This paper builds a binary tree for the target based on the bounding volume hierarchy technology,thereby achieving strict acceleration of the shadow judgment process and reducing the computational complexity from the ...This paper builds a binary tree for the target based on the bounding volume hierarchy technology,thereby achieving strict acceleration of the shadow judgment process and reducing the computational complexity from the original O(N^(3))to O(N^(2)logN).Numerical results show that the proposed method is more efficient than the traditional method.It is verified in multiple examples that the proposed method can complete the convergence of the current.Moreover,the proposed method avoids the error of judging the lit-shadow relationship based on the normal vector,which is beneficial to current iteration and convergence.Compared with the brute force method,the current method can improve the simulation efficiency by 2 orders of magnitude.The proposed method is more suitable for scattering problems in electrically large cavities and complex scenarios.展开更多
Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP) of CAS was established in Changchun, Jilin Province, on July 5, 1999 on the basis of consolidation of two former CAS institutes: Changchun Institute o...Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP) of CAS was established in Changchun, Jilin Province, on July 5, 1999 on the basis of consolidation of two former CAS institutes: Changchun Institute of Optics and Fine Mechanics, and Changchun Institute of Physics. The institute is an experimental unit of CAS Knowledge Innovation Program (KIP).展开更多
A novel modified physical optics algorithm is proposed to overcome the difficulties of near field scattering prediction for classical physical optics. The method is applied to calculating the near field radar cross se...A novel modified physical optics algorithm is proposed to overcome the difficulties of near field scattering prediction for classical physical optics. The method is applied to calculating the near field radar cross section of electrically large objects by taking into account the influence of the distinct wave propagation vector, the near field Green function, and the antenna radiation pattern. By setting up local reference coordinates, each partitioned facet has its own distinct wave front curvature. The radiation gain for every surface element is taken into consideration based on the modulation of the antenna radiation pattern. The Green function is refined both in amplitude and phase terms and allows for near field calculation. The scattered characteristics of the near field targets are studied by numerical simulations. The results show that the approach can achieve a satisfactory accuracy.展开更多
An iterative physical optics(IPO) model is proposed to solve extra large scale electric electromagnetic(EM) scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the for...An iterative physical optics(IPO) model is proposed to solve extra large scale electric electromagnetic(EM) scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the forward-backward methodology and its modification with underrelaxation iteration are developed to simulate the rough surface scattering; the local iteration methodology and the fast far field approximation(Fa FFA) in the matrix-vector product are proposed to reduce greatly the computational complexity. These techniques make Monte Carlo simulations possible. Thus, the average Doppler spectra of backscattered signals obtained from the simulations are compared for different incident angles and sea states. In particular, the simulations show a broadening of the Doppler spectra for a more complicated sea state at a low grazing angle(LGA).展开更多
The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme (PRA 79, 022304) has been suggested for generating Greenberger-Horne-Zeilinger state and cluster ...The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme (PRA 79, 022304) has been suggested for generating Greenberger-Horne-Zeilinger state and cluster state with atomic ensembles based on the Rydberg blockade. Using similar resources as the earlier scheme, here we propose an experimentally feasible scheme of preparing arbitrary four-qubit W class of maximally and non- maximally entangled states with atomic ensembles in a single step. Moreover, we carefully analyze the realistic noises and predict that four-qubit W states can be produced with high fidelity (F - 0.994) via our scheme.展开更多
The transverse inhomogeneous carrier-envelope phase (CEP) distribution of idler generated through difference-frequency-generation (DFG) in quadratic nonlinear crystals is theoretically studied. In practical CEP st...The transverse inhomogeneous carrier-envelope phase (CEP) distribution of idler generated through difference-frequency-generation (DFG) in quadratic nonlinear crystals is theoretically studied. In practical CEP stabilized DFG setups, the pump and the signal are usually Gaussian beams with non-uniform intensity distribution. Since the idler CEP is dependent on gain, this non-uniform intensity distribution leads to inhomogeneous gain across the aperture of the idler beam, resulting in a varying transverse idler CEP. Simulation results show that in practical settings, in the high-gain regime, transverse inhomogeneous CEP can be much smaller compared with π/2. However, when gain on the propagation axis reaches saturation, CEP difference can well exceed π/2.展开更多
