The angular spectrum gain characters and the power magnification characters of high gain non-walk-off colinear optical parametric oscillators have been studied using the non-colinear phase match method for the first t...The angular spectrum gain characters and the power magnification characters of high gain non-walk-off colinear optical parametric oscillators have been studied using the non-colinear phase match method for the first time. The experimental results of the KTiOAs04 and the KTiOP04 crystals are discussed in detail. At the high energy single resonant condition, low reflective ratio of the output mirror for the signal and long non-linear crystal are beneficial for small divergence angles. This method can also be used for other high gain non-walk-off phase match optical parametric orocesses.展开更多
The angular method(AS)cannot be used in long-distance propagation because it produces severe numerical errors due to the sampling problem in the transfer function.Two ways can solve this problem in AS for long-distanc...The angular method(AS)cannot be used in long-distance propagation because it produces severe numerical errors due to the sampling problem in the transfer function.Two ways can solve this problem in AS for long-distance propagation.One is zero-padding to make sure that the calculation window is wide enough,but it leads to a huge calculation burden.The other is a method called band-limited angular spectrum(BLAS),in which the transfer function is truncated and results in that the calculation accuracy decreases as the propagation distance increases.In this paper,a new method called modified scaling angular spectrum(MSAS)to solve the problem for long-distance propagation is proposed.A scaling factor is introduced in MSAS so that the sampling interval of the input plane can be adjusted arbitrarily unlike AS whose sampling interval is restricted by the detector’s pixel size.The sampling interval of the input plane is larger than the detector’s pixel size so the size of calculation window suitable for long-distance field propagation in the input plane is smaller than the size of the calculation window required by the zero-padding.Therefore,the method reduces the calculation redundancy and improves the calculation speed.The results from simulations and experiments show that MSAS has a good signal-to-noise ratio(SNR),and the calculation accuracy of MSAS is better than BLAS.展开更多
Eddy current (EC) distribution induced by EC sensors determines the interaction between the defectin the testing specimen and the EC, so quantitatively evaluating EC distribution is crucial to the design of ECsensors....Eddy current (EC) distribution induced by EC sensors determines the interaction between the defectin the testing specimen and the EC, so quantitatively evaluating EC distribution is crucial to the design of ECsensors. In this study, two indices based on the information entropy are proposed to evaluate the EC energyallocated in different directions. The EC vectors induced by a rotational field EC sensor varying in the timedomain are evaluated by the proposed methods. Then, the evaluating results are analyzed by the principle ofEC testing. It can be concluded that the two indices can effectively quantitatively evaluate the EC distributionsvarying in the time domain and are used to optimize the parameters of the rotational EC sensors.展开更多
Based on Fourier transform,the angular spectrum equation and its discrete model of the inverse source problem of the two-dimensional Helmholtz equation are derived.By transforming the two-dimensional inverse source pr...Based on Fourier transform,the angular spectrum equation and its discrete model of the inverse source problem of the two-dimensional Helmholtz equation are derived.By transforming the two-dimensional inverse source problem in the spatial domain into the inverse source problem in the one-dimensional Fourier domain,the source intensity angular spectrum vector in the Fourier domain is calculated by the one-dimensional method of moments.Then,using the discrete Fourier inverse transform,a multi-frequency angular spectrum method of moments is proposed to reconstruct the inverse source problem of the two-dimensional Helmholtz equation.The reconstruction accuracy and stability of this method are improved by optimizing the excitation wavenumber sequence.Simulation calculations show that the multi-frequency angular spectrum method of moments has high reconstruction accuracy and anti-noise ability,and can also design the reconstruction model according to the effective frequency band of the acoustic sensor to achieve the highest resolution.In addition,since the calculation of the coefficient matrix of the proposed method is independent of the distribution of the source intensity function and does not require regularization processing,when the size and resolution of the required source intensity distribution area are determined,after the coefficient matrix is calculated and saved,the source intensity function corresponding to the region of interest can be reconstructed according to different sound pressure detection data,with high calculation accuracy and efficiency.展开更多
