The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payl...The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.展开更多
With their intricate vectorial structures in space,optical skyrmions have significantly expanded the landscape of topological optics and light-matter interactions.We theoretically investigate high harmonic generation ...With their intricate vectorial structures in space,optical skyrmions have significantly expanded the landscape of topological optics and light-matter interactions.We theoretically investigate high harmonic generation in crystals driven by optical skyrmions.We find that although the skyrmion number is not conserved,the resulting high-order harmonics can exhibit a distinctive multi-vortex structure,whose features are shaped by both the topology of the optical skyrmions and the rotational symmetry of the crystal.The position of the vortex centers can be effectively tuned by employing different types of optical skyrmions.To elucidate the underlying physics,we develop a multi-absorption channel model based on the conservation laws of spin and orbital angular momentum.Our work explores the role of optical topology in extreme nonlinear light-matter interactions,offering new opportunities for the formation and manipulation of optical vortices and novel structured light fields in the visible and ultraviolet regimes.展开更多
High harmonic generation(HHG)provides an experimental method for producing attosecond pulses and probing electron dynamics.Achieving precise dipole phase measurements is critical for tailoring the harmonic emission ph...High harmonic generation(HHG)provides an experimental method for producing attosecond pulses and probing electron dynamics.Achieving precise dipole phase measurements is critical for tailoring the harmonic emission phase and identifying the HHG mechanism.However,achieving this feature by applying traditional two-beam far-field interferometry to solid materials remains challenging.In this study,we present a novel interferometric approach that utilizes a single laser beam to excite two ZnO microwires(MWs)simultaneously,thereby generating coherent high-harmonic sources that form interference fringes in the far-field region.We leverage the diameter-dependent field-enhancement effect in MWs to measure the intensity-dependent fringe shift,revealing that the intraband current mechanism dominates the below-bandgap harmonic,whereas the interband polarization mechanism dominates the above-bandgap harmonic.This study offers a robust method for measuring the dipole phase of solid-state HHG and inspires intensity-modulated high-harmonic applications in coherent imaging and microdevice design.展开更多
This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first ...This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first solved via Newton-Raphson iteration through a set of nonlinear equations,and then input-output variables are selected to estimate the linear transfer function of the original NTP system without perturbations.The applications and insights of the proposed algorithm are discussed,particularly in guiding existing frequency scan algorithms,which are restricted by time-domain signal generation or measurement.This improvement is achieved through linear stability analysis of NTP systems with perturbations.展开更多
In order to eliminate the meshing interference between the flexspline and circular spline after the taper deformation of the flexspline,the radial deformation difference method,major and minor axis fitting method,and ...In order to eliminate the meshing interference between the flexspline and circular spline after the taper deformation of the flexspline,the radial deformation difference method,major and minor axis fitting method,and ellipse fitting method are used to modify the tooth thickness of the flexspline and analyze the performance indexes such as the assembly stress,transmission error,and fatigue life.Firstly,the conjugate tooth profile is solved based on the quadruple-circular-arc tooth profile and modified kinematic method.Then,based on the finite element radial deformation of the flexspline,the principle and characteristics of three modification methods are analyzed,and the modification amount of each section of the flexspline tooth is calculated.Finally,the influence of the three modification methods on the performance of the harmonic drive is compared.The results show that the radial deformation difference method can initially determine the modification amount.The minimum static assembly stress is 406.22 MPa by the major and minor axis fitting method.The ellipse fitting method has the best dynamic performance,small transmission error fluctuation,a peak-to-peak value of 3.060",and a maximum fatigue life of 10^(7.558)cycles.展开更多
High-precision optical frequency measurement serves as a cornerstone of modern science and technology,enabling advancements in fields ranging from fundamental physics to quantum information technologies.Obtaining prec...High-precision optical frequency measurement serves as a cornerstone of modern science and technology,enabling advancements in fields ranging from fundamental physics to quantum information technologies.Obtaining precise photon frequencies,especially in the ultraviolet or even extreme ultraviolet regimes,is a key goal in both light–matter interaction experiments and engineering applications.High-order harmonic generation(HHG)is an ideal light source for producing such photons.In this work,we propose an optical temporal interference model(OTIM)that establishes an analogy with multi-slit Fraunhofer diffraction(MSFD)to manipulate fine-frequency photon generation by exploiting the temporal coherence of HHG processes.Our model provides a unified physical framework for three distinct non-integer HHG generation schemes:single-pulse,shaped-pulse,and laser pulse train approaches,which correspond to single-MSFD-like,double-MSFD-like,and multi-MSFD-like processes,respectively.Arbitrary non-integer HHG photons can be obtained using our scheme.Our approach provides a new perspective for accurately measuring and controlling photon frequencies in fields such as frequency comb technology,interferometry,and atomic clocks.展开更多