We investigate the effect of collision-induced coherence on coherent population transfer with the stimulated Raman adiabatic passage technique in a double A-type four-level system with a widely separated excited doubl...We investigate the effect of collision-induced coherence on coherent population transfer with the stimulated Raman adiabatic passage technique in a double A-type four-level system with a widely separated excited doublet. It is shown that when the two pulsed lasers with Rabi frequencies nearly comparable to the energy separation of the doublet are tuned to the particular frequency where the condition for quantum interference is satisfied, the very low transfer efficiency due to the nonadiabatic coupling between the two degenerate adiabatic states could be enhanced significantly with the increase of the collisional decay rates in a moderate range. The enhanced transfer efficiency results from the weakening of the nonadiabatic coupling between the two degenerate adiabatic states realized through collision-induced destructive quantum interference.展开更多
The particle sizes and porosities of simulated pore structures are probed by terahertz time-domain spectroscopy.A double-peak time-domain spectrum phenomenon is observed when the terahertz(THz) pulses illuminated a ...The particle sizes and porosities of simulated pore structures are probed by terahertz time-domain spectroscopy.A double-peak time-domain spectrum phenomenon is observed when the terahertz(THz) pulses illuminated a pore and a particle. The amplitudes of the two peaks depend strongly and monotonically on the particle size and porosity. A model is used to study the phenomenon, and the computational results agreed with the experimental measurements. These measurements indicate the terahertz spectroscopic behaviors of pores and particles, suggesting that terahertz spectroscopy can be used as a noncontact probe of porosity.展开更多
An efficient hybrid method based on the method of moments (MOM) and physical optics (PO) for the analysis of radiation characteristics of an electrically large antenna-radome system is presented. Specifically, MOM...An efficient hybrid method based on the method of moments (MOM) and physical optics (PO) for the analysis of radiation characteristics of an electrically large antenna-radome system is presented. Specifically, MOM is first applied to the antenna to find the current on its surface, and then the equivalent PO currents produced by the antenna radiation are assumed on the radome wall. When the coupling of the PO currents and antenna current is considered, the coupling matrix is divided into a series of partial matrices, in order to deduce the memory requirement and accelerate the evaluation process. Numerical results indicate that the proposed hybrid PO-MOM method is accurate and efficient.展开更多
We experimentally study the generation of a partially coherent non-diffractive beam by focusing a partially coherent vortex beam with an axieon. The investigation results show that when the partially coherent vortex b...We experimentally study the generation of a partially coherent non-diffractive beam by focusing a partially coherent vortex beam with an axieon. The investigation results show that when the partially coherent vortex beam is focused by the axicon, the beam is transferred into a partially coherent higher-order non-diffractive beam. In the non-diffractive zone, the transverse intensity distribution of the partially coherent higher-order non-diffractive beam is invariant during propagation. In addition, the range of the non-diffractive zone is related to the coherence of the partially coherent vortex beam. The poorer the coherence of the partially coherent vortex beam, the shorter the range of the non-diffractive zone.展开更多
In this paper, we investigate the loss caused by multiple humans blocking millimeter wave frequencies. We model human blockers as absorbing screens of infinite height with two knife-edges, We take a physical optics ap...In this paper, we investigate the loss caused by multiple humans blocking millimeter wave frequencies. We model human blockers as absorbing screens of infinite height with two knife-edges, We take a physical optics approach to computing the diffraction around the absorbing screens, This approach differs to the geometric optics approach described in much of the literature. The blocking model is validated by measuring the gain from multiple-human blocking configurations on an indoor link. The blocking gains predicted using Piazzi ' s numerical integration method (a physical optics method) agree well with measurements taken from approximately 2.7 dB to -50 dB. Thereofre, this model is suitable for real human blockers, The mean prediction error for the method is approximately -1.2 dB, and the standard deviation is approximately 5 dB.展开更多
