The Effect of Specular Reflectances on the Interaction of an Electromagnetic <Emphasis Type="Italic">E</Emphasis> Wave with a Thin Metal Film Placed between Two Dielectric Media

The interaction of an electromagnetic E wave with a thin metal film placed between two dielectric media is calculated in the case of different specular reflectances q₁ and q₂ for the reflection of electrons from the surface of the thin metal layer, in the case of variations in the values of dielectric permittivities ε₁ and ε₂ of the media, and in the case of different values of angle of incidence θ of the electromagnetic wave. The behavior of reflection coefficient R, transmission coefficient T, and absorption coefficient A in relation to the frequency of the external field is analyzed.     

On the theory of refractive radio-wave scattering

We consider in detail the frequency correlation of radio-wave fluctuations in one or several thick layers with strong large-scale inhomogeneities of turbulent origin. General expressions are obtained for the space-frequency fluctuation correlation of the radio-waves received. We analyze particular cases of radio wave scattering in turbulent media with inhomogeneities described by power-law spectra with indices p2 and p3. It is shown, in particular, that the coherence band of signals propagated in media with strong large-scale inhomogeneities is critically dependent on the spectral type of thOse inhomogeneities. The occurrence of an additional strongly scattering layer, which has radically different properties compared to the first layer, on the radio-wave path can increase or decrease considerably the frequency correlation of the radio waves received.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 10, pp. 1012–1022, October, 1995.     

Oscillating Dependence of the Acoustic Attenuation Coefficient in Thin Metal Layers

Dimensional and frequency dependences of the energy absorption coefficient of a longitudinal sound wave in a plane parallel metal layer are theoretically investigated for arbitrary relationship between the layer thickness d and the electron free path l. Exact and asymptotic (for thick (d >> l) and thin (d << l) metal layers) formulas are derived for the coefficient for an arbitrary angular dependence of the probability of specular reflection of charge carriers from the sample surface q(). A square-root dependence of the acoustic absorption coefficient on the thin film thickness is predicted. If the direction of sound wave propagation is perpendicular to the thin metal layer boundary, the acoustic absorption coefficient becomes an oscillating function of the layer thickness; its amplitude decreases with increasing kd, where k is the acoustic wave number.     

Photoluminescence of nanocrystalline silicon formed by rare-gas ion implantation

A new method is suggested for fabricating nanocrystalline silicon by using high-dose

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irradiation with rare-gas ions. In this case, a nanostructure is formed due to silicon self-assembling on the interface between amorphous layer and crystalline substrate. Two bands, at 720 and 930 nm, are found in the photoluminescence spectrum. These bands possibly originate from the quantum confinement effects in nanocrystals and may also be related to the regions of disordered silicon outside the amorphous layer containing nanocrystals. The intensity of the photoluminescence signal is studied as a function of duration of HF etching of samples and their subsequent exposure to atmosphere. The influence of thermal annealing on the photoluminescence spectrum is also studied.

     

Soft and hard wave excitation on an elastic covering in a turbulent boundary layer

We investigate the nonlinear stage of wave excitation on elastic coverings streamlined by a turbulent boundary layer of incompressible fluid. It has been shown that the traveling wave flutter instability leads to soft wave excitation, while the wave divergence instability defines hard wave excitation.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 3–4, pp. 211–216, March–April, 1995.     

Absorption of Long Waves by Nonresonant Parametric Microstructures

Using simple acoustical and mechanical models, we consider the conceptual possibility of designing an active absorbing (nonreflecting) coating in the form of a thin layer with small-scale stratification and fast time modulation of parameters. Algorithms for space-time modulation of the controlled-layer structure are studied in detail for a one-dimensional boundary-value problem. These algorithms do not require wave-field measurements, which eliminates the self-excitation problem that is characteristic of active systems. The majority of the considered algorithms of parametric control transform the low-frequency incident wave to high-frequency waves of the technological band for which the waveguiding medium inside the layer is assumed to be opaque (absorbing). The efficient use conditions are found for all the algorithms. It is shown that the absorbing layer can be as thin as desired with respect to minimum spatial scale of the incident wave and ensures efficient absorption in a wide frequency interval (starting from zero frequency) that is bounded from above only by a finite space-time resolution of the parameter-control operations. The structure of a three-dimensional parametric black coating whose efficiency is independent of the angle of incidence of an incoming wave is developed on the basis of the studied one-dimensional problems. The general solution of the problem of diffraction of incident waves from such a coating is obtained. This solution is analyzed in detail for the case of a disk-shaped element.     

