column
- REVIEW
- INSTRUMENTATION AND MEARMENT
- GENERAL
- THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
- NUCLEAR PHYSICS
- ATOMIC AND MOLECULAR PHYSICS
- ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
- COVER ARTICLE
- PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
- CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
- CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
- INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Display Method:
2025, 74(14): 148803.
doi: 10.7498/aps.74.20250591
Abstract:
As the core power unit of new energy vehicles, the accurate modeling of power batteries is of great significance for evaluating their operating status, diagnosing faults throughout their lifecycle, and ensuring safety control under multiple operating conditions. The electrochemical model represented by the P2D model serves as a mechanistic model that can characterize the internal electrochemical reaction process of batteries on a microscale. Its accurate description of the aging and heating behavior of power batteries is an important basis for evaluating the capacity degradation, increase in internal resistance, uneven heating, and inconsistent performance of battery modules. The paper summarizes the latest advances in electrochemical modeling of lithium-ion power batteries, analyzes the coupling methods and application status of electrochemical models with equivalent circuit models, aging models, and thermal models, and focuses on the problem of numerous parameters and difficult identification of electrochemical models. In this paper, the advantages and disadvantages of the single particle model, single particle model with electrolyte, electrochemical mean model, solid-liquid phase reconstruction model, one-dimensional electrochemical model and other methods are compared with each other and analyzed for reducing the order of power battery electrochemical models, the key difficulties in characterizing electrochemical model order reduction are pointed out, and the research trends of electrochemical model reduction order reconstruction methods are prospected, in order to provide direction for the research on electrochemical model reduction order reconstruction of power batteries.
As the core power unit of new energy vehicles, the accurate modeling of power batteries is of great significance for evaluating their operating status, diagnosing faults throughout their lifecycle, and ensuring safety control under multiple operating conditions. The electrochemical model represented by the P2D model serves as a mechanistic model that can characterize the internal electrochemical reaction process of batteries on a microscale. Its accurate description of the aging and heating behavior of power batteries is an important basis for evaluating the capacity degradation, increase in internal resistance, uneven heating, and inconsistent performance of battery modules. The paper summarizes the latest advances in electrochemical modeling of lithium-ion power batteries, analyzes the coupling methods and application status of electrochemical models with equivalent circuit models, aging models, and thermal models, and focuses on the problem of numerous parameters and difficult identification of electrochemical models. In this paper, the advantages and disadvantages of the single particle model, single particle model with electrolyte, electrochemical mean model, solid-liquid phase reconstruction model, one-dimensional electrochemical model and other methods are compared with each other and analyzed for reducing the order of power battery electrochemical models, the key difficulties in characterizing electrochemical model order reduction are pointed out, and the research trends of electrochemical model reduction order reconstruction methods are prospected, in order to provide direction for the research on electrochemical model reduction order reconstruction of power batteries.
2025, 74(14): 148703.
doi: 10.7498/aps.74.20250211
Abstract:
Terahertz (THz) time-domain spectroscopy and imaging techniques on a nanoscale are crucial for material research, device detection, and others. However, traditional far-field THz time-domain spectroscopy faces inherent diffraction limitations, which limits the applications of carrier dynamics analysis that require femtosecond time resolution and nanoscale spatial precision. We present a scattering-type scanning near-field optical microscopy that overcomes these limitations by combining ultrafast THz time-domain spectroscopy with atomic force microscopy (AFM). The utilization of the near-field interaction between the needle tip and the sample surface is demonstrated to facilitate the study of semiconductor materials and devices by using static THz spectroscopy with a lateral spatial resolution of ~60 nm. This, in turn, enables the acquisition of static THz conductivity distributions of the semiconductor materials. Additionally, it facilitates the acquisition of transient conductivity distributions of semiconductor materials and laser THz emission ultrafast via photoexcited transient carrier kinetic processes, which provides substantial support for studying the performances of materials and devices in nanometer spatial resolution, ultrafast time resolution, and THz spectroscopic imaging. The experimental results show that the system has a signal-to-noise ratio as high as 56.34 dB in the static THz time-domain spectral mode, and can effectively extract the fifth-order harmonic signals covering the 0.2–2.2 THz frequency band with a spatial resolution of up to ~60 nm. Carrier excitation and complexation processes in topological insulators are successfully observed by optical pump-THz probe with a time resolution better than 100 fs. Imaging of SRAM samples by the system reveals differences in THz scattering intensity due to non-uniformity in doping concentration, thereby validating its potential application in nanoscale defect detection. This study not only provides an innovative means for studying the nanoscale electrical characterization of semiconductor materials and devices, but also opens a new way for applying the THz technology to interdisciplinary subjects such as nanophotonics and spintronics. In the future, by integrating the superlens technology, optimizing the probe design, and introducing deep learning algorithms, it is expected to further improve the temporal- and spatial-resolution and detection efficiency of the system.
Terahertz (THz) time-domain spectroscopy and imaging techniques on a nanoscale are crucial for material research, device detection, and others. However, traditional far-field THz time-domain spectroscopy faces inherent diffraction limitations, which limits the applications of carrier dynamics analysis that require femtosecond time resolution and nanoscale spatial precision. We present a scattering-type scanning near-field optical microscopy that overcomes these limitations by combining ultrafast THz time-domain spectroscopy with atomic force microscopy (AFM). The utilization of the near-field interaction between the needle tip and the sample surface is demonstrated to facilitate the study of semiconductor materials and devices by using static THz spectroscopy with a lateral spatial resolution of ~60 nm. This, in turn, enables the acquisition of static THz conductivity distributions of the semiconductor materials. Additionally, it facilitates the acquisition of transient conductivity distributions of semiconductor materials and laser THz emission ultrafast via photoexcited transient carrier kinetic processes, which provides substantial support for studying the performances of materials and devices in nanometer spatial resolution, ultrafast time resolution, and THz spectroscopic imaging. The experimental results show that the system has a signal-to-noise ratio as high as 56.34 dB in the static THz time-domain spectral mode, and can effectively extract the fifth-order harmonic signals covering the 0.2–2.2 THz frequency band with a spatial resolution of up to ~60 nm. Carrier excitation and complexation processes in topological insulators are successfully observed by optical pump-THz probe with a time resolution better than 100 fs. Imaging of SRAM samples by the system reveals differences in THz scattering intensity due to non-uniformity in doping concentration, thereby validating its potential application in nanoscale defect detection. This study not only provides an innovative means for studying the nanoscale electrical characterization of semiconductor materials and devices, but also opens a new way for applying the THz technology to interdisciplinary subjects such as nanophotonics and spintronics. In the future, by integrating the superlens technology, optimizing the probe design, and introducing deep learning algorithms, it is expected to further improve the temporal- and spatial-resolution and detection efficiency of the system.
2025, 74(14): 140201.
doi: 10.7498/aps.74.20250071
Abstract:
This paper adopts the phase-field based lattice Boltzmann (LB) method to study the dynamic behaviors of soluble surfactant-laden droplets in a uniform electric field. First, two benchmark problems including the surfactant concentration distribution on a static droplet and the deformation of a leaky dielectric droplet in an electric field, are used to validate the reliability of the LB method. Then, we investigate the deformation, breakup, and coalescence behaviors of surfactant-laden droplets in an electric field. The obtained results are shown below. 1) Regarding deformation, the single droplet exhibits two distinct deformation modes: Prolate and oblate shapes. A higher electric capillary number and a higher concentration of bulk surfactants both promote greater droplet deformation. 2) Regarding breakup, a single droplet exhibits two distinct breakup modes: filamentous breakup and conical jetting breakup. Droplets containing surfactants are more like to break up. Specifically, surfactants reduce the retraction degree of the main droplet after filamentous breakup, while increasing the number of satellite droplets formed at the ends of the main droplet after jetting breakup. 3) Regarding coalescence, the double droplets exhibit two distinct processes: deformation coalescence and attractive coalescence. A higher electric capillary number facilitates droplet coalescence. Surfactants promote the deformation coalescence while retarding attractive coalescence, but the promotional effect dominates. Consequently, a higher concentration of bulk surfactants will enhance the tendency of droplet coalescence.
This paper adopts the phase-field based lattice Boltzmann (LB) method to study the dynamic behaviors of soluble surfactant-laden droplets in a uniform electric field. First, two benchmark problems including the surfactant concentration distribution on a static droplet and the deformation of a leaky dielectric droplet in an electric field, are used to validate the reliability of the LB method. Then, we investigate the deformation, breakup, and coalescence behaviors of surfactant-laden droplets in an electric field. The obtained results are shown below. 1) Regarding deformation, the single droplet exhibits two distinct deformation modes: Prolate and oblate shapes. A higher electric capillary number and a higher concentration of bulk surfactants both promote greater droplet deformation. 2) Regarding breakup, a single droplet exhibits two distinct breakup modes: filamentous breakup and conical jetting breakup. Droplets containing surfactants are more like to break up. Specifically, surfactants reduce the retraction degree of the main droplet after filamentous breakup, while increasing the number of satellite droplets formed at the ends of the main droplet after jetting breakup. 3) Regarding coalescence, the double droplets exhibit two distinct processes: deformation coalescence and attractive coalescence. A higher electric capillary number facilitates droplet coalescence. Surfactants promote the deformation coalescence while retarding attractive coalescence, but the promotional effect dominates. Consequently, a higher concentration of bulk surfactants will enhance the tendency of droplet coalescence.
2025, 74(14): 140202.
doi: 10.7498/aps.74.20250409
Abstract:
This study addresses the critical challenge of simulating pedestrian crowd dynamics in staircase environments, where existing models often neglect three-dimensional geometric constraints and dynamic interactions. We propose a dual-layer motion model (DLM) that integrates a hierarchical kinematic-dynamic coupling framework, geometric discretization methods, and crowd interaction mechanisms. The model abstracts pedestrians as a multi-node “bipedal single-point” system, distinguishing between an upper-layer centroid motion plane and a lower-layer dual-foot support space. This method combines spatiotemporal modeling and contact mechanics to address the complexity of stairwell dynamics. The lower layer uses cellular path planning to constrain stepping motions and ensures spatiotemporal consistency of the crowd through a quasi-synchronous state transition mechanism. The upper layer uses an ellipse-projection-based separating axis algorithm to detect collision conflicts and quantifies contact effects by using collision dynamics. Additionally, a quasi-synchronous state migration mechanism is introduced within a hybrid discrete-continuous time framework to coordinate gait cycles in large-scale multi-agent simulations and solve the problem of temporal asynchrony. Based on the stability control principle of inverted pendulum dynamics and combined with biomechanical regulation capabilities and motion threshold constraints, the perturbation effects of contact forces on pedestrian balance are quantified, enabling individual dynamic stability analysis. To validate the model, a parameterized stairwell scenario (step height: 0.15 m, tread depth: 0.26 m) is constructed to simulate the motion of heterogeneous pedestrians (mass: (65 ± 5) kg, height: (1.70 ± 0.2) m). The simulation results show that the model accurately captures the dynamic features of pedestrian movement in stairwells: the centroid displacement ratio is very close to the theoretical staircase slope, and the deviation between the crowd’s average speed and empirical data is less than 6%. Dynamic stability analysis reveals the evolution from individual local imbalance to group instability. Further parametric studies indicate that balancing target attraction weight (α) and repulsion weight (β) can regulate the cohesion of crowd behavior, while increasing the collision recovery coefficient (e) can amplify contact force fluctuations. In conclusion, the dual-layer model links motion planning and dynamic stability in the stairwell environments, providing high-fidelity insights into pedestrian safety. The results emphasize the interdependence between geometric constraints, biomechanical adjustments, and density-driven instability. Future research may extend the model to irregular stair geometries and incorporate heterogeneous pedestrian parameters to improve the predictive accuracy of evacuation optimization and architectural safety design.
2025, 74(14): 140301.
doi: 10.7498/aps.74.20250302
Abstract:
With the discovery of two-dimensional materials like graphene, the relativistic two-dimensional Dirac equation has received increasing attention from researchers. Accurately solving the Dirac equation in electromagnetic fields is the foundation for studying and manipulating quantum states of Dirac electrons. Sectioned series expansion method is successful and accurate in solving Schrödinger equation under complex electromagnetic fields. Dirac equation is a system of coupled first-order differential equations with undermined eigenvalues, and it is more difficult to solve. By applying the sectioned series expansion principle to Dirac equation and conducting series expansions in regular, Taylor and irregular regions, we obtain an accurate method with wide applicability. With the method, a universal criterion for bound states of Dirac electrons in electromagnetic fields is derived and the energy levels and wave functions of bound states can be accurately calculated. The criterion given in the main text body shows that the magnetic field and mass field help to confine Dirac electrons while the electric field tends to deconfine them due to Klein tunneling. When the highest power of the electric potential is equal to that of the magnetic vector potential or the mass field, confined-deconfiend states depend on the comparison of their coefficients. We apply the method to two cases: one is massive Dirac electron in Coulomb electric potential (relativistic two-dimensional hydrogen-like atom) and the other is Dirac electron in uniform mangetic field (mangetic vector potenial is A = 1/2Br) and linear electric potential V = Fr. The energy levels of the hydrogen-like atom are calculated and compared with analytical solutions, demonstrating the exceptional accuracy of the method. By solving Dirac equation under uniform magnetic field and linear electric potential, the method proves to be broadly applicable to the solutions of Dirac equation under complex electromagnetic fields. Under uniform magnetic field B and V = Fr, as the F increases, level orders of negative energy states change and at the critical point F = 0.5B, the bound states of positive ones still exist while only certain negative ones can exist on condition that their energies exceed zero. The sectioned series expansion method provides an effective computational framework for Dirac equation and it deepens our understanding of relativistic quantum mechanics.
With the discovery of two-dimensional materials like graphene, the relativistic two-dimensional Dirac equation has received increasing attention from researchers. Accurately solving the Dirac equation in electromagnetic fields is the foundation for studying and manipulating quantum states of Dirac electrons. Sectioned series expansion method is successful and accurate in solving Schrödinger equation under complex electromagnetic fields. Dirac equation is a system of coupled first-order differential equations with undermined eigenvalues, and it is more difficult to solve. By applying the sectioned series expansion principle to Dirac equation and conducting series expansions in regular, Taylor and irregular regions, we obtain an accurate method with wide applicability. With the method, a universal criterion for bound states of Dirac electrons in electromagnetic fields is derived and the energy levels and wave functions of bound states can be accurately calculated. The criterion given in the main text body shows that the magnetic field and mass field help to confine Dirac electrons while the electric field tends to deconfine them due to Klein tunneling. When the highest power of the electric potential is equal to that of the magnetic vector potential or the mass field, confined-deconfiend states depend on the comparison of their coefficients. We apply the method to two cases: one is massive Dirac electron in Coulomb electric potential (relativistic two-dimensional hydrogen-like atom) and the other is Dirac electron in uniform mangetic field (mangetic vector potenial is A = 1/2Br) and linear electric potential V = Fr. The energy levels of the hydrogen-like atom are calculated and compared with analytical solutions, demonstrating the exceptional accuracy of the method. By solving Dirac equation under uniform magnetic field and linear electric potential, the method proves to be broadly applicable to the solutions of Dirac equation under complex electromagnetic fields. Under uniform magnetic field B and V = Fr, as the F increases, level orders of negative energy states change and at the critical point F = 0.5B, the bound states of positive ones still exist while only certain negative ones can exist on condition that their energies exceed zero. The sectioned series expansion method provides an effective computational framework for Dirac equation and it deepens our understanding of relativistic quantum mechanics.
