Excitation Of Electromagnetic Waves Research Articles

Surface electromagnetic waves at a superfluid liquid—normal metal interface

Surface electromagnetic waves, which can propagate along the plane interface between a superfluid liquid and a normal metal, are investigated. The dispersion relations for surface waves with different polarizations of the optical anisotropy of the superfluid liquid are obtained and their possible frequency ranges are determined. It is shown that anisotropic optical contribution to the dielectric constant of the superfluid liquid can be determined from experiments on excitation of surface electromagnetic waves.

A possible origin of dayside Pc1 magnetic pulsations observed at high latitudes

Abstract. Induction magnetometer observations of dayside Pc1 activity at Barentsburg (BAB, Spitsbergen archipelago, 78.05°N, 14.12°E) are combined with data from two magnetometers located in Scandinavia and the Kola peninsula. Seven events with very large negative IMF Bz components were considered. For all of the events, the cusp location was expected to be significantly shifted equatorward from the statistical position such that the BAB magnetometer was located well inside the polar cap. The DMSP particle data indicated that the BAB magnetometer was indeed inside the polar cap, whereas other magnetometers were collocated with the ionospheric projections of the cusp, the low-latitude boundary layer or the boundary plasma sheet. Pc1 magnetic pulsations were observed only at BAB. In three cases, for which SuperDARN convection data were available, the Pc1 activity correlated with intervals of large-scale convection reconfiguration, such that the plasma flow crossing the BAB location was associated with newly-reconnected magnetic flux tubes drifting tailward. The convection reconfigurations were in response to a decrease in the IMF By component. We argue that the source of the observed Pc1 pulsations is anisotropic plasma of the depletion layer within the magnetosheath. The plasma anisotropy supports the excitation of electromagnetic ion cyclotron waves that are detectable with a ground-based magnetometer when the flux tubes containing the unstable plasma become connected to the Earth's ionosphere in the course of the dayside reconnection processes.

Transitions from electrostatic to electromagnetic whistler wave excitation

At frequencies below the electron cyclotron and above the lower hybrid frequency in a magnetoplasma, the refractive index is anisotropic and shows resonances at certain angles caused by electron inertia. For a radiating antenna in a plasma, the short wavelengths near this resonance angle may contribute to the radiation pattern of the antenna. A series of experiments is reported, in which waves were excited using a small 1-cm-diam electrostatically coupled antenna into a preformed plasma, densities (ne) from 1015 to 1018 m−3 and magnetic fields from 30 to 60 G. Maps of the wave amplitude and phase were made within the plasma by scanning the position of a b-dot probe. At low densities (e.g., ne<5×1016 m−3 at 50 G and 3 mTorr), a single amplitude maximum along the group velocity resonance cone angle was measured that decayed as the distance from the antenna increased. The observed radiation pattern in all cases was consistent with that of a point source in an unbounded plasma, and no global eigenmode resonances were found. As the density was increased, the apparent attenuation of the resonance cone waves increased and they appeared to withdraw into the antenna. At high densities (ne>5×1016 m−3) the radiation pattern was characterized by a monotonic increase in wave phase in the axial direction, a central maximum for Bz, and off-axis maxima for Bx and By which are consistent with the propagation of m=0 helicon waves, and no evidence of resonance cone structure. This change in the radiation pattern is reproduced numerically in a homogeneous plasma model including an electrostatically coupled antenna with the same geometry as that used in the experiment.

Surface-topography-induced enhanced transmission and directivity of microwave radiation through a subwavelength circular metal aperture

Strongly enhanced transmission of microwave radiation (λ0∼5 mm) is observed through a single subwavelength circular aperture of diameter d=2.5 mm in a metallic plate. The phenomenon is caused by resonant excitation of electromagnetic surface waves supported by four concentric grooves surrounding the aperture on the illuminated side of the sample. It is also shown that similar surface patterning on the output face of the sample results in very strong angular confinement (directivity) of the transmitted beam. A finite element code is used to investigate the electromagnetic fields on both the illuminated and the exit side of the structure, the predictions from which show excellent agreement with the experimental results.

Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs Heterostructures

We report the detection of novel zero-resistance states induced by electromagnetic wave excitation in ultra high mobility GaAs/AlGaAs heterostructure devices, at low magnetic fields, B, in the large filling factor limit. Vanishing resistance is observed in the vicinity of B=[4/(4 j+1)] B f , where B f=2πfm ∗/e , where m ∗ is the effective mass, e is the charge, and f is the microwave frequency. The dependence of the effect is reported as a function of f, the temperature, and the power.

Noncollinear excitation of surface electromagnetic waves: Enhancement of nonlinear optical surface response

We excite several independent surface electromagnetic waves on a metallic surface by use of femtosecond laser pulses of different frequencies. Due to nonlinear plasmon interaction, optical radiations at frequencies $2\ensuremath{\omega},$ ${\ensuremath{\omega}}_{1}+{\ensuremath{\omega}}_{2},$ and $2{\ensuremath{\omega}}_{2}\ensuremath{-}{\ensuremath{\omega}}_{1}$ are generated (where ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2}$ correspond laser beam frequencies). In the present paper we report experimental results and theoretical modeling of these multiphoton nonlinear optical effects from a metallic film sputtered onto a grating surface. The theoretical approach we use describes the multiphoton nonlinear optical effects in the presence of noncollinear interacting surface electromagnetic waves. In the experiments a sufficient enhancement of the nonlinear optical signals is achieved in the case where the incidence plane of light is parallel to the grating grooves.

Excitation of Electromagnetic Waves in a Plane Waveguide with Anisotropic Upper Wall

We solve the problem of propagation of electromagnetic ULF waves in a plane waveguide with anisotropic upper wall from an arbitrary source with allowance for an arbitrary inclination of the magnetic field. The procedure for calculating magnetic components of the signal radiated by horizontal and vertical dipoles is developed in detail. The solution is presented in the form of the Fourier–Bessel transform of the desired field components. Impedance-type boundary conditions were used for an arbitrary inclination of the magnetic field. The obtained solutions can be used for interpreting experiments on measuring the spectra of ULF electromagnetic noise in various geographical regions and calculating parameters of ULF signals from controlled sources.

Excitation of nonreciprocal electromagnetic surface waves in semibounded magnetized plasmas by an electron beam

The dispersion relation of nonreciprocal electromagnetic surface waves propagating on the magnetized plasma–vacuum interface is obtained. Furthermore, the dependency of penetration depth on the magnetic field strength and its directivity is investigated. Finally, it will be shown that by an electron beam flowing on the plasma surface, aforementioned waves can be excited.

Interaction of Electromagnetic and in Conductors and its Utilization

The paper deals with the interaction of electromagnetic and acoustic processes in a conducting medium in presence of an external magnetic field. The electromagnetic excitation of acoustic wave similarly as acoustic excitation of electromagnetic wave is described. The practical utilization consisting in contactless acoustic wave generation and detection is demonstrated.

Overheated plasma at the surface of a target with a periodic structure induced by femtosecond laser radiation

A periodic structure is induced at the surface of a metal target exposed to a series of p-polarized 200-femtosecond laser pulses with intensity close to the melting threshold of the target material. The period of the structure is determined by the interference between the incident pump wave and the surface electromagnetic wave. Exposure of the obtained structure to the same laser pulse, but with an intensity of ∼1016 W/cm2, provides resonant excitation of the surface electromagnetic waves at the plasma-vacuum interface. This leads to an increase in the X-ray output and the temperature of plasma hot electrons.

