We analyze the properties of a focused Laguerre–Gaussian(LG)beam propagating through anisotropic ocean turbulence based on the Huygens–Fresnel principle.Under the Rytov approximation theory,we derive the analytical ...We analyze the properties of a focused Laguerre–Gaussian(LG)beam propagating through anisotropic ocean turbulence based on the Huygens–Fresnel principle.Under the Rytov approximation theory,we derive the analytical formula of the channel capacity of the focused LG beam in the anisotropic ocean turbulence,and analyze the relationship between the capacity and the light source parameters as well as the turbulent ocean parameters.It is found that the focusing mirror can greatly enhance the channel capacity of the system at the geometric focal plane in oceanic turbulence.The results also demonstrate that the communication link can obtain high channel capacity by adopting longer beam wavelength,greater initial beam waist radius,and larger number of transmission channels.Further,the capacity of the system increases with the decrease of the mean squared temperature dissipation rate,temperature-salinity contribution ratio and turbulence outer scale factor,and with the increase of the kinetic energy dissipation rate per unit mass of fluid,turbulence inner scale factor and anisotropy factor.Compared to a Hankel–Bessel beam with diffraction-free characteristics and unfocused LG beam,the focused LG beam shows superior anti-turbulence interference properties,which provide a theoretical reference for research and development of underwater optical communication links using focused LG beams.展开更多
The ion-acoustic(IA) mode exhibiting various orbital angular momentum(OAM) states is examined in a plasma with drifting electrons.The constituent plasma species are modeled with a non-gyrotropic Maxwellian distributio...The ion-acoustic(IA) mode exhibiting various orbital angular momentum(OAM) states is examined in a plasma with drifting electrons.The constituent plasma species are modeled with a non-gyrotropic Maxwellian distribution and discussion of dispersion relation and growth rate of twisted IA waves under various conditions is presented.In the domain of kinetic model,the twisted IA waves are characterized by Laguerre-Gaussian(LG) solutions,where plasma distribution function and electric field are decomposed into axial and azimuthal components.The plasma response function is obtained under paraxial approximations and investigated for threshold condition of instability growth rate with helical electric field structures.The impact of an extra electron specie on the instability is demonstrated through a comparison of twisted waves for single and double electron species.展开更多
Orbital angular momentum(OAM),described by an azimuthal phase term expej lθT,has unbound orthogonal states with different topological charges l.Therefore,with the explosive growth of global communication capacity,esp...Orbital angular momentum(OAM),described by an azimuthal phase term expej lθT,has unbound orthogonal states with different topological charges l.Therefore,with the explosive growth of global communication capacity,especially for short-distance optical interconnects,light-carrying OAM has proved its great potential to improve transmission capacity and spectral efficiency in the space-division multiplexing system due to its orthogonality,security,and compatibility with other techniques.Meanwhile,100-m freespace optical interconnects become an alternative solution for the“last mile”problem and provide interbuilding communication.We experimentally demonstrate a 260-m secure optical interconnect using OAM multiplexing and 16-ary quadrature amplitude modulation(16-QAM)signals.We study the beam wandering,power fluctuation,channel cross talk,bit-error-rate performance,and link security.Additionally,we also investigate the link performance for 1-to-9 multicasting at the range of 260 m.Considering that the power distribution may be affected by atmospheric turbulence,we introduce an offline feedback process to make it flexibly controllable.展开更多
We theoretically studied the dynamic properties of the skyrmion driven by electromagnetic(EM)waves with spin angular momentum(SAM)and orbital angular momentum(OAM)using micromagnetic simulations.First,the guiding cent...We theoretically studied the dynamic properties of the skyrmion driven by electromagnetic(EM)waves with spin angular momentum(SAM)and orbital angular momentum(OAM)using micromagnetic simulations.First,the guiding centers of the skyrmion driven by EM waves with SAM,i.e.,left-handed and right-handed circularly polarized EM waves,present circular trajectories,while present elliptical trajectories under linear EM waves driving due to the superposition of oppositely polarized wave components.Second,the trajectories of the skyrmion driven by EM waves with OAM demonstrate similar behavior to that driven by linearly polarized EM waves.Because the wave vector intensity varies with the phase for both linearly polarized EM waves and EM waves with OAM,the angular momentum is transferred to the skyrmion non-uniformly,while the angular momentum is transferred to the skyrmion uniformly for left-handed and right-handed circularly polarized EM driving.Third,the dynamic properties of the skyrmion driven by EM waves with both SAM and OAM are investigated.It is found that the dynamic trajectories exhibit more complex behavior due to the contributions or competition of SAM and OAM.We investigate the characteristics of intrinsic gyration modes and frequency-dependent trajectories.Our research may provide insight into the dynamic properties of skyrmion manipulated by EM waves with SAM or OAM and provide a method for controlling skyrmion in spintronic devices.展开更多
The 2.5 m wide-field and high-resolution solar telescope(WeHoST)is currently under developing for solar observations.WeHoST aims to achieve high-resolution observations over a super-wide field of view(FOV)of5′×5...The 2.5 m wide-field and high-resolution solar telescope(WeHoST)is currently under developing for solar observations.WeHoST aims to achieve high-resolution observations over a super-wide field of view(FOV)of5′×5′,and a desired resolution of 0.3″.To meet the scientific requirements of WeHoST,the ground-layer adaptive optics(GLAO)with a specially designed wave front sensing system is as the primary consideration.We introduce the GLAO configuration,particularly the wave front sensing scheme.Utilizing analytic method,we simulate the performance of both classical AO and GLAO systems,optimize the wave front sensing system,and evaluate GLAO performance in terms of PSF uniformity and correction improvement across whole FOV.The results indicate that,the classical AO will achieve diffraction-limited resolution;the suggested GLAO configuration will uniformly improve the seeing across the full 5′×5′FOV,reducing the FWHM across the axis FOV to less than0.3″(λ≥705 nm,r0≥11 cm),which is more than two times improvement.The specially designed wave front sensor schedule offers new potential for WeHoST’s GLAO,particularly the multi-FOV GLAO and the flexibility to select the detected area.These capabilities will significantly enhance the scientific output of the telescope.展开更多