2025, 74(14): 140302.
doi: 10.7498/aps.74.20250268
Abstract:
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.
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.
2025, 74(14): 140303.
doi: 10.7498/aps.74.20250458
Abstract:
Hyperentanglement, as a high-dimensional quantum entanglement phenomenon with multiple degrees of freedom, plays a critical role in quantum communication, quantum computing, and high-dimensional quantum state manipulation. Unlike entangled states in a single degree of freedom, hyperentangled states establish entanglement relationships simultaneously in multiple degrees of freedom, such as polarization, path, and orbital angular momentum. Through entanglement-based distribution techniques, high-dimensional quantum information networks can be constructed. On this basis, a fully connected quantum network with hyperentanglement is constructed in this work, and the polarization and time-bin degree-of-freedom hyperentanglement is realized through the process of second-harmonic generation and spontaneous parametric down-conversion in periodically poled lithium niobate (PPLN) waveguide cascades. The hyperentangled state is then multiplexed into a single-mode fiber by using dense wavelength division multiplexing (DWDM) technology for transmission to terminal users. The quality of the entangled states in the two degrees of freedom is characterized using Franson-type interference and photon-pair coincidence measurement techniques. Polarization entangled states are subjected to quantum state tomography, and entanglement distribution technology is employed to achieve long-distance distribution and quantum key transmission within the network. Experimental results show that the two-photon interference visibility of both polarization and time-bin entanglement is greater than 95%, demonstrating the high quality of the hyperentanglement in the network. After 100-km-entanglement distribution, the fidelity of the quantum states in both degrees of freedom remains above 88%, indicating the effectiveness of long-distance entanglement distribution in this network. Additionally, it is verified that this network supports the distribution of quantum keys over a distance of more than 50 km between users. These results confirm the feasibility of a fully connected quantum network with hyperentanglement and demonstrate the potential for constructing large-scale metropolitan networks by using hyperentanglement. As a higher-dimensional entanglement, hyperentangled states can significantly enhance the capacity and efficiency of quantum information processing. Although the quantum communication is still in its early stages of development, achieving stable storage and transmission of entangled states in large-scale metropolitan networks remains a great challenge. By utilizing the frequency conversion properties and high integration characteristics of the periodically poled lithium niobate waveguides, the three-user hyperentangled quantum network constructed in this work provides a new solution for developing the large-scale metropolitan networks with high-dimensional quantum information networks. It is expected to provide a new platform for quantum tasks such as superdense coding and quantum teleportation.
Hyperentanglement, as a high-dimensional quantum entanglement phenomenon with multiple degrees of freedom, plays a critical role in quantum communication, quantum computing, and high-dimensional quantum state manipulation. Unlike entangled states in a single degree of freedom, hyperentangled states establish entanglement relationships simultaneously in multiple degrees of freedom, such as polarization, path, and orbital angular momentum. Through entanglement-based distribution techniques, high-dimensional quantum information networks can be constructed. On this basis, a fully connected quantum network with hyperentanglement is constructed in this work, and the polarization and time-bin degree-of-freedom hyperentanglement is realized through the process of second-harmonic generation and spontaneous parametric down-conversion in periodically poled lithium niobate (PPLN) waveguide cascades. The hyperentangled state is then multiplexed into a single-mode fiber by using dense wavelength division multiplexing (DWDM) technology for transmission to terminal users. The quality of the entangled states in the two degrees of freedom is characterized using Franson-type interference and photon-pair coincidence measurement techniques. Polarization entangled states are subjected to quantum state tomography, and entanglement distribution technology is employed to achieve long-distance distribution and quantum key transmission within the network. Experimental results show that the two-photon interference visibility of both polarization and time-bin entanglement is greater than 95%, demonstrating the high quality of the hyperentanglement in the network. After 100-km-entanglement distribution, the fidelity of the quantum states in both degrees of freedom remains above 88%, indicating the effectiveness of long-distance entanglement distribution in this network. Additionally, it is verified that this network supports the distribution of quantum keys over a distance of more than 50 km between users. These results confirm the feasibility of a fully connected quantum network with hyperentanglement and demonstrate the potential for constructing large-scale metropolitan networks by using hyperentanglement. As a higher-dimensional entanglement, hyperentangled states can significantly enhance the capacity and efficiency of quantum information processing. Although the quantum communication is still in its early stages of development, achieving stable storage and transmission of entangled states in large-scale metropolitan networks remains a great challenge. By utilizing the frequency conversion properties and high integration characteristics of the periodically poled lithium niobate waveguides, the three-user hyperentangled quantum network constructed in this work provides a new solution for developing the large-scale metropolitan networks with high-dimensional quantum information networks. It is expected to provide a new platform for quantum tasks such as superdense coding and quantum teleportation.
2025, 74(14): 140701.
doi: 10.7498/aps.74.20250212
Abstract:
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.
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.
2025, 74(14): 140702.
doi: 10.7498/aps.74.20250369
Abstract:
In high-energy density physics (HEDP) experiments, accurate diagnostics of physical parameters such as electron temperature, plasma density, and ionization state are essential for understanding matter behavior under extreme conditions. In these cases, X-ray spectroscopic technique, especially those using crystal spectrometers, is widely used to achieve high spectral resolution. However, a common challenge in such experiments lies in the inherent low brightness and poor spatial coherence of laboratory-based X-ray sources, which limit photon throughput, thus the diagnostic accuracy. Therefore, improving the X-ray optical transmission efficiency between the source and the detector is a key step to improve the performance of the whole system. Capillary X-ray optics, which function based on the principle of total internal reflection within hollow glass structures, provides a promising avenue for beam shaping, collimation, and focusing in the soft-to-hard X-ray range. These optical devices are usually divided into polycapillary type and monocapillary type. While polycapillary optics are composed of numerous micro-channels and used primarily for collimating or focusing divergent X-rays, monocapillary lenses—consisting of single curved channels—provide more precise beam control and are particularly suitable for customized X-ray pathways. Depending on the curvature of the inner reflective surface, monocapillaries are classified into conical, parabolic, and ellipsoidal geometries. In this study, we propose and analyze a novel design of a large-caliber conical glass tube, specifically tailored to address the issue of low light utilization in multi-channel focusing spectrographs with spatial resolution (FSSR). The proposed conical glass tube is made of a single large-diameter capillary structure, simplifying alignment requirements and reducing the surface manufacturing precision typically required by complex aspheric lenses. Its geometric configuration enables X-rays from extended or weak sources to be redirected and controlled to convergef, thereby improving photon collection without significantly altering beam divergence. To quantify the performance of this optical system, we develop a detailed mathematical ray-tracing model and implement it in MATLAB. The model combines physical parameters such as capillary inner diameter, taper angle, reflection loss, and source-detector geometry. Numerical simulations show that compared with traditional flat or slit based systems, the new conical design improves source utilization efficiency by 3.1 times. Furthermore, the lens exhibits a ring-shaped enhancement region in the output intensity profile, which can be regulated by adjusting the capillary geometry and source positioning. This feature enables the spatial customization of the beam profile, thereby facilitating optimized coupling with downstream spectroscopic components or imaging systems. In conclusion, the proposed large-aperture conical monocapillary X-ray lens provides a practical and efficient solution for enhancing X-ray optical transport in low-brightness source environments. Its simple construction, tunable focusing characteristics, and compatibility with diverse X-ray source types make it a compelling candidate for integration into a high-resolution X-ray diagnostic system, particularly in HEDP and laboratory-scale X-ray spectroscopy. This work not only introduces a novel optical approach but also provides a robust theoretical and simulation framework for guiding future experimental design and application of capillary-based X-ray optics.
In high-energy density physics (HEDP) experiments, accurate diagnostics of physical parameters such as electron temperature, plasma density, and ionization state are essential for understanding matter behavior under extreme conditions. In these cases, X-ray spectroscopic technique, especially those using crystal spectrometers, is widely used to achieve high spectral resolution. However, a common challenge in such experiments lies in the inherent low brightness and poor spatial coherence of laboratory-based X-ray sources, which limit photon throughput, thus the diagnostic accuracy. Therefore, improving the X-ray optical transmission efficiency between the source and the detector is a key step to improve the performance of the whole system. Capillary X-ray optics, which function based on the principle of total internal reflection within hollow glass structures, provides a promising avenue for beam shaping, collimation, and focusing in the soft-to-hard X-ray range. These optical devices are usually divided into polycapillary type and monocapillary type. While polycapillary optics are composed of numerous micro-channels and used primarily for collimating or focusing divergent X-rays, monocapillary lenses—consisting of single curved channels—provide more precise beam control and are particularly suitable for customized X-ray pathways. Depending on the curvature of the inner reflective surface, monocapillaries are classified into conical, parabolic, and ellipsoidal geometries. In this study, we propose and analyze a novel design of a large-caliber conical glass tube, specifically tailored to address the issue of low light utilization in multi-channel focusing spectrographs with spatial resolution (FSSR). The proposed conical glass tube is made of a single large-diameter capillary structure, simplifying alignment requirements and reducing the surface manufacturing precision typically required by complex aspheric lenses. Its geometric configuration enables X-rays from extended or weak sources to be redirected and controlled to convergef, thereby improving photon collection without significantly altering beam divergence. To quantify the performance of this optical system, we develop a detailed mathematical ray-tracing model and implement it in MATLAB. The model combines physical parameters such as capillary inner diameter, taper angle, reflection loss, and source-detector geometry. Numerical simulations show that compared with traditional flat or slit based systems, the new conical design improves source utilization efficiency by 3.1 times. Furthermore, the lens exhibits a ring-shaped enhancement region in the output intensity profile, which can be regulated by adjusting the capillary geometry and source positioning. This feature enables the spatial customization of the beam profile, thereby facilitating optimized coupling with downstream spectroscopic components or imaging systems. In conclusion, the proposed large-aperture conical monocapillary X-ray lens provides a practical and efficient solution for enhancing X-ray optical transport in low-brightness source environments. Its simple construction, tunable focusing characteristics, and compatibility with diverse X-ray source types make it a compelling candidate for integration into a high-resolution X-ray diagnostic system, particularly in HEDP and laboratory-scale X-ray spectroscopy. This work not only introduces a novel optical approach but also provides a robust theoretical and simulation framework for guiding future experimental design and application of capillary-based X-ray optics.
2025, 74(14): 141201.
doi: 10.7498/aps.74.20250448
Abstract:
The channel plasma characteristics of an artificially triggered lightning in Guangdong, China, are analyzed using slit-free spectroscopy technology. Based on spectral diagnostic methods, the maximum and minimum values of the triggered lightning channel current are determined to be about 30.9 kA and 25.6 kA (minimum), respectively, and the current is simulated using a modified transmission line model with linear current decay (MTLL). To investigate the electric field distribution, the finite-difference time-domain (FDTD) method and transmission line (TL) model are employed. At a distance of 58 m, assuming a return stroke velocity of 1.3 × 108 m/s, the TL-predicted radiation electric field deviates from experimental electric field, but is very close to the FDTD-simulation of the vertical electric field. Moreover, the analyses of magnetic fields at 58 m, 90 m, and 1.6 km are compared using FDTD simulations, dipole approximation, and charge magnetic field limit (CMFL) estimation. The discrepancies between calculated value and experimental values appear at 58 m and 90 m, which may be due to the near-field interference and measurement limitation. However, they become small at 1.6 km. This work is helpful for the study of lightning electromagnetic field properties and spectral diagnosis.
The channel plasma characteristics of an artificially triggered lightning in Guangdong, China, are analyzed using slit-free spectroscopy technology. Based on spectral diagnostic methods, the maximum and minimum values of the triggered lightning channel current are determined to be about 30.9 kA and 25.6 kA (minimum), respectively, and the current is simulated using a modified transmission line model with linear current decay (MTLL). To investigate the electric field distribution, the finite-difference time-domain (FDTD) method and transmission line (TL) model are employed. At a distance of 58 m, assuming a return stroke velocity of 1.3 × 108 m/s, the TL-predicted radiation electric field deviates from experimental electric field, but is very close to the FDTD-simulation of the vertical electric field. Moreover, the analyses of magnetic fields at 58 m, 90 m, and 1.6 km are compared using FDTD simulations, dipole approximation, and charge magnetic field limit (CMFL) estimation. The discrepancies between calculated value and experimental values appear at 58 m and 90 m, which may be due to the near-field interference and measurement limitation. However, they become small at 1.6 km. This work is helpful for the study of lightning electromagnetic field properties and spectral diagnosis.
2025, 74(14): 142101.
doi: 10.7498/aps.74.20250451
Abstract:
The properties of the color-flavor-locked (CFL) quark matter under strong magnetic fields at finite temperatures within a quasiparticle model are investigated in this work. Our results indicate that CFL quark matter pressure becomes anisotropic under strong magnetic fields, while its equation of state (EOS) and equivalent quark mass are both strongly affected by temperature, energy gap constant Δ, and strong magnetic field inside the CFL quark matter. The equivalent quark mass of CFL quark matter decreases with temperature and magnetic field strength increasing, which implies an inverse magnetic catalysis phenomenon. The results also indicate that the entropy per baryon of the CFL quark matter increases with temperature rising and decreases with Δ increasing. Furthermore, the properties of CFL magnetars in different isentropic stages are studied. The star mass and radius depend primarily on the strength and orientation of magnetic fieldinside the CFL magnestars. The maximum star mass increases with entropy per baryon increasing, while the star matter temperature rises at high isentropic stage. Moreover, the polytropic index of the CFL quark matter decreases with star mass increasing.
