Transverse Magnetic Components Research Articles

Conjugate Ionosphere‐Magnetosphere Observations of a Sub‐Alfvénic Compressional Intermediate‐m Wave: A Case Study Using EKB Radar and Van Allen Probes

AbstractA Pc5 wave was simultaneously observed in the ionosphere by EKB radar and in the magnetosphere by both Van Allen Probe spacecraft within a substorm activity. The wave was located in the nightside, in 1.5‐ to 3‐hr magnetic local time sector, and in the region corresponding to the magnetic shells with maximal distances 4.6–7.8 Earth's radii. As it was found using both the radar and spacecraft data, the wave had frequency of about 1.8 mHz and azimuthal wave number m≈−10; that is, the wave was westward propagating. The EKB radar data revealed the equatorward wave propagating in the ionosphere, which corresponded to the earthward propagation in the magnetosphere. Furthermore, the field‐aligned magnetic component was approximately 2 times larger than both transverse components and accompanied by antiphase pressure oscillations; that is, the wave is compressional and diamagnetic. According to both radar and spacecraft measurements, among two transverse magnetic components, the dominant one was the poloidal. The wave was possibly driven by substorm‐injected energetic protons registered by the spacecraft: the proton fluxes were modulated with the wave frequency at energies of about 90 keV, which corresponded to the energy of the drift wave‐particle resonance. The wave frequency was much lower than the minimal frequency of the field line resonance calculated using the spacecraft data. We conclude that the wave is not the Alfvén mode, but some kind of compressional wave, for example, the drift‐compressional mode.

The Spiral Solenoids and the Leaf Antenna in Phyllotaxis Differential Geometry

In this paper new classes of spiral thin filamentary wire magnetic coils and antennas are introduced theoretically. This study shows that the thin wire circular loop coil as well as the cylindrical solenoid are particular cases of these classes. If the small spiral filamentary wire leaf loop coil is driven by an alternating electrical current, it will radiate as an antenna, whose theoretical analysis is provided throughout the paper. The fundamental spiral coil named leaf coil is obtained by joining together the so called forward and backward spiral coils which define the new concept of the Phyllotaxis differential geometry. The other spiral coils are composed of symmetrically rotated leaf coils, combined together in such a way to eliminate the transverse magnetic components along the longitudinal z axis. The magnetic moments and the multi-pole expansions of the various types of spiral loop coils are obtained by using the Taylor series of the spiral vector magnetic potentials. According to the formulas and simulations, the magnetic flux density created by the long spiral solenoids is uniform and dovetails with the one created by the long cylindrical solenoid. The bifolium coil may be flattened along one axis to meet the requirements of specific geometrical needs in space technology. Furthermore the crown solenoids may be cooled down to low temperatures by exploiting the holes in between their coils. Applications of the spiral induction coils are countless and can be found in space technology measurements, spacecraft magnetic shielding, telemetry, telecommunication, electron optics, physics and engineer.

Polarization Split Lensing via Polarization and Phase Control with Metasurfaces at Visible Frequencies

Under the trend of miniaturization and reduction of system complexity, conventional bulky photonic elements are expected to be replaced by new compact and multi-functional photonic elements. In this letter, we propose a birefringent dielectric metasurface (DM) that could provide both phase and polarization control at visible wavelength. Within this platform, we successfully realize a multi-functional polarization split metalens. Such a single metalens can perform the multiple functions of a polarizing resolve imaging system without additional optical elements. Polarization properties of light are resolved, an arbitrarily polarized incident beam is split into two orthogonally polarized beams, in which the transverse magnetic (TM) component and the transverse electric (TE) component are focused on the right and left side of the central axis, respectively. The metalens maintains diffraction-limited focal spots with high focusing efficiencies (above 80%). This multi-functional metalens may found potential applications in polarization-resolved imaging, spectroscopy, and on-chip optoelectronic devices.

