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
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
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 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
This paper establishes an amplitude modulation heating model, simulating the far-field radiation of ELF/VLF signals generated by modulation heating, as well as the specific location and longitudinal extent of the radi...This paper establishes an amplitude modulation heating model, simulating the far-field radiation of ELF/VLF signals generated by modulation heating, as well as the specific location and longitudinal extent of the radiation source. We consider various modulation waveforms and find that square-wave modulation has the highest excitation efficiency for ELF/VLF signals, and that square-wave modulation with a smaller duty cycle(<50%) exhibits higher excitation efficiency for ELF/VLF signals, while the sin^(2)t waveform modulation yields the lowest proportion of harmonic energy in the generated signals. The amplitude of the second harmonic generated by the sin^(2)t waveform is less than one-tenth that of the fundamental frequency, and the energy of higher-frequency harmonics can be negligibly small compared with those of the fundamental wave. It is a challenging task to achieve a balance between enhancing the excitation efficiency of ELF/VLF signals and also suppressing harmonics generated by the modulated heating process. This is because the harmonics are correspondingly enhanced as the excitation efficiency of the signals is increased. However, we find that under conditions of varying effective radiant power and modulation frequency, as long as the modulation waveform is unchanged, the energy ratio between the fundamental frequency signal generated by modulated heating and each harmonic is relatively fixed, with changes only in signal intensity and the location of the radiation source zone. This implies that one can first select modulation waveforms that make the signal less prone to distortion, then increase the effective radiated power to enhance the signal strength, without concern for harmonic interference of the fundamental signal.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
Collagen characterization is crucial for disease diagnostics,prevention,and understanding,with growing focus on quantitative analysis at tissue and fibril levels.Numerous models have been developed to quantify structu...Collagen characterization is crucial for disease diagnostics,prevention,and understanding,with growing focus on quantitative analysis at tissue and fibril levels.Numerous models have been developed to quantify structural changes in collagen linked to various pathologies.However,many approaches remain limited to conceptual descriptions or rely on custom software,often requiring programming skills,which re-stricts their clinical application and potential impact.We introduce CollagenFitJ,a plugin for the open-source software platform ImageJ/FIJI,which represents a widely used microscopy image analysis tool.CollagenFitJ makes use of the cylindrical symmetry model for collagen to enable facile quantitative assessment of polarization-resolved second harmonic generation microscopy image stacks.The plugin’s main outputs are collagen structure-related maps(e.g.,orientation and anisotropy of collagen fibrils within the focal volume),which can be accompanied by distribution and randomness maps for a series of structure-related parameters.We describe and validate the use of CollagenFitJ on images acquired on rat-tail tendons,collagen capsules surrounding human thyroid nodules,and mouse colon tumors,using both scanning and widefield second harmonic generation microscopy datasets.The plugin was designed to be user-friendly,requiring little to no experience in image processing and coding to facilitate access for life scientists,medical staff,and microscopy practitioners with limited coding skills or time availability required for coding.展开更多
Designing novel two-dimensional structures and precisely modulating their second harmonic generation(SHG)attributes are key to advancing nonlinear photonic technologies.In this work,through first-principles calculatio...Designing novel two-dimensional structures and precisely modulating their second harmonic generation(SHG)attributes are key to advancing nonlinear photonic technologies.In this work,through first-principles calculations,we propose a novel tetrahedral phase of transition metal dichalcogenides(TMDs)and validate its structural feasibility in a family of compounds,i.e.,ZX_(2)(Z=Ti,Zr,Hf;X=S,Se,Te).Cohesive energy and phonon dispersion calculations further demonstrate that eight of nine possible ZX_(2)monolayers are dynamically stable.All the ZX_(2)monolayers exhibit pronounced out-of-plane SHG with nonlinear susceptibility components reaching the order of 10^(2)pm/V.Strain engineering imposes a profound influence on the SHG response of ZX_(2)monolayers by reducing symmetry and modifying nonlinear susceptibility components.The redshift and significant enhancement of the prominent peak in SHG spectra are also revealed due to strain-induced charge redistribution and band gap reduction.Intriguingly,strain-driven nonlinear optical switching effects are realized in the ZX_(2)monolayers,with a reversible switching of SHG component ordering under tensile and compressive strain.In such a case,the anisotropic SHG pattern transforms from fourfold to twofold symmetry under the strain.Our work demonstrates the efficacy of strain engineering in precisely enhancing SHG,paving the way for the integration of novel TMD structures into tunable and flexible nonlinear optical devices.展开更多
