Polarization Direction Research Articles

Three-dimensional carbon fiber networks with self-orienting nano-textures enabled by femtosecond laser processing

Here, an interconnected three-dimensional (3D) network of carbon fibers possessing nano-scaled ripples, or laser-induced periodic surface structures (LIPSS), is fabricated via laser processing with an 800-nm femtosecond laser. The unique architecture of the CF network realizes the coexistence of both ∼800-nm low-spatial frequency LIPSS (LSFL) and ∼100-nm high-spatial frequency LIPSS (HSFL) overlapping on the same fiber surface. It is suggested that LSFL formed through the interference with Fresnel diffraction patterns projected by the fiber edges, while HSFL formed through LSFL-splitting assisted by surface plasmons. Moreover, the fundamentally different formation mechanisms of the two types result in distinctively different LIPSS orientations, where the LSFL is structure-dependent and self-orients according to the fiber propagation direction, while the HSFL is structure-independent and self-orients perpendicularly to the polarization direction of the incident pulses. The findings not only introduce an optical approach to prepare nano-textured carbon materials for future energy and regenerative-medicine applications but also reveal important insights into the underlying formation mechanisms of LIPSS on complex three-dimensional surfaces.

AGN feedback in isolated galaxies with a SMUGGLE multiphase ISM

Abstract Feedback from active galactic nuclei (AGN) can strongly impact the host galaxies by driving high-velocity winds that impart substantial energy and momentum to the interstellar medium (ISM). In this work, we study the impact of these winds in isolated galaxies using high-resolution hydrodynamics simulations. Our simulations use the explicit ISM and stellar evolution model called Stars and MUltiphase Gas in GaLaxiEs (SMUGGLE). Additionally, using a super-Lagrangian refinement scheme, we resolve AGN feedback coupling to the ISM at ∼10-100 pc scales. We find that AGN feedback efficiently regulates the growth of SMBHs. However, its effect on star formation and outflows depends strongly on the relative strengths of AGN vs local stellar feedback and the geometrical structure of the gas disk. When the energy injected by AGN is subdominant to that of stellar feedback, there are no significant changes in the star formation rates or mass outflow rates of the host galaxy. Conversely, when the energy budget is dominated by the AGN, we see a significant decline in the star formation rates accompanied by an increase in outflows. Galaxies with thin gas disks like the Milky Way allow feedback to escape easily into the polar directions without doing much work on the ISM. In contrast, galaxies with thick and diffuse gas disks confine the initial expansion of the feedback bubble within the disk, resulting in more work done on the ISM. Phase space analysis indicates that outflows primarily comprise hot and diffuse gas, with a lack of cold and dense gas.

Low-power electrodeless 2.45 GHz microwave plasma generation in ambient air with dielectric resonators

Abstract Microwave (MW) plasma, as an electrodeless non-thermal plasma technique, holds significant potential for gas processing applications under near-ambient conditions. However, current MW plasma methods suffer from low energy efficiency due to the high power required for molecular breakdown via vibrational excitation. A promising approach to mitigate this challenge involves using a pair of high relative permittivity dielectric resonators (DRs) in close proximity to enhance the electric field within the small gap between them, thus reducing power consumption. In this study, we combined simulations and experiments to investigate the electric field enhancement effect of DRs with varying shapes, geometrical parameters (e.g., radius and height), gap distances, and orientations relative to the electric field polarization and MW propagation directions. Simulations performed using Ansys HFSS demonstrate that edge-to-edge configurations of hexagonal, square, and triangular prism DRs can achieve significant electric field enhancement over a broad range of geometric parameters. DRs fabricated from calcium titanate were tested experimentally using a simple setup with a kitchen microwave (2.45 GHz) at ambient pressure. With input power below 100 W, stable and highly confined plasma was generated using hexagonal and triangular prism DRs. These results suggest a simple, cost-effective, and low-power method for generating MW plasma under ambient conditions, offering particular advantages for chemical processing in rural areas utilizing renewable energy resources.

Polarimetric Compressed Sensing with Hollow, Self-Assembled Diffractive Films.