The near-infrared imaging channel constitutes a crucial component of the multichannel high-resolution imaging system of the New Vacuum Solar Telescope(NVST). We have successfully achieved high-resolution, narrowband i...The near-infrared imaging channel constitutes a crucial component of the multichannel high-resolution imaging system of the New Vacuum Solar Telescope(NVST). We have successfully achieved high-resolution, narrowband imaging of the chromosphere using He I 10830 A triplet within this channel, which significantly enhances the imaging observation capabilities of NVST. This paper provides a concise overview of the optical system associated with the near-infrared imaging channel, detailing data processing procedures and presenting several observed images. Leveraging a high-resolution image reconstruction algorithm, we were able to generate a narrowband image near the diffraction limit at 10830 A with a temporal resolution of less than 10 s.展开更多
The image quality of a large field survey telescope with a fast focal ratio of the primary mirror is high sensitivity to the optical elements’misalignments and the primary mirror’s deformations.To maintain good opti...The image quality of a large field survey telescope with a fast focal ratio of the primary mirror is high sensitivity to the optical elements’misalignments and the primary mirror’s deformations.To maintain good optical performance,the perturbations need to be aligned,and the tomographic reconstruction of these perturbations can be derived from wavefront sensing with multi-field points for alignment.This work undertakes a comprehensive examination related to the implementation and optimization of a multi-field split curvature wavefront sensing system,including defocus distance,signal pre-processing,deblending of overlapped doughnuts,field-dependent correction,and distorted coordinate correction.We also conduct experiments to demonstrate the application and performance of a multi-field split curvature wavefront sensing system in Mephisto.In the context of the decentering of the secondary mirror,the coefficient of determination(R)attains a high value of 0.993,indicating a robust linearity between the coma coefficients and the decentering of the secondary mirror.A comparative analysis of the simulated and experimental results shows that the difference between them is less than 0.1λ.展开更多
This paper addresses a multicircular circumnavigation control for UAVs with desired angular spacing around a nonstationary target.By defining a coordinated error relative to neighboring angular spacing,under the premi...This paper addresses a multicircular circumnavigation control for UAVs with desired angular spacing around a nonstationary target.By defining a coordinated error relative to neighboring angular spacing,under the premise that target information is perfectly accessible by all nodes,a centralized circular enclosing control strategy is derived for multiple UAVs connected by an undirected graph to allow for formation behaviors concerning the moving target.Besides,to avoid the requirement of target’s states being accessible for each UAV,fixed-time distributed observers are introduced to acquire the state estimates in a fixed-time sense,and the upper boundary of settling time can be determined offline irrespective of initial properties,greatly releasing the burdensome communication traffic.Then,with the aid of fixed-time distributed observers,a distributed circular circumnavigation controller is derived to force all UAVs to collaboratively evolve along the preset circles while keeping a desired angular spacing.It is inferred from Lyapunov stability that all errors are demonstrated to be convergent.Simulations are offered to verify the utility of proposed protocol.展开更多
Our Portable Adaptive Optics(PAO)system designed for high-contrast imaging of exoplanets with current 2-4 m class telescopes achieves a correction speed of nearly 1000 Hz,utilizing a Shack-Hartmann Wave Front Sensor(W...Our Portable Adaptive Optics(PAO)system designed for high-contrast imaging of exoplanets with current 2-4 m class telescopes achieves a correction speed of nearly 1000 Hz,utilizing a Shack-Hartmann Wave Front Sensor(WFS)in a 9×9 sub-aperture configuration.As we look towards adapting the PAO system for larger telescopes,an increase in the number of sub-apertures in the WFS and enhanced precision in wave front detection are imperative.Originally programmed in LabVIEW,our initial PAO software is based on a traditional centroid calculation module for nighttime wave front sensing and lacks adaptive processing of background noise.To address these limitations and to boost the PAO system's performance and accuracy in wave front detection,we propose a compressive neural network(Th-Net)combined with a specialized hybrid parallel programming approach for wave front detection.Our experimental results indicate that this hybrid parallel technique and Th-Net significantly enhance the PAO system's operational speed and wave front detection precision under uneven background noise.This work paves the way so that a duplicable and low-cost PAO system can be used for direct imaging of exoplanets with large telescopes.展开更多
Radiation pattern captures the electromagnetic performance of reflector antennas,which is significantly affected by the deformation of the primary reflector due to gravity and the displacement of the secondary reflect...Radiation pattern captures the electromagnetic performance of reflector antennas,which is significantly affected by the deformation of the primary reflector due to gravity and the displacement of the secondary reflector.During the design process of large reflector antennas,a substantial amount of time is often dedicated to iteratively adjusting structural parameters and validating electromagnetic performance.To improve the efficiency of the design process,we first propose an approximate calculation method of optical path difference(OPD)for the deformation of the primary reflector under gravity and the displacement of the secondary reflector.Then an OPD fitting function based on the modified Zernike polynomials is proposed to capture the phase difference of radiation over the aperture plane,based on which the radiation pattern will be obtained quickly by the aperture field integration method.Numerical experiments demonstrate the effectiveness of the proposed quick calculation method for analyzing the radiation pattern of a 10.4 m submillimeter telescope antenna at its highest operating frequency of 856 GHz.In comparison with the numerical simulation method based on GRASP(which is an antenna electromagnetic analysis tool combining physical optics(PO)and physical theory of diffraction(PTD)),the quick calculation method reduces the time for radiation pattern analysis from more than one hour to less than two minutes.Furthermore,the quick calculation method exhibits excellent accuracy for the figure of merit(FOM)of the radiation pattern.Therefore,the proposed quick calculation method can obtain the radiation pattern with high speed and accuracy.Compared to the time-consuming numerical simulation method(PO and PTD),it can be employed for quick analysis of the radiation pattern for the lateral displacement of the secondary reflector and the deformation of the primary reflector under gravity in the design process of a reflector antenna.展开更多
