Accepted
, , Received Date: 2025-03-04
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, , Received Date: 2025-02-21
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Femtosecond laser excited terahertz waves have been widely used in various fields. Herein, we demonstrate a novel method to generate terahertz radiation from a terahertz electro-optic crystal excited by infrared supercontinuum radiation (wavelengths > 1 μm), which is produced via the interaction between a femtosecond laser and a transparent solid medium. This approach yields single-cycle, low-frequency, broadband terahertz radiation. In the femtosecond laser-induced ionization process in a medium, both infrared supercontinuum radiation and terahertz radiation are simultaneously generated. When the resulting infrared supercontinuum radiation and terahertz radiation concurrently enter into an electro-optic crystal, the presence of the infrared supercontinuum radiation may interfere with the detection of the intrinsic terahertz radiation. By filtering the infrared supercontinuum radiation with narrowband filters, a new strategy is proposed for investigating the response of the electro-optic crystal in infrared spectral region.
, , Received Date: 2025-01-30
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Dielectric laser accelerators (DLAs), as compact particle accelerators, rely critically on their structural design to determine both the energy gain and beam quality of accelerated bunches. Although most existing DLAs are driven by near-infrared lasers with a wavelength of approximately 1 μm, the use of long-wave infrared (LWIR) lasers at a wavelength ten times that of this wavelength indicates that it is possible to achieve excellent beam quality without sacrificing acceleration gradient. To address the lack of optimized structural designs in the LWIR band where long-distance acceleration poses unique challenges—we introduce a deep learning–based design method for LWIR dielectric grating accelerator structures. Our approach integrates geometric parameters, material properties, and optical-field energy metrics into a unified evaluation framework and uses a surrogate model to predict particle energy gain with high precision. Optimal structural parameters are then extracted to realize the final design. The simulation results show that the energy gain is 99.5 keV (a year-over-year increase of 19.9% ), the transmission efficiency is 100%, the beam spot radius of 14.5 μm, and the average beam current is 20.4 fA, which is 6.9 times higher than similar near-infrared gratings, while maintaining equivalent beam brightness. This work provides a feasible technical route for designing high-netgain LWIR dielectric grating accelerators and a novel framework for optimizing the structure of complex optoelectronic devices.
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Three-dimensional ultrasonic waves with amplitudes of 14, 18, and 22 μm were applied during the solidification of (FeCoNiCrMn)92Mo8 high-entropy alloy, and its microstructural evolution and mechanical property were investigated. Under static condition, the solidification microstructure was composed of primary γ phase dendrites with FCC structure and stripe-shaped σ phase with tetragonal structure. As the ultrasonic amplitude increased, the mean transient cavitation intensity rose to trigger a significant nucleation rate increase of the primary γ phase to 5.6×1012 m-3·s-1, leading to the remarkable grain size reduction by two orders of magnitude. The maximum and average acoustic streaming velocity increased concurrently, which accelerated atomic diffusion at the liquid/solid interface, reducing Cr content in the primary γ phase from 18.6 at.% to 13.1 at.% and Mo content from 6.8 at.% to 3.4 at.%. This atomic redistribution subsequently caused the liquid composition approaching the eutectic point and facilitated the formation of (γ+σ) eutecticss, which took up more than 50% volume fraction. The two eutectic phases exhibited a semi-coherent interface relationship characterized by (110)γ//(110)σ and (1-1-1)γ//(-110)σ. Furthermore, due to the progressive enrichment of Cr atoms in the remaint liquid phase, a small amount of metastable μ phase with Cr content up to 62.3 at.% formed in the final microstructure. The maximum compressive yield strength of the ultrasonically solidified microstructure reached 876.2 MPa, which was nearly twice of that for static solidification microstructure, and the compressive strain reached 33.2%. The formation of (γ+σ) eutectics represented as the dominant factor to contribute an enhancement of 527.1 MPa to the alloy's yield strength.