The physical optics solution is presented for the calculation of scattering by the complex conducting bodies coated with anisotropic materials, which is based on the tangential plane approximation and the equivalent c...The physical optics solution is presented for the calculation of scattering by the complex conducting bodies coated with anisotropic materials, which is based on the tangential plane approximation and the equivalent currents on an anisotropic material backed by an infinite metal surface illuminated by the plane wave given in our previous work. The analytical scheme is proposed to realize fast computation of the solution. Numerical results for several coated bodies such as dihedral corner reflector and cone-cylinder geometry are given and discussed.展开更多
In order to improve the survivability of the aircraft,conceptual design and radar cross section(RCS) performance research are done. The CATIA software is used to design the 3D digital model of the shipborne early wa...In order to improve the survivability of the aircraft,conceptual design and radar cross section(RCS) performance research are done. The CATIA software is used to design the 3D digital model of the shipborne early warning aircraft, and some measures are taken to reduce the RCS characteristics of the early warning aircraft at the same time. Based on the physical optics method and the equivalent electromagnetic flow method,the aircraft's RCS characteristics and strength distribution characteristics are simulated numerically, and compared with the foreign advanced shipborne early warning aircraft. The simulation results show that under the X radar band, when the incident wave pitching angle is 0?, compared with the foreign advanced shipborne early warning aircraft, the forward RCS average value of the conceptual shipborne early warning aircraft is reduced to 24.49%, the lateral RCS average value is reduced to 5.04%, and the backward RCS average value is reduced to 39.26%. The research results of this paper are expected to provide theoretical basis and technical support for the conceptual design and the stealth design of the shipborne early warning aircraft.展开更多
As a marked extension of the traditional MoM-PO (method of moment-physical optics) hybrid method, a new hybridization of PO, SBR, and MoM (MoM-SBR/PO) is presented to calculate the multireflection contribution in ...As a marked extension of the traditional MoM-PO (method of moment-physical optics) hybrid method, a new hybridization of PO, SBR, and MoM (MoM-SBR/PO) is presented to calculate the multireflection contribution in the PO region efficiently by introducing the method of SBR based on RDN notion, which avoids the time-consuming iterative procedure and the choice of proper Green's function. As compared with the traditional MoM-PO hybrid method, the calculation efficiency of the proposed method is greatly improved, and its validity is verified by numerical results.展开更多
The La2Ti2O7:Pr^3+, which emits red color luminescence upon UV light excitation, is prepared by the conventional high-temperature solid-state method and its luminescent properties are systematically investigated. X-...The La2Ti2O7:Pr^3+, which emits red color luminescence upon UV light excitation, is prepared by the conventional high-temperature solid-state method and its luminescent properties are systematically investigated. X-ray diffraction, photoluminescence, afterglow emission spectra and long-lasting phosphorescence (LLP) decay curves are used to characterize this phosphor. After irradiation by a 290-nm UV light for 3 rain, the Pr^3+-doped La2Ti2O7 phosphor emits intense red emitting afterglow from the ^1D2 →^ 3H4 transitions, and its afterglow can be seen with the naked eye in the dark clearly for more than 1 h after removal of the excitation source. The afterglow decay curve of the Pr^3+-doped La2Ti2O7 phosphor contains a fast decay component and another slow decay one. The possible mechanism of this red light emitting LLP phosphor is also discussed based on the experimental results.展开更多
In this work, we review the developing progress of two-dimensional terahertz time-domain spectroscopy(THz-TDS) and its diverse applications, including analyzing the polarization of THz radiation from a laser-induced...In this work, we review the developing progress of two-dimensional terahertz time-domain spectroscopy(THz-TDS) and its diverse applications, including analyzing the polarization of THz radiation from a laser-induced plasma source and studying the corresponding physical mechanism, and characterizing the optical properties of crystals, etc.展开更多