High-harmonic x-ray undulator radiation for nanoscale-wavelength free-electron lasers

We explore the undulator radiation (UR) from relativistic electrons in two-frequency undulators intended for use in x-ray free-electron lasers (FELs). We use an exact analytical account for the major sources of spectral line broadening of the spontaneous UR to describe the UR spectrum, intensity and emission line shape. We also show possible partial compensation of the off-axis divergence by ad hoc imposed weak transverse constant magnetic components. The harmonic radiation of the two-frequency undulator is studied. High-harmonics amplification in the two-frequency undulator is underlined for possible use in x-ray FELs and the generation of powerful x-ray radiation is demonstrated. The evolution of high harmonic power is studied with the help of the developed phenomenological self-amplified spontaneous emission FEL model. The performance of a high-gain harmonic generation FEL with a two-frequency undulator–prebuncher is explored. Harmonic multiplication cascades are introduced in FELs to obtain nanometer x-ray FEL radiation in reduced size FELs at ~30 m with seed from commercially available excimer laser and ~0.5 GeV electrons.

Refractive index profilometry using the total internally reflected light field.

A full-field polarization-based technique is presented for quantitative evaluation of the spatial distribution of the refractive index in macro and micro samples. The sample is mounted on a glass-air interface of a prism, illuminated by a linearly polarized collimated light beam, and two intensity frames are digitally recorded with specific orientations of an analyzer. The pair of intensity data frames captured with this simple setup is combined through an algorithm specially developed for the purpose, to yield the phase difference between the transverse electric and transverse magnetic components of the total internally reflected light field. The phase difference is then related to the refractive index of the sample. Experimental results for refractive index variations in a laser-etched glass plate and red blood corpuscles are presented. One of the salient features of the proposed technique is that the depth of measurement is dependent on the penetration depth of the sample's evanescent field, which is typically of the order of a few hundred nanometers, thereby facilitating refractive index measurements along a thin section of the sample.

Dependence of the inverse opal magnetic form-factor on the degree of sintering: Micromagnetic study

Ni- and Co-based inverse opals can be considered as a three-dimensional network of nanoobjects connected with each other by elongated crosspieces (legs). Inverse opals magnetic properties strongly depend on the legs aspect ratio which can be tuned during fabrication process. We study this dependence by means of micromagnetic simulations. We have found the range of ice-rule validity and studied limiting cases of high and low legs aspect ratio. We also investigate the value of the transverse magnetization component which should appear if the external field is applied perpendicular to one of the legs. Legs aspect ratio which corresponds to the maximal value of this component has been found. Finally, we calculate the dependence of the magnetic form factor on the external field for considered models. These results can be directly compared with experiment.

Weakly diverging to tightly focused Gaussian beams: a single set of analytic expressions: continuation-symmetric beams.

The always diverging-converging laser beams, more rigorously referred to as Gaussian beams, are part of many physical and electro-optical systems. Obviously, a single set of analytic expressions describing these beams in a large span of divergence-convergence angles at the focal plane, and at any distance away from the focal plane, will prove very handy. We have recently published three such analytic sets, one set for linearly polarized beams and two sets for radially polarized beams. However, our published analytic set for linearly polarized beams describes nonsymmetric electric-magnetic field components. Specifically, the strong transverse magnetic field component does not become elliptic at very large divergence angles as it should be, and the other transverse magnetic component, indeed very weak, is missing altogether. Here we present an analytic set of expressions symmetrically describing linearly polarized Gaussian beams. The symmetry applies to the x-electric y-magnetic components and vice versa and to the two electric-magnetic z-components. An important property of the presented set of expressions is power conservation. That is, the electromagnetic power crossing a plane transverse to the propagation direction in a unit time is conserved. Power conservation assures beam description accuracy at any axial distance. The presented analytic expressions, although not strictly satisfying Maxwell's equations, describe Gaussian beams with very reasonable accuracy from low divergence angles up to divergence angles as large as 0.8 rad in a medium with refractive index of 1.5, i.e., up to a NA of 1.1. These expressions should then readily assist in the design of practically all laser-related systems and in the research of diverse physics and electro-optic fields.

What is the longitudinal magneto-optical Kerr effect?