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Recycling is a sustainable strategy for the effcient utilization of rare earth resources. Hydrogenation milling has been widely adopted due to its high effciency and environmental benefits. However, the formation of non-stable phases during the hydrogenation process significantly reduces recovery effciency, presenting new challenges for process optimization. In this study, a combination of first-principles calculations and machine learning methods was employed to systematically investigate the thermodynamic behavior of key rare earth hydrides—such as NdH2, NdH3, and Nd2H5 during the hydrogenation milling process using the Debye model for lattice vibrations. The results show that a temperature range around 630 K under a pressure of 600 kPa may offer an ideal operational condition for the hydrogenation milling process. Under these conditions, NdH2 can undergo spontaneous hydrogenation, and the formation of unstable phases can be effectively suppressed, thereby improving rare earth recovery effciency. This study also reveals the potential adverse effects of excessively high temperatures on the stability and reactivity of NdH2, further emphasizing the importance of operating within a specific temperature range. These findings provide new insights into the thermodynamic mechanisms of the hydrogenation process in Nd2Fe14B permanent magnet material. Furthermore, they offer theoretical guidance for the optimization of industrial hydrogenation milling parameters.
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Turbulence modeling relies critically on accurate characterization of large-scale structures, with the integral length scale L serving as a key parameter for industrial applications ranging from combustion stability optimization to wind farm design and aerodynamic load prediction. However, Direct numerical simulation (DNS) of turbulence faces inherent limitations in resolving all wavenumbers within the lowwavenumber region of the turbulent kinetic energy spectrum due to finite computational domain sizes. This unresolved low-wavenumber deficiency leads to incomplete characterization of large-scale structures and introduces systematic deviations in key statistical quantities, particularly the integral length scale L and turbulence dissipation coefficient Cε. As turbulence evolves, the spectral peak wavenumber kp migrates toward lower wavenumbers, exacerbating the loss of large-scale information and causing computed statistics to diverge from physical reality. In this study, we perform high-fidelity DNS of homogeneous isotropic decaying turbulence in a periodic cubic domain of side length 4π with 3843 grid points. DNS cases are performed by using a standard pseudospectral solver and a fourth-order Runge-Kutta time integration scheme, with a semi-implicit treatment of the viscous term. The spatial resolution kmaxη = 1.65 ensures adequate resolution of dissipative scales (η is the Kolmogorov scale). Simulations start from a fully developed field initialized with a spectrum matching Comte-Bellot and Corrsin’s experimental data and evolve within a time interval where turbulence exhibits established isotropic decay characteristics. Existing correction models, predominantly based on equilibrium turbulence assumptions, fail to capture the non-equilibrium dynamics governed by large-scale structures. Based on a generalized von Kármán spectrum model, we use a correction framework to account for unresolved low-wavenumber contributions in homogeneous isotropic decaying turbulence. DNS data reveal that the uncorrected integral scale Lm significantly underestimates the true L, with errors escalating as kL/kp increases, where kL is the minimum resolvable wavenumber in the simulation domain. After correction, L exhibits a temporal evolution following the Saffmann-predicted power-law relationship $L \propto t^{2 / 5}$, contrasting sharply with the underestimated pre-correction values. Despite the spectral correction substantially increasing the spectral integral scale L, its value remains less than the physically derived integral scale Λ computed from the velocity correlation function, primarily due to the finite domain size limiting large-scale statistics and the moderate grid resolution, though higher-resolution simulations with the same domain show L converging towards Λ. Notably, the unmodified dissipation coefficient Cε remains constant, consistent with equilibrium turbulence assumptions, whereas the corrected Cε evolves according to the non-equilibrium scaling law $C_{\varepsilon} \sim R e_\lambda^{-1}$. Further analysis confirms that the ratio L/λ shifts from Kolmogorov’s $R e_\lambda^1$ dependence to a Reynolds-number-independent plateau after correction, fundamentally altering the turbulence dissipation paradigm. This transition from equilibrium to non-equilibrium dissipation behavior underscores the dominant role of large-scale structures in regulating energy cascade dynamics. Our results demonstrate that finite Reynolds numbers or strong initial-condition effects amplify the nonequilibrium characteristics of turbulence, preventing full-scale equilibrium. These findings reconcile long-standing theoretical discrepancies and provide a paradigm for modeling scale interactions in turbulence.