In this paper,it is shown that the harmonic Bergman projection P_(ω)^(h),induced by a radial,induced by a radial weightω,is bounded and onto from L^(∞)(D)to the harmonic Bloch space B_(h)if and only ifω∈D,,which ...In this paper,it is shown that the harmonic Bergman projection P_(ω)^(h),induced by a radial,induced by a radial weightω,is bounded and onto from L^(∞)(D)to the harmonic Bloch space B_(h)if and only ifω∈D,,which is a class of radial weights satisfying the two-sided doubling conditions.As an application,the bounded and compact positive Toeplitz operators T_(μ,ω)on the endpoint case weighted harmonic Bergman space L_(h,ω)^(1)(D)are characterized.展开更多
The harmonic balance method(HBM)has been widely applied to get the periodic solution of nonlinear systems,however,its convergence rate as well as computation efficiency is dramatically degraded when the system is high...The harmonic balance method(HBM)has been widely applied to get the periodic solution of nonlinear systems,however,its convergence rate as well as computation efficiency is dramatically degraded when the system is highly non-smooth,e.g.,discontinuous.In order to accelerate the convergence,an enriched HBM is developed in this paper where the non-smooth Bernoulli bases are additionally introduced to enrich the conventional Fourier bases.The basic idea behind is that the convergence rate of the HB solution,as a truncated Fourier series,can be improved if the smoothness of the solution becomes finer.Along this line,using non-smooth Bernoulli bases can compensate the highly non-smooth part of the solution and then,the smoothness of the residual part for Fourier approximation is improved so as to achieve accelerated convergence.Numerical examples are conducted on systems with non-smooth restoring and/or external forces.The results confirm that the proposed enriched HBM indeed increases the convergence rate and the increase becomes more significant if more non-smooth bases are used.展开更多
For permanent magnet synchronous machines(PMSMs),accurate inductance is critical for control design and condition monitoring.Owing to magnetic saturation,existing methods require nonlinear saturation model and measure...For permanent magnet synchronous machines(PMSMs),accurate inductance is critical for control design and condition monitoring.Owing to magnetic saturation,existing methods require nonlinear saturation model and measurements from multiple load/current conditions,and the estimation is relying on the accuracy of saturation model and other machine parameters in the model.Speed harmonic produced by harmonic currents is inductance-dependent,and thus this paper explores the use of magnitude and phase angle of the speed harmonic for accurate inductance estimation.Two estimation models are built based on either the magnitude or phase angle,and the inductances can be from d-axis voltage and the magnitude or phase angle,in which the filter influence in harmonic extraction is considered to ensure the estimation performance.The inductances can be estimated from the measurements under one load condition,which is free of saturation model.Moreover,the inductance estimation is robust to the change of other machine parameters.The proposed approach can effectively improve estimation accuracy especially under the condition with low current magnitude.Experiments and comparisons are conducted on a test PMSM to validate the proposed approach.展开更多
The heterostructures incorporated with two or more distinctive two-dimensional(2D)materials have attracted great attention be-cause they could give rise to enhanced prop-erty in comparison with their individual counte...The heterostructures incorporated with two or more distinctive two-dimensional(2D)materials have attracted great attention be-cause they could give rise to enhanced prop-erty in comparison with their individual counterparts.Here,a water-assisted two-step rapid physical vapor deposition(rPVD)method was explored and used to synthesize Bi_(2)Te_(3)-Sb_(2)Te_(3)lateral het-erostructures(LHS)successfully.The Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is in nearly uniform size,and grows along three particular orientations with the intersection angles of 120°.Inter-estingly,we found that the water molecules play a significant role in determining the growth orientation,namely whether it will grow along the vertical or lateral direction in 2D structure.Hence,a growth mechanism of LHS based on the water-assisted two-step rPVD was present,which can be used as a general strategy and extended to the growth of other 2D heterostruc-tures or homostructures,such as SnS-SnSe LHS and SnS-SnS lateral homostructures.Fur-thermore,the second-harmonic generation intensity of the Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is much stronger than that of the Bi_(2)Te_(3)/Sb_(2)Te_(3)vertical heterostructures(VHS).This work opens a new approach for the synthesis of water-assisted lateral 2D heterostructures or homostruc-tures and offers a new method to enhance the second-harmonic generation properties of topo-logical insulating materials.展开更多