In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and proper...In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.展开更多
Orbital angular momentum(OAM), as a new degree of freedom, has recently been applied in holography technology.Due to the infinite helical mode index of OAM mode, a large number of holographic images can be reconstruct...Orbital angular momentum(OAM), as a new degree of freedom, has recently been applied in holography technology.Due to the infinite helical mode index of OAM mode, a large number of holographic images can be reconstructed from an OAM-multiplexing hologram. However, the traditional design of an OAM hologram is constrained by the helical mode index of the selected OAM mode, for a larger helical mode index OAM mode has a bigger sampling distance, and the crosstalk is produced for different sampling distances for different OAM modes. In this paper, we present the design of the OAM hologram based on a Bessel–Gaussian beam, which is non-diffractive and has a self-healing property during its propagation. The Fourier transform of the Bessel–Gaussian beam is the perfect vortex mode that has the fixed ring radius for different OAM modes. The results of simulation and experiment have demonstrated the feasibility of the generation of the OAM hologram with the Bessel–Gaussian beam. The quality of the reconstructed holographic image is increased, and the security is enhanced. Additionally, the anti-interference property is improved owing to its self-healing property of the Bessel-OAM holography.展开更多
A study of single-electron capture(SEC) in 18-240 keV O^(6+)-Ne collisions has been conducted employing a combination of experimental and theoretical methodologies.Utilizing a reaction microscope,state-selective SEC c...A study of single-electron capture(SEC) in 18-240 keV O^(6+)-Ne collisions has been conducted employing a combination of experimental and theoretical methodologies.Utilizing a reaction microscope,state-selective SEC cross sections and projectile scattering angle distributions were obtained.The translational energy spectra for SEC reveal the prevailing capture into n=3 states of the projectile ion,with a minor contribution from n=4 states.Notably,as the projectile's energy increases,the relative contribution of SEC n=4 states increases while that of SEC n=3 states diminishes.Furthermore,we computed state-selective relative cross sections and angular differential cross sections employing the classical molecular Coulomb over-the-barrier model(MCBM) and the multichannel Landau-Zener(MCLZ) model.A discernible discrepancy between the state-selective cross sections from the two theoretical models is apparent for the considered impact energies.However,regarding the angular differential cross sections,an overall agreement was attained between the current experimental results and the theoretical results from the MCLZ model.展开更多
Millimeter-wave transmission combined with Orbital Angular Momentum(OAM)has the advantage of reducing the loss of beam power and increasing the system capacity.However,to fulfill this advantage,the antennas at the tra...Millimeter-wave transmission combined with Orbital Angular Momentum(OAM)has the advantage of reducing the loss of beam power and increasing the system capacity.However,to fulfill this advantage,the antennas at the transmitter and receiver must be parallel and coaxial;otherwise,the accuracy of mode detection at the receiver can be seriously influenced.In this paper,we design an OAM millimeter-wave communication system for overcoming the above limitation.Specifically,the first contribution is that the power distribution between different OAM modes and the capacity of the system with different mode sets are analytically derived for performance analysis.The second contribution lies in that a novel mode selection scheme is proposed to reduce the total interference between different modes.Numerical results show that system performance is less affected by the offset when the mode set with smaller modes or larger intervals is selected.展开更多
The Mg-7Gd-4Y-2Zn-0.5Zr alloy chips were successfully recycled through isothermal sintering and equal channel angular pressing(ECAP).The mechanical properties and microstructure evolution of samples during the recycli...The Mg-7Gd-4Y-2Zn-0.5Zr alloy chips were successfully recycled through isothermal sintering and equal channel angular pressing(ECAP).The mechanical properties and microstructure evolution of samples during the recycling process were studied in detail.The eutectic phases in the as-cast alloy transform into long period-stacking ordered(LPSO)phases after homogenization,which can improve the plasticity of the material.After isothermal sintering,the density of the sample is lower than that of the homogenized sample,and oxide films are formed adjacent to the bonding interface of the metal chips.Hence,the plasticity of the sintered sample is poor.Dense samples are fabricated after ECAP.Although the grains are not refined compared to the sintered sample,the microstructure becomes more uniform due to recrystallization.Fiber interdendritic LPSO phase and kinked 14H-LPSO phase are formed in the alloy due to the shear deformation during the ECAP process,which improves the strength and plasticity of the sample significantly.Furthermore,the basal texture is weakened due to the Bc route of the ECAP process,which can increase the Schmid factor of the basal slip system and improve the elongation of the sample.After 2 ECAP passes,the fully densified recycled billet shows superior mechanical properties with an ultimate tensile strength of 307.1 MPa and elongation of 11.1%.展开更多
We propose an optical image watermarking scheme based on orbital angular momentum(OAM)holography.Multiple topological charges(TCs,l)of OAM,as multiple cryptographic sub-keys,are embedded into the host image along with...We propose an optical image watermarking scheme based on orbital angular momentum(OAM)holography.Multiple topological charges(TCs,l)of OAM,as multiple cryptographic sub-keys,are embedded into the host image along with the watermark information.Moreover,the Arnold transformation is employed to further enhance the security and the scrambling time(m)is also served as another cryptographic key.The watermark image is embedded into the host image by using the discrete wavelet transformation(DWT)and singular value decomposition(SVD)methods.Importantly,the interference image is utilized to further enhance security.The imperceptibility of our proposed method is analyzed by using the peak signal-to-noise ratio(PSNR)and the histogram of the watermarked host image.To demonstrate robustness,a series of attack tests,including Gaussian noise,Poisson noise,salt-and-pepper noise,JPEG compression,Gaussian lowpass filtering,cropping,and rotation,are conducted.The experimental results show that our proposed method has advanced security,imperceptibility,and robustness,making it a promising option for optical image watermarking applications.展开更多