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The magnetized coaxial gun is an efficient plasma injection device with significant applications in fusion fueling, astrophysical jet simulation, and magnetic reconnection studies. In this work, three typical discharge regions—spheromak region, diffusive region, and jet region—were observed using high-speed imaging and magnetic field measurements. The dynamic characteristics of the plasma in each region were systematically investigated. Based on ideal magnetohydrodynamic (MHD) theory, the magnetic field configurations, rotational behavior, and axial motion mechanisms of the plasma in different regions were carefully analyzed. The results show that in the spheromak region, the plasma reaches a Taylor-relaxed state, exhibits uniform rotation, and forms a stable compact torus (CT) structure. In the diffusive region, a relatively strong bias magnetic field leads to faster rotation, enhanced centrifugal force, and consequently, intense radial diffusion. In the jet region, due to the weaker bias field, the plasma accumulates at the tip of the inner electrode, exhibiting a clear pinch effect and forming a jet with axial instability. These findings not only deepen the understanding of the discharge physics of magnetized coaxial guns but also provide valuable experimental and theoretical support for numerical simulations and the development of efficient plasma sources.
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Optical encryption technologies show significant application potential in information security due to their advantages of parallel processing, large capacity, and low power consumption. Polarization, as an important degree of freedom of light, has attracted extensive research interest in optical encryption through polarization manipulation and multiplexing. However, current polarization control methods based on pixelated or interleaved metasurfaces still face significant challenges, including fabrication complexity and inevitable crosstalk resulting from coupling between the neighboring structures, which limit the number of achievable multiplexing channels. In this work, we propose a novel encryption approach based on longitudinally tunable, and cascaded polarization structures enabled by metalenses with vectorial foci. The intensity distributions on different observation planes are simulated using the Fresnel–Kirchhoff diffraction integral. Based on the geometric phase principle, the designed metalens consisting of TiO2 nanopillars with identical dimensions but spatially variant orientation angles, can generate multiple vectorial foci at distinct observation planes and reconstructs cascaded polarization structures. Here, any two cascaded polarization structures are encoded with mutually orthogonal polarization rotation angles. As the polarization direction of incident linearly polarized light changes, the polarization distribution encoded on the polarization structures can be dynamically modulated, consequently enabling ten-channel information encryption through polarizationdependent intensity redistribution. The encrypted information can only be decoded using the correct keys (incident wavelength, incident polarization state, output light polarization state, and observation position). This method integrates polarization rotation, polarization structure design, and longitudinal/cascaded control, significantly enhancing information capacity and security. It holds promising applications across diverse domains including optical display, encryption, and anti-counterfeiting.
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With the growing demand for sustainable energy technologies, ionic thermocells have attracted increasing attention for their potential in harvesting low-grade heat through direct thermal-to-electric energy conversion. Among the key performance metrics, the effective thermal conductivity (κeff) plays a crucial role in maintaining internal temperature gradients and enhancing overall energy conversion efficiency of thermocells. However, compared to the extensively studied thermopower (Stg) and electrical conductivity (σ), κeff has received relatively little systematic attention. This review summarizes recent advances in the regulation of thermal conductivity in ionic thermocells, focusing on its crucial role in thermoelectric performance. We discuss the influence of electrode materials, electrolyte compositions, and device architectures on heat transport, and highlight representative strategies involving materials engineering and structural design to optimize the synergy between thermal conduction and ionic conduction. Finally, we outline future directions such as material optimization, interface engineering, and improved thermal characterization techniques, to facilitate the development of next-generation high-performance thermocells.