Magnetically suspended rotor(MSR)systems have gained widespread industrial adoption owing to their frictionless operation and exceptional reliability.However,harmonic current generated by unbalanced mass and sensor ru...Magnetically suspended rotor(MSR)systems have gained widespread industrial adoption owing to their frictionless operation and exceptional reliability.However,harmonic current generated by unbalanced mass and sensor runout threatens the system stability.Repetitive control(RC)effectively suppresses harmonic current,but its parameter design relies on an accurate decoupling model of the system.The decoupling model for the MSR system is often simplified to a second-order linear system.Such a simplification,however,necessitates explicit consideration of system uncertainties caused by unmodeled nonlinearities during the RC design process.Especially under strong gyroscopic effects,the parameter uncertainty is further increased.In this article,an active disturbance rejection controller(ADRC)based on phase compensation(PC)is used to suppress coupling disturbances and improve the control performance of harmonic suppression.Firstly,the dynamic model of the MSR system is established,and both internal and external disturbances are thoroughly analyzed.Then,the RC-PCADRC scheme is designed,integrating the complementary strengths of RC and ADRC,with a particular emphasis on PC to improve stability margins.A comprehensive stability analysis is conducted,along with parameter optimization guidelines.Finally,the effectiveness and superiority of the proposed scheme are validated through both simulations and experiments.展开更多
The integration of a large number of power electronic converters,such as railway power conditioner(RPC),introduces a series of problems,including harmonic interaction,stability issues,and wideband resonance,into the r...The integration of a large number of power electronic converters,such as railway power conditioner(RPC),introduces a series of problems,including harmonic interaction,stability issues,and wideband resonance,into the railway power supply system.To address these challenges,this paper proposes a novel harmonic resonance prevention measure for RPC-network-train interaction system.Firstly,a harmonic model,a parallel resonance impedance model,a series resonance admittance model,and a control stability model are each established for the RPC-network-train interaction system.Secondly,a comprehensive resonance impact factor(CRIF)is proposed to efficiently and accurately identify the key components affecting resonance,and to provide the selection results of optimization parameters for resonance prevention.Next,the initially selected parameters are constrained by the requirements of ripple current,reactive power and stability.Subsequently,the impedance parameters(control parameters and filter parameters)of the RPC are optimized with the objective of reshaping the parallel resonance impedance and series resonance admittance of the RPC-network-train interaction system,ensuring the output current har-monics of RPC meet standards to achieve resonance prevention,while ensuring the stable operation of the RPC.Finally,the proposed resonance prevention measure is verified under both light load and heavy load conditions using a simulation platform and a hardware-in-the-loop experimental platform.展开更多
The generation of optical vortices from nonlinear photonic crystals(NPCs)with spatially modulated second-order nonlinearity offers a promising approach to extend the working wavelength and topological charge of vortex...The generation of optical vortices from nonlinear photonic crystals(NPCs)with spatially modulated second-order nonlinearity offers a promising approach to extend the working wavelength and topological charge of vortex beams for various applications.In this work,the second harmonic(SH)optical vortex beams generated from nonlinear fork gratings under Gaussian beam illumination are numerically investigated.The far-field intensity and phase distributions,as well as the orbital angular momentum(OAM)spectra of the SH beams,are analyzed for different structural topological charges and diffraction orders.Results reveal that higher-order diffraction and larger structural topological charges lead to angular interference patterns and non-uniform intensity distributions,deviating from the standard vortex profile.To optimize the SH vortex quality,the effects of the fundamental wave beam waist,crystal thickness,and grating duty cycle are explored.It is shown that increasing the beam waist can effectively suppress diffraction order interference and improve the beam’s quality.This study provides theoretical guidance for enhancing the performance of nonlinear optical devices based on NPCs.展开更多
Spherical harmonic analysis(SHA)and synthesis(SHS)are widely used by researchers in various fields.Both numerical integration and least-squares methods can be employed for analysis and synthesis.However,these approach...Spherical harmonic analysis(SHA)and synthesis(SHS)are widely used by researchers in various fields.Both numerical integration and least-squares methods can be employed for analysis and synthesis.However,these approaches,when calculated via summation,are computationally intensive.Although the Fast Fourier Transform(FFT)algorithm is efficient,it is traditionally limited to processing global grid points starting from zero longitude.In this paper,we derive an improved FFT algorithm for spherical harmonic analysis and synthesis.The proposed algorithm eliminates the need for grid points to start at zero longitude,thereby expanding the applicability of FFT-based methods.Numerical experiments demonstrate that the new algorithm retains the computational efficiency of conventional FFT while achieving accuracy comparable to the summation method.Consequently,it enables direct harmonic coefficient calculation from global grid data without requiring interpolation to align with zero longitude.Additionally,the algrithm can generate grid points with equi-angular spacing using the improved FFT algorithm,starting from non-zero longitudes.To address the loss of orthogonality in latitude due to discrete spherical grids,a quadrature weight factor-dependent on grid type(e.g.,regular or Gauss grid)-is incorporated,as summarized in this study.展开更多