Orbital angular momentum(OAM)holography has become a promising technique in information encryption,data storage and opto-electronic computing,owing to the infinite topological charge of one single OAM mode and the ort...Orbital angular momentum(OAM)holography has become a promising technique in information encryption,data storage and opto-electronic computing,owing to the infinite topological charge of one single OAM mode and the orthogonality of different OAM modes.In this paper,we propose a novel OAM hologram generation method based on a densely connected U-net(DCU),where the densely connected convolution blocks(DCB)replace the convolution blocks of the U-net.Importantly,the reconstruction process of the OAM hologram is integrated into DCU as its output layer,so as to eliminate the requirement to prepare training data for the OAM hologram,which is required by conventional neural networks through an iterative algorithm.The experimental and simulation results show that the OAM hologram can rapidly be generated with the well-trained DCU,and the reconstructed image's quality from the generated OAM hologram is significantly improved in comparison with those from the Gerchberg-Saxton generation method,the Gerchberg-Saxton based generation method and the U-net method.In addition,a 10-bit OAM multiplexing hologram scheme is numerically demonstrated to have a high capacity with OAM hologram.展开更多
A scheme for a quasi-monoenergetic high-flux neutron source with femtosecond duration and highly anisotropic angular distribution is proposed.This scheme is based on bulk acceleration of deuteron ions in an optical tr...A scheme for a quasi-monoenergetic high-flux neutron source with femtosecond duration and highly anisotropic angular distribution is proposed.This scheme is based on bulk acceleration of deuteron ions in an optical trap or density grating formed by two counter-propagating laser pulses at an intensity of-10^(16)W~cm^(2)in a near-critical-density plasma.The deuterons are first pre-accelerated to an energy of tens of keV in the ambipolar fields formed in the optical trap.Their energy is boosted to the MeV level by another one or two laser pulses at an intensity of-10^(20)W~cm^(2),enabling fusion reactions to be triggered with high efficiency.In contrast to previously proposed pitcher–catcher configurations,our scheme can provide spatially periodic acceleration structures and effective collisions between deuterons inside the whole target volume.Subsequently,neutrons are generated directly inside the optical trap.Our simulations show that neutron pulses with energy 2–8 MeV,yield 10^(18)–10^(19)n/s,and total number 106–107 in a duration-400 fs can be obtained with a 25μm target.Moreover,the neutron pulses exhibit unique angularly dependent energy spectra and flux distributions,predominantly along the axis of the energy-boosting lasers.Such microsize femtosecond neutron pulses may find many applications,such as high-resolution fast neutron imaging and nuclear physics research.展开更多
Orbital Angular Momentum(OAM)waves are characterized by helical wave fronts and orthogonality between different modes.Therefore,OAM waves have huge potential in improving wireless communications'channel capacity a...Orbital Angular Momentum(OAM)waves are characterized by helical wave fronts and orthogonality between different modes.Therefore,OAM waves have huge potential in improving wireless communications'channel capacity and radar imaging's resolution.Consequently,the generation and application of OAM waves have attracted a lot of attention.And many methods are proposed to generate OAM waves.Although antenna array is the most popular method of generating OAM waves,OAM waves generated by antenna array have redundant modes.However,all advantages of OAM waves are closely related to infinite OAM modes.Thus,to better apply OAM waves to wireless communications and radar,it is very important to reduce unnecessary OAM modes and improve the OAM mode purity.In order to improve the OAM mode purity,two combined antenna arrays composed of X direction antenna and Y direction antenna array are proposed in this paper.The X direction antenna array and the Y direction antenna array are supplied by the excitations with the same amplitude and fixed phase shift.The overall phase shift of the X direction antenna array isπ/2 more or less than that of the Y direction antenna array.The results of formulas and antenna models in CST show that the combined antenna arrays can generate OAM waves with less redundant modes in x component,y component and z component.Besides,the z component carries pure OAM modes.展开更多
It is found that when the parity–time symmetry phenomenon is introduced into the resonant optical gyro system and it works near the exceptional point,the sensitivity can in theory be significantly amplified at low an...It is found that when the parity–time symmetry phenomenon is introduced into the resonant optical gyro system and it works near the exceptional point,the sensitivity can in theory be significantly amplified at low angular rate.However,in fact,the exceptional point is easily disturbed by external environmental variables,which means that it depends on harsh experimental environment and strong control ability,so it is difficult to move towards practical application.Here,we propose a new angular rate sensor structure based on exceptional surface,which has the advantages of high sensitivity and high robustness.The system consists of two fiber-optic ring resonators and two optical loop mirrors,and one of the resonators contains a variable ratio coupler and a variable optical attenuator.We theoretically analyze the system response,and the effects of phase and coupling ratio on the system response.Finally,compared with the conventional resonant gyro,the sensitivity of this exceptional surface angular rate sensor can be improved by about 300 times at low speed.In addition,by changing the loss coefficient in the ring resonator,we can achieve a wide range of 600 rad/s.This scheme provides a new approach for the development of ultra-high sensitivity and wide range angular rate sensors in the future.展开更多
基金This work was supported by the Science and Technology Innovation Training Program of Nanjing University of Posts and Telecommunications(Grant No.CXXZD2023080)the National Natural Science Foundation of China(Grant Nos.61871234 and 62001249)+1 种基金the Natural Science Foundation of Nanjing University of Posts and Telecommunications(Grant No.NY222133)the Open Research Fund of National Laboratory of Solid State Microstructures(Grant No.M36055).
