Incident Plane Research Articles

Helicity-dependent photocurrent of topological surface states in the intrinsic magnetic topological insulator MnBi2Te4

Helicity-dependent photocurrent (HDPC) of the topological surface states (TSSs) in the intrinsic magnetic topological insulator MnBi2Te4 is investigated. It is revealed that the HDPC is mainly contributed by the circular photogalvanic effect (CPGE) current when the incident plane is perpendicular to the connection of the two electrodes, while the circular photon drag effect plays the dominant role when the incident plane is parallel to the connection of the two electrodes. The CPGE current shows an odd function dependence on incident angles, which is consistent with the C3v symmetry group of the TSSs in MnBi2Te4. The amplitude of the CPGE current increases with the decrease in temperature, which can be attributed to the increase in mobility at low temperatures, confirmed by the transport measurements. Furthermore, we modulate the CPGE of MnBi2Te4 by applying top gate and source–drain voltages. Compared to Bi2Te3 of the same thickness, the CPGE current of MnBi2Te4 can be more effectively tuned by the top gate because the Fermi level of MnBi2Te4 can be effectively regulated by the top gate, and it is tuned across the Dirac point. This work suggests that the intrinsic magnetic topological insulator MnBi2Te4 is a good candidate for designing opto-spintronics devices.

Analysis of EM Properties of High-speed Moving Cone-sphere Target Coated with Plasma Sheath based on Lorentz-FDTD Method

The study of the interaction between moving plasma-coated objects and electromagnetic (EM) waves is the essential factor for the EM problems of high-speed targets. In this paper, the physical model of a moving dispersive medium is developed based on the principle of special relativity to study the EM properties of high-speed moving targets coated with plasma sheath. First, the Lorentz transform is used to introduce the incident plane wave into moving frame. Second, based on the proposed EM model, the EM problems are solved in moving frame by the shift-operator (SO) FDTD numerical algorithm. Finally, the EM results are further converted back into the laboratory frame to analyze the scattered properties of high-speed plasma coated objects. The validity of the proposed algorithm is verified by comparison with the reference solution. On this basis, the influence of relativistic effects produced by the motion of the object and the EM properties of the plasma on the scattering fields of high-speed targets are investigated. This work expands the applicability of the FDTD method and provides a theoretical foundation for solving the scattering properties of high-speed plasma-coated complex shape objects through numerical methods.

Magnetothermally-controllable coating for scattering and absorption in the terahertz spectral regime

Plane-wave scattering and absorption characteristics of a spherical core composed of an isotropic material, and covered by InSb spherical coating are investigated in the terahertz spectral regime. The InSb coating is subjected to a magnetostatic field; hence it is a gyrotropic, uniaxial dielectric material comprised of two parameters: temperature and magnetostatic field. It is seen that the interplay of these two parameters can modify the various scattering efficiencies, depending on (i) the frequency of the incident plane wave, (ii) the incident plane-wave orientation with respect to the magnetostatic field's direction, and (iii) the identity of the core material. In particular, for a fixed orientation of the incident plane wave, the impact of the temperature and the magnetostatic field on the total scattering and the backscattering efficiencies becomes more pronounced at higher frequencies, compared to lower frequencies. The absorption efficiency, on the other hand, is strongly dependent upon these two parameters, regardless of the frequency. On fixing the two parameters of InSb, the role of the orientation of the incident plane wave with respect of the magnetostatic field' direction emerges in some spectral regimes for the total scattering and absorption efficiencies, and in high-frequency spectral regimes for the backscattering efficiency. These hold true for dielectric core, as well as for conductive core.

Non-metallic magnetostatically tunable metasurface absorber for terahertz waves

A non-metallic metasurface absorber containing VO2, InSb, and Teflon has been designed, simulated, and investigated for normally incident plane waves in the terahertz spectral regime. When the temperature exceeds 72°C, a backing layer of VO2 in its rutile phase instead of a conventional metal virtually eliminates transmission. Peak absorptance as high as 0.998, quality factor on the order of 200, and magnetostatic tunability of about 16GHz\, T−1 are achievable. Such metasurfaces can be made using standard microfabrication techniques.