A parametric study of the influence of ion and electron properties on the excitation of electromagnetic ion cyclotron waves in coronal mass ejections

Interplanetary coronal mass ejections (ICMEs) often possess a negative proton thermal anisotropy, Ap = T⟂,p/T∥,p − 1 < 0 (T∥, T⟂: parallel and perpendicular temperatures, respectively) so that right‐hand polarized electromagnetic ion cyclotron waves (EICWs) may be amplified by a kinetic instability [Farrugia et al., 1998a]. However, in view of the low proton beta of ICMEs, several physical parameters, besides Ap, need to be in the right range to excite this instability with significant growth rates. In this paper we present a parametric study of EICWs aimed at identifying those parameters which are most influential in fostering the emission of these waves in ICME scenarios. We analyze here the influence of: (1) thermal and suprathermal protons, (2) thermal alpha particles (αs), and (3) thermal electrons. We solve the dispersion relation of EICWs including protons, αs and electrons, all modeled with bi‐Maxwellian distribution functions, and a minority population of suprathermal protons using a kappa function for the velocity component along the field. For physical regimes of ICMEs we find that the instability depends critically on the values of the following parameters: proton beta, proton thermal anisotropy, relative abundance of the suprathermal protons, α‐to‐proton relative abundance, α‐to‐proton temperature ratio, α particle thermal anisotropy, electron‐to‐proton temperature ratio, and thermal anisotropy of electrons. The effect of these parameters on the instability is either direct (when they increase the number of resonant particles) or indirect (when they decrease the phase speed of the wave so that more particles can resonate). Data surveys on EICWs should take into account the whole set of parameters indicated here, since the expected level of wave excitation results from their combined action. The study may be useful in understanding the considerable level of magnetic fluctuations observed in interplanetary CMEs by the Wind spacecraft.

Zero‐Resistance States Induced by Electromagnetic‐Wave Excitation in GaAs/AlGaAs Heterostructures.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A large area multifilamentary plasma source

This paper discusses a large area multifilamentary plasma source used in the large volume plasma device. This source, based on directly heated filaments, is simple in design and produces quiescent (δn/n≈1%) plasmas of high density (⩽1018 m−3), low temperature (∼1–2 eV), over a large area (≈1.1 m2) and a large volume (≈1.6 m3). With the investment of ≈40 kW (1350 A, 30 V) power, the filaments are heated to ≈2000 K to yield emission current density ∼1 A cm−2 at the filament surface. Experiments demonstrate that this source is suitable for carrying out electromagnetic wave excitation studies in the electron magnetohydrodynamics regime. There are certain inherent difficulties associated with direct heating which sets a maximum limit to the filament length and with the requirement of field tailoring. As far as the present study is concerned, these difficulties are acceptable in comparison with the distinct advantages the source possesses, in terms of its low cost and technical features, making it user-friendly.

Waves in the plasma depletion layer derived from three magnetosheath passes made by WIND

We analyze theoretically wave activity in the plasma depletion layer (PDL) based on measurements made by the WIND spacecraft on 3 passes of the magnetosheath at low, southern magnetic latitudes and within 1 hour of noon. The passes occurred on November 30, December 12, and December 24, 1994. They were under moderate-to-low solar wind dynamic pressure, allowing a characterization of the near-subsolar PDL under typical solar wind conditions. Magnetic fluctuations transverse to the background field characteristic of electromagnetic ion cyclotron waves are present in all 3 PDLs and we illustrate this by the December 24, 1994 pass. We estimate numerically the electromagnetic ion cyclotron wave excitation, using measured parameters and supplementing these by average values for those other parameters which were not available. The activity increases as the magnetopause is approached, except for November 30. The interplay of the proton thermal anisotropy and the proton beta parallel to the magnetic field, quantities which are anticorrelated, may be used to explain the major similarities and differences of the theoretical results for the respective passes. These are the only 3 passes near the subsolar region for moderate-to-low dynamic pressure which have been examined to date, and the only ones made in this locale by Wind.

Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs heterostructures.

The observation of vanishing electrical resistance in condensed matter has led to the discovery of new phenomena such as, for example, superconductivity, where a zero-resistance state can be detected in a metal below a transition temperature T(c) (ref. 1). More recently, quantum Hall effects were discovered from investigations of zero-resistance states at low temperatures and high magnetic fields in two-dimensional electron systems (2DESs). In quantum Hall systems and superconductors, zero-resistance states often coincide with the appearance of a gap in the energy spectrum. Here we report the observation of zero-resistance states and energy gaps in a surprising setting: ultrahigh-mobility GaAs/AlGaAs heterostructures that contain a 2DES exhibit vanishing diagonal resistance without Hall resistance quantization at low temperatures and low magnetic fields when the specimen is subjected to electromagnetic wave excitation. Zero-resistance-states occur about magnetic fields B = 4/5 Bf and B = 4/9 Bf, where Bf = 2pifm*/e,m* is the electron mass, e is the electron charge, and f is the electromagnetic-wave frequency. Activated transport measurements on the resistance minima also indicate an energy gap at the Fermi level. The results suggest an unexpected radiation-induced, electronic-state-transition in the GaAs/AlGaAs 2DES.