文摘We analyze the properties of a focused Laguerre–Gaussian(LG)beam propagating through anisotropic ocean turbulence based on the Huygens–Fresnel principle.Under the Rytov approximation theory,we derive the analytical formula of the channel capacity of the focused LG beam in the anisotropic ocean turbulence,and analyze the relationship between the capacity and the light source parameters as well as the turbulent ocean parameters.It is found that the focusing mirror can greatly enhance the channel capacity of the system at the geometric focal plane in oceanic turbulence.The results also demonstrate that the communication link can obtain high channel capacity by adopting longer beam wavelength,greater initial beam waist radius,and larger number of transmission channels.Further,the capacity of the system increases with the decrease of the mean squared temperature dissipation rate,temperature-salinity contribution ratio and turbulence outer scale factor,and with the increase of the kinetic energy dissipation rate per unit mass of fluid,turbulence inner scale factor and anisotropy factor.Compared to a Hankel–Bessel beam with diffraction-free characteristics and unfocused LG beam,the focused LG beam shows superior anti-turbulence interference properties,which provide a theoretical reference for research and development of underwater optical communication links using focused LG beams.
文摘The ion-acoustic(IA) mode exhibiting various orbital angular momentum(OAM) states is examined in a plasma with drifting electrons.The constituent plasma species are modeled with a non-gyrotropic Maxwellian distribution and discussion of dispersion relation and growth rate of twisted IA waves under various conditions is presented.In the domain of kinetic model,the twisted IA waves are characterized by Laguerre-Gaussian(LG) solutions,where plasma distribution function and electric field are decomposed into axial and azimuthal components.The plasma response function is obtained under paraxial approximations and investigated for threshold condition of instability growth rate with helical electric field structures.The impact of an extra electron specie on the instability is demonstrated through a comparison of twisted waves for single and double electron species.
基金supported by the National Natural Science Foundation of China (Grant Nos.62125503,62261160388,and 62101198)the Natural Science Foundation of Hubei Province of China (Grant Nos.2021CFB011 and 2023AFA028)+2 种基金the Key R&D Program of Hubei Province of China (Grant Nos.2020BAB001 and 2021BAA024)Shenzhen Science and Technology Program (Grant No.JCYJ20200109114018750)the Innovation Project of Optics Valley Laboratory (Grant Nos.OVL2021BG004 and OVL2023ZD004).
文摘Orbital angular momentum(OAM),described by an azimuthal phase term expej lθT,has unbound orthogonal states with different topological charges l.Therefore,with the explosive growth of global communication capacity,especially for short-distance optical interconnects,light-carrying OAM has proved its great potential to improve transmission capacity and spectral efficiency in the space-division multiplexing system due to its orthogonality,security,and compatibility with other techniques.Meanwhile,100-m freespace optical interconnects become an alternative solution for the“last mile”problem and provide interbuilding communication.We experimentally demonstrate a 260-m secure optical interconnect using OAM multiplexing and 16-ary quadrature amplitude modulation(16-QAM)signals.We study the beam wandering,power fluctuation,channel cross talk,bit-error-rate performance,and link security.Additionally,we also investigate the link performance for 1-to-9 multicasting at the range of 260 m.Considering that the power distribution may be affected by atmospheric turbulence,we introduce an offline feedback process to make it flexibly controllable.
文摘We theoretically studied the dynamic properties of the skyrmion driven by electromagnetic(EM)waves with spin angular momentum(SAM)and orbital angular momentum(OAM)using micromagnetic simulations.First,the guiding centers of the skyrmion driven by EM waves with SAM,i.e.,left-handed and right-handed circularly polarized EM waves,present circular trajectories,while present elliptical trajectories under linear EM waves driving due to the superposition of oppositely polarized wave components.Second,the trajectories of the skyrmion driven by EM waves with OAM demonstrate similar behavior to that driven by linearly polarized EM waves.Because the wave vector intensity varies with the phase for both linearly polarized EM waves and EM waves with OAM,the angular momentum is transferred to the skyrmion non-uniformly,while the angular momentum is transferred to the skyrmion uniformly for left-handed and right-handed circularly polarized EM driving.Third,the dynamic properties of the skyrmion driven by EM waves with both SAM and OAM are investigated.It is found that the dynamic trajectories exhibit more complex behavior due to the contributions or competition of SAM and OAM.We investigate the characteristics of intrinsic gyration modes and frequency-dependent trajectories.Our research may provide insight into the dynamic properties of skyrmion manipulated by EM waves with SAM or OAM and provide a method for controlling skyrmion in spintronic devices.
基金supported by the National Natural Science Foundation of China(12103057,12127901)the Frontier Research Fund of the Institute of Optics and Electronics,Chinese Academy of Sciences(C21K002)+1 种基金the Youth Innovation Promotion Association,Chinese Academy of Sciences(2021378)the National Natural Science Foundation of China(U2031148)。
文摘The 2.5 m wide-field and high-resolution solar telescope(WeHoST)is currently under developing for solar observations.WeHoST aims to achieve high-resolution observations over a super-wide field of view(FOV)of5′×5′,and a desired resolution of 0.3″.To meet the scientific requirements of WeHoST,the ground-layer adaptive optics(GLAO)with a specially designed wave front sensing system is as the primary consideration.We introduce the GLAO configuration,particularly the wave front sensing scheme.Utilizing analytic method,we simulate the performance of both classical AO and GLAO systems,optimize the wave front sensing system,and evaluate GLAO performance in terms of PSF uniformity and correction improvement across whole FOV.The results indicate that,the classical AO will achieve diffraction-limited resolution;the suggested GLAO configuration will uniformly improve the seeing across the full 5′×5′FOV,reducing the FWHM across the axis FOV to less than0.3″(λ≥705 nm,r0≥11 cm),which is more than two times improvement.The specially designed wave front sensor schedule offers new potential for WeHoST’s GLAO,particularly the multi-FOV GLAO and the flexibility to select the detected area.These capabilities will significantly enhance the scientific output of the telescope.