Experimental characterization of a fully polarimetric pulsed terahertz spectroscopy system

A terahertz time domain pulsed spectroscopy system is modified to provide fully polarimetric radiation and analysis. The operation of this polarimetry system is characterized using a birefringent, x-cut quartz crystal. The modification is based on rotating the photoconductive antennas such that both the emitted and detected polarizations are out of the plane of incidence. Subsequently, broadband wire grid polarizers are used to select the incident and detected direction of linear polarization to be either parallel with (vertical) or perpendicular to (horizontal) the plane of incidence with the sample surface. The experiments are conducted in both transmission and reflection. Depending on the frequency, the phase retardation of the incoming electric field components along the two perpendicular optical axes of the quartz crystal changes differently. This results in the polarization of the light exiting the crystal changing with frequency. As a result, multiple frequencies are identified where the crystal behaves as a near ideal quarter-, half-, or full-wave retarder. Additionally, due to the time-domain nature of the experiment, transmitted and reflected electric fields are measured after multiple consecutive reflections within the crystal. This leads to a further, complex control over the final polarization state of the signal. Finally, images of a resolution standard are obtained demonstrating the characteristics of the polarimetry system.

Geometric attenuation function analysis based on V-grooved surfaces.

In this study, we present a simulation addressing the phenomena of shadowing and masking in TE and TM polarized incident plane waves interacting with V-grooved rough surfaces. Blinn's theory on light attenuation posits that such a rough surface is represented by a symmetric, elongated V-shaped groove cavity, considering only the tilt angles of the slopes. Our numerical analysis considers variables such as polarization (TE or TM), wavelength, tilt, and slant of the incident or viewing direction, as well as the material properties of the rough surfaces, to accurately calculate light attenuation on V-grooved rough surfaces. The findings indicate enhanced precision in the measurement of light attenuation on these complex geometries.

Improving the longitudinal spot width of an optimizingly designed point-like scatterer-arrayed transcranial ultrasonic lens

As a non-invasive therapy to promote the effect of the thrombolytic agent in the acute phase of cerebral infarction, transcranial irradiation by ultrasonic waves at the site of the occlusion has been validated and is expected to achieve clinical application. Such irradiation may, however, cause damage to the brain by interference of reflected waves within the skull. In order to avoid such a phenomenon, we proposed a transcranial acoustic lens formed by optimizing the arrangement of point-like scatterers. The optimum arrangement of scatterers was determined so that the sound field vanishes within the skull except at the focus(es) and becomes higher at the focus(es) than in the surrounding regions. The ultrasonic waves are strongly scattered by air bubbles in the water-like medium, so we attempted to install a crossbar switch in the medium covering the head and constructed an acoustic lens by producing an instantaneously adaptive air bubble array. This lens can focus an incident plane wave to the diffraction limit in the direction perpendicular to the incident direction, while the peak width in the propagation direction is more than five times higher. In this work, in order to practically improve it, we propose to arrange a point-like scatterer so as to partially cover the head and further increase the number of layers. The shape of the skull is modeled based on CT data, and more realistic parameters are employed than in a previous paper [T. Ueta, J. Appl. Phys. 132, 144504 (2022)].

On the area-averaged effective sound absorption coefficient of porous materials excited by a monopole

The area-averaged effective sound absorption coefficient (SAC) of a rigid-backed homogeneous porous material subjected to a monopole excitation is calculated as the absorbed-to-incident sound power ratio. Using Allard's model to describe the sound propagation above the porous material, an analytical model for this power-based SAC is proposed and proves to give a good approximation of the sound absorption performance under monopole excitation of sufficiently large areas of material. The impact of factors on the power-based SAC, such as monopole height, material radial dimension used to calculate the sound powers, and material properties is discussed. The power-based SAC frequency-dependent behavior is analyzed through sound intensity field assessments at the material surface and is compared to normal incident plane wave and diffuse field SACs. The sound absorption behavior of sound absorbers under monopole excitation exhibits notable distinctions and peculiar results compared to those observed under plane wave and diffuse fields, particularly at low frequencies and for sources close to the material.