Sensing light's polarization and wavefront direction enables surface curvature assessment, material identification, shadow differentiation, and improved image quality in turbid environments. Traditional polarization cameras utilize multiple sensor measurements per pixel and polarization-filtering optics, which result in reduced image resolution. We propose a nanophotonic pipeline that enables compressive sensing and reduces the sampling requirements with a low-refractive-index, self-assembled optical encoder. These nanostructures scatter light into lattice modes, which encode the wavefront direction and the polarization ellipticity in the linearly polarized components of the diffracted, interference patterns. Combining optical encoders with a neural network, the system predicts pointing and polarization when the interference patterns are adequately sampled. A comparison of "ordered" and "random" optical encoders shows that the latter both blurs the interference patterns and achieves higher resolution. Our work centers on the unexpected modulation and spatial multiplexing of incident light polarization by self-assembled hollow nanocavity arrays as a class of materials distinct from traditional metasurfaces that will not only enable encoding for polarization and optical computing but also for compressed sensing and imaging.

Engineering Nonvolatile Polarization in 2D α-In2Se3/α-Ga2Se3 Ferroelectric Junctions

The advent of two-dimensional (2D) ferroelectrics offers a new paradigm for device miniaturization and multifunctionality. Recently, 2D α-In2Se3 and related III–VI compound ferroelectrics manifest room-temperature ferroelectricity and exhibit reversible spontaneous polarization even at the monolayer limit. Here, we employ first-principles calculations to investigate group-III selenide van der Waals (vdW) heterojunctions built up by 2D α-In2Se3 and α-Ga2Se3 ferroelectric (FE) semiconductors, including structural stability, electrostatic potential, interfacial charge transfer, and electronic band structures. When the FE polarization directions of α-In2Se3 and α-Ga2Se3 are parallel, both the α-In2Se3/α-Ga2Se3 P↑↑ (UU) and α-In2Se3/α-Ga2Se3 P↓↓ (NN) configurations possess strong built-in electric fields and hence induce electron–hole separation, resulting in carrier depletion at the α-In2Se3/α-Ga2Se3 heterointerfaces. Conversely, when they are antiparallel, the α-In2Se3/α-Ga2Se3 P↓↑ (NU) and α-In2Se3/α-Ga2Se3 P↑↓ (UN) configurations demonstrate the switchable electron and hole accumulation at the 2D ferroelectric interfaces, respectively. The nonvolatile characteristic of ferroelectric polarization presents an innovative approach to achieving tunable n-type and p-type conductive channels for ferroelectric field-effect transistors (FeFETs). In addition, in-plane biaxial strain modulation has successfully modulated the band alignments of the α-In2Se3/α-Ga2Se3 ferroelectric heterostructures, inducing a type III–II–III transition in UU and NN, and a type I–II–I transition in UN and NU, respectively. Our findings highlight the great potential of 2D group-III selenides and ferroelectric vdW heterostructures to harness nonvolatile spontaneous polarization for next-generation electronics, nonvolatile optoelectronic memories, sensors, and neuromorphic computing.

Self-Powered Filterless Narrowband UV Photodetection Triggered by Asymmetric Charge Carrier Generation in a Wide-Bandgap Halide Perovskite Ferroelectric.

Narrowband photodetection with selective light detection in ultraviolet (UV) range is particularly pronounced in specialized such as targeted wavelength imaging and UV-phototherapy. In contrast to conventional strategies, ferroelectric materials with pronounced bulk photovoltaic effect (BPVE) provide a novel asymmetric carrier generation concept for achieving filterless spectrally selective photodetection. Herein, for the first time, the realization of self-powered filterless narrowband UV photodetection is demonstrated in bulk single crystals of a newly developed halide perovskite ferroelectric, 2FEA2EA2Pb2Cl10 (2FEEPC), which exhibits a wide bandgap of 3.36eV and a remarkable spontaneous polarization (≈3.5 µCcm-2). Benefiting from the strongly distorted inorganic framework with asymmetric delocalized electronic states, 2FEEPC demonstrates a highly wavelength-dependent BPVE along the polar direction, showing a high narrowband detecting performance with a response peak at UV wavelength of 355nm and a full-width-at-half-maximum (FWHM) of ≈15nm. More interestingly, the ferro-pyro-phototronic effect of 2FEEPC endows a colossal gain of up to 600% for photopyroelectric current. This work presents an unprecedented approach to achieve self-powered filterless narrowband photodetection, thereby shedding light on the development of photosensitive ferroelectrics for spectrally photoelectric applications.