The properties of the color-flavor-locked (CFL) quark matter under strong magnetic fields at finite temperatures within a quasiparticle model are investigated in this work. Our results indicate that CFL quark matter pressure becomes anisotropic under strong magnetic fields, while its equation of state (EOS) and equivalent quark mass are both strongly affected by temperature, energy gap constant Δ, and strong magnetic field inside the CFL quark matter. The equivalent quark mass of CFL quark matter decreases with temperature and magnetic field strength increasing, which implies an inverse magnetic catalysis phenomenon. The results also indicate that the entropy per baryon of the CFL quark matter increases with temperature rising and decreases with Δ increasing. Furthermore, the properties of CFL magnetars in different isentropic stages are studied. The star mass and radius depend primarily on the strength and orientation of magnetic fieldinside the CFL magnestars. The maximum star mass increases with entropy per baryon increasing, while the star matter temperature rises at high isentropic stage. Moreover, the polytropic index of the CFL quark matter decreases with star mass increasing.
2025, 74(14): 143101.
doi: 10.7498/aps.74.20250324
Abstract:
Steam condensation is a common physical phenomenon in nature and plays an important role in various industrial processes. Therefore, the regulation mechanism of steam condensation process has been widely concerned by scholars in recent years. In this paper, the molecular dynamics simulation method is used to study the vapor condensation behavior of copper surface by establishing a secondary microstructure model. The influences of different geometrical characteristics on the condensation process are discussed by analyzing the nucleation and merging time of droplets, the vapor condensation snapshot, the total number of condensed water molecules, and the total number of water molecules in the maximum condensed drop. With the increase of column width or column height ratio, the molecular weight of the total condensed water first increases and then decreases.
Steam condensation is a common physical phenomenon in nature and plays an important role in various industrial processes. Therefore, the regulation mechanism of steam condensation process has been widely concerned by scholars in recent years. In this paper, the molecular dynamics simulation method is used to study the vapor condensation behavior of copper surface by establishing a secondary microstructure model. The influences of different geometrical characteristics on the condensation process are discussed by analyzing the nucleation and merging time of droplets, the vapor condensation snapshot, the total number of condensed water molecules, and the total number of water molecules in the maximum condensed drop. With the increase of column width or column height ratio, the molecular weight of the total condensed water first increases and then decreases.
2025, 74(14): 144101.
doi: 10.7498/aps.74.20250130
Abstract:
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.
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.
2025, 74(14): 144201.
doi: 10.7498/aps.74.20250485
Abstract:
Topological pumping based on Thouless pumping can be effectively applied to optical waveguide array systems to achieve robust light manipulation with strong disturbance resistance. One of its typical models, the Rice-Mele (R-M) model, enables directional light field to transmit from the leftmost (rightmost) waveguide to the rightmost (leftmost) waveguide, which can be utilized to realize fabrication-tolerant optical couplers. Adiabatic evolution is a critical factor influencing the transport of topological eigenstates. However, it requires the system’s parameter variation to be sufficiently slow, which leads to excessively long waveguide lengths, limiting device compactness. To reduce the size, non-adiabatic evolution offers a feasible alternative. Meanwhile, the adiabatic properties of topological pumping models introduce new degrees of freedom, expanding possibilities for light manipulation. Based on the R-M model, this work analyzes the relationship between adiabatic property and structure length L, investigates light field evolution behavior when adiabatic condition is violated, and explores the transition from adiabatic to non-adiabatic regimes. When adiabatic condition is satisfied (L1 = 1000 μm), the light field evolution aligns with the eigen edge state. The output mode is manifested as an edge state and localized at the edge waveguide. As length shortens (L2 = 250 μm and L4 = 30 μm), the deviation between light field and eigen edge state arises, and the eigen bulk states get involved in the light field. The output modes are manifested as the superposition of edge state and bulk state, with energy spreading to other waveguides. At a specific length (L3 = 110 μm), the light-field undergoes non-adiabatic evolution: initially deviating from the edge state and later returning to the edge state. This phenomenon is termed adiabatic equivalent evolution. The output mode is localized at the edge waveguide, which is the same as the adiabatic evolution. By analyzing the fidelity between output mode and eigen edge state, we demonstrate that the adiabaticity can effectively regulate fidelity, achieving signal on/off at the edge waveguide. As structural length decreases, fidelity gradually declines and exhibits an oscillating behavior. When fidelity approaches to 1, the adiabatic equivalent evolution emerges. The first-order perturbation approximation reveals that these oscillations stem from destructive interference between edge and bulk states, thereby confirming their intrinsic origin in band interference. This mechanism enables eigen edge state output at shorter lengths than adiabatic requirements, providing a reliable approach for miniaturizing devices. Furthermore, the fabrication tolerance is analyzed. Within the whole waveguides width deviation range of –35–+30 nm (relative deviation range of –7%–+6%), the transmission of edge waveguide through the adiabatic equivalent evolution is larger than 0.9. This work analyses light-field evolution process and underlying physics for topological pumping in non-adiabatic regimes, supplements theoretical methods for analyzing non-adiabatic evolution, and provides strategies for achieving eigen edge state output at reduced lengths. This work provides some feasible principles for designing topological optical waveguide arrays, guiding the development of compact and robust on-chip photonic devices such as optical couplers and splitters, which have broad application prospects in integrated photonics.
Topological pumping based on Thouless pumping can be effectively applied to optical waveguide array systems to achieve robust light manipulation with strong disturbance resistance. One of its typical models, the Rice-Mele (R-M) model, enables directional light field to transmit from the leftmost (rightmost) waveguide to the rightmost (leftmost) waveguide, which can be utilized to realize fabrication-tolerant optical couplers. Adiabatic evolution is a critical factor influencing the transport of topological eigenstates. However, it requires the system’s parameter variation to be sufficiently slow, which leads to excessively long waveguide lengths, limiting device compactness. To reduce the size, non-adiabatic evolution offers a feasible alternative. Meanwhile, the adiabatic properties of topological pumping models introduce new degrees of freedom, expanding possibilities for light manipulation. Based on the R-M model, this work analyzes the relationship between adiabatic property and structure length L, investigates light field evolution behavior when adiabatic condition is violated, and explores the transition from adiabatic to non-adiabatic regimes. When adiabatic condition is satisfied (L1 = 1000 μm), the light field evolution aligns with the eigen edge state. The output mode is manifested as an edge state and localized at the edge waveguide. As length shortens (L2 = 250 μm and L4 = 30 μm), the deviation between light field and eigen edge state arises, and the eigen bulk states get involved in the light field. The output modes are manifested as the superposition of edge state and bulk state, with energy spreading to other waveguides. At a specific length (L3 = 110 μm), the light-field undergoes non-adiabatic evolution: initially deviating from the edge state and later returning to the edge state. This phenomenon is termed adiabatic equivalent evolution. The output mode is localized at the edge waveguide, which is the same as the adiabatic evolution. By analyzing the fidelity between output mode and eigen edge state, we demonstrate that the adiabaticity can effectively regulate fidelity, achieving signal on/off at the edge waveguide. As structural length decreases, fidelity gradually declines and exhibits an oscillating behavior. When fidelity approaches to 1, the adiabatic equivalent evolution emerges. The first-order perturbation approximation reveals that these oscillations stem from destructive interference between edge and bulk states, thereby confirming their intrinsic origin in band interference. This mechanism enables eigen edge state output at shorter lengths than adiabatic requirements, providing a reliable approach for miniaturizing devices. Furthermore, the fabrication tolerance is analyzed. Within the whole waveguides width deviation range of –35–+30 nm (relative deviation range of –7%–+6%), the transmission of edge waveguide through the adiabatic equivalent evolution is larger than 0.9. This work analyses light-field evolution process and underlying physics for topological pumping in non-adiabatic regimes, supplements theoretical methods for analyzing non-adiabatic evolution, and provides strategies for achieving eigen edge state output at reduced lengths. This work provides some feasible principles for designing topological optical waveguide arrays, guiding the development of compact and robust on-chip photonic devices such as optical couplers and splitters, which have broad application prospects in integrated photonics.
2025, 74(14): 144202.
doi: 10.7498/aps.74.20250395
Abstract:
The bunching and antibunching effects of light fields reflect the spatiotemporal correlation of photons and are key indicators for distinguishing classical and non-classical quantum statistics. They play a crucial role in quantum information processing and precise measurement. In this paper, we investigate the super-bunching and antibunching effects of the full-time-delay higher-order coherence function \begin{document}$ {g^{(n)}} $\end{document} Under ideal conditions, the high-order coherence of squeezed thermal states and squeezed number states is analyzed by changing compression parameter \begin{document}$ r $\end{document} \begin{document}$ \alpha $\end{document} \begin{document}$ n $\end{document} \begin{document}$ r \in [0, 1] $\end{document} \begin{document}$ {g^{({2})}} = 9.98 \times 10^5$\end{document} \begin{document}$ {g^{({3})}} = 8.98 \times 10^6$\end{document} \begin{document}$ {g^{({4})}} = 8.96 \times 10^{12}$\end{document} \begin{document}$ {g^{({5})}} = 2.24 \times 10^{14}$\end{document} \begin{document}$ {g^{({2})}} \in [1.60 \times 10^{-5}, 1.09] $\end{document} \begin{document}$ {g^{({3})}} \in [9.02 \times 10^{-6}, 1.16] $\end{document} \begin{document}$ {g^{({4})}} \in [4.75 \times 10^{-6}, 1.22] $\end{document} \begin{document}$ {g^{({5})}} \in [9.39 \times 10^{-6}, 1.30]) $\end{document} Simultaneously, this study analyzes the high-order photon coherence of squeezed thermal states and squeezed number states under experimental conditions, with background noise \begin{document}$\gamma $\end{document} \begin{document}$\eta $\end{document} \begin{document}$ \alpha $\end{document} \begin{document}$ \alpha $\end{document} \begin{document}$ \alpha = 0.5$\end{document} \begin{document}$ {g^{({2})}} = 2.149 $\end{document} \begin{document}$ {g^{({3})}} = 6.389 $\end{document} \begin{document}$ {g^{({4})}} = 23.228 $\end{document} \begin{document}$ {S^{({2})}} = 5.47$\end{document} \begin{document}$ {S^{(3)}}= 4.86 $\end{document} \begin{document}$ n $\end{document} \begin{document}$S$\end{document} In addition, the variation characteristics of the high-order photon coherence function of the squeezed thermal state light field under the full time-delay conditions are investigated. The full time-delay high-order coherence \begin{document}$ {g^{(n)}} $\end{document} \begin{document}$ {\tau _{{\text{STS}}}} $\end{document} Based on the theoretical framework established in this work, future experiments may focus on adjusting the pump power, intracavity loss, and crystal temperature of optical parametric amplifiers to jointly control the squeezing degree and mean photon number, enabling stable generation of squeezed thermal states in different parameter regimes. Additionally, the precise measurement of higher-order coherence can be achieved using cascaded HBT detection systems with multiple inputs and high temporal resolution. In summary, by considering environmental noise, detection efficiency, and time delay, and by adjusting the average photon number, the number of squeezed photons, and the squeezing parameters, this method can prepare super-bunching squeezed thermal states and squeezed number states, whose higher-order coherence can be continuously adjusted over a wide range, thereby facilitating efficient quantum state preparation and manipulation, as well as high-resolution quantum imaging.
2025, 74(14): 144203.
doi: 10.7498/aps.74.20250223
Abstract:
Cavity quantum electrodynamics (QED) serves as a fundamental platform for studying light-matter interactions at a single-particle level and has been extensively investigated in fundamental physics and quantum information. Recent development of parametrically squeezed techniques has demonstrated that they have the remarkable ability to exponentially enhance coherent atom-cavity coupling. However, the full extent to which these techniques can manipulate quantum optical phenomena requires further exploration. This work systematically investigates the influence of optical parametric amplification on single-photon excited atom-cavity systems within a parametrically driven cavity. In the proposed model, optical parametric amplification converts the driving photons into a squeezed cavity mode, which enhances the atom-cavity interaction into the strong coupling region. Through analytical derivation of atomic and cavity radiation spectra, we demonstrate that the optical parametric amplification induces splitting of atomic radiation spectra while exerting negligible effects on spectral intensity. Conversely, the cavity transmission spectrum exhibits both pronounced splitting and nonlinear intensity amplification. Notably, as driving field intensity approaches a critical intensity regime, the cavity radiation spectrum intensity is significantly enhanced. The underlying mechanism is parametric driving amplification, which converts the driving light into a squeezed cavity mode. When this squeezed mode is mapped back to the fundamental mode of the cavity through Bogoliubov squeezing transformation, the pump photons within the squeezed cavity mode are converted into the photons that contribute to the radiation spectrum of the cavity, thereby amplifying its intensity. This parametric enhancement method not only deepens the basic understanding of light-matter interactions, but also establishes a practical framework for improving the single-photon detection sensitivity in cavity-based quantum systems. These findings have broad prospects for quantum sensing and information processing applications.
Cavity quantum electrodynamics (QED) serves as a fundamental platform for studying light-matter interactions at a single-particle level and has been extensively investigated in fundamental physics and quantum information. Recent development of parametrically squeezed techniques has demonstrated that they have the remarkable ability to exponentially enhance coherent atom-cavity coupling. However, the full extent to which these techniques can manipulate quantum optical phenomena requires further exploration. This work systematically investigates the influence of optical parametric amplification on single-photon excited atom-cavity systems within a parametrically driven cavity. In the proposed model, optical parametric amplification converts the driving photons into a squeezed cavity mode, which enhances the atom-cavity interaction into the strong coupling region. Through analytical derivation of atomic and cavity radiation spectra, we demonstrate that the optical parametric amplification induces splitting of atomic radiation spectra while exerting negligible effects on spectral intensity. Conversely, the cavity transmission spectrum exhibits both pronounced splitting and nonlinear intensity amplification. Notably, as driving field intensity approaches a critical intensity regime, the cavity radiation spectrum intensity is significantly enhanced. The underlying mechanism is parametric driving amplification, which converts the driving light into a squeezed cavity mode. When this squeezed mode is mapped back to the fundamental mode of the cavity through Bogoliubov squeezing transformation, the pump photons within the squeezed cavity mode are converted into the photons that contribute to the radiation spectrum of the cavity, thereby amplifying its intensity. This parametric enhancement method not only deepens the basic understanding of light-matter interactions, but also establishes a practical framework for improving the single-photon detection sensitivity in cavity-based quantum systems. These findings have broad prospects for quantum sensing and information processing applications.