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Diffuse discharges generated under fast nanosecond-pulse rising edges possess a larger discharge radius compared to classic streamer discharges. However, existing simulation studies often employ boundary ranges similar to those used for simulating streamer discharges, thereby neglecting the influence of the boundary range on their characteristics. This study investigates the characteristics of diffuse discharges in atmospheric-pressure air using a fluid model. The research focuses on the influence of plasma and Poisson equation boundary ranges on discharge evolution, particularly the top and right boundaries of the rectangular computational domain. Numerical simulations and experimental comparisons reveal several key findings: When both plasma and Poisson equation boundaries are set to 5cm×5cm (exceeding six times the maximum discharge radius), the simulated discharge width and propagation velocity agree well with experimental measurements. However, a consistent delay is observed in the simulated arrival time at the plate electrode, highlighting inherent limitations of current fluid models in accurately simulating temporal scales. Reducing the plasma boundaries results in negligible fluctuations in electric field intensity and electron density at the discharge head, indicating a minimal impact on macroscopic discharge characteristics. Narrowing the Poisson equation’s right boundary significantly reduces the discharge width while simultaneously increasing the discharge width relative to the domain size. Asymmetric propagation patterns emerge between the upper and lower halves of the discharge gap. Nevertheless, appropriate reduction of the right boundary improves morphological consistency with experimental observations, suggesting practical optimization strategies. Conversely, reducing the top boundary weakens the electric field “focusing effect” at the discharge head, homogenizes the spatial field distribution, and delays acceleration, thereby exacerbating deviations from experimental data. These results demonstrate that Poisson boundary conditions critically govern spatiotemporal discharge dynamics. Top boundary truncation severely compromises simulation accuracy, whereas adjusting the right boundary allows for a balanced optimization between computational efficiency and result reliability. This work provides theoretical guidance for selecting boundary conditions in the numerical modeling of diffuse discharges.
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The inevitable distortions in optical coherence tomography (OCT) imaging often lead to mismatches between the imaging space and the real space, significantly affecting measurement accuracy. To address this issue, this study proposes a machine learning-based OCT image distortion correction method. A calibration plate with uniformly distributed circular hole arrays was sequentially imaged at different marked planes. The point showing minimal deviation between its coordinates and the mean coordinates across all imaging planes was selected as the reference marker. A mathematical model was then used to reconstruct all marker point coordinates in the reference plane, establishing a mapping relationship between the calibration plate's imaging space and the real physical space. A multilayer perceptron (MLP) was employed to learn this mapping relationship. The network architecture consisted of multiple fully connected modules, each containing a linear layer and an activation function except for the output layer. The optimal model was selected based on validation set performance and subsequently applied to analyze the spatial distribution of points. Using a swept-source OCT system, lens images were acquired and corrected through the trained model to obtain the anterior surface point cloud. Combined with ray tracing reconstruction of the posterior surface, the lens curvature radius and central thickness were calculated. Experimental results demonstrated that after correction, the lens curvature radius was measured with an accuracy of 10μm (error < 1%), while the central thickness was determined with a precision of 3μm (relative error: 0.3%). This method demonstrates high precision and reliability, offering an effective solution for improving OCT measurement accuracy.