Earth＇s variable rotation is mainly produced by the variability of the AAM（atmospheric angular momentum）. In particular, the axial AAM component X_3, which undergoes especially strong variations,induces changes in ...Earth＇s variable rotation is mainly produced by the variability of the AAM（atmospheric angular momentum）. In particular, the axial AAM component X_3, which undergoes especially strong variations,induces changes in the Earth＇s rotation rate. In this study we analysed maps of regional input into the effective axial AAM from 1948 through 2011 from NCEP/NCAR reanalysis. Global zonal circulation patterns related to the LOD（length of day） were described. We applied MSSA（Multichannel Singular Spectrum Analysis） jointly to the mass and motion components of AAM, which allowed us to extract annual, semiannual, 4-mo nth, quasi-biennial, 5-year, and low-frequency oscillations. PCs（Principal components） strongly related to ENSO（El Nino southern oscillation） were released. They can be used to study ENSO-induced changes in pressure and wind fields and their coupling to LOD. The PCs describing the trends have captured slow atmospheric circulation changes possibly related to climate variability.展开更多
Given the enhanced channel capacity of wave chirality,acoustic communications based on the orbital angular momentum(OAM)of acoustic-vortex(AV)beams are of significant interest for underwater data transmissions.However...Given the enhanced channel capacity of wave chirality,acoustic communications based on the orbital angular momentum(OAM)of acoustic-vortex(AV)beams are of significant interest for underwater data transmissions.However,the stringent beam alignment is required for the coaxial arrangement of transceiver arrays to ensure the accuracy and reliability of OAM decoding.To avoid the required multiple measurements of the traditional orthogonality based algorithm,the beam alignment algorithm based on the OAM spectrum decomposition is proposed for AV communications by using simplified ring-arrays.Numerical studies of the single-OAM and OAM-multiplexed AV beams show that the error of the OAM spectrum increases with the translation distance and the deflection angle of the transceiver arrays.To achieve an ideal arrangement,two methods of the single-array translation alignment and the dual-array deflection alignment are developed based on the least standard deviation of the OAM spectrum(SD-OAM).By decreasing the SD-OAM towards zero using transceiver arrays of 16 transmitters and 16 receivers,accurate beam alignments are accomplished by multiple adjustments in three dimensions.The proposed method is also demonstrated by experimental measurements of the OAM dispersion and the SD-OAM for misaligned beams.The results demonstrate the feasibility of the rapid beam alignment based on the OAM spectrum decomposition by using simplified transceiver ring-arrays,and suggest more application potentials for acoustic communications.展开更多
In order to increase the capacity of encrypted information and reduce the loss of information transmission, a three-dimensional(3 D) scene encryption algorithm based on the phase iteration of the angular spectrum doma...In order to increase the capacity of encrypted information and reduce the loss of information transmission, a three-dimensional(3 D) scene encryption algorithm based on the phase iteration of the angular spectrum domain is proposed in this paper. The algorithm, which adopts the layer-oriented method, generates the computer generated hologram by encoding the three-dimensional scene. Then the computer generated hologram is encoded into three pure phase functions by adopting the phase iterative algorithm based on angular spectrum domain,and the encryption process is completed. The three-dimensional scene encryption can improve the capacity of the information,and the three-phase iterative algorithm can guarantee the security of the encryption information. The numerical simulation results show that the algorithm proposed in this paper realized the encryption and decryption of three-dimensional scenes. At the same time, it can ensure the safety of the encrypted information and increase the capacity of the encrypted information.展开更多
Traditionally, “ eddy feeds zonal flow” in the atmosphere is considered as a result of decaying unstable waves. We show that disturbances made of non-modal solutions -the continuous-spec-trum disturbances-can also e...Traditionally, “ eddy feeds zonal flow” in the atmosphere is considered as a result of decaying unstable waves. We show that disturbances made of non-modal solutions -the continuous-spec-trum disturbances-can also effectively transport zonal angular momentum and interact with the zonal basic flow. These disturbances, though stable, eventually decay, losing their energy to strengthen the westerly jets in the atmosphere. Calculations with observational data illustrate that the atmospheric zonal flow is maintained primarily by continuous-spectrum disturbances rather than by unstable waves. Angular momen-tum transport by continuous-spectrum disturbances is one order of magnitude larger than that by all kinds of normal modes (referred as discrete-spectrum disturbances) including unstable waves. Key words Maintenance of zonal flow - Continuous-spectrum - Angular momentum - Transport This research was partly supported by the Chinese Program on Basic Research and by the Institute of Atmospheric Physics, Chinese Academy of Sciences. It was also supported by NASA Grant NAGW 3517, and DOE Grant DEFG0285-ER60314 to the State University of New York at Stony Brook.展开更多
Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra...Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra of Laguerre-Gaussian（LG） beams under both weak/medium and strong atmospheric turbulences. We propose fixing the radius to the extreme point of the intensity distribution, review the expression for the OAM spectrum under weak/medium turbulence,derive the OAM spectrum expression for an LG beam under strong turbulence, and simplify both of them to concise forms.Then, we investigate the accuracy of the simplified expressions through simulations. We find that the simplified expressions permit accurate calculation of the OAM spectrum for large transmitted OAM numbers under any type of turbulence. Finally,we use the simplified expressions to analytically address the broadening of the OAM spectrum caused by atmospheric turbulence. This work should contribute to the concise theoretical derivation of analytical expressions for OAM channel matrices for FSO-OAM communications and the analytical study of the laws governing OAM spectra.展开更多
A twin gridded ionization chamber with dual parameter data acquisition sys-tem is used to study neutron induced charged particle emission reaction.The angulardistribution and cross section of n-particles from the <...A twin gridded ionization chamber with dual parameter data acquisition sys-tem is used to study neutron induced charged particle emission reaction.The angulardistribution and cross section of n-particles from the <sup>64</sup>Zn（n,α）<sup>61</sup>Ni reaction are meas-ured at neutron energy 5 MeV.展开更多
The extreme ultraviolet(XUV)light beam carrying orbital angular momentum(OAM)can be produced via high-order harmonic generation(HHG)due to the interaction of an intense vortex infrared laser and a gas medium.Here we s...The extreme ultraviolet(XUV)light beam carrying orbital angular momentum(OAM)can be produced via high-order harmonic generation(HHG)due to the interaction of an intense vortex infrared laser and a gas medium.Here we show that the OAM spectrum of vortex HHG can be readily tailored by varying the radial node(from 0 to 2)in the driving laser consisting of two mixed Laguerre-Gaussian(LG)beams.We find that due to the change in spatial profile of HHG,the distribution range of the OAM spectrum can be broadened and its shape can be modified by increasing the radial node.We also show that the OAM mode range becomes much wider and its distribution shape becomes more symmetric when the harmonic order is increased from the plateau to the cutoff when the driving laser has the nonzero radial nodes.Through the map of coherence length and the evolution of harmonic field in the medium,we reveal that the favorable off-axis phase-matching conditions are greatly modified due to the change of intensity and phase distributions of driving laser with the radial node.We anticipate this work to stimulate some interests in generating the XUV vortex beam with tunable OAM spectrum through the gaseous HHG process achieved by manipulating the mode properties of the driving laser beam.展开更多
文摘The angular spectrum gain characters and the power magnification characters of high gain non-walk-off colinear optical parametric oscillators have been studied using the non-colinear phase match method for the first time. The experimental results of the KTiOAs04 and the KTiOP04 crystals are discussed in detail. At the high energy single resonant condition, low reflective ratio of the output mirror for the signal and long non-linear crystal are beneficial for small divergence angles. This method can also be used for other high gain non-walk-off phase match optical parametric orocesses.
基金Project supported by the National Natural Science Foundation of China(Grant No.61705254)the Key Research and Development Program of Shaanxi Province of China(Grant No.2020GY-114).
文摘The angular method(AS)cannot be used in long-distance propagation because it produces severe numerical errors due to the sampling problem in the transfer function.Two ways can solve this problem in AS for long-distance propagation.One is zero-padding to make sure that the calculation window is wide enough,but it leads to a huge calculation burden.The other is a method called band-limited angular spectrum(BLAS),in which the transfer function is truncated and results in that the calculation accuracy decreases as the propagation distance increases.In this paper,a new method called modified scaling angular spectrum(MSAS)to solve the problem for long-distance propagation is proposed.A scaling factor is introduced in MSAS so that the sampling interval of the input plane can be adjusted arbitrarily unlike AS whose sampling interval is restricted by the detector’s pixel size.The sampling interval of the input plane is larger than the detector’s pixel size so the size of calculation window suitable for long-distance field propagation in the input plane is smaller than the size of the calculation window required by the zero-padding.Therefore,the method reduces the calculation redundancy and improves the calculation speed.The results from simulations and experiments show that MSAS has a good signal-to-noise ratio(SNR),and the calculation accuracy of MSAS is better than BLAS.