Conventional approaches for obtaining the second and third harmonics typically employ several nonlinear crystals to generate them,which is restricted in application due to the complexity of the optical path and the bu...Conventional approaches for obtaining the second and third harmonics typically employ several nonlinear crystals to generate them,which is restricted in application due to the complexity of the optical path and the bulkiness of the device.In this work,we present a comprehensive theoretical and numerical investigation of the simultaneous generation and competition between the second harmonic waves(SHW)and the third harmonic waves(THW)in a single nonlinear crystal.Through analyzing both small-signal and large-signal regimes,we reveal the complex coupling mechanisms between SHW and THW generation processes.Using periodically poled lithium niobate as an example,we demonstrate that the relative conversion efficiencies between SHW and THW can be freely adjusted by controlling the input fundamental wave power.This work provides new insights for designing efficient frequency converters capable of generating both SHW and THW outputs with controllable intensity ratios.展开更多
This study examines the high-order harmonic radiation behavior of MgO crystals driven by combined pulses based on the numerical solution of the semiconductor Bloch equation.We found that compared with the monochromati...This study examines the high-order harmonic radiation behavior of MgO crystals driven by combined pulses based on the numerical solution of the semiconductor Bloch equation.We found that compared with the monochromatic pulse,the MgO crystal can radiate a continuous harmonic spectrum with two platforms driven by the three-color combined pulse.The reason is that under the three-color combined pulse,the electron ionization and recombination can be effectively controlled within a half-optical cycle of the laser pulse.Using this continuous spectrum,we synthesized an isolated attosecond pulse with a duration of approximately 370 as.This study provides a new perspective on all-solid-state compact optical devices.展开更多
This study systematically investigates the attractor characteristics of harmonic solitons in a passively modelocked fiber laser.Through comprehensive analysis in both time and frequency domains,we examine the evolutio...This study systematically investigates the attractor characteristics of harmonic solitons in a passively modelocked fiber laser.Through comprehensive analysis in both time and frequency domains,we examine the evolution of pulse width,spectral bandwidth,and energy across different harmonic orders.The results demonstrate typical soliton attractor behaviors,including attractiveness,dissipativity,and self-organization.In the transition regions between harmonic orders,breathing harmonic soliton states are captured using the time-stretched dispersive Fourier transform.By comparing the breathing dynamics with the stable states,the existence and self-organizing nature of soliton attractors are further confirmed.Finally,harmonic soliton attractors are employed as programmable light sources to achieve ternary optical coding.展开更多
Many existing watermarking approaches aim to provide a Robust Reversible Data Hiding(RRDH)method.However,most of these approaches degrade under geometric and non-geometric attacks.This paper presents a novel RRDH appr...Many existing watermarking approaches aim to provide a Robust Reversible Data Hiding(RRDH)method.However,most of these approaches degrade under geometric and non-geometric attacks.This paper presents a novel RRDH approach using Polar Harmonic Fourier Moments(PHFMs)and linear interpolation.The primary objective is to enhance the robustness of the embedded watermark and improve the imperceptibility of the watermarked image.The proposed method leverages the high-fidelity and anti-geometric transformation properties of PHFMs.The image is transformed into the frequency domain of RRDH,after which compensation data is embedded using a twodimensional RDH scheme.Linear interpolation modification is applied to reduce the modifications caused by the embedded data,minimize complexity,and preserve imperceptibility features.As a result,both the robustness and reliability of the embedded data are effectively recovered.Experimental results demonstrate that our approach achieves superior visual quality and strong resistance to geometric transformation attacks.Extensive calculations show that the proposed RRDH method outperforms existing methods.The imperceptibility metrics achieved include a Peak Signalto-Noise Ratio(PSNR)of 52 dB and a Structural Similarity Index Measure(SSIM)of 0.9990,reflecting high fidelity and minimal degradation in the watermarked image.Additionally,robustness measurements indicate a PSNR of 43 dB,along with reduced computational complexity.展开更多
This paper presents a novel approach to design a compact circular rat-race coupler with an ultrawide stopband, with the aim to reduce its size while maintaining performance. The design methodology begins with a common...This paper presents a novel approach to design a compact circular rat-race coupler with an ultrawide stopband, with the aim to reduce its size while maintaining performance. The design methodology begins with a common miniaturization technique to replace the conventional quarter-wavelength transmission line with an equivalent low-pass filter loaded with parallel coupled line and radial stubs. Since the latter leads to produce higher order harmonics, parasitic open-ended stubs are then properly introduced in the structure not only to overcome the issue but also to produce controllable transmission zeros. A versatile analytical model is also developed taking into account manufacturing restrictions, which makes it possible to extract the physical parameters of the coupler unit-cell for a given desired compactness percentage with respect to the conventional rat-race coupler. A prototype is fabricated and measured to validate the design,demonstrating the predicted behavior fairly achieved by numerical analysis. A significant size reduction of about 86.1% was achieved compared to the conventional design, while effectively suppressing higher order modes up to 23.4 GHz(including the 13th harmonic based on |S11|>-5 dB and |S21|<-17 dB)with high isolation level(|S41|<-17 dB) between the ports.展开更多