基金supported by Yunnan Revitalization Talent Support Program(202305AS350029 and 202305AT350005)Yunnan Key Laboratory of Solar Physics and Space Science(202205AG070009)。
文摘The near-infrared imaging channel constitutes a crucial component of the multichannel high-resolution imaging system of the New Vacuum Solar Telescope(NVST). We have successfully achieved high-resolution, narrowband imaging of the chromosphere using He I 10830 A triplet within this channel, which significantly enhances the imaging observation capabilities of NVST. This paper provides a concise overview of the optical system associated with the near-infrared imaging channel, detailing data processing procedures and presenting several observed images. Leveraging a high-resolution image reconstruction algorithm, we were able to generate a narrowband image near the diffraction limit at 10830 A with a temporal resolution of less than 10 s.
基金supported by the National Natural Science Foundation of China(grant No.12173062)。
文摘The image quality of a large field survey telescope with a fast focal ratio of the primary mirror is high sensitivity to the optical elements’misalignments and the primary mirror’s deformations.To maintain good optical performance,the perturbations need to be aligned,and the tomographic reconstruction of these perturbations can be derived from wavefront sensing with multi-field points for alignment.This work undertakes a comprehensive examination related to the implementation and optimization of a multi-field split curvature wavefront sensing system,including defocus distance,signal pre-processing,deblending of overlapped doughnuts,field-dependent correction,and distorted coordinate correction.We also conduct experiments to demonstrate the application and performance of a multi-field split curvature wavefront sensing system in Mephisto.In the context of the decentering of the secondary mirror,the coefficient of determination(R)attains a high value of 0.993,indicating a robust linearity between the coma coefficients and the decentering of the secondary mirror.A comparative analysis of the simulated and experimental results shows that the difference between them is less than 0.1λ.
基金supported in part by the National Natural Science Foundation of China under Grant Nos.62173312,61922037,61873115,and 61803348in part by the National Major Scientific Instruments Development Project under Grant 61927807+6 种基金in part by the State Key Laboratory of Deep Buried Target Damage under Grant No.DXMBJJ2019-02in part by the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi under Grant 2020L0266in part by the Shanxi Province Science Foundation for Youths under Grant No.201701D221123in part by the Youth Academic North University of China under Grant No.QX201803in part by the Program for the Innovative Talents of Higher Education Institutions of Shanxiin part by the Shanxi“1331Project”Key Subjects Construction under Grant 1331KSCin part by the Supported by Shanxi Province Science Foundation for Excellent Youths。
文摘This paper addresses a multicircular circumnavigation control for UAVs with desired angular spacing around a nonstationary target.By defining a coordinated error relative to neighboring angular spacing,under the premise that target information is perfectly accessible by all nodes,a centralized circular enclosing control strategy is derived for multiple UAVs connected by an undirected graph to allow for formation behaviors concerning the moving target.Besides,to avoid the requirement of target’s states being accessible for each UAV,fixed-time distributed observers are introduced to acquire the state estimates in a fixed-time sense,and the upper boundary of settling time can be determined offline irrespective of initial properties,greatly releasing the burdensome communication traffic.Then,with the aid of fixed-time distributed observers,a distributed circular circumnavigation controller is derived to force all UAVs to collaboratively evolve along the preset circles while keeping a desired angular spacing.It is inferred from Lyapunov stability that all errors are demonstrated to be convergent.Simulations are offered to verify the utility of proposed protocol.
文摘Our Portable Adaptive Optics(PAO)system designed for high-contrast imaging of exoplanets with current 2-4 m class telescopes achieves a correction speed of nearly 1000 Hz,utilizing a Shack-Hartmann Wave Front Sensor(WFS)in a 9×9 sub-aperture configuration.As we look towards adapting the PAO system for larger telescopes,an increase in the number of sub-apertures in the WFS and enhanced precision in wave front detection are imperative.Originally programmed in LabVIEW,our initial PAO software is based on a traditional centroid calculation module for nighttime wave front sensing and lacks adaptive processing of background noise.To address these limitations and to boost the PAO system's performance and accuracy in wave front detection,we propose a compressive neural network(Th-Net)combined with a specialized hybrid parallel programming approach for wave front detection.Our experimental results indicate that this hybrid parallel technique and Th-Net significantly enhance the PAO system's operational speed and wave front detection precision under uneven background noise.This work paves the way so that a duplicable and low-cost PAO system can be used for direct imaging of exoplanets with large telescopes.
基金supported by Open Fund of State Key Laboratory of Infrared Physics,Shanghai Institute of Technical Physics,Chinese Academy of Sciences。
文摘Radiation pattern captures the electromagnetic performance of reflector antennas,which is significantly affected by the deformation of the primary reflector due to gravity and the displacement of the secondary reflector.During the design process of large reflector antennas,a substantial amount of time is often dedicated to iteratively adjusting structural parameters and validating electromagnetic performance.To improve the efficiency of the design process,we first propose an approximate calculation method of optical path difference(OPD)for the deformation of the primary reflector under gravity and the displacement of the secondary reflector.Then an OPD fitting function based on the modified Zernike polynomials is proposed to capture the phase difference of radiation over the aperture plane,based on which the radiation pattern will be obtained quickly by the aperture field integration method.Numerical experiments demonstrate the effectiveness of the proposed quick calculation method for analyzing the radiation pattern of a 10.4 m submillimeter telescope antenna at its highest operating frequency of 856 GHz.In comparison with the numerical simulation method based on GRASP(which is an antenna electromagnetic analysis tool combining physical optics(PO)and physical theory of diffraction(PTD)),the quick calculation method reduces the time for radiation pattern analysis from more than one hour to less than two minutes.Furthermore,the quick calculation method exhibits excellent accuracy for the figure of merit(FOM)of the radiation pattern.Therefore,the proposed quick calculation method can obtain the radiation pattern with high speed and accuracy.Compared to the time-consuming numerical simulation method(PO and PTD),it can be employed for quick analysis of the radiation pattern for the lateral displacement of the secondary reflector and the deformation of the primary reflector under gravity in the design process of a reflector antenna.