We use out-of-time order correlators(OTOCs)to investigate the quantum instability and Ehrenfest time for an inverted harmonic oscillator(IHO).For initial states located in the stable manifolds of the IHO we find that ...We use out-of-time order correlators(OTOCs)to investigate the quantum instability and Ehrenfest time for an inverted harmonic oscillator(IHO).For initial states located in the stable manifolds of the IHO we find that the corresponding OTOC exhibits identical evolutionary characteristics to the saddle point before the Ehrenfest time.For initial states located in the unstable manifolds,the OTOCs still grow exponentially but the time to maintain exponential growth is related to the center position of its wave packet in phase space.Moreover,we use the Husimi Q function to visualize the quantum wave packets during exponential growth of the OTOCs.Our results show that quantum instability exists at arbitrary orbits in the IHO system,and the Ehrenfest time in the IHO system depends not only on the photon number of the initial system but also on the central positions of the initial states in phase space.展开更多
We investigate theoretically the effects of chirped laser pulses on high-order harmonic generation(HHG)from solids.We find that the harmonic spectra display redshifts for the driving laser pulses with negative chirp a...We investigate theoretically the effects of chirped laser pulses on high-order harmonic generation(HHG)from solids.We find that the harmonic spectra display redshifts for the driving laser pulses with negative chirp and blueshifts for those with positive chirp,which is due to the change in the instantaneous frequency of the driving laser for different chirped pulses.The analysis of crystal-momentum-resolved(k-resolved)HHG reveals that the frequency shifts are equal for the harmonics generated by different crystal momentum channels.The frequency shifts in the cutoff region are larger than those in the plateau region.With the increase of the absolute value of the chirp parameters,the frequency shifts of HHG become more significant,leading to the shifts from odd-to even-order harmonics.We also demonstrate that the frequency shifts of harmonic spectra are related to the duration of the chirped laser field,but are insensitive to the laser intensity and dephasing time.展开更多
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 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 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.
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 Key R&D Program of China (No. 2022YFE0204100)the National Natural Science Foundation of China (12205067 and 12375199)the Fundamental Research Funds for the Central Universities (Grant No. HIT.OCEF. 2022036)。
文摘This paper establishes an amplitude modulation heating model, simulating the far-field radiation of ELF/VLF signals generated by modulation heating, as well as the specific location and longitudinal extent of the radiation source. We consider various modulation waveforms and find that square-wave modulation has the highest excitation efficiency for ELF/VLF signals, and that square-wave modulation with a smaller duty cycle(<50%) exhibits higher excitation efficiency for ELF/VLF signals, while the sin^(2)t waveform modulation yields the lowest proportion of harmonic energy in the generated signals. The amplitude of the second harmonic generated by the sin^(2)t waveform is less than one-tenth that of the fundamental frequency, and the energy of higher-frequency harmonics can be negligibly small compared with those of the fundamental wave. It is a challenging task to achieve a balance between enhancing the excitation efficiency of ELF/VLF signals and also suppressing harmonics generated by the modulated heating process. This is because the harmonics are correspondingly enhanced as the excitation efficiency of the signals is increased. However, we find that under conditions of varying effective radiant power and modulation frequency, as long as the modulation waveform is unchanged, the energy ratio between the fundamental frequency signal generated by modulated heating and each harmonic is relatively fixed, with changes only in signal intensity and the location of the radiation source zone. This implies that one can first select modulation waveforms that make the signal less prone to distortion, then increase the effective radiated power to enhance the signal strength, without concern for harmonic interference of the fundamental signal.
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.
基金supported by the Ministry of Research,Innovation and Digitalization,CNCS-UEFISCDI[Grant Nos.RO-NO-2019-0601(MEDYCONAI),PN-III-P4-PCE-2021-0444(RESONANO)]PN-IV-P1-PCE-2023-1137+2 种基金supported in part by IN2SIGHT,European Union’s Horizon 2020(GA.no.964481)by the Research Council of Lithuania(LMTLTAgreement No.P-MIP-23-237).