2025, 74(14): 144204.
doi: 10.7498/aps.74.20250247
Abstract:
Deep ultraviolet (DUV) picosecond lasers, operating in a 200–280 nm wavelength range, possess significant advantages, such as high photon energy and high resolution. These attributes make them highly promising for applications like semiconductor detection, ensuring the production of high-quality, defect-free semiconductor devices, as well as for advanced scientific research and industrial processing. High-power DUV picosecond lasers are typically generated via nonlinear frequency conversion of infrared lasers based on master oscillator power amplifier (MOPA) configurations. Among various DUV laser technologies, systems based on β-BBO crystals are particularly valuable due to their simple design and cost-effectiveness. However, the linear two-photon absorption, as well as the formation of dynamic color centers in BBO, are significant limitations for high-power, high-repetition-rate UV radiation, leading to thermal effects. Hence, it is important to carefully study the performance characteristics of BBO for high-power, high-repetition-rate pulse generation in the UV at 266 nm. This study presents a high-power, all-solid-state DUV picosecond laser developed using a 1064 nm Nd:YVO4 MOPA amplification architecture. In this experimental setup, a 50 mW, 7.8 ps, 20 MHz all-fiber SESAM mode-locked laser is used as a seed source, achieving 140 W in amplified output power 8.33 ps in pulse duration at 1064 nm via MOPA. In the nonlinear frequency conversion process, the amplified laser pulses are initially focused onto an LBO crystal for secondary harmonic generation (SHG). Precise temperature control of the LBO crystal can generate a 532 nm output with 73 W in power and 6.93 ps in pulse duration, while achieving 52.64% in conversion efficiency. Two-photon absorption is a key factor limiting the further enhancement of deep ultraviolet (DUV) laser power. By investigating the transmittance and temperature rise of a high-power dual-wavelength laser in a β-BBO crystal, the results indicate that strong two-photon absorption occurs under high-power DUV irradiation. This absorption induces significant thermal effects, resulting in a temperature gradient within the crystal and leading to phase mismatch, which severely affects frequency conversion efficiency and output stability. To solve this problem and further increase the DUV output power, a large-spot pumping scheme (spot size: 1.5 mm × 1 mm) is adopted in this work. Under a pump peak power density of less than 1.11 GW/cm2, the thermal gradient caused by two-photon absorption is effectively suppressed, achieving maximum fourth-harmonic output power of 11 W. The corresponding single-pulse energy reaches 13.75 μJ. The root mean square (RMS) jitter, measured in an 8-hour period, is less than 0.96%. This all-solid-state DUV laser demonstrates excellent performance characteristics, including high average power, stability, resolution, and peak power, making it a strong candidate for applications requiring efficient and high-precision processing or detection. By further increasing the pump power and optimizing the temperature control system, the output power of the laser can be significantly enhanced, thereby broadening its applicability and competitiveness in high-end fields such as semiconductor manufacturing, advanced research, and industrial processing.
2025, 74(14): 144301.
doi: 10.7498/aps.74.20250419
Abstract:
A novel target depth estimation method based on normal mode intensity match is proposed for shallow water environment by using horizontal array to overcome the performance degradation observed in traditional approaches under the condition that seabed parameters are not matched. Firstly, horizontal wavenumbers and normal mode intensities are estimated through wavenumber domain beamforming. Secondly, modal function of normal mode inversion is performed by solving the modal function characteristic equation by using the finite difference method. Thirdly, the match degree between inverted and estimated normal mode intensities is evaluated to estimate target depth. The numerical simulation results show that the proposed method can accurately estimate the target depth in shallow water scenarios without knowing the seabed parameters. Furthermore, the performance of the method is analyzed under different conditions including different seabed parameters, array apertures and source frequencies. The results reveal three conclusions: 1) the mismatch of seabed parameters has no influence on the method; 2) the effective performance of full depth source estimation requires no less than 128 array elements, a frequency band range of 50–150 Hz, and the signal-to-noise radio of the element on a horizontal line array exceeding –10 dB; 3) the method has robust performance against sound speed profile mismatch. Finally, the feasibility of the proposed method is validated by the experimental data received by a horizontally towing 77-element array during the shallow-water sea trial in the South China Sea.
A novel target depth estimation method based on normal mode intensity match is proposed for shallow water environment by using horizontal array to overcome the performance degradation observed in traditional approaches under the condition that seabed parameters are not matched. Firstly, horizontal wavenumbers and normal mode intensities are estimated through wavenumber domain beamforming. Secondly, modal function of normal mode inversion is performed by solving the modal function characteristic equation by using the finite difference method. Thirdly, the match degree between inverted and estimated normal mode intensities is evaluated to estimate target depth. The numerical simulation results show that the proposed method can accurately estimate the target depth in shallow water scenarios without knowing the seabed parameters. Furthermore, the performance of the method is analyzed under different conditions including different seabed parameters, array apertures and source frequencies. The results reveal three conclusions: 1) the mismatch of seabed parameters has no influence on the method; 2) the effective performance of full depth source estimation requires no less than 128 array elements, a frequency band range of 50–150 Hz, and the signal-to-noise radio of the element on a horizontal line array exceeding –10 dB; 3) the method has robust performance against sound speed profile mismatch. Finally, the feasibility of the proposed method is validated by the experimental data received by a horizontally towing 77-element array during the shallow-water sea trial in the South China Sea.
2025, 74(14): 144302.
doi: 10.7498/aps.74.20250353
Abstract:
In the near-field of a subsonic jet, complex energy transport and transformation processes occur between kinetic energy, thermal energy, and acoustic energy, which play a crucial role in jet instability and noise radiation. Accurately characterizing the transport features of each energy component is essential for developing effective noise suppression technologies. According to Myers’ exact energy equation for total disturbances in arbitrary steady flow [1991 J. Fluid Mech. 226 383 ], the present study develops a modified energy equation based on hydro-acoustic mode decomposition to separate the contributions of vortical, entropic, and acoustic modes to the total disturbance energy. The method begins with the decomposition formulas for velocity, pressure, and density, following the hydro-acoustic mode decomposition method proposed by Han et al. [2023 Phys. Fluids 35 076107 ]. In Myers’ energy equation framework, the disturbances of primitive variables (velocity, pressure, and density) are expressed as linear combinations of their vortical, entropic, and acoustic components. With this formula, the vortical (entropic, acoustic) energy is defined as being contributed only by the disturbance of the corresponding mode, while the nonlinear energy is attributed to interaction between vortical, entropic, and acoustic components. This approach yields a modified energy equation capable of distinguishing the individual contributions of vortical, entropic, and acoustic modes to both total disturbance energy and energy flux, thus making it particularly suitable for analyzing energy transport characteristics in the near flow field. The developed equation is used to analyze a subsonic jet with a Mach number of 0.9, revealing different spatial distributions and transport mechanisms of hydrodynamic energy and acoustic energy. The results indicate that vortical energy and entropic energy are mainly concentrated in the near-field, convecting downstream at a velocity about 0.8 times the jet velocity. In contrast, acoustic energy exhibits dual propagation characteristics: it radiates outward to the far field through acoustic waves outside the potential core, while propagating upstream through trapped waves inside the potential core. The energy related to multi-mode nonlinear interactions is mainly concentrated in the jet wake and propagates without obvious directionality. The total disturbance energy is mainly contributed by vortical energy, while the acoustic energy only accounts for a small part of the total disturbance energy, approximately 10–3 of the total. This refined analysis provides deeper insights into the complex energy dynamics in subsonic jets and valuable information for predicting and controlling jet noise strategies. The modified energy equation provides a robust framework for understanding and quantifying the intricate energy transport processes in jet flows.
In the near-field of a subsonic jet, complex energy transport and transformation processes occur between kinetic energy, thermal energy, and acoustic energy, which play a crucial role in jet instability and noise radiation. Accurately characterizing the transport features of each energy component is essential for developing effective noise suppression technologies. According to Myers’ exact energy equation for total disturbances in arbitrary steady flow [
2025, 74(14): 144303.
doi: 10.7498/aps.74.20250430
Abstract:
Ultrasound thrombolysis primarily relies on transient shockwaves and microjets from collapsing cavitation bubbles to mechanically disrupt thrombus structures. Although it shows clinical potential, its efficacy is still limited by low cavitation energy transfer efficiency and unpredictable tissue damage, due to incomplete understanding of single bubble dynamics and the synergistic mechanisms of multi-bubble interactions. This study introduces a hyper-viscoelastic constitutive model incorporating blood clot mechanics to analyze stress accumulation under sequential microbubble impacts. A gas-liquid-solid coupling multi-physics model quantifies bubble collapse dynamics near thrombi, and integrates structural damping terms to represent energy dissipation during fluid-solid interactions. Parameter analysis shows that the intensity of jet impact is positively correlated with thrombus mass and ultrasound amplitude, but inversely related to dimensionless distance, ultrasound frequency, and initial bubble radius. The proposed rate-dependent Ogden-Prony model effectively captures thrombus behaviors under transient impacts, including strain hardening, rate-dependent strengthening, and stress relaxation. Sequential jet impacts induce cumulative stress through strain hardening, with multi-bubble synergy achieving significantly higher stresses than single-bubble impact. Optimal bubble radius distribution can amplify the normal/shear stress inside thrombi—maximum normal stress generated by the double bubble impact sequences is 6.02 MPa, exceeding the tensile strength of the thrombus, while the maximum stress generated by single bubble impact is 1.45 MPa. The key quantitative relationships between bubble cluster parameters, dimensionless distance, thrombus mass, and stress accumulation provide optimization guidelines for ultrasound thrombolysis. Notably, controlled multi-bubble jet impact sequences with attenuated pressure peaks demonstrate enhanced therapeutic potential through cumulative mechanical effects rather than a single high-intensity impact.
2025, 74(14): 144205.
doi: 10.7498/aps.74.20250526
Abstract:
Topologically protected waveguides have aroused increasing interest due to their robustness against disorder and defects. In parallel, the advent of non-Hermitian physics with its inherent gain-and-loss mechanisms has introduced new tools for manipulating wave localization and transport. However, most attempts to combine non-Hermitian effects with topological systems uniformly impose the non-Hermitian skin effect (NHSE) on all modes, without selectivity targeting topological states. In this work, we propose a scheme thatachieves topologically selective NHSE by combining sub-symmetry-protected boundary modes with long-range non-reciprocal couplings. In an improved Su–Schrieffer–Heeger (SSH) chain, we analytically demonstrate that robust zero-energy edge modes can be preserved even in spectra filled with bulk states, while selectively applying the NHSE to the trivial bulk states to achieve the spatial separation between topological state and bulk state. By adjusting the long-range couplings a non-Hermitian phase transition can be observed in the complex energy spectrum: it transitions from a closed loop (circle) to an open arc, and ultimately to a reversely coiled loop. These transitions correspond respectively to a leftward NHSE, the disappearance of the NHSE, and a rightward NHSE. According to the calculations of the generalized Brillouin zone (GBZ), we confirm this transition by observing the GBZ passing through the unit circle, indicating a change in the direction of NHSE.We further extend our model to a two-dimensional higher-order SSH lattice, where selective non-Hermitian modulation enables clear spatial separation between topological corner states and bulk modes. To quantify this, we compute the local density of states (LDOS) in the complex energy plane for site 0 (a topologically localized corner) and site 288 (a region exhibiting NHSE). The comparison of LDOS between the two sites reveals that the topological states are primarily localized at site 0, while the bulk states affected by NHSE accumulate at site 288.To validate the theoretical predictions, we perform finite-element simulations of optical resonator arrays by using whispering-gallery modes. By adjusting the coupling distances and incorporating gain/loss through refractive index engineering, we replicate the modified SSH model and confirm the selective localization of topological and bulk modes.Our results provide a robust method for selectively exciting and spatially controlling the topological states in non-Hermitian systems, and also lay a foundation for future low-crosstalk high-stability topological photonic devices.
Topologically protected waveguides have aroused increasing interest due to their robustness against disorder and defects. In parallel, the advent of non-Hermitian physics with its inherent gain-and-loss mechanisms has introduced new tools for manipulating wave localization and transport. However, most attempts to combine non-Hermitian effects with topological systems uniformly impose the non-Hermitian skin effect (NHSE) on all modes, without selectivity targeting topological states. In this work, we propose a scheme thatachieves topologically selective NHSE by combining sub-symmetry-protected boundary modes with long-range non-reciprocal couplings. In an improved Su–Schrieffer–Heeger (SSH) chain, we analytically demonstrate that robust zero-energy edge modes can be preserved even in spectra filled with bulk states, while selectively applying the NHSE to the trivial bulk states to achieve the spatial separation between topological state and bulk state. By adjusting the long-range couplings a non-Hermitian phase transition can be observed in the complex energy spectrum: it transitions from a closed loop (circle) to an open arc, and ultimately to a reversely coiled loop. These transitions correspond respectively to a leftward NHSE, the disappearance of the NHSE, and a rightward NHSE. According to the calculations of the generalized Brillouin zone (GBZ), we confirm this transition by observing the GBZ passing through the unit circle, indicating a change in the direction of NHSE.We further extend our model to a two-dimensional higher-order SSH lattice, where selective non-Hermitian modulation enables clear spatial separation between topological corner states and bulk modes. To quantify this, we compute the local density of states (LDOS) in the complex energy plane for site 0 (a topologically localized corner) and site 288 (a region exhibiting NHSE). The comparison of LDOS between the two sites reveals that the topological states are primarily localized at site 0, while the bulk states affected by NHSE accumulate at site 288.To validate the theoretical predictions, we perform finite-element simulations of optical resonator arrays by using whispering-gallery modes. By adjusting the coupling distances and incorporating gain/loss through refractive index engineering, we replicate the modified SSH model and confirm the selective localization of topological and bulk modes.Our results provide a robust method for selectively exciting and spatially controlling the topological states in non-Hermitian systems, and also lay a foundation for future low-crosstalk high-stability topological photonic devices.
2025, 74(14): 145101.
doi: 10.7498/aps.74.20250376
Abstract:
Microscopic and macroscopic magnetic responses are widely used for non-destructive testing and evaluating stress. The basic principle is that the magnetic domain pattern and magnetic domain dynamics are highly dependent on applied tensile stress. Understanding the evolution of magnetic domains under the action of multi-field coupling is critical for developing novel magnetic non-destructive testing technology. In this work, the influences of stress on magnetic domain and magneto-acoustic emission signals in polycrystalline materials are investigated based on the magneto-optical Kerr imaging and magneto-acoustic emission detection system. On a macroscopic scale, the mapping relationship between the magneto-acoustic emission signal and stress is established. Microscopically, the influences of the stress and grain boundaries on the magnetic domain patterns are investigated. And a mapping relationship between percentage of supplementary domains and stress is built. Finally, the interrelation between the domain wall dynamics and the magneto-acoustic emission signal is revealed from the nucleation of supplementary domains and their stress-dependent evolution. The results indicate that the magnetoelastic effect reduces the density of supplementary domains and 90° domains, which weakens the magneto-acoustic emission signal. The stress-magneto-acoustic model and the influence of the stress on the magnetic domain in this work reveal the mechanism of magneto-acoustic emission technique for stress measurement. It also provides a theoretical foundation for developing stress-magnetic-acoustic models and magnetic non-destructive testing technology.