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SiGe-based electronics possess a promising prospect in the space exploration field owing to a controllable bandgap of SiGe alloys and high compatibility with Si technology, but they may be susceptible to energetic particles in space radiation environments. In order to interpret the potential displacement damage in SiGe-based electronics, Monte Carlo simulations were conducted to investigate the displacement damage in SiGe alloys and SiGe/Si heterostructures induced by 1 ~ 1000 MeV protons. The displacement damage in SiGe alloys was explored via the energy spectra and species as well as the pertinent distribution of damage energy of proton-induced primary knock-on atoms (PKAs), while the displacement damage in SiGe/Si heterostructures was probed by the distribution of damage energy caused by forward- and reverse-incident protons. Low-energy protons (1 ~ 100 MeV) primarily generated Si PKAs and Ge PKAs in SiGe alloys through Coulomb scattering and elastic collisions, and the corresponding damage energy distribution presented a distinct Bragg peak at the end of the proton range. Meanwhile, high-energy protons (300 ~ 1000 MeV) aroused significant inelastic collisions in SiGe alloys, leading to a sequence of other PKA types, and the related damage energy distribution was predominantly located at the front of the proton range. In addition, the damage energy in SiGe/Si heterostructures generally decreased as the proton energy increased, and reverse-incident protons (10 MeV and 100 MeV) caused greater damage energy on the side of Si substrate at the interface than forward-incident protons, resulting in more noticeable fluctuations in damage energy on both sides of the interface than forward-incident protons, which could lead to severe displacement damage. Besides, Ge content could affect the PKA species, damage energy distribution, and nonionizing energy loss. As for high-energy protons, a high Ge content may lead to a great nonionizing energy loss, whereas the Ge content had an insignificant effect on the total damage energy of small-size SiGe/Si heterostructures. In summary, this work indicates that the proton-induced displacement damage in SiGe alloys and SiGe/Si heterostructures is closely dependent on the proton energy, and low-energy protons were prone to generate massive self-recoil atoms and induce significant displacement damage in small-size SiGe/Si heterostructures, which will provide conducive insights into research on the displacement damage effect and radiation hardening techniques of SiGe-based electronics.
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Two-phase heat transfer technology utilizing dielectric liquids has emerged as one of the efficient solutions for thermal management in high-power electronic devices. However, in practical applications, dielectric liquids exhibit significant boiling hysteresis due to the cause of interfacial materials and thermophysical properties, which in turn affects the boiling heat transfer performance. Owing to small spatial and temporal scales of bubble nucleation initiation, macroscopic experiments and traditional simulation methods still face certain limitations. In this study, non-equilibrium molecular dynamics and mechanical pressure control method are utilized to investigate the bubble nucleation and boiling heat transfer characteristics of R1336mm(Z) liquid film over different heating surface materials (i.e., copper atoms, aluminum atoms, and silicon atoms). Additionally, the heterogeneous nucleation mechanism of dielectric liquid is discussed from two perspectives: phonon vibrational density of states and potential energy restriction. On one hand, surface materials with high solid-liquid interaction forces and low-frequency vibrations, represented by copper atoms, can generate substantial interfacial heat flux and attract a large number of liquid-phase molecules near the heated wall. However, such material inevitably increases the energy barrier of bubble nucleation. On the other hand, surface materials with weak solid-liquid interaction forces and medium-to-high-frequency vibrations, represented by silicon atoms, can achieve reasonable phonon vibrational coupling with dielectric liquid to bridge interfacial thermal transport. Such material can reduce the potential energy restriction on the nanofilm, thus facilitating the formation of local liquid clusters into bubble nuclei. These findings can provide a comprehensive understanding of the underlying mechanisms of bubble nucleation and heat transfer in dielectric liquids and thus offer valuable insights for thermal management enhancement strategies in high-power electronic devices.
, , Received Date: 2025-03-03
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Based on the basic principles of quantum mechanics, quantum key distribution (QKD) provides unconditional security for long-distance communication. However, existing QKD with relevant source protocols have limited tolerance for source correlation, which greatly reduces the key generation rate and limits the secure transmission distance, thereby limiting their practical deployment. In this work, we propose an improved QKD with correlated source protocol to overcome these limitations by discarding the traditional loss-tolerant security frameworks. Our approach adopts the standard BB84 protocol for the security analysis, under the assumption that the source correlation has a bounded range and characterized inner product of the states. We theoretically analyze the performance of the improved protocol at different levels of source correlation and channel loss. Numerical simulations show that our protocol achieves a much higher secret key rate and longer transmission distance than traditional schemes. In the case of typical parameters and 0 dB loss, our protocol achieves about 1.5－3 times improvement in secret key rate. Additionally, the maximum tolerable loss is enhanced by about 2－6 dB. This highlights a promising direction for enhancing the robustness and practicality of QKD with correlated sources systems, paving the way for their deployment in real-world quantum communication networks.
, , Received Date: 2025-04-30
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