文摘Collagen characterization is crucial for disease diagnostics,prevention,and understanding,with growing focus on quantitative analysis at tissue and fibril levels.Numerous models have been developed to quantify structural changes in collagen linked to various pathologies.However,many approaches remain limited to conceptual descriptions or rely on custom software,often requiring programming skills,which re-stricts their clinical application and potential impact.We introduce CollagenFitJ,a plugin for the open-source software platform ImageJ/FIJI,which represents a widely used microscopy image analysis tool.CollagenFitJ makes use of the cylindrical symmetry model for collagen to enable facile quantitative assessment of polarization-resolved second harmonic generation microscopy image stacks.The plugin’s main outputs are collagen structure-related maps(e.g.,orientation and anisotropy of collagen fibrils within the focal volume),which can be accompanied by distribution and randomness maps for a series of structure-related parameters.We describe and validate the use of CollagenFitJ on images acquired on rat-tail tendons,collagen capsules surrounding human thyroid nodules,and mouse colon tumors,using both scanning and widefield second harmonic generation microscopy datasets.The plugin was designed to be user-friendly,requiring little to no experience in image processing and coding to facilitate access for life scientists,medical staff,and microscopy practitioners with limited coding skills or time availability required for coding.
基金supported by the National Natural Science Foundation of China(Grant Nos.12304220,12174157,12074150,and 12374174)the Natural Science Foundation of Jiangsu Province(Grant No.BK20230518)+2 种基金the China Postdoctoral Science Foundation(Grant No.2023M731383)the College Student Innovation Project(Grant No.202410299946X)the Scientific Research Project of Jiangsu University(Grant No.22A397).
文摘Designing novel two-dimensional structures and precisely modulating their second harmonic generation(SHG)attributes are key to advancing nonlinear photonic technologies.In this work,through first-principles calculations,we propose a novel tetrahedral phase of transition metal dichalcogenides(TMDs)and validate its structural feasibility in a family of compounds,i.e.,ZX_(2)(Z=Ti,Zr,Hf;X=S,Se,Te).Cohesive energy and phonon dispersion calculations further demonstrate that eight of nine possible ZX_(2)monolayers are dynamically stable.All the ZX_(2)monolayers exhibit pronounced out-of-plane SHG with nonlinear susceptibility components reaching the order of 10^(2)pm/V.Strain engineering imposes a profound influence on the SHG response of ZX_(2)monolayers by reducing symmetry and modifying nonlinear susceptibility components.The redshift and significant enhancement of the prominent peak in SHG spectra are also revealed due to strain-induced charge redistribution and band gap reduction.Intriguingly,strain-driven nonlinear optical switching effects are realized in the ZX_(2)monolayers,with a reversible switching of SHG component ordering under tensile and compressive strain.In such a case,the anisotropic SHG pattern transforms from fourfold to twofold symmetry under the strain.Our work demonstrates the efficacy of strain engineering in precisely enhancing SHG,paving the way for the integration of novel TMD structures into tunable and flexible nonlinear optical devices.
基金supported by the National Natural Science Foundation of China(12171075)the Science and Technology Research Project of Education Department of Jilin Province(JJKH20241406KJ)Zhan’s research was supported by the Doctoral Startup Fund of Liaoning University of Technology(XB2024029).
文摘In this paper,it is shown that the harmonic Bergman projection P_(ω)^(h),induced by a radial,induced by a radial weightω,is bounded and onto from L^(∞)(D)to the harmonic Bloch space B_(h)if and only ifω∈D,,which is a class of radial weights satisfying the two-sided doubling conditions.As an application,the bounded and compact positive Toeplitz operators T_(μ,ω)on the endpoint case weighted harmonic Bergman space L_(h,ω)^(1)(D)are characterized.
基金supported by the National Natural Science Foundation of China (Grant No. 12372028)the National Key Research and Development Program of China (Grant No. 2020YFC2201101)the Guangdong Basic and Applied Basic Research Foundation (Grant No.2022A1515011809)。
文摘The harmonic balance method(HBM)has been widely applied to get the periodic solution of nonlinear systems,however,its convergence rate as well as computation efficiency is dramatically degraded when the system is highly non-smooth,e.g.,discontinuous.In order to accelerate the convergence,an enriched HBM is developed in this paper where the non-smooth Bernoulli bases are additionally introduced to enrich the conventional Fourier bases.The basic idea behind is that the convergence rate of the HB solution,as a truncated Fourier series,can be improved if the smoothness of the solution becomes finer.Along this line,using non-smooth Bernoulli bases can compensate the highly non-smooth part of the solution and then,the smoothness of the residual part for Fourier approximation is improved so as to achieve accelerated convergence.Numerical examples are conducted on systems with non-smooth restoring and/or external forces.The results confirm that the proposed enriched HBM indeed increases the convergence rate and the increase becomes more significant if more non-smooth bases are used.