Angle and Polarization Insensitive RCS Reduction Metasurface Based on Hybrid Mechanism of Polarization Conversion and Absorption

AbstractThis article introduces the concept, theory, and design of an angle and polarization insensitive radar cross section (RCS) reduction metasurface, using a hybrid mechanism of polarization conversion and absorption. By introducing ladder‐ and rectangle‐shaped metallic patches in the vertical dimension of a 3‐D structure, polarization conversion rate (PCR) deterioration, brought by the increase of equivalent substrate thickness at oblique incidences, can be suppressed. Furthermore, lumped resistors are loaded at proper places in each polarization conversion cell, to achieve the power absorption while maintain the angular insensitivity of the PCR. With the above hybrid mechanism, a stable 10‐dB RCS reduction can be achieved regardless of the angle of incidence in a wide range and polarization directions. An equivalent circuit model is established for explaining the physical mechanism of the proposed metasurface. For validation, a prototype is fabricated and tested. Measurement results indicate that, for both monostatic RCS at the normal incidence and specular RCS of off‐normal incidences from 0° to 45°, a 10‐dB TE‐ and TM‐mode RCS reduction can be achieved in the entire X‐band (8–12 GHz) and Ku‐band (12–18 GHz).

Solving electrostatic and electroelastic problems with the node's residual descent method

Piezoelectric materials are extensively used in engineering for the fabrication of sensors, transducers, and actuators. Due to the coupling characteristics, anisotropy, and arbitrariness of polarization directions, the tasks of mesh generation, numerical integration, and global equation formulation involved in numerical computations are complex and nontrivial. To solve electrostatic and electroelastic problems, an easily implementable node's residual descent method (NRDM) is established in this study. The capability and accuracy of NRDM are validated through the solution of three-dimensional electrostatic, linear elastic, and electroelastic problems, achieving relative errors of 0.17%–1.60% for stress and 0.02%–0.15% for other variables. Fundamental and higher-order variables exhibit second-order accuracy, with convergence rates ranging from 1.98 to 2.27 using a first-order generalized finite difference scheme. This comprehensively validates the double derivation technique. The electroelastic coupling problems can be addressed by explicitly calculating electric displacement and stress based on the stress–charge form of piezoelectric constitutive equations during the iteration process. Additionally, the local basis coordinate technique is seamlessly integrated, enabling the solution of anisotropic piezoelectric problems with arbitrary polarization directions through explicit tensor operations.

Theoretical insights into the interface engineering of β-Ga2O3 devices with ferroelectric HfO2 gate dielectric: Impact of polarization direction

Theoretical insights into the interface engineering of β-Ga2O3 devices with ferroelectric HfO2 gate dielectric: Impact of polarization direction

Automated differentiation of wide QRS complex tachycardia using QRS complex polarity

BackgroundWide QRS complex tachycardia (WCT) differentiation into ventricular tachycardia (VT) and supraventricular wide complex tachycardia (SWCT) remains challenging despite numerous 12-lead electrocardiogram (ECG) criteria and algorithms. Automated solutions leveraging computerized ECG interpretation (CEI) measurements and engineered features offer practical ways to improve diagnostic accuracy. We propose automated algorithms based on (i) WCT QRS polarity direction (WCT Polarity Code [WCT-PC]) and (ii) QRS polarity shifts between WCT and baseline ECGs (QRS Polarity Shift [QRS-PS]).MethodsIn a three-part study, we derive and validate machine learning (ML) models—logistic regression (LR), artificial neural network (ANN), Random Forests (RF), support vector machine (SVM), and ensemble learning (EL)—using engineered (WCT-PC and QRS-PS) and previously established WCT differentiation features. Part 1 uses WCT ECG measurements alone, Part 2 pairs WCT and baseline ECG features, and Part 3 combines all features used in Parts 1 and 2ResultsAmong 235 WCT patients (158 SWCT, 77 VT), 103 had gold standard diagnoses. Part 1 models achieved AUCs of 0.86–0.88 using WCT ECG features alone. Part 2 improved accuracy with paired ECGs (AUCs 0.90–0.93). Part 3 showed variable results (AUC 0.72–0.93), with RF and SVM performing best.ConclusionsIncorporating engineered parameters related to QRS polarity direction and shifts can yield effective WCT differentiation, presenting a promising approach for automated CEI algorithms.