This paper reports that an output window for optically pumped terahertz (THz) laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate (approximating to 5 mm th...This paper reports that an output window for optically pumped terahertz (THz) laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate (approximating to 5 mm thick). Unlike the conventional process of depositing a gold film approximating to 100 nm on negative photoresist using electron-beam evaporation, a nickel film approximating to 1.5 μm thick is directly deposited on the clean surface of dielectric substrate using magnetron sputtering and then a positive photoresist is spun onto the nickel metal surface at 6000 r for 60 s. A transmittance spectrum of the output window in a certain frequency range (say, from zero to 1 THz) has been obtained by using THz time domain spectroscopy. Moreover a transmittance spectrum simulated numerically has also been estimated with respect to the output window using the transmission-line model (TLM) containing attenuation component from dielectric substrate. The simulation results show that the TLM can explain well the experimental curve in a certain frequency range from zero to 1 THz. Thus it is demonstrated that the improved optical component can be efficiently used as both output coupler and output window for optically pumped THz lasers.展开更多
The radar cross section (RCS) of dispenser and its components is computed by graphical electromagnetic computing (GRECO) method, which bases on physical optics (PO) method. A satisfied agreement is gotten between comp...The radar cross section (RCS) of dispenser and its components is computed by graphical electromagnetic computing (GRECO) method, which bases on physical optics (PO) method. A satisfied agreement is gotten between computed and measured results outdoor. The results show that the main scattering source of the dispenser is the mirror reflecting of the body; in the most crucial nose-on region, the nose mirror reflecting plays important role; the corner reflecting is important to the fins' RCS. The corresponding measures to reduce dispenser's RCS are proposed. It is indicated that to reduce RCS, shaping should be adopts first, while aerodynamic characteristics and stealth characteristics should be considered synthetically during the design of dispenser.展开更多
The radiation characteristics of a doubly curved shaped reflector antenna with random holes is analyzed by physical optics (PO) method, and the probability model of the random holes and its numerical realization metho...The radiation characteristics of a doubly curved shaped reflector antenna with random holes is analyzed by physical optics (PO) method, and the probability model of the random holes and its numerical realization method are presented. The radiation patterns show that in the azimuth plane the peak sidelobe level becomes much higher as the reflector surface with random holes. The simulation results can provide a theoretical guidance for the radar attackers.展开更多
For electromagnetic scattering of 3?D complex electrically large conducting targets,a new hybrid algorithm,MoM?PO/SBR algorithm,is presented to realize the interaction of information between method of moment(MoM)and p...For electromagnetic scattering of 3?D complex electrically large conducting targets,a new hybrid algorithm,MoM?PO/SBR algorithm,is presented to realize the interaction of information between method of moment(MoM)and physical optics(PO)/shooting and bouncing ray(SBR).In the algorithm,the COC file that based on the Huygens equivalent principle is introduced,and the conversion interface between the equivalent surface and the target is established.And then,the multi?task flow model presented in this paper is adopted to conduct CPU/graphics processing unit(GPU)tests of the algorithm under three modes,i.e.,MPI/OpenMP,MPI/compute unified device architecture(CUDA)and multi?task programming model(MTPM).Numerical results are presented and compared with reference solutions in order to illustrate the accuracy and the efficiency of the proposed algorithm.展开更多
基金the National Natural Science Foundation of China under Grants No.62231021 and No.92373201.
文摘This paper builds a binary tree for the target based on the bounding volume hierarchy technology,thereby achieving strict acceleration of the shadow judgment process and reducing the computational complexity from the original O(N^(3))to O(N^(2)logN).Numerical results show that the proposed method is more efficient than the traditional method.It is verified in multiple examples that the proposed method can complete the convergence of the current.Moreover,the proposed method avoids the error of judging the lit-shadow relationship based on the normal vector,which is beneficial to current iteration and convergence.Compared with the brute force method,the current method can improve the simulation efficiency by 2 orders of magnitude.The proposed method is more suitable for scattering problems in electrically large cavities and complex scenarios.
文摘Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP) of CAS was established in Changchun, Jilin Province, on July 5, 1999 on the basis of consolidation of two former CAS institutes: Changchun Institute of Optics and Fine Mechanics, and Changchun Institute of Physics. The institute is an experimental unit of CAS Knowledge Innovation Program (KIP).