We explore the commonly used classification scheme for the magneto-optical Kerr effect (MOKE), which essentially utilizes a dual definition based simultaneously on the Cartesian coordinate components of the magnetization vector with respect to the plane of incidence reference frame and specific elements of the reflection matrix, which describes light reflection from a ferromagnetic surface. We find that an unambiguous correspondence in between reflection matrix elements and magnetization components is valid only in special cases, while in more general cases, it leads to inconsistencies due to an intermixing of the presumed separate effects of longitudinal, transverse and polar MOKE. As an example, we investigate in this work both theoretically and experimentally a material that possesses anisotropic magneto-optical properties in accordance with its crystal symmetry. The derived equations, which specifically predict a so-far unknown polarization effect for the transverse magnetization component, are confirmed by detailed experiments on epitaxial hcp Co films. The results indicate that magneto-optical anisotropy causes significant deviations from the commonly employed MOKE data interpretation. Our work addresses the associated anomalies, provides a suitable analysis route for reliable MOKE magnetometry procedures, and proposes a revised MOKE terminology scheme.

Polarization characteristics of electroluminescence and net modal gain in highly stacked InAs/GaAs quantum-dot laser devices

We studied the polarization anisotropy of electroluminescence (EL) and net modal gain characteristics of laser device structures containing 40 stacked InAs/GaAs quantum dot (QD) layers. The electronic coupling between the closely stacked QDs enhanced the transverse-magnetic (TM) polarization component owing to the heavy- and light-hole mixing. Thereby, the [110]-waveguide devices exhibited a laser oscillation of not only the transverse-electric (TE) but also the TM component. Laser oscillation occurred at 1137 nm from the first excited state for the 300-μm-long cavity, while it occurred at 1167 nm from the ground state for the 1000-μm-long cavity. The polarization anisotropy of the EL intensity strongly depended on the injection current density. The polarized EL intensity was almost isotropic at low injection current density. As the injection current density was increased, the TE component was gradually enhanced, which resulted in a markedly TE-dominant anisotropy above the threshold current density for laser oscillation. The net modal gains evaluated using the Hakki-Paoli method also exhibited a TE-enhanced characteristic with increasing injection current density. As the EL spectra of the TE component have an inhomogeneous broadening narrower than that of the TM component, the TE-mode intensity is likely to be enhanced by the concentration of the injected carriers.

Magnetoplasmonic RF mixing and nonlinear frequency generation

We present the design of a magnetoplasmonic Mach-Zehnder interferometer (MZI) modulator facilitating radio-frequency (RF) mixing and nonlinear frequency generation. This is achieved by forming the MZI arms from long-range dielectric-loaded plasmonic waveguides containing bismuth-substituted yttrium iron garnet (Bi:YIG). The magnetization of the Bi:YIG can be driven in the nonlinear regime by RF magnetic fields produced around adjacent transmission lines. Correspondingly, the nonlinear temporal dynamics of the transverse magnetization component are mapped onto the nonreciprocal phase shift in the MZI arms, and onto the output optical intensity signal. We show that this tunable mechanism can generate harmonics, frequency splitting, and frequency down-conversion with a single RF excitation, as well as RF mixing when driven by two RF signals. This magnetoplasmonic component can reduce the number of electrical sources required to generate distinct optical modulation frequencies and is anticipated to satisfy important applications in integrated optics.

Resolution enhancement using plasmonic metamask for wafer-scale photolithography in the far field.

Resolution enhancement in far-field photolithography is demonstrated using a plasmonic metamask in the proximity regime, in which Fresnel diffraction is dominant. The transverse magnetic component of the diffracted wave from the photomask, which reduces the pattern visibility and lowers the resolution, was successfully controlled by coupling with the anti-symmetric mode of the excited surface plasmon. We obtained a consistently finely-patterned photoresist surface at a distance of up to 15 μm from the mask surface for 3-μm-pitch slits because of conserved field visibility when propagating from the near-field to the proximity regime. We confirmed that sharp edge patterning is indeed possible when using a wafer-scale photomask in the proximity photolithography regime. Our plasmonic metamask method produces cost savings for ultra-large-scale high-density display fabrication by maintaining longer photomask lifetimes and by allowing sufficient tolerance for the distance between the photomask and the photoresist.

