drift space in external inhomogeneous magnetic field. Numerical simulation, which was conducting, show possibility forming of virtual cathode with help of compression relativistic beam by external magnetic field.
Show AbstractA new principle of the electron beam grouping with cyclotron rotation in inhomogeneous magnetic fields is proposed. It is shown that the electron 3D grouping may not be accompanied by an increase in space charge density in contrast to the electron bunching during the one-dimensional motion of the electrons.
Show AbstractThe results of numerical simulation of the interaction between the relativistic electron beam focused by uniform magnetic field and the field of generator with axisymmetric periodic waveguide are reported. The theoretic and numerical analysis of resonance effect of focusing magnetic field were carried out. The range of resonance amplification and cyclotron absorption were revealed and studied.
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