Coherent and Squeezed States for Light in Homogeneous Conducting Linear Media by an Invariant Operator Method

With the choice of Coulomb gauge, we investigated coherent state and squeezed state of the light propagating through homogeneious conducting linear media with no charge density using quantum results of the LR invariant operator method. We described coherent and squeezed properties of electric and magnetic fields. The fields in coherent and squeezed states are decayed exponentially with time due to the conductivity of the media. We studied probability density of the coherent wave packet and the highly squeezed wave packets. The uncertainty relation between the two orthogonal phase amplitudes, â₁ and â₂, in coherent state is same as the uncertainty relation in vacuum number state. The envelope of the relative noise in coherent state alternately become large and small with time and position. The uncertainty relation between canonical variables are varied depending on the value of conductivity in squeezed state, but not lowered below /2 which is quantum-mechanically acceptable minimum uncertainty.     

On the Generalized πN Potential A New Representation from Fixed-t Dispersion Relations

Starting from a recent paper [13] we derive a new representation of the left-hand cut contribution for the πN system. This representation makes it possible to calculate the generalized πN potential accurately from phase shifts and high energy models, because it contains only the imaginary parts of the partial wave amplitudes in the physical region. The analytic properties, the region of convergence and the physical content of this representation is discussed. We propose to use this left-hand cut contribution in bootstrap calculations, because it is more reliable than the approximate expressions which have been used in previous papers. – The left-hand cut contributions are calculated and compared with the nucleon and Δ (1236) approximation for the ƒ, ƒ, ƒ and ƒ partial wave amplitudes.     

TM Nonlinear electromagnetic waves guided by an inhomogeneous medium

Analytical dispersion relations and the power flow expression for TM (polarized) nonlinear electromagnetic surface waves propagating along the interface of an inhomogeneous and dielectric nonlinear media have been investigated theoretically. An inhomogeneous dielectric cover has the dielectric permittivity=a+bz, which is contacted with a strongly nonlinear Kerr like layer. The existence conditions for these waves to be propagated are studied. These waves have no counterpart in the linear isotropic regime. The power flow versus the wave index, and the consequence interface nonlinearity might be evaluated for a variety of inhomogeneity parameters, which are found to be inhomogeneity dependent, and could lead to optical hysterisis and bistability.On leave from: Department of Electrical Engineering and Electronics, UMIST, P.O. Box 88, Manchester M60 1QD, U.K.     

Wave nonreciprocity in inhomogeneous gyrotropic media and multilayer systems: I. Inhomogeneous gyrotropic media

The propagation of electromagnetic waves in naturally (or structurally) gyrotropic inhomogeneous media is considered. A new mechanism of wave nonreciprocity is found, which is caused by the simultaneous presence of a gradient of one of the parameters of a medium and natural (or structural) gyrotropy. The problem of light transmission through a layer of a naturally gyrotropic inhomogeneous medium of finite thickness is solved by the method of addition of layers. Specific features of this nonreciprocity are considered. It is shown that such a system can operate as a one-sided reflector at certain angles of incidence of light. The mechanisms of enhancement of the nonreciprocity effects are investigated. It is shown that multiple reflections in a layer of finite thickness and diffraction of light by periodic inhomogeneities of a medium increase the nonreciprocity effects by several (from 2 to 5) orders of magnitude. This phenomenon, in turn, opens new fields of application of the nonreciprocity effects. Another interesting manifestation of wave nonreciprocity is revealed, which consists in asymmetry of the curve R(?):R(?)≠R(??) (R is the reflectance and ? is the angle of incidence).     

A compact automatic wavemeter for use with tunable infrared diode lasers

We have studied the magnetic-dipole and electric-quadrupole contributions to second-harmonic generation (SHG) of centro-symmetric media. It can be shown that the phenomenological parameters , , can be arranged to form an effective -tensor, which describes dipole-forbidden SHG as the effect of a surface layer upon excitation with a single plane electromagnetic wave. An experimental technique is proposed allowing a determination of the usually very small term due to magnetic-dipole interaction using coherent compensation of its contribution by a coverage with an appropriate dye monolayer.     