Rado-Weertman Boundary Equation Revisited in Terms of the Free-Energy Density of a Thin Film

Historically, the first boundary conditions to be formulated and used in the theory of ferromagnetic thin films, the Rado–Weertman (RW) conditions, have a general advantage of being a simple differential equation, 2Aex ∂m ∂n − Ksurfm = 0. A key role in this equation is played by the phenomenological quantity Ksurf known as the surface anisotropy energy density; Aex denotes the exchange stiffness constant, and m is the amplitude of the transverse component of dynamic magnetization. In the present paper we use a microscopic theory to demonstrate that the surface anisotropy energy density of a thin film is directly related with its free-energy density, a fact not observed in the literature to date. Using two local free-energy densities F surf and F , defined separately on the surface and in the bulk, respectively, we prove that Ksurf = d ( F surf − F bulk ) , where d is the lattice constant. The above equation allows to determine the explicit configuration dependence of the surface anisotropy constant Ksurf on the direction cosines of the magnetization vector for any system with a known formula for the free energy. On the basis of this general formula the physical boundary conditions to be fulfilled for a fundamental uniform mode and surface modes to occur in a thin film are formulated as simple relations between the surface and bulk free-energy densities that apply under conditions of occurrence of specific modes.

Triple quantum filtered spectroscopy of homonuclear three spin-1/2 systems employing isotropic mixing

We report the design and performance evaluation of novel pulse sequences for triple quantum filtered spectroscopy in homonuclear three spin-1/2 systems, employing isotropic mixing (IM) to excite triple quantum coherence (TQC). Our approach involves the generation of combination single quantum coherences (cSQC) from antisymmetric longitudinal or transverse magnetization components employing isotropic mixing (IM). cSQC’s are then converted to TQC by a selective 180° pulse on one of the spins. As IM ideally causes magnetization to evolve under the influence of the spin coupling Hamiltonian alone, TQC is generated at a faster rate compared to sequences involving free precession. This is expected to be significant when the spins have large relaxation rates. Our approach is demonstrated experimentally by TQC filtered 1D spectroscopy on a 1H AX2 system (propargyl bromide in the presence of a paramagnetic additive), as well as a 31P linear AMX system (ATP in agar gel). The performance of the IM-based sequences for TQC excitation are compared against the standard three pulse sequence (Ernst et al., 1987) and an AX2 spin pattern recognition sequence (Levitt and Ernst, 1983). The latter reaches the unitary bound on TQC preparation efficiency starting from thermal equilibrium in AX2 systems, not considering relaxation. It is shown that in systems where spins relax rapidly, the new IM-based sequences indeed perform significantly better than the above two known TQC excitation sequences, the sensitivity enhancement being especially pronounced in the case of the proton system investigated. An overview of the differences in relaxation behavior is presented for the different approaches. Applications are envisaged to Overhauser DNP experiments and to in vivo NMR.

Excitation of hypersound by multiplication of the ferromagnetic resonance frequency in a magnetostriction transducer

With reference to the problem of increasing the frequency of hypersound excited by a magnetostriction transducer, the feasibility of multiplication of the frequency by multiplication of the eigenfrequency of the elastic resonator is considered. It is shown that efficient multiplication is possible only in odd harmonics of the excitation signal. For interpretation of the phenomenon observed, a model of nonlinear excitation due to multiplication of the values of the longitudinal and transverse magnetization components is proposed.

ATTENUATION OF CORONAL MAGNETIC FIELDS IN SOLAR MICROWAVE BURSTS

Based on the observed data by the Nobeyama Radio Observatory and the nonthermal gyrosynchrotron theory, the calculated magnetic field in a loop-like radio source of the 2001 October 23 flare attenuates from hundreds to tens of Gauss,. except in the region with very weak magnetic fields. Meanwhile, the viewing angle between the magnetic field and line of sight has a similar attenuation from tens to around ten degrees, implying that the transverse magnetic component attenuates much faster than the longitudinal one. All of these results can be understood by the magnetic energy release process in solar flares. Moreover, the column density of nonthermal electrons decreases from 109-10 to 107-8 cm(-2) during the flare, except in the region with very weak magnetic fields, where its value is larger than that with strong magnetic fields due to the mirroring effect. The calculated error and harmonic number of gyrofrequency better suit the region with strong magnetic fields.