We theoretically investigate the elliptical high-order harmonic generation from H_(2)^(+)in two-color cross-linearlypolarized laser fields by numerically solving the two-dimensional time-dependent Schr¨odinger eq...We theoretically investigate the elliptical high-order harmonic generation from H_(2)^(+)in two-color cross-linearlypolarized laser fields by numerically solving the two-dimensional time-dependent Schr¨odinger equation.Numerical simulations show that the crossing-angle-dependent harmonic ellipticity exhibits a prominent antisymmetric structure,which tends to disappear as the internuclear distance increases.Furthermore,ground-state electrons experience resonant transitions to the first excited state at larger internuclear distances,where the disruption of symmetric electron motion suppresses the antisymmetric structure.Additionally,a near-circularly-polarized attosecond pulse can be obtained by modulating the crossing angle.展开更多
Molecular high-order harmonic spectroscopy is a significant advancement in ultrafast science, enabling the measurement of multielectron dynamics with attosecond temporal resolution. The fine structures observed in the...Molecular high-order harmonic spectroscopy is a significant advancement in ultrafast science, enabling the measurement of multielectron dynamics with attosecond temporal resolution. The fine structures observed in the molecular harmonic spectrum provide crucial insights into the structural or multielectron dynamical effects induced by intense laser fields. In this study, we measure the high-order harmonic spectrum of aligned CO_(2) molecules contributed from short trajectories. Two distinct groups of minima are identified in the plateau region. Our findings indicate that the deeper-lying molecular orbitals and two-center interference play significant roles in molecular harmonic generation. The results pave the way for advancing the understanding of multielectron dynamics in polyatomic molecules under intense laser fields.展开更多
Second harmonic generation(SHG),a fundamental and widely-studied phenomenon in nonlinear optics,has attracted significant attention for its ability to convert fundamental frequencies into their second harmonics.While ...Second harmonic generation(SHG),a fundamental and widely-studied phenomenon in nonlinear optics,has attracted significant attention for its ability to convert fundamental frequencies into their second harmonics.While the dominant SHG research has been focused on the optical and infrared regimes,its investigation in the microwave range presents challenges due to the requirements of materials with higher nonlinear coefficients and high-power microwave sources.Here,we provide an overview of methods together with underlying mechanisms for SHG in microwave frequencies,and discuss prospects and insights into the future developments of SHG-based technologies.The discussions on both numerical analyses and experimental studies will offer guidance for further SHG research and communication advancements in microwave regime.展开更多
In this paper,a 12/14-pole permanent magnet in-wheel motor is studied for potential in-wheel application,and the torque and loss are improved simultaneously based on designing and optimizing the corresponding dominant...In this paper,a 12/14-pole permanent magnet in-wheel motor is studied for potential in-wheel application,and the torque and loss are improved simultaneously based on designing and optimizing the corresponding dominant harmonics.The key of this study is to evaluate the contributions of harmonics on torque and loss,and further determines the harmonics related to them.Based on this,the torque enhancement factor and loss suppression factor are defined based on the selected dominant harmonics.And,the two factors are set as the optimization objectives,aiming at improving the characteristics of torque and loss.At the same time,to achieve an efficient optimization,a layered optimization method is presented,which includes magnet source layer and permeance layer.Based on the optimization,the motor torque is improved effectively,while the rotor iron loss is also reduced significantly.Then,a prototype motor is manufactured for experimental test.Finally,the simulation analysis and test results verify the validation of the studied motor and the proposed optimization method based on dominant harmonics.展开更多
基金the National Key Research&Development Program of China(Grant No.2022YFC2203901)the State Key Laboratory of Spatial Datum(Grant No.SKLSD2025-KF-03)+1 种基金Fundamental Research Funds for the Central UniversitiesSun Yat-sen University for the support。
文摘The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12234002, 92250303, 12474486, 12504301, and 12504396)the National Key Research and Development Program of China (Grant No. 2024YFA1612101)。
文摘With their intricate vectorial structures in space,optical skyrmions have significantly expanded the landscape of topological optics and light-matter interactions.We theoretically investigate high harmonic generation in crystals driven by optical skyrmions.We find that although the skyrmion number is not conserved,the resulting high-order harmonics can exhibit a distinctive multi-vortex structure,whose features are shaped by both the topology of the optical skyrmions and the rotational symmetry of the crystal.The position of the vortex centers can be effectively tuned by employing different types of optical skyrmions.To elucidate the underlying physics,we develop a multi-absorption channel model based on the conservation laws of spin and orbital angular momentum.Our work explores the role of optical topology in extreme nonlinear light-matter interactions,offering new opportunities for the formation and manipulation of optical vortices and novel structured light fields in the visible and ultraviolet regimes.