Six‐wave mixing induced by free‐carrier plasma in silicon nanowire waveguides

Nonlinear wave mixing in mesoscopic silicon structures is a fundamental nonlinear process with broad impact and applications. Silicon nanowire waveguides, in particular, have large third‐order Kerr nonlinearity, enabling salient and abundant four‐wave‐mixing dynamics and functionalities. Besides the Kerr effect, in silicon waveguides two‐photon absorption generates high free‐carrier densities, with corresponding fifth‐order nonlinearity in the forms of free‐carrier dispersion and free‐carrier absorption. However, whether these fifth‐order free‐carrier nonlinear effects can lead to six‐wave‐mixing dynamics still remains an open question until now. Here we report the demonstration of free‐carrier‐induced six‐wave mixing in silicon nanowires. Unique features, including inverse detuning dependence of six‐wave‐mixing efficiency and its higher sensitivity to pump power, are originally observed and verified by analytical prediction and numerical modeling. Additionally, asymmetric sideband generation is observed for different laser detunings, resulting from the phase‐sensitive interactions between free‐carrier six‐wave‐mixing and Kerr four‐wave‐mixing dynamics. These discoveries provide a new path for nonlinear multi‐wave interactions in nanoscale platforms.

     

Viscous Shock Wave and Boundary Layer Solution to an Inflow Problem for Compressible Viscous Gas

The inflow problem for a one-dimensional compressible viscous gas on the half line (0,+) is investigated. The asymptotic stability on both the viscous shock wave and a superposition of the viscous shock wave and the boundary layer solution is established under some smallness conditions. The proofs are given by an elementary energy method.     

The Rayleigh phonon dispersion on Cu(100): A stress induced frequency shift?

The dispersion of the Rayleigh wave on Cu(100) has been measured by high resolution electron energy loss spectroscopy (EELS) throughout the two-dimensional Brillouin zone in the . The experimental data can be matched with a nearest neighbour central force model when the force constant between the first and second layerk ₁₂ is stiffened by 20%. However, the data are likewise explained by assuming stress within the surface layer. The stress could arise from a tendency of the surface layer to contract.     

Evolution of surface plasmon–polariton wave in a thin metal film: The modulation‐instability effect

The modulation instability development of intensive surface plasmon–polariton waves in a thin metal film is studied. It is shown both analytically and numerically that the modulation‐instability effect can give rise to spatial redistribution and longitudinal localization of surface plasmon–polariton wave energy on the subwavelength scale. Analytical expressions for the driving parameters of the modulation instability process ? nonlinearity and dispersion ? are derived. The impact of the film thickness and dielectric permittivities of constituents on the dynamics of surface plasmon–polariton wave transformation is considered. Numerical simulations show that in the layer structure comprising a silver film of subwavelength thickness a train of subpicosecond optical pulses with high repetition rate can be generated.

     

Evolution of Annular Self-controlled Electron–Nucleus Collapse in Condensed Targets

We considered peculiarities of the evolution of a region with sharp boundaries that is filled with a partially ionized plasma and is a part of the volume of a condensed target. The creation of such a region in the near-surface layer of the target can be related to the action of an external impulse symmetric ionizator or to the action of an intense small-extension shock wave on the target surface. We defined the conditions such that their fulfilment during the establishment of the equilibrium between the Coulomb attraction of electrons and ions with atom ionization multiplicity Z^*₁ and the kinetic pressure of electrons causes both the compression of this region and its ionization to the state with Z^*₂ > Z^*₁. The last leads to a further additional compression and ionization. Under these conditions, the spontaneous avalanche-like ionization of atoms of the target to the state of bare nuclei occurs synchronously with the avalanche-like metallization and the self-compression of the target. We showed that the avalanche-like ionization and the self-compression of the target happen in the case where the gas of degenerate electrons has drift momentum. If the region with initial ionization has the form of thin spherical layer, the process of avalanche-like ionization and self-compression of the target in this region is accompanied by the accelerated movement of the plasma layer to the target center. One of the reasons for the accelerated movement is the surface tension in a bounded domain of the nonequilibrium plasma layer neutralized by ions of the target. With increase in the velocity of movement of this layer to the target center, the additional self-compression of the system of electrons and nuclei to the state of degenerate electron gas occurs. At the leading edge of the running layer with extremely high electron density which is neutralized by nuclei of the target, the formation of a collapse of the electron--nucleus system proceeds, and the binding energy maximum for the electron--nucleus system shifts from A60 to A 60. This result makes possible the fast synthesis of superheavy nuclei. The decay of the collapse state, a partial restoration of the target structure, its rapid cooling, and the condensation of a part of the products of nuclear reactions happen in the target volume at the trailing edge of the moving plasma layer. Upon such a scanning propagation of the wave with high electron density, all the target substance is involved, step-by-step, to the process of nuclear transformations. At the target center, the moving plasma layer is squeezed with the formation of the state of quasistationary collapse under inertial confinement. Then the collapse state decays irreversibly.     