Investigation of Corrosion Inhibitors by Nuclear Quadrupole Resonance Relaxometry Method

The changes taking place with the corrosion-resistant coating, but not the state of the surface subjected to corrosion are investigated in this paper in contrast to traditional approaches. The authors used the method of nitrogen relaxometry NQR and multi-exponential inversion of decay of longitudinal and transverse components of the nuclear magnetization is applied for the first time for this purpose. The results of experimental studies of changes in the distributions of spin-spin and spin-lattice relaxation of crystallite powder of sodium nitrite and urotropin, the mixture of which is used as a corrosion inhibitor of ferrous metals are considered.

Identification of the propagation mode of a solar wind wave associated with Pc5 pulsations in the magnetosphere

Abstract. A case study of a magnetohydrodynamic (MHD) wave in the solar wind that is strongly correlated with a magnetospheric field line resonance observed by the SuperDARN (Super Dual Auroral Radar Network) radar at Sanae, Antarctica is presented. The data from the ACE (Advanced Composition Explorer) satellite at the solar libration point are analysed. The data time series are bandpass filtered at the pulsation frequency and the analytic signal deduced. From these data the partition of energy between the field components is computed. It is shown that energy is equally partitioned between the kinetic energy and transverse magnetic potential energy densities. The energy flux vector is closely aligned with the background magnetic field. The transverse magnetic and velocity components are in antiphase. This is the first identification of the triggering wave as a transverse Alfvén wave which originates upstream from the space craft and is propagated to the magnetosphere to trigger the pulsation.

Polarization-insensitive optical gain characteristics of highly stacked InAs/GaAs quantum dots

The polarized optical gain characteristics of highly stacked InAs/GaAs quantum dots (QDs) with a thin spacer layer fabricated on an n+-GaAs (001) substrate were studied in the sub-threshold gain region. Using a 4.0-nm-thick spacer layer, we realized an electronically coupled QD superlattice structure along the stacking direction, which enabled the enhancement of the optical gain of the [001] transverse-magnetic (TM) polarization component. We systematically studied the polarized electroluminescence properties of laser devices containing 30 and 40 stacked InAs/GaAs QDs. The net modal gain was analyzed using the Hakki-Paoli method. Owing to the in-plane shape anisotropy of QDs, the polarization sensitivity of the gain depends on the waveguide direction. The gain showing polarization isotropy between the TM and transverse-electric polarization components is high for the [110] waveguide structure, which occurs for higher amounts of stacked QDs. Conversely, the isotropy of the [−110] waveguide is easily achieved even if the stacking is relatively low, although the gain is small.

Longitudinal structure of ballooning MHD disturbances in a model magnetosphere

Large-scale toroidal Pc5 pulsations are commonly treated as Alfven oscillations of a magnetic field line. According to observations, their longitudinal structure is described well by theory. At the same time, the longitudinal structure of azimuthal small-scale poloidal Pc5 pulsations is virtually unknown. These pulsations are associated with ballooning disturbances described by a system of coupled equations for Alfvenic and slow magnetosonic (SMS) modes. In this work, the Voigt model is used to describe the equilibrium finite-pressure plasma configuration in an inhomogeneous magnetosphere plasma in a curved magnetic field. Spectral characteristics and the spatial structure of natural ballooning modes are calculated for this model. The model calculations demonstrate the possibility of different longitudinal scales for transverse and longitudinal magnetic components of oscillations near the top of the field line.

Micromagnetic Simulation on Ground State Domain Structures of Barium Hexaferrite (BaFe<sub>12</sub>O<sub>19</sub>)

We have systematically investigated the domain structures of Barium Hexaferrite (BaFe12O19) by means of a micromagnetic simulation under zero external magnetic field. A hexagonal-shaped and cylindrical-shaped models are used in this simulation with respect to the diameter variation from 50 nm to 600 nm. A transition domain structure is found from a single-domain (SD) to multi-domain (MD) at a certain diameter. The hexagonal-shaped occurs in diameter 430 nm and cylindrical-shaped in diameter 410 nm. Interestingly, the domain wall of MD structure exhibits a Bloch-wall type. The domain wall width is determined by full width half maximum (FWHM) method from the transverse magnetization component data. The domain wall width from simulation showed close to Kittel’s formula