Hybridization of electromagnetic multipoles in a nanoscatterer in the presence of another nanoscatterer

Coupling between multipolar modes of different orders has not been investigated in depth, despite its fundamental and practical relevance in the context of optical metamaterials and metasurfaces. Here, we use an electromagnetic multipole expansion of both the scattered fields and the oscillating electric currents to reveal the multipolar excitations in a nanoparticle positioned close to another nanoparticle. The considered single-particle multipoles radically differ from multipoles excited in a pair of nanoparticles. Using the expansion, we reveal the multipole character of the electric currents and the contributions of the multipole moments to the scattering cross section of each particle, including the effect of their interaction. We find that light scattered by the particles plays the role of an inhomogeneous incident field for each of the particles, leading to hybridization of the originally independent orthogonal multipole resonances. For an incident plane wave polarized along the nanoparticle pair, the hybridization of the dipole and quadrupole resonances gives rise to a significant narrowband resonance in the spectrum of the dipole scattering, which can be of interest for various applications, e.g. in surface-enhanced fluorescence and Raman spectroscopy. In general, this work shows that the multipole-multipole interaction between nanoparticles must be treated by taking into account also such hybridized multipole resonances.

Transmission-mode geometric-phase signatures of circular Bragg phenomenon

A dielectric structurally chiral medium (DSCM) exhibits the circular Bragg phenomenon, whereby circular-polarization-state selective reflection occurs in a specific spectral regime that depends on the direction of propagation of the incident plane wave. Theoretical analysis shows that the geometric-phase spectrum of the plane wave transmitted through a DSCM slab contains a signature of the circular Bragg phenomenon, provided that the incident plane wave is not right-circularly polarized, regardless of the structural handedness of the DSCM. As the number of structural periods in the DSCM slab increases with the structural period fixed, the spectrum of the transmission-mode geometric phase evolves but without an easily discernible pattern. A reversal of structural handedness affects but does not lead to a simple change in the transmission-mode geometric phase.

Optical diffraction properties of three superimposed self-organized nanostructures induced by a laser process.

Controlling the diffraction properties of materials over a large area holds great promise for a wide range of optical applications. Laser-based techniques have emerged as a viable solution to address this need. Here, we present the diffraction properties of laser-induced self-organized structures, which consist of three interlaced grating-like structures: self-organized nanoparticles, self-organized cracks, and laser marking lines. Under normal incidence external illumination, the sample exhibits an asymmetric diffraction pattern. However, when the incidence angle is tilted, circular diffraction patterns are observed in the plane perpendicular to both the sample and the incidence plane. These phenomena are attributed to the combination effect of the diffraction gratings. To elucidate the underlying physics of multiple diffraction, we use rigorous coupled-wave analysis (RCWA) and grating equations written in direction cosine space, extended to account for the presence of three superimposed gratings. Exploiting the laser-induced diffraction properties of these samples may have great potential for various industrial implementations, including security, display, and design.

Dynamically tunable photonic spin Hall effect based on insulating-metallic phase transition of Vanadium Dioxide