Time-resolved nonlinear surface plasmon optics

A new surface-sensitive method of time-resolved optical studies is proposed. The method consists in the independent excitation of several surface electromagnetic waves (SEW) by two laser femtosecond pulse beams with varied time delay Δτ and distance Δr between corresponding excitation regions on the surface. To fulfill the phase-matching condition for plasmon-photon coupling, metal grating is used. Due to nonlinear plasmon interaction, the optical radiation with ω1 + ω2 and 2ω1 − ω2 (where ω1, ω2 are corresponding laser beam frequencies) is generated. The intensity of this nonlinear response versus Δτ and Δr are studied. The direct measurements of the SEW temporal properties are presented. Experiments of this type are important for the development of femtosecond surface plasmon optics.

FIELD STRUCTURE IN THE CROSS SECTION OF A FERRITE INHOMOGENEOUS ANISOTROPIC INSERT OF A RECTANGULAR WAVEGUIDE

We develop a physico-mathematical model describing excitation and distribution of electromagnetic waves in an anisotropic waveguide or resonator in the three-dimensional case. We develop a theoretical approach for discretization of the Maxwell equations in an arbitrary medium in the presence of bounding walls of a waveguide or resonator. The resulting system of linear algebraic equations for the electric-field components in an inhomogeneous anisotropic medium is solved by the method of biconjugate gradient. The results of calculating the electric field lines in the cross section of an anisotropic insert of a rectangular waveguide are presented.

Excitation and Reception of Electromagnetic, Magnetostatic and Spin Waves in Ferrite Films

The paper presents a new universal formulation of electromagnetic fields in microwave ferrite-dielectric waveguiding structures from the given magnetic field distribution of an external source. The solution is derived from the linearized Landau-Lifshits equation using an orthogonality condition for eigenwaves of a magnetization. The magnetization excited in ferrite is obtained in an electrodynamic, magnetostatic or dipole-exchange approximation, depending on the approximation used for eigenwaves. Results are applied for the formulation and the analytical solution of self-consistent electrodynamic problems of an excitation and a reception of waves in ferrite films by transmission lines of an arbitrary type. Numerical calculations are performed for filters and delay lines on the base of symmetric strip-lines using surface and forward volume magnetostatic waves in ferrite films.

Resonance excitation of polaritons by bulk electromagnetic waves in the layered systems with anisotropic substrates

The possible resonance excitation of surface electromagnetic waves by the bulk waves at the interface between a positive transparent uniaxial crystal and an isotropic medium has been predicted. The existence of the surface waves is provided by anisotropy of one of the boundary media. The tensor relation between the vector amplitudes of an exciting bulk electromagnetic wave and the excited surface wave is established. The ratio of the moduli of the tangential components of these amplitudes is analyzed as a function of the angle of incidence and the polarization of the bulk wave. The numerical calculations are performed for the surface waves at the interface between paratellurite TeO2 and a KRS-6 (TlBr 30%-TlCl 70%) crystal.

Polarization spectroscopy of a conducting surface

A method of polarization spectroscopy for a conducting surface characterized by a high sensitivity to the state of the surface and its transition layer is proposed. The method uses excitation of surface electromagnetic waves (SEWs) by a linearly polarized probe beam incident on the surface under study and compensation for the phase shift between the p and s components arising upon the SEW excitation. The applicability and competitiveness of the method in both the visible and the IR range is established. The method is tested on an LEF-3M ellipsometer in the visible range by studying the oxidation process in an evaporated copper film.