Microscopic and macroscopic magnetic responses are widely used for non-destructive testing and evaluating stress. The basic principle is that the magnetic domain pattern and magnetic domain dynamics are highly dependent on applied tensile stress. Understanding the evolution of magnetic domains under the action of multi-field coupling is critical for developing novel magnetic non-destructive testing technology. In this work, the influences of stress on magnetic domain and magneto-acoustic emission signals in polycrystalline materials are investigated based on the magneto-optical Kerr imaging and magneto-acoustic emission detection system. On a macroscopic scale, the mapping relationship between the magneto-acoustic emission signal and stress is established. Microscopically, the influences of the stress and grain boundaries on the magnetic domain patterns are investigated. And a mapping relationship between percentage of supplementary domains and stress is built. Finally, the interrelation between the domain wall dynamics and the magneto-acoustic emission signal is revealed from the nucleation of supplementary domains and their stress-dependent evolution. The results indicate that the magnetoelastic effect reduces the density of supplementary domains and 90° domains, which weakens the magneto-acoustic emission signal. The stress-magneto-acoustic model and the influence of the stress on the magnetic domain in this work reveal the mechanism of magneto-acoustic emission technique for stress measurement. It also provides a theoretical foundation for developing stress-magnetic-acoustic models and magnetic non-destructive testing technology.
2025, 74(14): 145201.
doi: 10.7498/aps.74.20250244
Abstract:
In recent years, dual-frequency capacitively coupled plasma discharge technology has demonstrated remarkable advantages in the fields of material processing. In this paper, a one-dimensional PIC/MCC (particle-in-cell/Monte Carlocollision) simulation method is used to discuss the influence of low frequency on the discharge characteristics of capacitively coupled argon/methane plasma driven by dual-frequency (20/100 MHz) dipole, with an external magnetic field added. The simulation results show that when the high frequency is an integer multiple of the low frequency, the superposition of high and low frequencies is significant, and the sheath oscillation is more obvious. As low frequency increases, the electron density, charge density, high-energy electron density and electron heating rate all increase. Specifically, as low frequency increase, the electron density increases to 14%, the electron temperature near the sheath decreases by about 12%, the electron energy probability distribution (EEPF) shows a double Maxwellian distribution, the populations of both low-energy electrons and high-energy electrons increase, and at the same time, the densities of various ions and the angle and energy distributions of \begin{document}${\text{CH}}_{4}^{+} $\end{document} \begin{document}${\text{CH}}_{3}^{+} $\end{document} In the Ar/CH4 plasma driven by dual-frequency, with external magnetic field added, the controlling of ion energy can effectively optimize the structure and performance of carbon-containing films. By regulating discharge parameters to control the incident angle of the ions on the substrate, carbon-containing atoms can be deposited in a specific direction, thereby achieving the directional growth of carbon-containing films. This is significant for the preparation of graphene films, carbon nanotube arrays, etc. Meanwhile, the regulation of the incident angle of ions is helpful to improve the binding force between the carbon film and the substrate. It is found in this study that when the incident angle of the ions is around 0.32, the average energy of the ions reaches its peak. This peak is most significant at a low frequency of 15 MHz. The results in this paper provide a theoretical reference for preparing carbon films.
2025, 74(14): 145202.
doi: 10.7498/aps.74.20250113
Abstract:
Laser-produced plasma extreme ultraviolet (LPP-EUV) source is one of the key technologies in advanced lithography systems. Recently, solid-state lasers have been proposed as an alternative drive laser for the next-generation LPP-EUV source. Compared with currently used CO2 lasers, solid-state lasers have higher electrical-optical efficiency, more compact size, and better pulse shape tunability. Although limited to shorter operating wavelengths, the solid-state lasers have higher critical plasma density and optical depth. Consequently, re-absorption and spectral broadening cause lower conversion efficiency (CE). Therefore, to optimize EUV emission features and improve CE, a 0.532-μm pre-pulse laser is utilized in this work to modulate the plasma density distribution. The pre-pulse and a 1.064-μm Nd: YAG laser (the main pulse) are incident on an Sn slab target co-axially. The EUV energy and spectra of the Sn plasma are characterized at various delay times. It is demonstrated that compared with the 1.064-μm single pulse, the 0.532-μm pre-pulse laser with short delay times of 10 ns and 20 ns respectively results in a 4% increase in CE at 26° and 18% increase at 39°. The angular distribution of EUV energy is modulated by the 0.532-μm pre-pulse. An isotropic emission can be obtained within a certain delay time. The spectral feature near 13.5 nm is optimized, and a spectral purity of 12.2% is improved by 69%. The laser spot sizes of 0.3 mm and 1 mm for the pre-pulse are compared in the experiment. The results show that the 1-mm spot size has a better modulation effect on the EUV emission. Moreover, the time-resolved visible-band plasma profile is captured by an ICCD with 1.6-ns gate width. The plasma size and the distance to the target surface are increased by the 0.532-μm pre-pulse, which suggests that the energy of the main pulse is deposited in the low-density pre-plasma plume instead of in the plasma near the target surface. The lower plasma density leads to an increase in CE and spectral purity. The angular distribution of EUV energy is found to be closely related to the plasma morphology, and defined as the ratio of the longitudinal size to lateral size of the plasma. This indicates that the variation of plasma morphology can influence the angular distribution of EUV energy, which is caused by the 0.532-μm pre-pulse. This work has guiding significance for optimizing the emission characteristics of solid-state laser driven EUV sources.
Laser-produced plasma extreme ultraviolet (LPP-EUV) source is one of the key technologies in advanced lithography systems. Recently, solid-state lasers have been proposed as an alternative drive laser for the next-generation LPP-EUV source. Compared with currently used CO2 lasers, solid-state lasers have higher electrical-optical efficiency, more compact size, and better pulse shape tunability. Although limited to shorter operating wavelengths, the solid-state lasers have higher critical plasma density and optical depth. Consequently, re-absorption and spectral broadening cause lower conversion efficiency (CE). Therefore, to optimize EUV emission features and improve CE, a 0.532-μm pre-pulse laser is utilized in this work to modulate the plasma density distribution. The pre-pulse and a 1.064-μm Nd: YAG laser (the main pulse) are incident on an Sn slab target co-axially. The EUV energy and spectra of the Sn plasma are characterized at various delay times. It is demonstrated that compared with the 1.064-μm single pulse, the 0.532-μm pre-pulse laser with short delay times of 10 ns and 20 ns respectively results in a 4% increase in CE at 26° and 18% increase at 39°. The angular distribution of EUV energy is modulated by the 0.532-μm pre-pulse. An isotropic emission can be obtained within a certain delay time. The spectral feature near 13.5 nm is optimized, and a spectral purity of 12.2% is improved by 69%. The laser spot sizes of 0.3 mm and 1 mm for the pre-pulse are compared in the experiment. The results show that the 1-mm spot size has a better modulation effect on the EUV emission. Moreover, the time-resolved visible-band plasma profile is captured by an ICCD with 1.6-ns gate width. The plasma size and the distance to the target surface are increased by the 0.532-μm pre-pulse, which suggests that the energy of the main pulse is deposited in the low-density pre-plasma plume instead of in the plasma near the target surface. The lower plasma density leads to an increase in CE and spectral purity. The angular distribution of EUV energy is found to be closely related to the plasma morphology, and defined as the ratio of the longitudinal size to lateral size of the plasma. This indicates that the variation of plasma morphology can influence the angular distribution of EUV energy, which is caused by the 0.532-μm pre-pulse. This work has guiding significance for optimizing the emission characteristics of solid-state laser driven EUV sources.
2025, 74(14): 146801.
doi: 10.7498/aps.74.20250441
Abstract:
Two-dimensional planar heterojunctions composed of single-layer transition metal dichalcogenides have great potential applications in low-power, high-performance, and flexible optoelectronic devices. The localized atomic structure and crystal defects at interface govern the electronic, magnetic, optical, catalytic, and topological quantum properties. However, accurate characterization of interface atomic structure is still a challenge, so far. To determine the accurate atomic position, a spherical aberration-corrected electron microscope with segmented detector is employed, and the calculation is performed by integrated differential phase contrast (iDPC) imaging algorithm. By using the iDPC method, the atomic structure of WS2-MoSe2 monolayer heterojunction interface is characterized, and the W, Se, Mo, and S atoms are imaged simultaneously. Statistics show that the angles between the lattices on both sides of the WS2-MoSe2 planar heterojunction are distributed around 29° and 35°. Additionally, it is found that the lattice near the boundary experiences the strains of approximately 4‰ and 2% in the two lattice vector directions, with significant distortion occurring only at the interface. In this work, several typical atomic configurations, including merge type, quadrilateral type, and pentagonal type are found. The interface atomic configuration can help to release stress at the lateral interface. This study provides a useful method for accurately characterizing the structures for planar heterojunctions of monolayer transition metal dichalcogenide. It is of great significance for in-depth research on the structure-property relationship at single-atom resolution in various interface structures.
Two-dimensional planar heterojunctions composed of single-layer transition metal dichalcogenides have great potential applications in low-power, high-performance, and flexible optoelectronic devices. The localized atomic structure and crystal defects at interface govern the electronic, magnetic, optical, catalytic, and topological quantum properties. However, accurate characterization of interface atomic structure is still a challenge, so far. To determine the accurate atomic position, a spherical aberration-corrected electron microscope with segmented detector is employed, and the calculation is performed by integrated differential phase contrast (iDPC) imaging algorithm. By using the iDPC method, the atomic structure of WS2-MoSe2 monolayer heterojunction interface is characterized, and the W, Se, Mo, and S atoms are imaged simultaneously. Statistics show that the angles between the lattices on both sides of the WS2-MoSe2 planar heterojunction are distributed around 29° and 35°. Additionally, it is found that the lattice near the boundary experiences the strains of approximately 4‰ and 2% in the two lattice vector directions, with significant distortion occurring only at the interface. In this work, several typical atomic configurations, including merge type, quadrilateral type, and pentagonal type are found. The interface atomic configuration can help to release stress at the lateral interface. This study provides a useful method for accurately characterizing the structures for planar heterojunctions of monolayer transition metal dichalcogenide. It is of great significance for in-depth research on the structure-property relationship at single-atom resolution in various interface structures.
2025, 74(14): 147101.
doi: 10.7498/aps.74.20250411
Abstract:
The ground-state properties and collective excitations in a weakly interacting Bose gas with Raman-type spin-orbit coupling in one dimension are systematically investigated by numerically solving static and time-dependent Gross-Pitaevskii equations in this work. Our analysis focuses on three different quantum phases, i.e., stripe phase, plane-wave phase, and zero-momentum phase, which are characterized by key static properties including condensate momentum, spin polarization, and ground-state energy. The dynamic behaviors of total-density collective modes, i.e., the dipole mode that drives harmonic oscillations of the atomic cloud's center of mass and the breathing mode that is responsible for periodic expansion and contraction of density profile, are all explored using time-dependent simulations. Mode frequencies exhibit non-monotonic dependence on Rabi frequency in the three phases, and are significantly suppressed at the transition point between the plane-wave and the zero-momentum phases. Additionally, the spin-dependent collective excitations, particularly the spin-dipole and spin-breathing modes, are studied, which are governed by the time-dependent spin density distribution\begin{document}$(\delta n(x, t) \equiv n_\uparrow(x, t)-n_\downarrow(x, t)\,)$\end{document}
The ground-state properties and collective excitations in a weakly interacting Bose gas with Raman-type spin-orbit coupling in one dimension are systematically investigated by numerically solving static and time-dependent Gross-Pitaevskii equations in this work. Our analysis focuses on three different quantum phases, i.e., stripe phase, plane-wave phase, and zero-momentum phase, which are characterized by key static properties including condensate momentum, spin polarization, and ground-state energy. The dynamic behaviors of total-density collective modes, i.e., the dipole mode that drives harmonic oscillations of the atomic cloud's center of mass and the breathing mode that is responsible for periodic expansion and contraction of density profile, are all explored using time-dependent simulations. Mode frequencies exhibit non-monotonic dependence on Rabi frequency in the three phases, and are significantly suppressed at the transition point between the plane-wave and the zero-momentum phases. Additionally, the spin-dependent collective excitations, particularly the spin-dipole and spin-breathing modes, are studied, which are governed by the time-dependent spin density distribution
2025, 74(14): 147301.
doi: 10.7498/aps.74.20250423
Abstract:
Nano-plasmonic chiral structures exhibit stronger plasmonic circular dichroism than most organic materials. In addition to the circular dichroism response, the interaction between light and nano-plasmonic chiral structure also involves the photothermal and optomechanical effects. However, the synergy between the photothermal and optomechanical effects under circularly polarized light excitation remains poorly understood. This work investigates the synergy of the photothermal and optomechanical effects in chiral gold nanorod trimers. The asymmetric photothermal and optomechanical effects in gold nanorod trimers with adjacent homochiral centers are analyzed by finite element simulation. The simulation results show that the dynamic structure of the chiral gold nanorod trimer is activated when the photothermal temperature reaches the threshold value. At the same time, the asymmetric optical torque generated by left- and right-handed circularly polarized light will lead to asymmetric changes in the geometry of the gold nanorod trimer, especially in the twist angle of the chiral center, so that the spectral response of the gold nanorod trimer is polarization-dependent. More significantly, based on the synergy of the photothermal and optomechanical effects, experimental results show that the chiral gold nanorod oligomers can be used to control the asymmetric enhancement and suppression of the plasmonic circular dichroic spectral response through the enantioselective interaction of left- and right-handed circularly polarized light. This study provides an important reference for designing advanced nano-photonics devices.
Nano-plasmonic chiral structures exhibit stronger plasmonic circular dichroism than most organic materials. In addition to the circular dichroism response, the interaction between light and nano-plasmonic chiral structure also involves the photothermal and optomechanical effects. However, the synergy between the photothermal and optomechanical effects under circularly polarized light excitation remains poorly understood. This work investigates the synergy of the photothermal and optomechanical effects in chiral gold nanorod trimers. The asymmetric photothermal and optomechanical effects in gold nanorod trimers with adjacent homochiral centers are analyzed by finite element simulation. The simulation results show that the dynamic structure of the chiral gold nanorod trimer is activated when the photothermal temperature reaches the threshold value. At the same time, the asymmetric optical torque generated by left- and right-handed circularly polarized light will lead to asymmetric changes in the geometry of the gold nanorod trimer, especially in the twist angle of the chiral center, so that the spectral response of the gold nanorod trimer is polarization-dependent. More significantly, based on the synergy of the photothermal and optomechanical effects, experimental results show that the chiral gold nanorod oligomers can be used to control the asymmetric enhancement and suppression of the plasmonic circular dichroic spectral response through the enantioselective interaction of left- and right-handed circularly polarized light. This study provides an important reference for designing advanced nano-photonics devices.