Terahertz‐Wave Polarization Space‐Division Multiplexing Meta‐Devices based on Spin‐Decoupled Phase Control

AbstractThis study presents a generalized design strategy for novel terahertz‐wave polarization space‐division multiplexing meta‐devices, functioning as multi‐polarization generators, modulators, and analyzers. It introduces the spin‐decoupled phase control method by combining gradient phase design with circular polarization multiplexing techniques, enabling exceptional flexibility in controlling the polarization directions and spatial distributions of multiple output beams. The meta‐device M‐4D is significantly demonstrated as proof of concept, which converts an incident linearly polarized wave into four beams with distinct polarization angles. Additionally, the advanced meta‐devices M‐2B and M‐4B are designed to generate two‐vector and four‐vector Bessel beams with tunable spatial polarization distributions. These meta‐devices demonstrate dynamic multi‐polarization beam modulation, validated through simulations and experiments. The proposed method significantly expands the design methodology for multi‐beam polarization control using all‐dielectric metasurfaces and holds promising potential for applications in imaging, sensing, particle manipulation, communication, and information processing. Moreover, it holds potential for adaptation to other spectral ranges.

Ultrahigh Piezoelectricity in Truss‐Based Ferroelectric Ceramics Metamaterials

AbstractConventional porous ferroelectric materials sacrifice their piezoelectric constants for improving various figures of merit due to a rapidly decreased dielectric constant. Here, novel truss‐based ferroelectric metamaterials that simultaneously offer ultrahigh piezoelectric constants and ultralow dielectric constants, originating from the unique combination of truss loading states and polarization direction, are discovered. The homogenization method alongside an analytical model is proposed to predict and elucidate their extraordinary properties, while a customized ferroceramic additive manufacturing platform is resorted to fabricate them. Unlike porous ferroelectrics, ultrahigh piezoelectric constants at low relative densities (ρr ≈0.1) are attained. For example, with appropriate scaling, the experimental values of d31, d33, and d42 for a ferroelectric octet truss with ρr = 0.1, can reach 849, −659, and 836 pC N−1, respectively, which are 3.14, 6, and 2 times higher than the counterpart of bulk BaTiO3 ceramics. Combined with the ultralow dielectric constant, extremely high ferroelectric figures of merit, e.g., piezoelectric voltage constant of 11.098 Vm N−1, piezoelectric energy harvesting figure of merit 9422 × 10−12 m2 N−1, and pyroelectric voltage sensitivity of 56.7 × 10−3 m2 C−1, are also observed. The multifunctional ferroelectric metamaterials open new avenues for their applications in self‐powered ultrasensitive accelerometers, high‐performance noncontact sensors, and wearable input devices.

Development of research on mechanisms of acupuncture intervention on ischemic stroke and its relationship with microglia

Microglia, the main phagocytic cells in the brain, play a key role in inflammatory response and neuroprotection in ischemic stroke, and are potential targets for the treatment of ischemic stroke. Multiple studies have confirmed that the effect of acupuncture on ischemic stroke is closely related to its effect in regulating the activities of microglia. In the present paper, we reviewed the role of microglia in ischemic stroke and the current research status of acupuncture intervention, and prospects the future research direction. Past researches showed that microglia have a bidirectional role in the pathological process of cerebral ischemia, that is, M1 microglia can secrete pro-inflammatory cytokines, participate in the damage of the blood-brain barrier, and aggravate the damage of neurotoxicity, and M2 microglia can secrete anti-inflammatory cytokines, nerve growth factors, neurotrophic factors, improve neuroplasticity and promote vascular remodeling. Acupuncture can exert brain protective effects by regulating the activation and polarization direction of microglia, inhibiting inflammatory reactions, maintaining the integrity of the blood-brain barrier, promoting vascular remodeling, and promoting nerve regeneration. However, whether acupuncture intervention in different periods can affect the response of microglia and how it affects, and whether different acupuncture parameters have different effects on the regulation of microglia, it needs further research. In addition, more in-depth and multi-angle systematic studies on polarization of microglia, secretion factors, cell relationships, upstream and downstream regulatory factors and other aspects with microglia are definitely needed.