基金Foundation item:the National Natural Science Foundation of China(No.51807086)the Young Doctoral Fund of Education Department of Gansu Province(No.2021QB-047)the Hongliu Youth Fund of Lanzhou University of Technology(No.07/062003)。
文摘Eddy current (EC) distribution induced by EC sensors determines the interaction between the defectin the testing specimen and the EC, so quantitatively evaluating EC distribution is crucial to the design of ECsensors. In this study, two indices based on the information entropy are proposed to evaluate the EC energyallocated in different directions. The EC vectors induced by a rotational field EC sensor varying in the timedomain are evaluated by the proposed methods. Then, the evaluating results are analyzed by the principle ofEC testing. It can be concluded that the two indices can effectively quantitatively evaluate the EC distributionsvarying in the time domain and are used to optimize the parameters of the rotational EC sensors.
基金supported by the National Natural Science Foundation of China(51775121,12364055).
文摘Based on Fourier transform,the angular spectrum equation and its discrete model of the inverse source problem of the two-dimensional Helmholtz equation are derived.By transforming the two-dimensional inverse source problem in the spatial domain into the inverse source problem in the one-dimensional Fourier domain,the source intensity angular spectrum vector in the Fourier domain is calculated by the one-dimensional method of moments.Then,using the discrete Fourier inverse transform,a multi-frequency angular spectrum method of moments is proposed to reconstruct the inverse source problem of the two-dimensional Helmholtz equation.The reconstruction accuracy and stability of this method are improved by optimizing the excitation wavenumber sequence.Simulation calculations show that the multi-frequency angular spectrum method of moments has high reconstruction accuracy and anti-noise ability,and can also design the reconstruction model according to the effective frequency band of the acoustic sensor to achieve the highest resolution.In addition,since the calculation of the coefficient matrix of the proposed method is independent of the distribution of the source intensity function and does not require regularization processing,when the size and resolution of the required source intensity distribution area are determined,after the coefficient matrix is calculated and saved,the source intensity function corresponding to the region of interest can be reconstructed according to different sound pressure detection data,with high calculation accuracy and efficiency.
基金supported by Russian Foundation for Basic Research grants No. 17-05-00989, No. 16-05-00753,NRU HSE and visiting grants positions at Paris observatory and Wuhan university for the first authorpartially supported by grants by NSF/IGFA Belmont Forum Project (Grant No. ICER-1342644)the Chinese Academy of Sciences/SAFEA International Partnership Program for Creative Research Teams(Grant No. KZZD-EW-TZ-05)
文摘Earth＇s variable rotation is mainly produced by the variability of the AAM（atmospheric angular momentum）. In particular, the axial AAM component X_3, which undergoes especially strong variations,induces changes in the Earth＇s rotation rate. In this study we analysed maps of regional input into the effective axial AAM from 1948 through 2011 from NCEP/NCAR reanalysis. Global zonal circulation patterns related to the LOD（length of day） were described. We applied MSSA（Multichannel Singular Spectrum Analysis） jointly to the mass and motion components of AAM, which allowed us to extract annual, semiannual, 4-mo nth, quasi-biennial, 5-year, and low-frequency oscillations. PCs（Principal components） strongly related to ENSO（El Nino southern oscillation） were released. They can be used to study ENSO-induced changes in pressure and wind fields and their coupling to LOD. The PCs describing the trends have captured slow atmospheric circulation changes possibly related to climate variability.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11934009,11974187,and 12174198)
文摘Given the enhanced channel capacity of wave chirality,acoustic communications based on the orbital angular momentum(OAM)of acoustic-vortex(AV)beams are of significant interest for underwater data transmissions.However,the stringent beam alignment is required for the coaxial arrangement of transceiver arrays to ensure the accuracy and reliability of OAM decoding.To avoid the required multiple measurements of the traditional orthogonality based algorithm,the beam alignment algorithm based on the OAM spectrum decomposition is proposed for AV communications by using simplified ring-arrays.Numerical studies of the single-OAM and OAM-multiplexed AV beams show that the error of the OAM spectrum increases with the translation distance and the deflection angle of the transceiver arrays.To achieve an ideal arrangement,two methods of the single-array translation alignment and the dual-array deflection alignment are developed based on the least standard deviation of the OAM spectrum(SD-OAM).By decreasing the SD-OAM towards zero using transceiver arrays of 16 transmitters and 16 receivers,accurate beam alignments are accomplished by multiple adjustments in three dimensions.The proposed method is also demonstrated by experimental measurements of the OAM dispersion and the SD-OAM for misaligned beams.The results demonstrate the feasibility of the rapid beam alignment based on the OAM spectrum decomposition by using simplified transceiver ring-arrays,and suggest more application potentials for acoustic communications.