Spin–orbit coupling and spin transport

Recent achievements in semiconductor spintronics are discussed. Special attention is paid to spin–orbit interaction, coupling of electron spins to external electric fields, and spin transport in media with spin–orbit coupling, including the mechanisms of spin-Hall effect. Importance of spin-transport parameters at spin-precession wave vector k_so is emphasized, and existence of an universal relation between spin currents and spin accumulation at the spatial scale of is conjectured.     

A Brinkman penalization method for compressible flows in complex geometries

To simulate flows around solid obstacles of complex geometries, various immersed boundary methods had been developed. Their main advantage is the efficient implementation for stationary or moving solid boundaries of arbitrary complexity on fixed non-body conformal Cartesian grids. The Brinkman penalization method was proposed for incompressible viscous flows by penalizing the momentum equations. Its main idea is to model solid obstacles as porous media with porosity, , and viscous permeability approaching zero. It has the pronounced advantages of mathematical proof of error bound, strong convergence, and ease of numerical implementation with the volume penalization technique. In this paper, it is extended to compressible flows. The straightforward extension of penalizing momentum and energy equations using Brinkman penalization with respective normalized viscous, η, and thermal, η_T, permeabilities produces unsatisfactory results, mostly due to nonphysical wave transmissions into obstacles, resulting in considerable energy and mass losses in reflected waves. The objective of this paper is to extend the Brinkman penalization technique to compressible flows based on a physically sound mathematical model for compressible flows through porous media. In addition to penalizing momentum and energy equations, the continuity equation for porous media is considered inside obstacles. In this model, the penalized porous region acts as a high impedance medium, resulting in negligible wave transmissions. The asymptotic analysis reveals that the proposed Brinkman penalization technique results in the amplitude and phase errors of order O((η)^1/2) and O((η/η_T)^1/43/4), when the boundary layer within the porous media is respectively resolved or unresolved. The proposed method is tested using 1- and 2-D benchmark problems. The results of direct numerical simulation are in excellent agreement with the analytical solutions. The numerical simulations verify the accuracy and convergence rates.     

Electromagnetic waves in thin-film superconducting lines

Conclusions The distinctive features discussed about the propagation of electromagnetic waves in a structure containing a thin-film superconducting line are associated with the fact that the screening properties of the superconducting layer are determined by the distribution of superconducting currents in it. In the quasistatic case under discussion this distribution depends on the nature of the nonuniformity of the magnetic field along the normal to the layer. At specified angles of incidence of a wave the layer is equivalent to an ideal conductor or a diamagnetic; in the intermediate region the screening effect is far smaller. Due to this a thin-film superconducting line possesses some directionality of the leakage of the nonuniform waves when ₁ > ₂. The wave which is emergent at a specified angle which depends on the parameters of the layered structure (₁, ₂,l, _L) possesses the maximum amplitude.When ₁ < ₂, the structure in question does not have a sharply pronounced directionality of the leakage, and at angles of incidence on a thin layer corresponding to total internal reflection it supports the propagation of waves along a line with as small a film thickness as desired. The unscreening effect of a superconducting layer is exhibited here in the fact that the propagation of waves excited in the line occurs at specified angles of incidence onto the layer mainly along its outer surface.Institute of Applied Physics, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Vol. 25, No. 5, pp. 527–535, May, 1982.