The photonic spin Hall effect (PSHE) can manifest as the spin-dependent splitting (perpendicular to the plane of incidence) of a light beam, i.e., transverse beam shift. Introducing dynamically tunable PSHE into post-fabricated systems has great potential for the new type of photonic devices and its tuning range can be manipulated with different reconfigurable methods. Most of these methods are based on modifying the refractive index of bulk or interface materials. However, the perturbation on the refractive index is usually small, leading to difficulty in enhancing PSHE. Fortunately, the changes in the refractive index of Vanadium Dioxide (VO2) with insulating-metallic phase transition can be larger in several orders than that of other materials, making it possible for enhancing PSHE to have greater tuning range. Here, to explore the dynamically tunable PSHE based on the insulating-metallic phase transition of VO2, the transverse beam shift (as an indicator of PSHE) was calculated with a full wave theory at a wavelength of 1550 nm in a layered structure. Without a gold layer, only the PSHE of the H-polarized beam shows significant tunability in the insulating-metallic phase transition of VO2. With the Au layer, the PSHE of the H- and V-polarized beam is enhanced around the Brewster and Brewster-like (originating from the destructive interference between the nanosized layers) angle, respectively. For H- and V-polarized beams, the tuning range of PSHE is mainly determined by the insulating phase of VO2 and can be enhanced with the Au layer. Finally, as an example, the enhanced tuning range makes the output of a two-digit binary code conversion based on PSHE easier to recognize. These results offer us possible ways to control the tuning range of PSHE in post-fabricated systems and provide more potential for new applications.

Absolute doubly differential angular sputtering yields for 20 keV Kr+ on polycrystalline Cu

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness.

Electrically tunable dual polarization states of light using lithium niobate-based nanograting.

Tuning polarization states of light electrically has unique advantages in the integration of optoelectronic devices. Here, a lithium niobate-based nanograting is proposed to dynamically tune the polarization state of both the reflected and transmitted lights simultaneously in the near-infrared range. By judiciously designing the nanograting, a quasi-bound state in the continuum (qBIC) is excited under the excitation of an obliquely incident plane wave. The excited mode with a high quality-factor and enhanced local electric field can respond to a refractive index change in nanograting structures as small as 10-4 level, which can be generated with a low external voltage via the electro-optic effect. As a result, both the polarization states of reflected and transmitted lights can be dynamically tuned from a right circular polarization to a linear polarization state. The proposed lithium niobate-based nanograting for tuning dual polarization states of light with a qBIC mode suggests a promising electrical scheme for achieving high speed optoelectronic devices.

Optimized Excitation in Microwave-induced Thermoacoustic Imaging for Artifact Suppression.

Microwave-induced thermoacoustic imaging (M-TAI) allows the visualization of macroscopic and microscopic structures of bio-tissues. However, it suffers from severe inherent artifacts that might misguide the subsequent diagnostics and treatments of diseases. To overcome this limitation, we propose an optimized excitation strategy. In detail, the strategy integrates dynamically compound specific absorption rate (SAR) and co-planar configuration of polarization state, incident wave vector and imaging plane. Starting from the theoretical analysis, we interpret the underlying mechanism supporting the superiority of the optimized excitation strategy to achieve an effect equivalent to homogenizing the deposited electromagnetic energy in bio-tissues. The following numerical simulations demonstrate that the strategy enables better preservation of the conductivity weighting of samples while increasing Pearson correlation coefficient. Furthermore, the in vitro and in vivo M-TAI experiments validate the effectiveness and robustness of this optimized excitation strategy in artifact suppression, allowing the simultaneous identification of both boundary and inside fine structures within bio-tissues. All the results suggest that the optimized excitation strategy can be expanded to diverse scenarios, inspiring more suitable strategies that remarkably suppress the inherent artifacts in M-TAI.

Uniqueness in inverse scattering problems with phaseless near-field data generated by superpositions of two incident plane waves at a fixed frequency

Uniqueness in inverse scattering problems with phaseless near-field data generated by superpositions of two incident plane waves at a fixed frequency

Design of Perfectly Conducting Objects That Are Invisible to an Incident Plane Wave

Design of Perfectly Conducting Objects That Are Invisible to an Incident Plane Wave