基金supported by the National Key R&D Program of China (Grant Nos.2023YFA1406801 and 2022YFA1604301)the National Natural Science Foundation of China (Grant Nos.12434013,12595343,12404393,and 12174011)。
文摘High harmonic generation(HHG)provides an experimental method for producing attosecond pulses and probing electron dynamics.Achieving precise dipole phase measurements is critical for tailoring the harmonic emission phase and identifying the HHG mechanism.However,achieving this feature by applying traditional two-beam far-field interferometry to solid materials remains challenging.In this study,we present a novel interferometric approach that utilizes a single laser beam to excite two ZnO microwires(MWs)simultaneously,thereby generating coherent high-harmonic sources that form interference fringes in the far-field region.We leverage the diameter-dependent field-enhancement effect in MWs to measure the intensity-dependent fringe shift,revealing that the intraband current mechanism dominates the below-bandgap harmonic,whereas the interband polarization mechanism dominates the above-bandgap harmonic.This study offers a robust method for measuring the dipole phase of solid-state HHG and inspires intensity-modulated high-harmonic applications in coherent imaging and microdevice design.
基金supported by China Southern Power Grid Corporation(036000KC23090005(GDKJXM20231027)).
文摘This paper presents a programmable frequency scan algorithm based on harmonic balance.The core idea involves treating systems under perturbation as nonlinear time-periodic(NTP)systems.Steady-state harmonics are first solved via Newton-Raphson iteration through a set of nonlinear equations,and then input-output variables are selected to estimate the linear transfer function of the original NTP system without perturbations.The applications and insights of the proposed algorithm are discussed,particularly in guiding existing frequency scan algorithms,which are restricted by time-domain signal generation or measurement.This improvement is achieved through linear stability analysis of NTP systems with perturbations.
文摘In order to eliminate the meshing interference between the flexspline and circular spline after the taper deformation of the flexspline,the radial deformation difference method,major and minor axis fitting method,and ellipse fitting method are used to modify the tooth thickness of the flexspline and analyze the performance indexes such as the assembly stress,transmission error,and fatigue life.Firstly,the conjugate tooth profile is solved based on the quadruple-circular-arc tooth profile and modified kinematic method.Then,based on the finite element radial deformation of the flexspline,the principle and characteristics of three modification methods are analyzed,and the modification amount of each section of the flexspline tooth is calculated.Finally,the influence of the three modification methods on the performance of the harmonic drive is compared.The results show that the radial deformation difference method can initially determine the modification amount.The minimum static assembly stress is 406.22 MPa by the major and minor axis fitting method.The ellipse fitting method has the best dynamic performance,small transmission error fluctuation,a peak-to-peak value of 3.060",and a maximum fatigue life of 10^(7.558)cycles.
基金supported by the National Natural Science Foundation of China(Grant No.12304379)the Natural Science Foundation of Liaoning Province(Grant No.2024BS-269)the Guangdong Basic and Applied Basic Research Foundation(Grant No.025A1515011117)。
文摘High-precision optical frequency measurement serves as a cornerstone of modern science and technology,enabling advancements in fields ranging from fundamental physics to quantum information technologies.Obtaining precise photon frequencies,especially in the ultraviolet or even extreme ultraviolet regimes,is a key goal in both light–matter interaction experiments and engineering applications.High-order harmonic generation(HHG)is an ideal light source for producing such photons.In this work,we propose an optical temporal interference model(OTIM)that establishes an analogy with multi-slit Fraunhofer diffraction(MSFD)to manipulate fine-frequency photon generation by exploiting the temporal coherence of HHG processes.Our model provides a unified physical framework for three distinct non-integer HHG generation schemes:single-pulse,shaped-pulse,and laser pulse train approaches,which correspond to single-MSFD-like,double-MSFD-like,and multi-MSFD-like processes,respectively.Arbitrary non-integer HHG photons can be obtained using our scheme.Our approach provides a new perspective for accurately measuring and controlling photon frequencies in fields such as frequency comb technology,interferometry,and atomic clocks.