基金Project(U2202255)supported by the National Natural Science Foundation of ChinaProject(2024JJ2076)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(2023Z092)supported by the Key Technology Research Program of Ningbo,China。
文摘In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.62375140 and 62001249)the Open Research Fund of the National Laboratory of Solid State Microstructures (Grant No.M36055)。
文摘Orbital angular momentum(OAM), as a new degree of freedom, has recently been applied in holography technology.Due to the infinite helical mode index of OAM mode, a large number of holographic images can be reconstructed from an OAM-multiplexing hologram. However, the traditional design of an OAM hologram is constrained by the helical mode index of the selected OAM mode, for a larger helical mode index OAM mode has a bigger sampling distance, and the crosstalk is produced for different sampling distances for different OAM modes. In this paper, we present the design of the OAM hologram based on a Bessel–Gaussian beam, which is non-diffractive and has a self-healing property during its propagation. The Fourier transform of the Bessel–Gaussian beam is the perfect vortex mode that has the fixed ring radius for different OAM modes. The results of simulation and experiment have demonstrated the feasibility of the generation of the OAM hologram with the Bessel–Gaussian beam. The quality of the reconstructed holographic image is increased, and the security is enhanced. Additionally, the anti-interference property is improved owing to its self-healing property of the Bessel-OAM holography.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11934004,12064040,and 11974358)the National Key Research and Development Program of China(Grant No.2022YFA1602500)Strategic Key Research Program of the Chinese Academy of Sciences(Grant No.XDB34020000)。
文摘A study of single-electron capture(SEC) in 18-240 keV O^(6+)-Ne collisions has been conducted employing a combination of experimental and theoretical methodologies.Utilizing a reaction microscope,state-selective SEC cross sections and projectile scattering angle distributions were obtained.The translational energy spectra for SEC reveal the prevailing capture into n=3 states of the projectile ion,with a minor contribution from n=4 states.Notably,as the projectile's energy increases,the relative contribution of SEC n=4 states increases while that of SEC n=3 states diminishes.Furthermore,we computed state-selective relative cross sections and angular differential cross sections employing the classical molecular Coulomb over-the-barrier model(MCBM) and the multichannel Landau-Zener(MCLZ) model.A discernible discrepancy between the state-selective cross sections from the two theoretical models is apparent for the considered impact energies.However,regarding the angular differential cross sections,an overall agreement was attained between the current experimental results and the theoretical results from the MCLZ model.
基金supported in part by The National Natural Science Foundation of China(62071255,62171232,61771257)The Major Projects of the Natural Science Foundation of the Jiangsu Higher Education Institutions(20KJA510009)+3 种基金The Open Research Fund of Key Lab of Broadband Wireless Communication and Sensor Network Technology(Nanjing University of Posts and Telecommunications),Ministry of Education(JZNY201914)The open research fund of National and Local Joint Engineering Laboratory of RF Integration and Micro-Assembly Technology,Nanjing University of Posts and Telecommunications(KFJJ20170305)The Research Fund of Nanjing University of Posts and Telecommunications(NY218012)Henan province science and technology research projects High and new technology(No.182102210106).
文摘Millimeter-wave transmission combined with Orbital Angular Momentum(OAM)has the advantage of reducing the loss of beam power and increasing the system capacity.However,to fulfill this advantage,the antennas at the transmitter and receiver must be parallel and coaxial;otherwise,the accuracy of mode detection at the receiver can be seriously influenced.In this paper,we design an OAM millimeter-wave communication system for overcoming the above limitation.Specifically,the first contribution is that the power distribution between different OAM modes and the capacity of the system with different mode sets are analytically derived for performance analysis.The second contribution lies in that a novel mode selection scheme is proposed to reduce the total interference between different modes.Numerical results show that system performance is less affected by the offset when the mode set with smaller modes or larger intervals is selected.
基金supported by the fund of the National Natural Science Foundation of China(51875127,52275322).
文摘The Mg-7Gd-4Y-2Zn-0.5Zr alloy chips were successfully recycled through isothermal sintering and equal channel angular pressing(ECAP).The mechanical properties and microstructure evolution of samples during the recycling process were studied in detail.The eutectic phases in the as-cast alloy transform into long period-stacking ordered(LPSO)phases after homogenization,which can improve the plasticity of the material.After isothermal sintering,the density of the sample is lower than that of the homogenized sample,and oxide films are formed adjacent to the bonding interface of the metal chips.Hence,the plasticity of the sintered sample is poor.Dense samples are fabricated after ECAP.Although the grains are not refined compared to the sintered sample,the microstructure becomes more uniform due to recrystallization.Fiber interdendritic LPSO phase and kinked 14H-LPSO phase are formed in the alloy due to the shear deformation during the ECAP process,which improves the strength and plasticity of the sample significantly.Furthermore,the basal texture is weakened due to the Bc route of the ECAP process,which can increase the Schmid factor of the basal slip system and improve the elongation of the sample.After 2 ECAP passes,the fully densified recycled billet shows superior mechanical properties with an ultimate tensile strength of 307.1 MPa and elongation of 11.1%.