文摘A novel modified physical optics algorithm is proposed to overcome the difficulties of near field scattering prediction for classical physical optics. The method is applied to calculating the near field radar cross section of electrically large objects by taking into account the influence of the distinct wave propagation vector, the near field Green function, and the antenna radiation pattern. By setting up local reference coordinates, each partitioned facet has its own distinct wave front curvature. The radiation gain for every surface element is taken into consideration based on the modulation of the antenna radiation pattern. The Green function is refined both in amplitude and phase terms and allows for near field calculation. The scattered characteristics of the near field targets are studied by numerical simulations. The results show that the approach can achieve a satisfactory accuracy.
基金supported by the National Natural Science Foundation of China(61372033)
文摘An iterative physical optics(IPO) model is proposed to solve extra large scale electric electromagnetic(EM) scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the forward-backward methodology and its modification with underrelaxation iteration are developed to simulate the rough surface scattering; the local iteration methodology and the fast far field approximation(Fa FFA) in the matrix-vector product are proposed to reduce greatly the computational complexity. These techniques make Monte Carlo simulations possible. Thus, the average Doppler spectra of backscattered signals obtained from the simulations are compared for different incident angles and sea states. In particular, the simulations show a broadening of the Doppler spectra for a more complicated sea state at a low grazing angle(LGA).
基金Supported by the National Natural Science Foundation of China under Grant No 10774192, the Fund of Innovation of Graduate School of National University of Defense Technology under Grant No 080201.
文摘The generation of various entangled states is an essential task in quantum information processing. Recently, a scheme (PRA 79, 022304) has been suggested for generating Greenberger-Horne-Zeilinger state and cluster state with atomic ensembles based on the Rydberg blockade. Using similar resources as the earlier scheme, here we propose an experimentally feasible scheme of preparing arbitrary four-qubit W class of maximally and non- maximally entangled states with atomic ensembles in a single step. Moreover, we carefully analyze the realistic noises and predict that four-qubit W states can be produced with high fidelity (F - 0.994) via our scheme.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60890202, 60725418 and 10776005, and the National Basic Research Program of China under Grant No 2007CB815104.
文摘The transverse inhomogeneous carrier-envelope phase (CEP) distribution of idler generated through difference-frequency-generation (DFG) in quadratic nonlinear crystals is theoretically studied. In practical CEP stabilized DFG setups, the pump and the signal are usually Gaussian beams with non-uniform intensity distribution. Since the idler CEP is dependent on gain, this non-uniform intensity distribution leads to inhomogeneous gain across the aperture of the idler beam, resulting in a varying transverse idler CEP. Simulation results show that in practical settings, in the high-gain regime, transverse inhomogeneous CEP can be much smaller compared with π/2. However, when gain on the propagation axis reaches saturation, CEP difference can well exceed π/2.
文摘We investigate the effect of collision-induced coherence on coherent population transfer with the stimulated Raman adiabatic passage technique in a double A-type four-level system with a widely separated excited doublet. It is shown that when the two pulsed lasers with Rabi frequencies nearly comparable to the energy separation of the doublet are tuned to the particular frequency where the condition for quantum interference is satisfied, the very low transfer efficiency due to the nonadiabatic coupling between the two degenerate adiabatic states could be enhanced significantly with the increase of the collisional decay rates in a moderate range. The enhanced transfer efficiency results from the weakening of the nonadiabatic coupling between the two degenerate adiabatic states realized through collision-induced destructive quantum interference.
基金Project supported by the National Key Basic Research Program of China(Grant No.2014CB744302)the Specially Funded Program on National Key Scientific Instruments and Equipment Development,China(Grant No.2012YQ140005)the Beijing Natural Science Foundation(Grant No.4122064)
文摘The particle sizes and porosities of simulated pore structures are probed by terahertz time-domain spectroscopy.A double-peak time-domain spectrum phenomenon is observed when the terahertz(THz) pulses illuminated a pore and a particle. The amplitudes of the two peaks depend strongly and monotonically on the particle size and porosity. A model is used to study the phenomenon, and the computational results agreed with the experimental measurements. These measurements indicate the terahertz spectroscopic behaviors of pores and particles, suggesting that terahertz spectroscopy can be used as a noncontact probe of porosity.