2025, 74(14): 147302.
doi: 10.7498/aps.74.20250361
Abstract:
In an electronic double-layer system composed of two spatially adjacent but electrically insulated conductors, when current flows through one conductor (drive layer), its charge carriers transfer energy/momentum to the charge carriers in the other conductor (drag layer) through interlayer Coulomb coupling, thus generating a measurable voltage or current in the drag layer. This phenomenon is known as the interlayer drag effect. This effect provides a critical approach for studying quasiparticle interactions and investigating interlayer-correlated quantum states. Two-dimensional layered materials with highly tunable properties provide new opportunities for exploring the drag effect. In this study, we fabricate an electronic double-layer structure consisting of graphene and NbSe2 to systematically investigate the drag effect between a two-dimensional semimetal and a two-dimensional superconductor, wherein a thin hBN layer serves as the insulating spacer. When graphene acts as the drive layer and NbSe2 acts as the drag layer, a significant positive drag response is observed within the superconducting transition temperature range of NbSe2. In contrast, the drag signal vanishes when NbSe2 is in its normal metallic state. The measurements of magnetic field dependence reveal that the drag response disappears under high fields where the superconductivity of NbSe2 is suppressed, further confirming its direct correlation with the superconducting transition. The gate-voltage modulation experiments reveal that the drag response peaks when adjusting the Fermi level of graphene across the Dirac point. This is attributed to the reduced screening of interlayer interactions due to the ultra-low carrier concentration at this point. Notably, the sign of the supercurrent drag does not depend on the carrier type in graphene, ruling out the traditional momentum-transfer drag mechanism. Our results collectively demonstrate the realization of supercurrent drag effect, which has been attributed to Coulomb coupling between the quantum fluctuations of the superconducting phases in a superconductor and the charge densities in a normal conductor in previous study. Notably, by comparing different devices, it is found that this type of supercurrent drag responses occurs only in the thin NbSe2 layers cleaved in air. No significant signals are detected in thick NbSe2 layers or thin layers cleaved under the protection of argon. These results establish the importance of superconducting inhomogeneity in NbSe2 for generating supercurrent drag effect, indicating that drag measurements can also serve as a novel probe for investigating superconducting properties. Further investigation into the polarity and intensity of supercurrent drag signals may advance our understanding of inhomogeneous superconductivity, as well as interactions between normal carriers and Cooper pairs.
In an electronic double-layer system composed of two spatially adjacent but electrically insulated conductors, when current flows through one conductor (drive layer), its charge carriers transfer energy/momentum to the charge carriers in the other conductor (drag layer) through interlayer Coulomb coupling, thus generating a measurable voltage or current in the drag layer. This phenomenon is known as the interlayer drag effect. This effect provides a critical approach for studying quasiparticle interactions and investigating interlayer-correlated quantum states. Two-dimensional layered materials with highly tunable properties provide new opportunities for exploring the drag effect. In this study, we fabricate an electronic double-layer structure consisting of graphene and NbSe2 to systematically investigate the drag effect between a two-dimensional semimetal and a two-dimensional superconductor, wherein a thin hBN layer serves as the insulating spacer. When graphene acts as the drive layer and NbSe2 acts as the drag layer, a significant positive drag response is observed within the superconducting transition temperature range of NbSe2. In contrast, the drag signal vanishes when NbSe2 is in its normal metallic state. The measurements of magnetic field dependence reveal that the drag response disappears under high fields where the superconductivity of NbSe2 is suppressed, further confirming its direct correlation with the superconducting transition. The gate-voltage modulation experiments reveal that the drag response peaks when adjusting the Fermi level of graphene across the Dirac point. This is attributed to the reduced screening of interlayer interactions due to the ultra-low carrier concentration at this point. Notably, the sign of the supercurrent drag does not depend on the carrier type in graphene, ruling out the traditional momentum-transfer drag mechanism. Our results collectively demonstrate the realization of supercurrent drag effect, which has been attributed to Coulomb coupling between the quantum fluctuations of the superconducting phases in a superconductor and the charge densities in a normal conductor in previous study. Notably, by comparing different devices, it is found that this type of supercurrent drag responses occurs only in the thin NbSe2 layers cleaved in air. No significant signals are detected in thick NbSe2 layers or thin layers cleaved under the protection of argon. These results establish the importance of superconducting inhomogeneity in NbSe2 for generating supercurrent drag effect, indicating that drag measurements can also serve as a novel probe for investigating superconducting properties. Further investigation into the polarity and intensity of supercurrent drag signals may advance our understanding of inhomogeneous superconductivity, as well as interactions between normal carriers and Cooper pairs.
2025, 74(14): 147303.
doi: 10.7498/aps.74.20250358
Abstract:
Co-based Heusler alloys have emerged as highly promising systems within the Heusler alloy family due to their high Curie temperatures and potential half-metallicity. Since the concept of half-metallic ferromagnets is proposed, these alloys have attracted significant attention because of their high spin polarization, excellent magnetic performance, and thermal stability. The existing studies predominantly focus on spin-transport properties, but systematic studies on their magnetostriction remain scarce. The electronic structure and magnetism of Co-based Heusler alloys are critically dependent on atomic-site ordering: their spin polarization, Curie temperature, and magnetocrystalline anisotropy are closely related to crystal structure, such as L21 and B2. A highly ordered L21 structure is essential for maintaining half-metallicity, as structural disorder can induce significant changes in electronic hybridization and exchange interactions, thereby significantly changing macroscopic magnetism. Additionally, ordering control is also expected to modulate magnetostriction by modifying lattice symmetry and local distortions. Notably, in Fe–Ga alloys, disorder engineering has been employed to induce local short-range order and lattice distortion, thereby enhancing magnetostriction, a mechanism that may similarly operate in Co-based systems. However, the higher lattice symmetry and stronger orbital hybridization in these alloys can lead to fundamentally distinct mechanisms, which needs to be validated experimentally. This study focuses on the Co2FeAlxSi1–x system to systematically probe the relationship between composition-driven structural evolution (i.e., L21 to B2 transition) and magnetostrictive performance through adjusting Al/Si ratio. The study aims to clarify the correlation between composition-induced structural evolution and magnetostrictive behavior, thereby revealing the regulatory role of atomic ordering in magnetoelastic coupling and providing theoretical insight for designing high-performance magnetostrictive materials. The correlation between atomic site ordering and magnetostriction in Heusler alloy Co2FeAlxSi1–x (x = 0, 0.25, 0.5, 0.75, 1) is systematically investigated in experiment. The results reveal that Al doping drives a structural transition from the highly ordered L21 phase to the disordered B2 phase, inducing a coexisting L21/B2 interface state at x = 0.25–0.5, with the calculated ordering parameters \begin{document}$S_{L2_1}/S_{B2} $\end{document}
2025, 74(14): 147701.
doi: 10.7498/aps.74.20250213
Abstract:
With the continuous growth of global demand for renewable energy, the utilization of rainwater resources has gradually become a focal point of research. Piezoelectric energy harvesting has received significant attention because the harvester has simple structure, high energy conversion efficiency, and self-powering capability. However, traditional piezoelectric energy harvesters are limited by the narrow resonance frequency bandwidth and the insufficient waterproofing ability, which restricts the adaptability of energy conversion to variable environmental excitations. To solve this problem, a broadband piezoelectric cantilever energy harvester for rainwater energy harvesting is designed in this work. The influence mechanisms of droplet impact parameters, waterproof encapsulation technology, and MFC cantilever structure on the electrical output performance are studied through theoretical analysis, numerical simulation, and experimental validation. It reveals that the droplet’s Weber number exhibits a direct proportionality with the impact force, which is distributed within the 0–80 Hz frequency range. Simulations and experimental results demonstrate that the U-shaped piezoelectric energy harvester significantly outperforms other designs in terms of broadening the resonant frequency range and extending oscillation duration, achieving an oscillation time of 23.7 s, a charge transfer of 2.82 μC, and an output power density of 37.76 W/m2 under a single impact. It demonstrates its efficient energy harvesting capability in a wide resonance frequency range. Additionally, the U-shaped design also improves its waterproof performance, thus further enhancing its applicability in rainwater environments. This study provides a novel, universally applicable approach for collecting rainwater energy, expands the application scenarios of piezoelectric energy harvesting technology, and provides theoretical references and practical guidance for designing and applying broadband energy harvesters.
With the continuous growth of global demand for renewable energy, the utilization of rainwater resources has gradually become a focal point of research. Piezoelectric energy harvesting has received significant attention because the harvester has simple structure, high energy conversion efficiency, and self-powering capability. However, traditional piezoelectric energy harvesters are limited by the narrow resonance frequency bandwidth and the insufficient waterproofing ability, which restricts the adaptability of energy conversion to variable environmental excitations. To solve this problem, a broadband piezoelectric cantilever energy harvester for rainwater energy harvesting is designed in this work. The influence mechanisms of droplet impact parameters, waterproof encapsulation technology, and MFC cantilever structure on the electrical output performance are studied through theoretical analysis, numerical simulation, and experimental validation. It reveals that the droplet’s Weber number exhibits a direct proportionality with the impact force, which is distributed within the 0–80 Hz frequency range. Simulations and experimental results demonstrate that the U-shaped piezoelectric energy harvester significantly outperforms other designs in terms of broadening the resonant frequency range and extending oscillation duration, achieving an oscillation time of 23.7 s, a charge transfer of 2.82 μC, and an output power density of 37.76 W/m2 under a single impact. It demonstrates its efficient energy harvesting capability in a wide resonance frequency range. Additionally, the U-shaped design also improves its waterproof performance, thus further enhancing its applicability in rainwater environments. This study provides a novel, universally applicable approach for collecting rainwater energy, expands the application scenarios of piezoelectric energy harvesting technology, and provides theoretical references and practical guidance for designing and applying broadband energy harvesters.
2025, 74(14): 147801.
doi: 10.7498/aps.74.20250337
Abstract:
Optical systems based on bound states in the continuum (BIC) generally possess higher quality factor (Q) values and narrower operational linewidths than traditional photonic crystals or metasurfaces. The higher Q values offer extensive possibilities for high-performance optoelectronic devices. However, the narrower linewidths often pose challenges in practical applications, as fabrication errors during production inevitably lead to discrepancies between real optical devices and their ideal designs, which results in mismatches between actual and ideal operating wavelengths. To solve this problem, we explore the dynamic tuning effect of liquid crystal (LC) on quasi-bound states in the continuum (q-BIC) so as to compensate for wavelength shifts caused by fabrication errors. A photonic crystal slab with cross-shaped holes serves as the platform for generating q-BIC. Compared with the modulation induced by the tilt angles of incident light on q-BIC, LC has a less influence on the system’s Q factor when the same operational wavelength is shifted. For instance, shifting the central wavelength λ0 of q-BIC by 5.32 nm by using a tilted incident angle results in the Q factor decreasing to 24.16% (from 3809.05 to 920.28). Whereas shifting the central wavelength λ0 by 5.63 nm through the tilt angle θ of LC leads Q factor to increase 14.27% (from 3809.05 to 4352.65). This demonstrates the significant potential of LC dynamic tuning in high-Q and ultra-narrowband q-BIC devices. Finally, the mechanism of LC within the q-BIC system is discussed. The smaller influence of LC on the Q factor is attributed to its minimal disruption of the q-BIC system’s symmetry. Although LC also affects system symmetry within the cross-shaped holes, after adjusting the asymmetry parameters of the system, the Q factor and the LC tuning process can be well matched. The results of our research provides valuable references for carrying on extensive research on q-BIC.
Optical systems based on bound states in the continuum (BIC) generally possess higher quality factor (Q) values and narrower operational linewidths than traditional photonic crystals or metasurfaces. The higher Q values offer extensive possibilities for high-performance optoelectronic devices. However, the narrower linewidths often pose challenges in practical applications, as fabrication errors during production inevitably lead to discrepancies between real optical devices and their ideal designs, which results in mismatches between actual and ideal operating wavelengths. To solve this problem, we explore the dynamic tuning effect of liquid crystal (LC) on quasi-bound states in the continuum (q-BIC) so as to compensate for wavelength shifts caused by fabrication errors. A photonic crystal slab with cross-shaped holes serves as the platform for generating q-BIC. Compared with the modulation induced by the tilt angles of incident light on q-BIC, LC has a less influence on the system’s Q factor when the same operational wavelength is shifted. For instance, shifting the central wavelength λ0 of q-BIC by 5.32 nm by using a tilted incident angle results in the Q factor decreasing to 24.16% (from 3809.05 to 920.28). Whereas shifting the central wavelength λ0 by 5.63 nm through the tilt angle θ of LC leads Q factor to increase 14.27% (from 3809.05 to 4352.65). This demonstrates the significant potential of LC dynamic tuning in high-Q and ultra-narrowband q-BIC devices. Finally, the mechanism of LC within the q-BIC system is discussed. The smaller influence of LC on the Q factor is attributed to its minimal disruption of the q-BIC system’s symmetry. Although LC also affects system symmetry within the cross-shaped holes, after adjusting the asymmetry parameters of the system, the Q factor and the LC tuning process can be well matched. The results of our research provides valuable references for carrying on extensive research on q-BIC.
2025, 74(14): 148501.
doi: 10.7498/aps.74.20250276
Abstract:
Deep-trench isolation (DTI) bipolar transistors have been increasingly adopted in high-performance, highly integrated advanced semiconductor devices due to their superior electrical characteristics and isolation capabilities. However, existing research has shown that DTI bipolar transistors exhibit a lower linear energy transfer (LET) threshold for single-event effects (SEEs) and a larger saturated cross-section than traditional structures, making the traditional rectangular parallelepiped (RPP) model unsuitable for such devices. In this study, we investigate the influence of proton incidence angle on single-event effects in high-speed DTI bipolar transistors. Proton multi-angle irradiation experiments reveal that the incidence angle significantly changes the amplitude characteristics of single-event transient voltage pulses at the collector. By introducing a nested sensitive volume in TCAD numerical simulations, the sensitive region of the DTI device is accurately defined. Geant4 simulations further demonstrate that with the increase of proton incidence angle, the integral cross-section of secondary ions in the sensitive volume significantly increases, which is determined to be the primary reason for the voltage amplitudes at the collector and base increasing with augment of tilt angle. This work provides theoretical support for radiation hardening of DTI bipolar transistors against single-event effects.