基金supported by the Youth Innovation Promotion Association CAS under Grant 2023042the Major Science Facility Project of the Shandong Provincial Natural Science Foundation under Grant ZR2022DKX005。
文摘Magnetically suspended rotor(MSR)systems have gained widespread industrial adoption owing to their frictionless operation and exceptional reliability.However,harmonic current generated by unbalanced mass and sensor runout threatens the system stability.Repetitive control(RC)effectively suppresses harmonic current,but its parameter design relies on an accurate decoupling model of the system.The decoupling model for the MSR system is often simplified to a second-order linear system.Such a simplification,however,necessitates explicit consideration of system uncertainties caused by unmodeled nonlinearities during the RC design process.Especially under strong gyroscopic effects,the parameter uncertainty is further increased.In this article,an active disturbance rejection controller(ADRC)based on phase compensation(PC)is used to suppress coupling disturbances and improve the control performance of harmonic suppression.Firstly,the dynamic model of the MSR system is established,and both internal and external disturbances are thoroughly analyzed.Then,the RC-PCADRC scheme is designed,integrating the complementary strengths of RC and ADRC,with a particular emphasis on PC to improve stability margins.A comprehensive stability analysis is conducted,along with parameter optimization guidelines.Finally,the effectiveness and superiority of the proposed scheme are validated through both simulations and experiments.
基金supported in part by the National Natural Science Foundation of China under Grant No.52277126.
文摘The integration of a large number of power electronic converters,such as railway power conditioner(RPC),introduces a series of problems,including harmonic interaction,stability issues,and wideband resonance,into the railway power supply system.To address these challenges,this paper proposes a novel harmonic resonance prevention measure for RPC-network-train interaction system.Firstly,a harmonic model,a parallel resonance impedance model,a series resonance admittance model,and a control stability model are each established for the RPC-network-train interaction system.Secondly,a comprehensive resonance impact factor(CRIF)is proposed to efficiently and accurately identify the key components affecting resonance,and to provide the selection results of optimization parameters for resonance prevention.Next,the initially selected parameters are constrained by the requirements of ripple current,reactive power and stability.Subsequently,the impedance parameters(control parameters and filter parameters)of the RPC are optimized with the objective of reshaping the parallel resonance impedance and series resonance admittance of the RPC-network-train interaction system,ensuring the output current har-monics of RPC meet standards to achieve resonance prevention,while ensuring the stable operation of the RPC.Finally,the proposed resonance prevention measure is verified under both light load and heavy load conditions using a simulation platform and a hardware-in-the-loop experimental platform.
基金supported by the National Nat-ural Science Foundation of China(Nos.12192251,12174185,92163216,and 62288101).
文摘The generation of optical vortices from nonlinear photonic crystals(NPCs)with spatially modulated second-order nonlinearity offers a promising approach to extend the working wavelength and topological charge of vortex beams for various applications.In this work,the second harmonic(SH)optical vortex beams generated from nonlinear fork gratings under Gaussian beam illumination are numerically investigated.The far-field intensity and phase distributions,as well as the orbital angular momentum(OAM)spectra of the SH beams,are analyzed for different structural topological charges and diffraction orders.Results reveal that higher-order diffraction and larger structural topological charges lead to angular interference patterns and non-uniform intensity distributions,deviating from the standard vortex profile.To optimize the SH vortex quality,the effects of the fundamental wave beam waist,crystal thickness,and grating duty cycle are explored.It is shown that increasing the beam waist can effectively suppress diffraction order interference and improve the beam’s quality.This study provides theoretical guidance for enhancing the performance of nonlinear optical devices based on NPCs.
基金supported by The National Natural Science Foundation of China(42374004).