基金supported by the Natural Science ResearchProject of the Colleges and Universities of Anhui Province(KJ2016A056)Natural Science Foundation of Anhui Province of China(1508085MF121)National Natural Science Foundation of China(61572032)。
文摘In order to increase the capacity of encrypted information and reduce the loss of information transmission, a three-dimensional(3 D) scene encryption algorithm based on the phase iteration of the angular spectrum domain is proposed in this paper. The algorithm, which adopts the layer-oriented method, generates the computer generated hologram by encoding the three-dimensional scene. Then the computer generated hologram is encoded into three pure phase functions by adopting the phase iterative algorithm based on angular spectrum domain,and the encryption process is completed. The three-dimensional scene encryption can improve the capacity of the information,and the three-phase iterative algorithm can guarantee the security of the encryption information. The numerical simulation results show that the algorithm proposed in this paper realized the encryption and decryption of three-dimensional scenes. At the same time, it can ensure the safety of the encrypted information and increase the capacity of the encrypted information.
文摘Traditionally, “ eddy feeds zonal flow” in the atmosphere is considered as a result of decaying unstable waves. We show that disturbances made of non-modal solutions -the continuous-spec-trum disturbances-can also effectively transport zonal angular momentum and interact with the zonal basic flow. These disturbances, though stable, eventually decay, losing their energy to strengthen the westerly jets in the atmosphere. Calculations with observational data illustrate that the atmospheric zonal flow is maintained primarily by continuous-spectrum disturbances rather than by unstable waves. Angular momen-tum transport by continuous-spectrum disturbances is one order of magnitude larger than that by all kinds of normal modes (referred as discrete-spectrum disturbances) including unstable waves. Key words Maintenance of zonal flow - Continuous-spectrum - Angular momentum - Transport This research was partly supported by the Chinese Program on Basic Research and by the Institute of Atmospheric Physics, Chinese Academy of Sciences. It was also supported by NASA Grant NAGW 3517, and DOE Grant DEFG0285-ER60314 to the State University of New York at Stony Brook.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61575027 and 61471051)
文摘Studying orbital angular momentum（OAM） spectra is important for analyzing crosstalk in free-space optical（FSO）communication systems. This work offers a new method of simplifying the expressions for the OAM spectra of Laguerre-Gaussian（LG） beams under both weak/medium and strong atmospheric turbulences. We propose fixing the radius to the extreme point of the intensity distribution, review the expression for the OAM spectrum under weak/medium turbulence,derive the OAM spectrum expression for an LG beam under strong turbulence, and simplify both of them to concise forms.Then, we investigate the accuracy of the simplified expressions through simulations. We find that the simplified expressions permit accurate calculation of the OAM spectrum for large transmitted OAM numbers under any type of turbulence. Finally,we use the simplified expressions to analytically address the broadening of the OAM spectrum caused by atmospheric turbulence. This work should contribute to the concise theoretical derivation of analytical expressions for OAM channel matrices for FSO-OAM communications and the analytical study of the laws governing OAM spectra.
基金The project supported by the National Natural Science Foundation of China and China National Nuclear Corporation
文摘A twin gridded ionization chamber with dual parameter data acquisition sys-tem is used to study neutron induced charged particle emission reaction.The angulardistribution and cross section of n-particles from the <sup>64</sup>Zn（n,α）<sup>61</sup>Ni reaction are meas-ured at neutron energy 5 MeV.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12274230,91950102,and 11834004)the Funding of Nanjing University of Science and Technology (Grant No.TSXK2022D005)。
文摘The extreme ultraviolet(XUV)light beam carrying orbital angular momentum(OAM)can be produced via high-order harmonic generation(HHG)due to the interaction of an intense vortex infrared laser and a gas medium.Here we show that the OAM spectrum of vortex HHG can be readily tailored by varying the radial node(from 0 to 2)in the driving laser consisting of two mixed Laguerre-Gaussian(LG)beams.We find that due to the change in spatial profile of HHG,the distribution range of the OAM spectrum can be broadened and its shape can be modified by increasing the radial node.We also show that the OAM mode range becomes much wider and its distribution shape becomes more symmetric when the harmonic order is increased from the plateau to the cutoff when the driving laser has the nonzero radial nodes.Through the map of coherence length and the evolution of harmonic field in the medium,we reveal that the favorable off-axis phase-matching conditions are greatly modified due to the change of intensity and phase distributions of driving laser with the radial node.We anticipate this work to stimulate some interests in generating the XUV vortex beam with tunable OAM spectrum through the gaseous HHG process achieved by manipulating the mode properties of the driving laser beam.