2025, 74(14): 148502.
doi: 10.7498/aps.74.20250297
Abstract:
This study tackles the significant challenge of phase separation in mixed halide (Br–/Cl–) perovskite systems, which severely affects the spectral stability of blue perovskite light-emitting diodes (PeLEDs). A compositional engineering strategy is proposed, precisely controlling the Cs:Pb molar ratio (1∶1 to 1.1∶1) in precursor solutions to construct a CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 composite phase structure. Transmission electron microscopy (TEM) mapping and X-ray diffraction (XRD) analysis confirm that Cs4Pb(Br1–xClx)6 nanocrystals (5–8 nm in diameter) grow in situ and uniformly encapsulate CsPb(Br1–xClx)3 microparticles (50–100 nm). This composite architecture has double functional advantages: 1) the Cs4PbX6 shell acts as a physical barrier, reducing halide ion migration activation energy and suppressing phase segregation during continuous operation; 2) the wide-bandgap (3.9–4.3 eV) Cs4PbX6 induces quantum confinement effects, confining carriers within CsPbX3 while passivating defect states, thereby improving perovskite performance. The optimized PeLED achieves notable improvements in brightness, external quantum efficiency, and operational stability, maintaining stable emission at 478 nm under a 50 mA/cm² current density. This is achieved by inhibiting halide phase separation and enhancing the efficiency of carrier recombination achieved by the cesium-lead halide heterojunction system. This work provides fundamental insights into phase-stable perovskite design via composite crystallization kinetics, providing a viable pathway toward commercial-grade blue PeLEDs for full-color displays.
This study tackles the significant challenge of phase separation in mixed halide (Br–/Cl–) perovskite systems, which severely affects the spectral stability of blue perovskite light-emitting diodes (PeLEDs). A compositional engineering strategy is proposed, precisely controlling the Cs:Pb molar ratio (1∶1 to 1.1∶1) in precursor solutions to construct a CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 composite phase structure. Transmission electron microscopy (TEM) mapping and X-ray diffraction (XRD) analysis confirm that Cs4Pb(Br1–xClx)6 nanocrystals (5–8 nm in diameter) grow in situ and uniformly encapsulate CsPb(Br1–xClx)3 microparticles (50–100 nm). This composite architecture has double functional advantages: 1) the Cs4PbX6 shell acts as a physical barrier, reducing halide ion migration activation energy and suppressing phase segregation during continuous operation; 2) the wide-bandgap (3.9–4.3 eV) Cs4PbX6 induces quantum confinement effects, confining carriers within CsPbX3 while passivating defect states, thereby improving perovskite performance. The optimized PeLED achieves notable improvements in brightness, external quantum efficiency, and operational stability, maintaining stable emission at 478 nm under a 50 mA/cm² current density. This is achieved by inhibiting halide phase separation and enhancing the efficiency of carrier recombination achieved by the cesium-lead halide heterojunction system. This work provides fundamental insights into phase-stable perovskite design via composite crystallization kinetics, providing a viable pathway toward commercial-grade blue PeLEDs for full-color displays.
2025, 74(14): 148701.
doi: 10.7498/aps.74.20250390
Abstract:
With the development of hardware-optimized deployment of spiking neural networks (SNNs), SNN processors based on field-programmable gate arrays (FPGAs) have become a research hotspot due to their efficiency and flexibility. However, existing methods rely on multi-timestep training and reconfigurable computing architectures, which increases computational and memory overhead, thus reducing deployment efficiency. This work presents an efficient and lightweight residual SNN accelerator that combines algorithm and hardware co-design to optimize inference energy efficiency. In terms of algorithm, we employ single-timesteps training, integrate grouped convolutions, and fuse batch normalization (BN) layers, thus compressing the network to only 0.69M parameters. Quantization-aware training (QAT) further constrains all parameters to 8-bit precision. In terms of hardware, the reuse of intra-layer resources maximizes FPGA utilization, a full pipeline cross-layer architecture improves throughput, and on-chip block RAM (BRAM) stores network parameters and intermediate results to improve memory efficiency. The experimental results show that the proposed processor achieves a classification accuracy of 87.11% on the CIFAR-10 dataset, with an inference time of 3.98 ms per image and an energy efficiency of 183.5 FPS/W. Compared with mainstream graphics processing unit (GPU) platforms, it achieves more than double the energy efficiency. Furthermore, compared with other SNN processors, it achieves at least a fourfold increase in inference speed and a fivefold improvement in energy efficiency.
With the development of hardware-optimized deployment of spiking neural networks (SNNs), SNN processors based on field-programmable gate arrays (FPGAs) have become a research hotspot due to their efficiency and flexibility. However, existing methods rely on multi-timestep training and reconfigurable computing architectures, which increases computational and memory overhead, thus reducing deployment efficiency. This work presents an efficient and lightweight residual SNN accelerator that combines algorithm and hardware co-design to optimize inference energy efficiency. In terms of algorithm, we employ single-timesteps training, integrate grouped convolutions, and fuse batch normalization (BN) layers, thus compressing the network to only 0.69M parameters. Quantization-aware training (QAT) further constrains all parameters to 8-bit precision. In terms of hardware, the reuse of intra-layer resources maximizes FPGA utilization, a full pipeline cross-layer architecture improves throughput, and on-chip block RAM (BRAM) stores network parameters and intermediate results to improve memory efficiency. The experimental results show that the proposed processor achieves a classification accuracy of 87.11% on the CIFAR-10 dataset, with an inference time of 3.98 ms per image and an energy efficiency of 183.5 FPS/W. Compared with mainstream graphics processing unit (GPU) platforms, it achieves more than double the energy efficiency. Furthermore, compared with other SNN processors, it achieves at least a fourfold increase in inference speed and a fivefold improvement in energy efficiency.
2025, 74(14): 148702.
doi: 10.7498/aps.74.20250433
Abstract:
The rapid monitoring devices, but there are still challenges in achieving medical-grade accuracy in quantitative pulmonary function assessment. This study integrates water molecule-responsive flexible sensing technology, wearable devices, and cloud-based intelligent analysis platform to develop the first medical-grade flexible respiratory sensing system (SFMS). By utilizing the synergistic effect of bionic microcavity differential pressure sensing and humidity-sensitive interfaces, combined with a pressure difference-flux dynamic model, the system can simultaneously resolve peak expiratory flow (PEF) and forced vital capacity (FVC), accurately obtaining core pulmonary function indicators such as FEV1/FVC. Clinical validation of 454 cases demonstrates high consistency with gold-standard spirometry (intraclass correlation coefficient [ICC] = 0.93–0.97), with a sensitivity of 89.7% and specificity of 92.3% in differentiating chronic obstructive pulmonary disease (COPD) from asthma. Technologically, this work pioneers a medical-grade flexible sensor for quantitative pulmonary testing, and eliminates dependence on specialized operators through an embedded edge computing architecture that supports real-time cloud data interaction. The system establishes disease-specific profiles through multi-parametric physiological correlation analysis. Practically, its low cost, portability, and user-friendly operation facilitate seamless integration into primary healthcare and home health management, providing technical tools for hierarchical diagnosis and treatment of chronic respiratory diseases. Aligned with WHO's Respiratory Health Action Plan, this innovation enables universal monitoring to advance early screening and long-term disease management. As this innovation possesses significant clinical translation potential, it provides a groundbreaking solution for building a comprehensive prevention and control framework for respiratory diseases.
The rapid monitoring devices, but there are still challenges in achieving medical-grade accuracy in quantitative pulmonary function assessment. This study integrates water molecule-responsive flexible sensing technology, wearable devices, and cloud-based intelligent analysis platform to develop the first medical-grade flexible respiratory sensing system (SFMS). By utilizing the synergistic effect of bionic microcavity differential pressure sensing and humidity-sensitive interfaces, combined with a pressure difference-flux dynamic model, the system can simultaneously resolve peak expiratory flow (PEF) and forced vital capacity (FVC), accurately obtaining core pulmonary function indicators such as FEV1/FVC. Clinical validation of 454 cases demonstrates high consistency with gold-standard spirometry (intraclass correlation coefficient [ICC] = 0.93–0.97), with a sensitivity of 89.7% and specificity of 92.3% in differentiating chronic obstructive pulmonary disease (COPD) from asthma. Technologically, this work pioneers a medical-grade flexible sensor for quantitative pulmonary testing, and eliminates dependence on specialized operators through an embedded edge computing architecture that supports real-time cloud data interaction. The system establishes disease-specific profiles through multi-parametric physiological correlation analysis. Practically, its low cost, portability, and user-friendly operation facilitate seamless integration into primary healthcare and home health management, providing technical tools for hierarchical diagnosis and treatment of chronic respiratory diseases. Aligned with WHO's Respiratory Health Action Plan, this innovation enables universal monitoring to advance early screening and long-term disease management. As this innovation possesses significant clinical translation potential, it provides a groundbreaking solution for building a comprehensive prevention and control framework for respiratory diseases.
2025, 74(14): 148704.
doi: 10.7498/aps.74.20250258
Abstract:
This study solves the key challenge of real-time beam monitoring in ultra-high dose rate X-ray FLASH (XFLASH) radiotherapy, in which the traditional ionization chambers suffer serious electron-ion recombination losses at extreme dose rates (≥40 Gy/s). We propose a low-pressure ionization chamber (LPIC) as a novel beam monitor to achieve accurate dose measurement while maintaining beam penetration characteristics required for clinical applications. The LPIC is designed to have two independent chambers to accommodate high-voltage, collecting, and protecting electrodes. Key parameters include a 1-mm electrode gap and a reduced chamber pressure (~5 kPa) to mitigate recombination effects. Theoretical analysis based on the Boag model and numerical simulations (using the numerical-ks-calculator program) quantifies the dependence of recombination loss on pressure (P), electrode spacing (d ), and voltage (Uc). MCNP simulations evaluate X-ray transmission through chamber windows (Be, Al, Ti) with thickness up to 1000 μm. According to the national standards (GB/T15213-2016), a prototype LPIC is constructed and tested on a 10-MeV XFLASH accelerator (dose rate: 80 Gy/s) for plateau characteristics, dose repeatability, linearity, and dose-rate response. Theoretical analysis based on the Boag model reveals that the values of recombination ratio R scale with\begin{document}$P^3$\end{document} \begin{document}$d^2$\end{document} \begin{document}$U_{\rm c}^{-1} $\end{document} \begin{document}$(R = 0.2256P^3;\; R = 0.0534U_{\rm c}^{-1};\; R = 0.00548d^2) $\end{document}
This study solves the key challenge of real-time beam monitoring in ultra-high dose rate X-ray FLASH (XFLASH) radiotherapy, in which the traditional ionization chambers suffer serious electron-ion recombination losses at extreme dose rates (≥40 Gy/s). We propose a low-pressure ionization chamber (LPIC) as a novel beam monitor to achieve accurate dose measurement while maintaining beam penetration characteristics required for clinical applications. The LPIC is designed to have two independent chambers to accommodate high-voltage, collecting, and protecting electrodes. Key parameters include a 1-mm electrode gap and a reduced chamber pressure (~5 kPa) to mitigate recombination effects. Theoretical analysis based on the Boag model and numerical simulations (using the numerical-ks-calculator program) quantifies the dependence of recombination loss on pressure (P), electrode spacing (d ), and voltage (Uc). MCNP simulations evaluate X-ray transmission through chamber windows (Be, Al, Ti) with thickness up to 1000 μm. According to the national standards (GB/T15213-2016), a prototype LPIC is constructed and tested on a 10-MeV XFLASH accelerator (dose rate: 80 Gy/s) for plateau characteristics, dose repeatability, linearity, and dose-rate response. Theoretical analysis based on the Boag model reveals that the values of recombination ratio R scale with
2025, 74(14): 148801.
doi: 10.7498/aps.74.20250194
Abstract:
Hydrogen is widely regarded as an ideal alternative energy source because of its high efficiency, abundance, pollution-free and renewable properties. One of the main challenges is to find efficient materials that can store hydrogen safely with fast kinetics, favorable thermodynamics, and high hydrogen density under ambient conditions. The nanomaterial is one of the most promising hydrogen storage materials because of its high surface-to-volume rate, unique electronic structure and novel chemical and physical properties. In this study, the hydrogen storage properties of Na-decorated Bn (n = 3–10) clusters are investigated using dispersion-corrected density functional theory and atomic density matrix propagation (ADMP) simulations. The results show that Na atoms can stably bind to Bn clusters, forming BnNa2 complexes. The average binding energies (1.876–2.967 eV) of Na atoms on the host clusters are significantly higher than the cohesive energy of bulk Na (1.113 eV), which effectively prevents Na atoms from gathering on the cluster surface. Furthermore, when Na atoms bind to Bn (n = 3–10) clusters, electrons transfer from Na to B atoms, resulting in positively charged Na atoms. Hydrogen molecules are moderately polarized under the electric field and adsorbed around Na atoms through electrostatic interactions. The H–H bonds are slightly stretched but not broken. The Na-decorated Bn clusters can adsorb up to 10 hydrogen molecules with average adsorption energies of 0.063–0.095 eV/H2 and maximum hydrogen storage densities reaching 11.57%–20.45%. Almost no structural change is observed in the host clusters after adsorbing hydrogen. Molecular dynamics simulations reveal that the desorption rate of hydrogen molecules increases with temperature rising. At ambient temperature (300 K), BnNa2 (n = 3–8) clusters achieve complete dehydrogenation within 262 fs, while B9Na2 and B10Na2 clusters exhibit a dehydrogenation rate of 90% within 1000 fs. The Na-decorated Bn (n = 3–10) clusters not only exhibit excellent properties for hydrogen storage but also enable efficient dehydrogenation at ambient temperature. Thus, BnNa2 (n = 3–10) clusters can be regarded as highly promising candidates for hydrogen storage.