文摘Spherical harmonic analysis(SHA)and synthesis(SHS)are widely used by researchers in various fields.Both numerical integration and least-squares methods can be employed for analysis and synthesis.However,these approaches,when calculated via summation,are computationally intensive.Although the Fast Fourier Transform(FFT)algorithm is efficient,it is traditionally limited to processing global grid points starting from zero longitude.In this paper,we derive an improved FFT algorithm for spherical harmonic analysis and synthesis.The proposed algorithm eliminates the need for grid points to start at zero longitude,thereby expanding the applicability of FFT-based methods.Numerical experiments demonstrate that the new algorithm retains the computational efficiency of conventional FFT while achieving accuracy comparable to the summation method.Consequently,it enables direct harmonic coefficient calculation from global grid data without requiring interpolation to align with zero longitude.Additionally,the algrithm can generate grid points with equi-angular spacing using the improved FFT algorithm,starting from non-zero longitudes.To address the loss of orthogonality in latitude due to discrete spherical grids,a quadrature weight factor-dependent on grid type(e.g.,regular or Gauss grid)-is incorporated,as summarized in this study.
基金supported by the Science and Technology Project of Guangdong Province,China(Grant No.2020B010190001)the National Natural Science Foundation of China(Grant No.12434016)+1 种基金the National Key Research and Development Program of China(Grant No.2023YFA1406900)the Fund of the National Postdoctoral Researcher Program(Grant No.GZB20240785).
文摘Conventional approaches for obtaining the second and third harmonics typically employ several nonlinear crystals to generate them,which is restricted in application due to the complexity of the optical path and the bulkiness of the device.In this work,we present a comprehensive theoretical and numerical investigation of the simultaneous generation and competition between the second harmonic waves(SHW)and the third harmonic waves(THW)in a single nonlinear crystal.Through analyzing both small-signal and large-signal regimes,we reveal the complex coupling mechanisms between SHW and THW generation processes.Using periodically poled lithium niobate as an example,we demonstrate that the relative conversion efficiencies between SHW and THW can be freely adjusted by controlling the input fundamental wave power.This work provides new insights for designing efficient frequency converters capable of generating both SHW and THW outputs with controllable intensity ratios.
基金supported by the Natural Science Foundation of Zhejiang Province,China(Grant No.Y23A040001)the National Natural Science Foundation of China(Grant Nos.12374029,12074145,and 11975012)+4 种基金the National Key Research and Development Program of China(Grant No.2019YFA0307700)the Research Foundation for Basic Research of Jilin ProvinceChina(Grant No.20220101003JC)the National College Students Innovation and Entrepreneurship Training Program(Grant No.202310350062)the Graduate Innovation Fund of Jilin University(Grant No.2024CX041)。
文摘This study examines the high-order harmonic radiation behavior of MgO crystals driven by combined pulses based on the numerical solution of the semiconductor Bloch equation.We found that compared with the monochromatic pulse,the MgO crystal can radiate a continuous harmonic spectrum with two platforms driven by the three-color combined pulse.The reason is that under the three-color combined pulse,the electron ionization and recombination can be effectively controlled within a half-optical cycle of the laser pulse.Using this continuous spectrum,we synthesized an isolated attosecond pulse with a duration of approximately 370 as.This study provides a new perspective on all-solid-state compact optical devices.
基金supported by the National Natural Science Foundation of China(Grant No.12475008)the Scientific Research and Developed Fund of Zhejiang A&F University(Grant No.2021FR0009)。
文摘This study systematically investigates the attractor characteristics of harmonic solitons in a passively modelocked fiber laser.Through comprehensive analysis in both time and frequency domains,we examine the evolution of pulse width,spectral bandwidth,and energy across different harmonic orders.The results demonstrate typical soliton attractor behaviors,including attractiveness,dissipativity,and self-organization.In the transition regions between harmonic orders,breathing harmonic soliton states are captured using the time-stretched dispersive Fourier transform.By comparing the breathing dynamics with the stable states,the existence and self-organizing nature of soliton attractors are further confirmed.Finally,harmonic soliton attractors are employed as programmable light sources to achieve ternary optical coding.
文摘Many existing watermarking approaches aim to provide a Robust Reversible Data Hiding(RRDH)method.However,most of these approaches degrade under geometric and non-geometric attacks.This paper presents a novel RRDH approach using Polar Harmonic Fourier Moments(PHFMs)and linear interpolation.The primary objective is to enhance the robustness of the embedded watermark and improve the imperceptibility of the watermarked image.The proposed method leverages the high-fidelity and anti-geometric transformation properties of PHFMs.The image is transformed into the frequency domain of RRDH,after which compensation data is embedded using a twodimensional RDH scheme.Linear interpolation modification is applied to reduce the modifications caused by the embedded data,minimize complexity,and preserve imperceptibility features.As a result,both the robustness and reliability of the embedded data are effectively recovered.Experimental results demonstrate that our approach achieves superior visual quality and strong resistance to geometric transformation attacks.Extensive calculations show that the proposed RRDH method outperforms existing methods.The imperceptibility metrics achieved include a Peak Signalto-Noise Ratio(PSNR)of 52 dB and a Structural Similarity Index Measure(SSIM)of 0.9990,reflecting high fidelity and minimal degradation in the watermarked image.Additionally,robustness measurements indicate a PSNR of 43 dB,along with reduced computational complexity.