基金Project supported by the National Natural Science Foundation of China(Grant No.62375140)the Natural Science Foundation of Suqian,Jiangsu Province,China(Grant No.S202108)+1 种基金the Open Research Fund of the National Laboratory of Solid State Microstructures(Grant No.M36055)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant No.KYCX21-0745)。
文摘We propose an optical image watermarking scheme based on orbital angular momentum(OAM)holography.Multiple topological charges(TCs,l)of OAM,as multiple cryptographic sub-keys,are embedded into the host image along with the watermark information.Moreover,the Arnold transformation is employed to further enhance the security and the scrambling time(m)is also served as another cryptographic key.The watermark image is embedded into the host image by using the discrete wavelet transformation(DWT)and singular value decomposition(SVD)methods.Importantly,the interference image is utilized to further enhance security.The imperceptibility of our proposed method is analyzed by using the peak signal-to-noise ratio(PSNR)and the histogram of the watermarked host image.To demonstrate robustness,a series of attack tests,including Gaussian noise,Poisson noise,salt-and-pepper noise,JPEG compression,Gaussian lowpass filtering,cropping,and rotation,are conducted.The experimental results show that our proposed method has advanced security,imperceptibility,and robustness,making it a promising option for optical image watermarking applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.62375140 and 61871234)the Open Research Fund of National Laboratory of Solid State Microstructures(Grant No.M36055).
文摘Orbital angular momentum(OAM)holography has become a promising technique in information encryption,data storage and opto-electronic computing,owing to the infinite topological charge of one single OAM mode and the orthogonality of different OAM modes.In this paper,we propose a novel OAM hologram generation method based on a densely connected U-net(DCU),where the densely connected convolution blocks(DCB)replace the convolution blocks of the U-net.Importantly,the reconstruction process of the OAM hologram is integrated into DCU as its output layer,so as to eliminate the requirement to prepare training data for the OAM hologram,which is required by conventional neural networks through an iterative algorithm.The experimental and simulation results show that the OAM hologram can rapidly be generated with the well-trained DCU,and the reconstructed image's quality from the generated OAM hologram is significantly improved in comparison with those from the Gerchberg-Saxton generation method,the Gerchberg-Saxton based generation method and the U-net method.In addition,a 10-bit OAM multiplexing hologram scheme is numerically demonstrated to have a high capacity with OAM hologram.
基金supported by the National Natural Science Foundation of China(Grant Nos.11991074,11975154,12135009,12005287,and 12225505)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA25050100).
文摘A scheme for a quasi-monoenergetic high-flux neutron source with femtosecond duration and highly anisotropic angular distribution is proposed.This scheme is based on bulk acceleration of deuteron ions in an optical trap or density grating formed by two counter-propagating laser pulses at an intensity of-10^(16)W~cm^(2)in a near-critical-density plasma.The deuterons are first pre-accelerated to an energy of tens of keV in the ambipolar fields formed in the optical trap.Their energy is boosted to the MeV level by another one or two laser pulses at an intensity of-10^(20)W~cm^(2),enabling fusion reactions to be triggered with high efficiency.In contrast to previously proposed pitcher–catcher configurations,our scheme can provide spatially periodic acceleration structures and effective collisions between deuterons inside the whole target volume.Subsequently,neutrons are generated directly inside the optical trap.Our simulations show that neutron pulses with energy 2–8 MeV,yield 10^(18)–10^(19)n/s,and total number 106–107 in a duration-400 fs can be obtained with a 25μm target.Moreover,the neutron pulses exhibit unique angularly dependent energy spectra and flux distributions,predominantly along the axis of the energy-boosting lasers.Such microsize femtosecond neutron pulses may find many applications,such as high-resolution fast neutron imaging and nuclear physics research.
基金supported by the National Science Foundation of China(NSFC 62073334).
文摘Orbital Angular Momentum(OAM)waves are characterized by helical wave fronts and orthogonality between different modes.Therefore,OAM waves have huge potential in improving wireless communications'channel capacity and radar imaging's resolution.Consequently,the generation and application of OAM waves have attracted a lot of attention.And many methods are proposed to generate OAM waves.Although antenna array is the most popular method of generating OAM waves,OAM waves generated by antenna array have redundant modes.However,all advantages of OAM waves are closely related to infinite OAM modes.Thus,to better apply OAM waves to wireless communications and radar,it is very important to reduce unnecessary OAM modes and improve the OAM mode purity.In order to improve the OAM mode purity,two combined antenna arrays composed of X direction antenna and Y direction antenna array are proposed in this paper.The X direction antenna array and the Y direction antenna array are supplied by the excitations with the same amplitude and fixed phase shift.The overall phase shift of the X direction antenna array isπ/2 more or less than that of the Y direction antenna array.The results of formulas and antenna models in CST show that the combined antenna arrays can generate OAM waves with less redundant modes in x component,y component and z component.Besides,the z component carries pure OAM modes.
基金supported in part by the National Natural Science Foundation of China (Grant Nos.62273314,U21A20141,and 51821003)Fundamental Research Program of Shanxi Province (Grant No.202303021224008)Shanxi Province Key Laboratory of Quantum Sensing and Precision Measure-ment (Grant No.201905D121001).
文摘It is found that when the parity–time symmetry phenomenon is introduced into the resonant optical gyro system and it works near the exceptional point,the sensitivity can in theory be significantly amplified at low angular rate.However,in fact,the exceptional point is easily disturbed by external environmental variables,which means that it depends on harsh experimental environment and strong control ability,so it is difficult to move towards practical application.Here,we propose a new angular rate sensor structure based on exceptional surface,which has the advantages of high sensitivity and high robustness.The system consists of two fiber-optic ring resonators and two optical loop mirrors,and one of the resonators contains a variable ratio coupler and a variable optical attenuator.We theoretically analyze the system response,and the effects of phase and coupling ratio on the system response.Finally,compared with the conventional resonant gyro,the sensitivity of this exceptional surface angular rate sensor can be improved by about 300 times at low speed.In addition,by changing the loss coefficient in the ring resonator,we can achieve a wide range of 600 rad/s.This scheme provides a new approach for the development of ultra-high sensitivity and wide range angular rate sensors in the future.