Coherence effects in LIPSS formation on silicon wafers upon picosecond laser pulse irradiations

Abstract Using different laser irradiation patterns to modify silicon surface, it has been demonstrated that, at rather small overlapping between irradiation spots, highly regular laser-induced periodic surface structures (LIPSS) can be produced already starting from the second laser pulse, provided that polarization direction coincides with the scanning direction. If the laser irradiation spot is shifted from the previous one perpendicular to light polarization, LIPSS are not formed even after many pulses. This coherence effect is explained by a three-wave interference, surface electromagnetic waves (SEWs) generated within the irradiated spot, SEWs scattered from the crater edge formed by the previous laser pulse, and the incoming laser pulse, providing conditions for amplification of the periodic light-absorption pattern. To study possible consequences of SEW scattering from the laser-modified regions, where the refractive index can change due to material melting, amorphization, and the residual stress formed by previous laser pulses, hydrodynamic modelling and simulations have been performed within the melting regime. The simulations show that stress and vertical displacement could be amplified upon laser scanning. Both mechanisms, three-wave interference and stress accumulation, could enable an additional degree of controlling surface structuring.

Extra-cavity modulating a dark bisoliton

Abstract Although the concept of modulating optical solitons out of fiber laser cavities has already been proposed, to more flexibly change optical solitons’ time or frequency domain properties, compared with traditional intra-cavity modulation. The extra-cavity modulation of dark bisolitons has seldom been touched upon. In this manuscript, we theoretically conduct the research about modulating a dark bisoliton at 1 μm wavelength regime, in an extra-cavity modulation system. The modulation system is composed of different modulation elements. In the simulation, we consider the variations of different parameters. And modulated dark bisoliton’s orthogonal polarization components will show unique variation properties as these soliton parameters vary. For example, as time delay in orthogonal directions varies, a new small pulse peak appears at the position of continuous wave background in vertical polarization direction at output port, when time delay reaches to a specific value. These simulation results further explore the extra-cavity modulation of dark pulses in nonlinear optical fiber modulation systems, which are useful to understand the dark bisolitons’ dynamics in extra-cavity modulation systems. And these results have potential applications in the field of high-speed and long-distance optical fiber communication.

Continuous‐wave and cavity‐dumped 1064 nm Nd:YVO4 laser based on the magneto‐optical effect

AbstractIn this paper, continuous‐wave and cavity‐dumped Nd:YVO4 lasers are studied. Firstly, through theoretical analysis and numerical simulation, the output characteristics of a continuous‐wave laser based on the magneto‐optical effect are analysed using the rate equation. The continuous adjustment of output power and pump threshold power is realised using the magneto‐optical effect to rotate the polarisation direction of laser. The theoretical simulation results show that the output power of the laser could be effectively controlled under different magnetic field intensities. On this basis, the authors explore the cavity‐dumped laser system based on the magneto‐optical effect. By adjusting the intensity of the magnetic field and rising edge time, the pulse width and waveform could be flexibly adjusted. The relationship between the magnetic field intensity in the low Q period and the spot radius of the pump and the signal beam and the output energy and the output pulse waveform is analysed. These research results lay a foundation for further optimising the design and application of magneto‐optical effect lasers.

Orientation dependence of residual current in graphene by few-cycle linearly polarized light

Abstract The orientation dependence of residual current in graphene using linearly polarized light is theoretically investigated by numerically solving the time-dependent Schrödinger equation. We find that the residual current exhibits an unexplored small-period sinusoidal modulation in addition to a large-period sinusoidal modulation as a function of polarization angle. Via decomposing the residual current into two components, parallel and perpendicular to the laser polarization direction, we confirm that the large-period modulation comes from the parallel current component, while the small-period modulation is from the perpendicular component. These two current components are both influenced by the asymmetric population distribution as a consequence of the Landau-Zener-Stückelberg interference. The result here demonstrates a strong link between graphene symmetry and residual current and provides some insights into the development of light-field-driven petahertz information technology.