文摘This paper presents a novel approach to design a compact circular rat-race coupler with an ultrawide stopband, with the aim to reduce its size while maintaining performance. The design methodology begins with a common miniaturization technique to replace the conventional quarter-wavelength transmission line with an equivalent low-pass filter loaded with parallel coupled line and radial stubs. Since the latter leads to produce higher order harmonics, parasitic open-ended stubs are then properly introduced in the structure not only to overcome the issue but also to produce controllable transmission zeros. A versatile analytical model is also developed taking into account manufacturing restrictions, which makes it possible to extract the physical parameters of the coupler unit-cell for a given desired compactness percentage with respect to the conventional rat-race coupler. A prototype is fabricated and measured to validate the design,demonstrating the predicted behavior fairly achieved by numerical analysis. A significant size reduction of about 86.1% was achieved compared to the conventional design, while effectively suppressing higher order modes up to 23.4 GHz(including the 13th harmonic based on |S11|>-5 dB and |S21|<-17 dB)with high isolation level(|S41|<-17 dB) between the ports.
基金supported by the National Natural Science Foundation of China(Grant Nos.11974229,12204291,and 11404204)the Fund from Graduate Students of Shanxi Normal University,China(Grant No.2023XSY044).
文摘We theoretically investigate the elliptical high-order harmonic generation from H_(2)^(+)in two-color cross-linearlypolarized laser fields by numerically solving the two-dimensional time-dependent Schr¨odinger equation.Numerical simulations show that the crossing-angle-dependent harmonic ellipticity exhibits a prominent antisymmetric structure,which tends to disappear as the internuclear distance increases.Furthermore,ground-state electrons experience resonant transitions to the first excited state at larger internuclear distances,where the disruption of symmetric electron motion suppresses the antisymmetric structure.Additionally,a near-circularly-polarized attosecond pulse can be obtained by modulating the crossing angle.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 92250306 and 12304302)the Natural Science Foundation of Jilin Province, China (Grant Nos. YDZJ202101ZYTS157 and YDZJ202201ZYTS314)the Scientific Research Foundation of Jilin Province Education Department, China (Grant No. JJKH20230283KJ)。
文摘Molecular high-order harmonic spectroscopy is a significant advancement in ultrafast science, enabling the measurement of multielectron dynamics with attosecond temporal resolution. The fine structures observed in the molecular harmonic spectrum provide crucial insights into the structural or multielectron dynamical effects induced by intense laser fields. In this study, we measure the high-order harmonic spectrum of aligned CO_(2) molecules contributed from short trajectories. Two distinct groups of minima are identified in the plateau region. Our findings indicate that the deeper-lying molecular orbitals and two-center interference play significant roles in molecular harmonic generation. The results pave the way for advancing the understanding of multielectron dynamics in polyatomic molecules under intense laser fields.
基金supported by the National Natural Science Foun-dation of China(No.12274339).
文摘Second harmonic generation(SHG),a fundamental and widely-studied phenomenon in nonlinear optics,has attracted significant attention for its ability to convert fundamental frequencies into their second harmonics.While the dominant SHG research has been focused on the optical and infrared regimes,its investigation in the microwave range presents challenges due to the requirements of materials with higher nonlinear coefficients and high-power microwave sources.Here,we provide an overview of methods together with underlying mechanisms for SHG in microwave frequencies,and discuss prospects and insights into the future developments of SHG-based technologies.The discussions on both numerical analyses and experimental studies will offer guidance for further SHG research and communication advancements in microwave regime.
文摘In this paper,a 12/14-pole permanent magnet in-wheel motor is studied for potential in-wheel application,and the torque and loss are improved simultaneously based on designing and optimizing the corresponding dominant harmonics.The key of this study is to evaluate the contributions of harmonics on torque and loss,and further determines the harmonics related to them.Based on this,the torque enhancement factor and loss suppression factor are defined based on the selected dominant harmonics.And,the two factors are set as the optimization objectives,aiming at improving the characteristics of torque and loss.At the same time,to achieve an efficient optimization,a layered optimization method is presented,which includes magnet source layer and permeance layer.Based on the optimization,the motor torque is improved effectively,while the rotor iron loss is also reduced significantly.Then,a prototype motor is manufactured for experimental test.Finally,the simulation analysis and test results verify the validation of the studied motor and the proposed optimization method based on dominant harmonics.