基金the National Natural Science Foundation of China (60471040)
文摘An efficient hybrid method based on the method of moments (MOM) and physical optics (PO) for the analysis of radiation characteristics of an electrically large antenna-radome system is presented. Specifically, MOM is first applied to the antenna to find the current on its surface, and then the equivalent PO currents produced by the antenna radiation are assumed on the radome wall. When the coupling of the PO currents and antenna current is considered, the coupling matrix is divided into a series of partial matrices, in order to deduce the memory requirement and accelerate the evaluation process. Numerical results indicate that the proposed hybrid PO-MOM method is accurate and efficient.
基金Project supported by the National Natural Science Foundation of China (Grant No.60977068)the Foundations of the State Key Laboratory for Transient Optical and Photonic Technology of Chinese Academy of Sciences (Grant No.SKL ST200912)
文摘We experimentally study the generation of a partially coherent non-diffractive beam by focusing a partially coherent vortex beam with an axieon. The investigation results show that when the partially coherent vortex beam is focused by the axicon, the beam is transferred into a partially coherent higher-order non-diffractive beam. In the non-diffractive zone, the transverse intensity distribution of the partially coherent higher-order non-diffractive beam is invariant during propagation. In addition, the range of the non-diffractive zone is related to the coherence of the partially coherent vortex beam. The poorer the coherence of the partially coherent vortex beam, the shorter the range of the non-diffractive zone.
文摘In this paper, we investigate the loss caused by multiple humans blocking millimeter wave frequencies. We model human blockers as absorbing screens of infinite height with two knife-edges, We take a physical optics approach to computing the diffraction around the absorbing screens, This approach differs to the geometric optics approach described in much of the literature. The blocking model is validated by measuring the gain from multiple-human blocking configurations on an indoor link. The blocking gains predicted using Piazzi ' s numerical integration method (a physical optics method) agree well with measurements taken from approximately 2.7 dB to -50 dB. Thereofre, this model is suitable for real human blockers, The mean prediction error for the method is approximately -1.2 dB, and the standard deviation is approximately 5 dB.
文摘The physical optics solution is presented for the calculation of scattering by the complex conducting bodies coated with anisotropic materials, which is based on the tangential plane approximation and the equivalent currents on an anisotropic material backed by an infinite metal surface illuminated by the plane wave given in our previous work. The analytical scheme is proposed to realize fast computation of the solution. Numerical results for several coated bodies such as dihedral corner reflector and cone-cylinder geometry are given and discussed.
基金supported by the National Natural Science Foundation of China(51375490)
文摘In order to improve the survivability of the aircraft,conceptual design and radar cross section(RCS) performance research are done. The CATIA software is used to design the 3D digital model of the shipborne early warning aircraft, and some measures are taken to reduce the RCS characteristics of the early warning aircraft at the same time. Based on the physical optics method and the equivalent electromagnetic flow method,the aircraft's RCS characteristics and strength distribution characteristics are simulated numerically, and compared with the foreign advanced shipborne early warning aircraft. The simulation results show that under the X radar band, when the incident wave pitching angle is 0?, compared with the foreign advanced shipborne early warning aircraft, the forward RCS average value of the conceptual shipborne early warning aircraft is reduced to 24.49%, the lateral RCS average value is reduced to 5.04%, and the backward RCS average value is reduced to 39.26%. The research results of this paper are expected to provide theoretical basis and technical support for the conceptual design and the stealth design of the shipborne early warning aircraft.
文摘As a marked extension of the traditional MoM-PO (method of moment-physical optics) hybrid method, a new hybridization of PO, SBR, and MoM (MoM-SBR/PO) is presented to calculate the multireflection contribution in the PO region efficiently by introducing the method of SBR based on RDN notion, which avoids the time-consuming iterative procedure and the choice of proper Green's function. As compared with the traditional MoM-PO hybrid method, the calculation efficiency of the proposed method is greatly improved, and its validity is verified by numerical results.
基金Supported by the National Natural Science Foundations of China under Grant No 50872130.