Hydrogen is widely regarded as an ideal alternative energy source because of its high efficiency, abundance, pollution-free and renewable properties. One of the main challenges is to find efficient materials that can store hydrogen safely with fast kinetics, favorable thermodynamics, and high hydrogen density under ambient conditions. The nanomaterial is one of the most promising hydrogen storage materials because of its high surface-to-volume rate, unique electronic structure and novel chemical and physical properties. In this study, the hydrogen storage properties of Na-decorated Bn (n = 3–10) clusters are investigated using dispersion-corrected density functional theory and atomic density matrix propagation (ADMP) simulations. The results show that Na atoms can stably bind to Bn clusters, forming BnNa2 complexes. The average binding energies (1.876–2.967 eV) of Na atoms on the host clusters are significantly higher than the cohesive energy of bulk Na (1.113 eV), which effectively prevents Na atoms from gathering on the cluster surface. Furthermore, when Na atoms bind to Bn (n = 3–10) clusters, electrons transfer from Na to B atoms, resulting in positively charged Na atoms. Hydrogen molecules are moderately polarized under the electric field and adsorbed around Na atoms through electrostatic interactions. The H–H bonds are slightly stretched but not broken. The Na-decorated Bn clusters can adsorb up to 10 hydrogen molecules with average adsorption energies of 0.063–0.095 eV/H2 and maximum hydrogen storage densities reaching 11.57%–20.45%. Almost no structural change is observed in the host clusters after adsorbing hydrogen. Molecular dynamics simulations reveal that the desorption rate of hydrogen molecules increases with temperature rising. At ambient temperature (300 K), BnNa2 (n = 3–8) clusters achieve complete dehydrogenation within 262 fs, while B9Na2 and B10Na2 clusters exhibit a dehydrogenation rate of 90% within 1000 fs. The Na-decorated Bn (n = 3–10) clusters not only exhibit excellent properties for hydrogen storage but also enable efficient dehydrogenation at ambient temperature. Thus, BnNa2 (n = 3–10) clusters can be regarded as highly promising candidates for hydrogen storage.
2025, 74(14): 148802.
doi: 10.7498/aps.74.20250372
Abstract:
Organic cations in hybrid organic-inorganic perovskite solar cells are susceptible to decomposition under high temperatures and ultraviolet light, leading their power conversion efficiency (PCE) to decrease. All-inorganic perovskite solar cells exhibit both high PCE and superior photothermal stability, making them promising candidates for single-junction and tandem photovoltaic applications. The mixed-halide perovskite CsPbI2Br has received much attention as a top cell in semi-transparent and tandem solar cells due to its excellent thermal stability and suitable bandgap (1.90 eV). Although the PCE of CsPbI2Br-based solar cells is approaching its theoretical limit, the energy loss caused by non-radiative recombination remains a major barrier to further improving performance. This non-radiative recombination is mainly caused by inadequate band alignment between the absorption layer and the transport layer, resulting in the loss of open-circuit voltage (VOC) and decrease of short-circuit current density (JSC). Two-dimensional perovskite passivation formed through solution processing can mitigate interfacial recombination, but it can also impede efficient charge transport. Constructing three-dimensional perovskite structures not only provides an effective solution to these limitations but also enhances sunlight absorption and facilitates carrier transport. In this study, we propose a dual-absorption-layer perovskite heterojunction (DPHJ) strategy, which involves integrating a staggered type-II perovskite heterojunction (p-pCsPbI2Br-CsPbIBr2) into the absorption layer of the top cell in an all-perovskite tandem solar cell. The simulation result indicates that stacking a 100-nm-thick CsPbIBr2 layer atop a 300-nm-thick CsPbI2Br layer greatly enhances the PCE of the single-junction device from 19.46% to 22.29%. This improvement is mainly attributed to band bending at the CsPbI2Br/CsPbIBr2 interface, which enhances the built-in electric field, facilitates carrier transport, and suppresses non-radiative recombination within the absorption layer. Compared with the tandem solar cell utilizing a single-absorption-layer CsPbI2Br top cell, the DPHJ-based tandem solar cell significantly increases VOC from 2.16 to 2.25 V and JSC from 15.96 to 16.76 mA⋅cm–2. As a result, the DPHJ-based tandem solar cell achieves a high theoretical PCE of 32.47%. In addition, the DPHJ-based tandem solar cell exhibits a significantly enhanced external quantum efficiency in a wavelength range of 500–580 nm, which can be attributed to the band-edge absorption of CsPbIBr2. This enhanced absorption generates more photogenerated carriers, thereby significantly improving the JSC. The VOC and PCE values in this study exceed those experimentally reported values of current CsPbI2Br single-junction and all-perovskite tandem solar cells. Compared with the single-layer CsPbI2Br (E2 = 101.9 meV, electron-phonon coupling strength\begin{document}$ {\gamma _{{\text{ac}}}} = 1.2 \times {10^{ - 2}},{\text{ }}{\gamma _{{\text{LO}}}} = 6.9 \times {10^3} $\end{document} \begin{document}$ {\gamma _{{\text{ac}}}} = 1.1 \times {10^{ - 2}},{\text{ }}{\gamma _{{\text{LO}}}} = $\end{document} \begin{document}$ 6.3 \times {10^3} $\end{document}
Organic cations in hybrid organic-inorganic perovskite solar cells are susceptible to decomposition under high temperatures and ultraviolet light, leading their power conversion efficiency (PCE) to decrease. All-inorganic perovskite solar cells exhibit both high PCE and superior photothermal stability, making them promising candidates for single-junction and tandem photovoltaic applications. The mixed-halide perovskite CsPbI2Br has received much attention as a top cell in semi-transparent and tandem solar cells due to its excellent thermal stability and suitable bandgap (1.90 eV). Although the PCE of CsPbI2Br-based solar cells is approaching its theoretical limit, the energy loss caused by non-radiative recombination remains a major barrier to further improving performance. This non-radiative recombination is mainly caused by inadequate band alignment between the absorption layer and the transport layer, resulting in the loss of open-circuit voltage (VOC) and decrease of short-circuit current density (JSC). Two-dimensional perovskite passivation formed through solution processing can mitigate interfacial recombination, but it can also impede efficient charge transport. Constructing three-dimensional perovskite structures not only provides an effective solution to these limitations but also enhances sunlight absorption and facilitates carrier transport. In this study, we propose a dual-absorption-layer perovskite heterojunction (DPHJ) strategy, which involves integrating a staggered type-II perovskite heterojunction (p-pCsPbI2Br-CsPbIBr2) into the absorption layer of the top cell in an all-perovskite tandem solar cell. The simulation result indicates that stacking a 100-nm-thick CsPbIBr2 layer atop a 300-nm-thick CsPbI2Br layer greatly enhances the PCE of the single-junction device from 19.46% to 22.29%. This improvement is mainly attributed to band bending at the CsPbI2Br/CsPbIBr2 interface, which enhances the built-in electric field, facilitates carrier transport, and suppresses non-radiative recombination within the absorption layer. Compared with the tandem solar cell utilizing a single-absorption-layer CsPbI2Br top cell, the DPHJ-based tandem solar cell significantly increases VOC from 2.16 to 2.25 V and JSC from 15.96 to 16.76 mA⋅cm–2. As a result, the DPHJ-based tandem solar cell achieves a high theoretical PCE of 32.47%. In addition, the DPHJ-based tandem solar cell exhibits a significantly enhanced external quantum efficiency in a wavelength range of 500–580 nm, which can be attributed to the band-edge absorption of CsPbIBr2. This enhanced absorption generates more photogenerated carriers, thereby significantly improving the JSC. The VOC and PCE values in this study exceed those experimentally reported values of current CsPbI2Br single-junction and all-perovskite tandem solar cells. Compared with the single-layer CsPbI2Br (E2 = 101.9 meV, electron-phonon coupling strength
2025, 74(14): 148901.
doi: 10.7498/aps.74.20250314
Abstract:
The acceleration of urbanization has rendered accurate prediction of intra-urban population mobility a fundamental requirement for urban planning and policy formulation. However, the adaptability and performance of existing mobility models on different spatial scales are still poorly understood, and there is a clear lack of a systematic evaluation framework that integrates spatial granularity, travel distance, and population heterogeneity. This study addresses these gaps by proposing a cross-scale comparative framework to evaluate three representative mobility models under varying urban conditions: the gravity model (GM), the radiation model (RM), and the population-weighted opportunities model (PWO). Using high-resolution mobile phone data from Shanghai, we construct three groups of controlled experiments to assess the performance of the model on spatial (grid size), distance, and population density scales. Furthermore, the multivariate analysis of variance (MANOVA) is further used to decompose the relative contributions of different spatial factors to prediction errors.The results indicate that there is distinct scale sensitivity between the models. Based on Newton’s principle of gravity, the GM exhibits high robustness over longer distances (>5 km), but its performance decreases under fine spatial granularity due to spatial heterogeneity. GM accuracy improves with population density but decreases significantly when regional area disparity exceeds a threshold, with prediction performance dropping by over 40% when grid size difference exceeds 3 km. The RM, based on the nearest-best-opportunity assumption, performs well for short-distance, origin-driven flows, such as commuting, but introduces systematic bias on a small scales. Its sensitivity to origin population density renders it more suitable for high-density urban cores. The PWO model enhances RM by combining destination population weights, demonstrating superior compatibility with spatial heterogeneity in dense and polycentric cities. Although it performs best in short distances (<5 km) PWO will fail as the driving distance increases.The MANOVA results demonstrate that GM is primarily influenced by population density and area scale, whereas RM and PWO exhibit greater sensitivity to distance and destination-related factors. On the basis of these findings, we propose a model selection strategy suitable for mobility drivers: GM is recommended for long-distance traffic prediction in spatially homogeneous regions, while PWO is recommended for short distance traffic prediction between densely populated small areas. RM serves as a complementary model when origin-driven flows dominate.This study not only elucidates the physical mechanisms behind the performance of scale-dependent model but also provides an actionable decision-making framework for model selection in different urban mobility scenarios. Future research will further improve predictive accuracy through the following methods: 1) developing hybrid models that integrate strengths of multiple frameworks; 2) incorporating multi-source spatial data (e.g. POIs land use); 3) coupling traditional models with deep learning approaches to enhance non-linear pattern recognition while maintaining interpretability.By revealing the scale sensitivity of mobility models, this work lays theoretical and methodological foundations for multi-scenario mobility prediction in smart city planning and fine-grained urban governance.
The acceleration of urbanization has rendered accurate prediction of intra-urban population mobility a fundamental requirement for urban planning and policy formulation. However, the adaptability and performance of existing mobility models on different spatial scales are still poorly understood, and there is a clear lack of a systematic evaluation framework that integrates spatial granularity, travel distance, and population heterogeneity. This study addresses these gaps by proposing a cross-scale comparative framework to evaluate three representative mobility models under varying urban conditions: the gravity model (GM), the radiation model (RM), and the population-weighted opportunities model (PWO). Using high-resolution mobile phone data from Shanghai, we construct three groups of controlled experiments to assess the performance of the model on spatial (grid size), distance, and population density scales. Furthermore, the multivariate analysis of variance (MANOVA) is further used to decompose the relative contributions of different spatial factors to prediction errors.The results indicate that there is distinct scale sensitivity between the models. Based on Newton’s principle of gravity, the GM exhibits high robustness over longer distances (>5 km), but its performance decreases under fine spatial granularity due to spatial heterogeneity. GM accuracy improves with population density but decreases significantly when regional area disparity exceeds a threshold, with prediction performance dropping by over 40% when grid size difference exceeds 3 km. The RM, based on the nearest-best-opportunity assumption, performs well for short-distance, origin-driven flows, such as commuting, but introduces systematic bias on a small scales. Its sensitivity to origin population density renders it more suitable for high-density urban cores. The PWO model enhances RM by combining destination population weights, demonstrating superior compatibility with spatial heterogeneity in dense and polycentric cities. Although it performs best in short distances (<5 km) PWO will fail as the driving distance increases.The MANOVA results demonstrate that GM is primarily influenced by population density and area scale, whereas RM and PWO exhibit greater sensitivity to distance and destination-related factors. On the basis of these findings, we propose a model selection strategy suitable for mobility drivers: GM is recommended for long-distance traffic prediction in spatially homogeneous regions, while PWO is recommended for short distance traffic prediction between densely populated small areas. RM serves as a complementary model when origin-driven flows dominate.This study not only elucidates the physical mechanisms behind the performance of scale-dependent model but also provides an actionable decision-making framework for model selection in different urban mobility scenarios. Future research will further improve predictive accuracy through the following methods: 1) developing hybrid models that integrate strengths of multiple frameworks; 2) incorporating multi-source spatial data (e.g. POIs land use); 3) coupling traditional models with deep learning approaches to enhance non-linear pattern recognition while maintaining interpretability.By revealing the scale sensitivity of mobility models, this work lays theoretical and methodological foundations for multi-scenario mobility prediction in smart city planning and fine-grained urban governance.
2025, 74(14): 148902.
doi: 10.7498/aps.74.20250338
Abstract:
In the face of the surge of air transport demand and the increasing risk of flight conflicts, it is very important to effectively manage flight conflicts and accurately identify key conflict aircraft. This paper presents a novel method for identifying critical nodes in flight conflict networks by integrating complex network theory with a weighted cycle ratio (WCR). By modeling aircraft as nodes and conflict relationships as edges, we construct a flight conflict network where the urgency of conflicts is reflected in edge weights. We extend the traditional cycle ratio (CR) concept to propose the WCR, which accounts for both the topological structure of the network and the urgency of conflicts. Furthermore, we combine the WCR with node strength (NS) to form an adjustable mixed indicator (MI) that adaptively balances the importance of nodes based on their involvement in cyclic conflict structure and their individual conflict strength. Through extensive simulations, including node deletion experiments and network robustness analyses, we demonstrate that our method can precisely pinpoint critical nodes in flight conflict networks. The results indicate that regulating these critical nodes can significantly reduce network complexity and conflict risks. Importantly, the effectiveness of our method increases with the complexity of the flight conflict network, making it particularly suitable for scenarios with high aircraft density and complex conflict patterns. Overall, this study not only deepens the theoretical understanding of complex aviation network analysis but also provides a practical tool for improving air traffic control efficiency and safety, thereby contributing to achieving more environmentally friendly and sustainable air transportation.
In the face of the surge of air transport demand and the increasing risk of flight conflicts, it is very important to effectively manage flight conflicts and accurately identify key conflict aircraft. This paper presents a novel method for identifying critical nodes in flight conflict networks by integrating complex network theory with a weighted cycle ratio (WCR). By modeling aircraft as nodes and conflict relationships as edges, we construct a flight conflict network where the urgency of conflicts is reflected in edge weights. We extend the traditional cycle ratio (CR) concept to propose the WCR, which accounts for both the topological structure of the network and the urgency of conflicts. Furthermore, we combine the WCR with node strength (NS) to form an adjustable mixed indicator (MI) that adaptively balances the importance of nodes based on their involvement in cyclic conflict structure and their individual conflict strength. Through extensive simulations, including node deletion experiments and network robustness analyses, we demonstrate that our method can precisely pinpoint critical nodes in flight conflict networks. The results indicate that regulating these critical nodes can significantly reduce network complexity and conflict risks. Importantly, the effectiveness of our method increases with the complexity of the flight conflict network, making it particularly suitable for scenarios with high aircraft density and complex conflict patterns. Overall, this study not only deepens the theoretical understanding of complex aviation network analysis but also provides a practical tool for improving air traffic control efficiency and safety, thereby contributing to achieving more environmentally friendly and sustainable air transportation.