Poynting and polarization vectors mixed imaging condition of source time‐reversal imaging

AbstractSource time‐reversal imaging based on wave equation theory can achieve high‐precision source location in complex geological models. For the time‐reversal imaging method, the imaging condition is critical to the location accuracy and imaging resolution. The most commonly used imaging condition in time‐reversal imaging is the scalar cross correlation imaging condition. However, scalar cross‐correlation imaging condition removes the directional information of the wavefield through modulus operations to avoid the direct dot product of mutually orthogonal P‐ and S‐waves, preventing the imaging condition from leveraging the wavefield propagation direction to suppress imaging artefacts. We previously tackled this issue by substituting the imaging wavefield with the energy current density vectors of the decoupled wavefield, albeit at the cost of increased computational and storage demands. To balance artifact suppression with reduced computational and memory overhead, this work introduces the Poynting and polarization vectors mixed imaging condition. Poynting and polarization vectors mixed imaging condition utilizes the polarization and propagation direction information of the wavefield by directly dot multiplying the undecoupled velocity polarization vector with the Poynting vector, eliminating the need for P‐ and S‐wave decoupling or additional memory. Compared with scalar cross‐correlation imaging condition, this imaging condition can accurately image data with lower signal‐to‐noise ratios. Its performance is generally consistent with previous work but offers higher computational efficiency and lower memory usage. Synthetic data tests on the half‐space model and the three‐dimensional Marmousi model demonstrate the effectiveness of this method in suppressing imaging artefacts, as well as its efficiency and ease of implementation.

Manipulation of Unconventional Spin Polarization in Non-Collinear Exchange-Spring Magnetic Structures.

Manipulating the polarization of spin current is essential for understanding the mechanism of charge-to-spin conversion and achieving efficient electrically driven magnetization switching. Here, a novel exchange-spring magnetic structure is introduced formed by the coupling of perpendicular magnetic anisotropy (PMA) CoTb and in-plane magnetic anisotropy (IMA) Co films. When a spin current with the polarization along the y-direction flows through this exchange-spring (x-z plane) structure, the interaction between the y-spin and the local exchange field with a non-collinear spatial distribution gives rise to substantial unconventional spin polarizations in the x- and z-directions, enabling field-free spin-orbit torque driven perpendicular magnetization switching at room temperature. More importantly, the polarization directions of this unconventional spin current can be reversed depending on whether the interfacial exchange coupling is ferromagnetic or antiferromagnetic. This work establishes a platform to explore emergent mechanisms for manipulating unconventional spin polarization with rich non-collinear magnetic exchange spin structures.

A Novel Frequency-Division Deep Learning Approach for Magnetotelluric Data Quality Enhancement

High signal-to-noise ratio magnetotelluric (MT) data are crucial for accurately interpreting subsurface structures. Recently, deep learning has become popular for MT denoising due to its ability to avoid parameter tuning and enable real-time processing. These methods typically fit or predict signals in noisy segments after identifying and segmenting signal and noise in the time domain. However, these methods struggle to preserve both low- and high-frequency signals effectively due to high noise levels in these segments. To address this issue, we propose a novel deep learning denoising method that separately recovers low- and high-frequency signals using distinct strategies. Low-frequency signals are fitted using an inverse autoencoder with a channel attention mechanism, effectively removing high-frequency components. High-frequency signals are then predicted using a bidirectional long short-term memory network (BiLSTM) combined with a squeeze-and-excitation (SE) mechanism, enhancing prediction by considering both global and local signal characteristics. Additionally, we introduce the multivariate state estimation technique (MSET) for real-time signal-noise identification. MSET analyzes residuals after separating low-frequency signals to identify noise. Denoising is performed only on segments with significant noise, preserving more effective signals. Finally, the fitted low-frequency dominant component and predicted high-frequency component are combined to form the denoised MT signals. This combined approach significantly improves the restoration quality of effective signals compared to existing methods. Experimental results demonstrate that our method exhibits superior denoising capabilities in both quantitative and qualitative evaluations, including apparent resistivity-phase curves and polarization direction analysis, offering enhanced performance over current deep learning methods.