基金supported in part by the National Natural Science Foundation of China(62473387)the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(SML2023SP241)the Department of Science and Technology of Guangdong Province(2021QN020085)。
文摘For permanent magnet synchronous machines(PMSMs),accurate inductance is critical for control design and condition monitoring.Owing to magnetic saturation,existing methods require nonlinear saturation model and measurements from multiple load/current conditions,and the estimation is relying on the accuracy of saturation model and other machine parameters in the model.Speed harmonic produced by harmonic currents is inductance-dependent,and thus this paper explores the use of magnitude and phase angle of the speed harmonic for accurate inductance estimation.Two estimation models are built based on either the magnitude or phase angle,and the inductances can be from d-axis voltage and the magnitude or phase angle,in which the filter influence in harmonic extraction is considered to ensure the estimation performance.The inductances can be estimated from the measurements under one load condition,which is free of saturation model.Moreover,the inductance estimation is robust to the change of other machine parameters.The proposed approach can effectively improve estimation accuracy especially under the condition with low current magnitude.Experiments and comparisons are conducted on a test PMSM to validate the proposed approach.
基金supported by the Natural Science Foundation of Fujian Province of China(2022J01646)。
文摘The heterostructures incorporated with two or more distinctive two-dimensional(2D)materials have attracted great attention be-cause they could give rise to enhanced prop-erty in comparison with their individual counterparts.Here,a water-assisted two-step rapid physical vapor deposition(rPVD)method was explored and used to synthesize Bi_(2)Te_(3)-Sb_(2)Te_(3)lateral het-erostructures(LHS)successfully.The Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is in nearly uniform size,and grows along three particular orientations with the intersection angles of 120°.Inter-estingly,we found that the water molecules play a significant role in determining the growth orientation,namely whether it will grow along the vertical or lateral direction in 2D structure.Hence,a growth mechanism of LHS based on the water-assisted two-step rPVD was present,which can be used as a general strategy and extended to the growth of other 2D heterostruc-tures or homostructures,such as SnS-SnSe LHS and SnS-SnS lateral homostructures.Fur-thermore,the second-harmonic generation intensity of the Bi_(2)Te_(3)-Sb_(2)Te_(3)LHS is much stronger than that of the Bi_(2)Te_(3)/Sb_(2)Te_(3)vertical heterostructures(VHS).This work opens a new approach for the synthesis of water-assisted lateral 2D heterostructures or homostruc-tures and offers a new method to enhance the second-harmonic generation properties of topo-logical insulating materials.
基金supported by the National Natural Science Foundation of China under Grant Nos.12275078,11875026,12035005,2020YFC2201400the innovative research group of Hunan Province under Grant No.2024JJ1006。
文摘We use out-of-time order correlators(OTOCs)to investigate the quantum instability and Ehrenfest time for an inverted harmonic oscillator(IHO).For initial states located in the stable manifolds of the IHO we find that the corresponding OTOC exhibits identical evolutionary characteristics to the saddle point before the Ehrenfest time.For initial states located in the unstable manifolds,the OTOCs still grow exponentially but the time to maintain exponential growth is related to the center position of its wave packet in phase space.Moreover,we use the Husimi Q function to visualize the quantum wave packets during exponential growth of the OTOCs.Our results show that quantum instability exists at arbitrary orbits in the IHO system,and the Ehrenfest time in the IHO system depends not only on the photon number of the initial system but also on the central positions of the initial states in phase space.
基金Project supported by the Natural Science Foundation of Jilin Province of China(Grant No.20230101014JC)the National Natural Science Foundation of China(Grant No.12374265)。
文摘We investigate theoretically the effects of chirped laser pulses on high-order harmonic generation(HHG)from solids.We find that the harmonic spectra display redshifts for the driving laser pulses with negative chirp and blueshifts for those with positive chirp,which is due to the change in the instantaneous frequency of the driving laser for different chirped pulses.The analysis of crystal-momentum-resolved(k-resolved)HHG reveals that the frequency shifts are equal for the harmonics generated by different crystal momentum channels.The frequency shifts in the cutoff region are larger than those in the plateau region.With the increase of the absolute value of the chirp parameters,the frequency shifts of HHG become more significant,leading to the shifts from odd-to even-order harmonics.We also demonstrate that the frequency shifts of harmonic spectra are related to the duration of the chirped laser field,but are insensitive to the laser intensity and dephasing time.