DUAL-BAND BANDSTOP FILTERS BASED ON ULTRA THIN FREQUENCY SELECTIVE SURFACES

In this paper, we present designs for terahertz filters with two independent stopbands based on periodic metallic resonant structures patterned on the dielectric substrate. Two simple and thin structures are proposed to realize required characteristics for single-polarized and dual polarized filter designs. To realize single polarized one, a unit cell of the proposed periodic structure consists of two sets rectangular shape conducting metal patches patterned on the top of the dielectric substrate, and the dual-band response is due the lattice resonances observed in the unit cell. To realize dual polarized filter design, a modified unit cell is considered with additional patches on the bottom of the dielectric substrate. The patches on the bottom layer are the same ones as on the top layer but orthogonally oriented. For this case, polarization-independent frequency response can be obtained after geometric optimization of the unit cell because the top and the bottom layers resonantly interact with only the TE or TM incident plane wave to minimize cross coupling effects between the layers. In order to intensively understand the transmission performance of the proposed filters, a large number of simulations using integral equation method are performed based on the different values for permittivity, period of the unit cell, dielectric thickness, and geometric dimensions. The electric field distributions are analyzed to understand the mechanism of the resonance behavior.

Некоторые детали строения северной центриклинали Косью-Уньинской синклинали (р. Илыч, Северный Урал)

The latest most detailed geological map of the Upper Pechora transverse subsidence, compiled by V. V. Yudin, shows an undisturbed western wing passing into the centricline of the Kosyu-Un’ya syncline, composed of Middle Ordovician and Silurian deposits falling to the southeast in the area of the middle course of the Ilych River (from the mouth of the Shezhimyu River to Anna-Di Island). Detailed studies of the sections uncovered in this area, as well as analysis of the literary and field materials of the predecessors, allowed updating ideas about the stratigraphic confinement of some strata and the structure of the area as in general. According to our data, deposits from the Middle Ordovician to the Ludlov unit of the Silurian are revealed within the northern centricline of the Kos’yu-Un’ya syncline, which are divided into three block scales (Shezhimdisk, Mikolael and Ust’Bol’shekosyu), bounded by faults with a plane of incidence inclined to the east-southeast at angles of 30–40°. Tectonic confinement of the complexly dislocated Lower Devonian sediments of the Valgan formation observed at the northern centricline of the fold to the east of the mouth of the Kos’yu River and previously referred to the eastern wing of the Kos’yu-Un’ya syncline, is currently being discussed. According to their lithological composition, they belong to the Shantym facies complex and are probably already part of another tectonic structure — the Valgan «monocline» of the eastern subzone of the Upper Pechora transverse subsidence.

Memory dependent triple-phase-lag thermo-elasticity in thermo-diffusive medium

The objective of the paper is to look at the propagation and reflection of plane waves in a thermo-diffusion isotropic medium. The reflection of plane waves in a thermo-diffusion medium was investigated in this study with reference to triple phase lag thermo-elasticity. The memory dependent derivative (MDD) is applied for this investigation. The fundamental equations are framed and solved for a particular plane. The four plane waves that are propagating across the medium are, shown namely: longitudinal displacement, P-wave, thermal diffusion T-wave, mass diffusion MD-wave and shear vertical SV-wave. These four plane wave velocities are listed for a specific medium, illustrating the impact of the diffusion coefficient and are graphically represented. Expressions for the reflection coefficient for the incidence plane wave are produced from research on the reflection of plane waves from the stress-free surface. It should be noted that these ratios are graphically represented and shown when diffusion and memory dependent derivative (MDD) factors are in play. The new model is relevant to many different fields, including semiconductors, earth- engineering, and electronics, among others, where thermo-diffusion elasticity is significant. Diffusion is a technique that can be applied to the production of integrated circuits, MOS transistors, doped polysilicon gates for the base and emitter in transistors, as well as for efficient oil extraction from oil reserves. Wave propagation in a thermos-diffusion elastic media provides crucial information about the presence of fresh and enhanced waves in a variety of technical and geophysical contexts. For experimental seismologists, developers of new materials, and researchers, this model might be useful in revising earthquake estimates.