文摘The La2Ti2O7:Pr^3+, which emits red color luminescence upon UV light excitation, is prepared by the conventional high-temperature solid-state method and its luminescent properties are systematically investigated. X-ray diffraction, photoluminescence, afterglow emission spectra and long-lasting phosphorescence (LLP) decay curves are used to characterize this phosphor. After irradiation by a 290-nm UV light for 3 rain, the Pr^3+-doped La2Ti2O7 phosphor emits intense red emitting afterglow from the ^1D2 →^ 3H4 transitions, and its afterglow can be seen with the naked eye in the dark clearly for more than 1 h after removal of the excitation source. The afterglow decay curve of the Pr^3+-doped La2Ti2O7 phosphor contains a fast decay component and another slow decay one. The possible mechanism of this red light emitting LLP phosphor is also discussed based on the experimental results.
基金supported by the National Basic Research Program of China under Grant No.2014CB339802,No.2011CB808100the National Natural Science Foundation of China under Grant No.11174156
文摘In this work, we review the developing progress of two-dimensional terahertz time-domain spectroscopy(THz-TDS) and its diverse applications, including analyzing the polarization of THz radiation from a laser-induced plasma source and studying the corresponding physical mechanism, and characterizing the optical properties of crystals, etc.
基金Project supported by the Creative Foundation of Wuhan National Laboratory for Optoelectronics (Grant No. Z080007)partly by the National Basic Research Program of China (973 Program)(Grant No. 61328)
文摘This paper reports that an output window for optically pumped terahertz (THz) laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate (approximating to 5 mm thick). Unlike the conventional process of depositing a gold film approximating to 100 nm on negative photoresist using electron-beam evaporation, a nickel film approximating to 1.5 μm thick is directly deposited on the clean surface of dielectric substrate using magnetron sputtering and then a positive photoresist is spun onto the nickel metal surface at 6000 r for 60 s. A transmittance spectrum of the output window in a certain frequency range (say, from zero to 1 THz) has been obtained by using THz time domain spectroscopy. Moreover a transmittance spectrum simulated numerically has also been estimated with respect to the output window using the transmission-line model (TLM) containing attenuation component from dielectric substrate. The simulation results show that the TLM can explain well the experimental curve in a certain frequency range from zero to 1 THz. Thus it is demonstrated that the improved optical component can be efficiently used as both output coupler and output window for optically pumped THz lasers.
文摘The radar cross section (RCS) of dispenser and its components is computed by graphical electromagnetic computing (GRECO) method, which bases on physical optics (PO) method. A satisfied agreement is gotten between computed and measured results outdoor. The results show that the main scattering source of the dispenser is the mirror reflecting of the body; in the most crucial nose-on region, the nose mirror reflecting plays important role; the corner reflecting is important to the fins' RCS. The corresponding measures to reduce dispenser's RCS are proposed. It is indicated that to reduce RCS, shaping should be adopts first, while aerodynamic characteristics and stealth characteristics should be considered synthetically during the design of dispenser.
文摘The radiation characteristics of a doubly curved shaped reflector antenna with random holes is analyzed by physical optics (PO) method, and the probability model of the random holes and its numerical realization method are presented. The radiation patterns show that in the azimuth plane the peak sidelobe level becomes much higher as the reflector surface with random holes. The simulation results can provide a theoretical guidance for the radar attackers.
文摘For electromagnetic scattering of 3?D complex electrically large conducting targets,a new hybrid algorithm,MoM?PO/SBR algorithm,is presented to realize the interaction of information between method of moment(MoM)and physical optics(PO)/shooting and bouncing ray(SBR).In the algorithm,the COC file that based on the Huygens equivalent principle is introduced,and the conversion interface between the equivalent surface and the target is established.And then,the multi?task flow model presented in this paper is adopted to conduct CPU/graphics processing unit(GPU)tests of the algorithm under three modes,i.e.,MPI/OpenMP,MPI/compute unified device architecture(CUDA)and multi?task programming model(MTPM).Numerical results are presented and compared with reference solutions in order to illustrate the accuracy and the efficiency of the proposed algorithm.