bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of magnetic flux density and cooling rate on orientation behavior of Tb0.27Dy0.73Fe1.95 alloy during solidification process
Authors: Gao Peng-Fei  , Liu Tie  , Chai Shao-Wei  , Dong Meng  , Wang Qiang  ,   Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China
Published: December 2020

The rare-earth giant magnetostrictive material Tb0.27Dy0.73Fe1.95 is one of the most important functional magnetic materials. Their superior properties include high saturation magnetostrictive coefficient at room temperature, high electromechanical coupling coefficients, high output power, fast response, high energy density, and non-contact drive. Thus, they can be used to build sensors, precision machinery, magnetomechanical transducers, and adaptive vibration-control systems. In this material, the magnetic phase (Tb, Dy)Fe2 has a typical MgCu2-type cubic Laves phase structure and exhibits different magnetostrictive properties along different crystal orientations. The 111 direction of this phase is the easy magnetization axis, along which the linear magnetostriction is higher than other directions. Thus, researchers have focused on preparing (Tb, Dy)Fe2 with a crystallographic orientation along or close to the 111 direction. Generally, the directional solidification method is used to prepare the Tb0.27Dy0.73Fe1.95 alloy. However, a crystal orientated along the 110 or 112 direction is always obtained and both of these directions require a high external magnetic field for improved magnetostrictive performance. The 111 preferred growth orientation can be acquired using seed crystal technology. However, the relatively low growth velocity can cause the appearance of the linear (Tb, Dy)Fe3 phase which induces a high brittleness of the material. Therefore, new methods to prepare Tb0.27Dy0.73Fe1.95 products with high 111 orientation at higher growth velocity are required. In this paper, we solidify the Tb0.27Dy0.73Fe1.95 alloys under various high magnetic field and cooling rate conditions. We study the effects of the magnetic flux density and cooling rate on the crystal orientation of the (Tb, Dy)Fe2 phase and the magnetization behavior of the alloys. It is found that after field-treated solidification, a high 111 orientation of (Tb, Dy)Fe2 along the magnetic field direction can be produced. As a consequence, the magnetostriction without applying stress remarkably increases. By increasing the magnetic flux density applied during the solidification of the Tb0.27Dy0.73Fe1.95 alloys, the 111 orientation of (Tb, Dy)Fe2 could be obtained at higher cooling rates. Ranging from 4 T to 10 T, with increasing cooling rate the magnetic flux density, at which the 111 or 110 orientation of (Tb, Dy)Fe2 occurs, increases or decreases, respectively. The saturated magnetization of the alloys increases with increasing cooling rate. The application of the magnetic fields does not affect the saturated magnetization.
The focused vectorial fields with ultra-long depth of focus generated by the tunable complex filter
Authors: Wang Ji-Ming  , He Chong-Jun  , Liu You-Wen  , Yang Feng  , Tian Wei  , Wu Tong  ,   Department of Applied Physics, College of Science, Nanjing University of Aeronatutics and Astronautics, Nanjing 211106, China;,   College of Mechanical and Electrical Engineering, Nanjing University of Aeronatutics and Astronautics, Nanjing 210016, China
Published: December 2020

According to the diffraction integral theory of vector field and the pupil filtering method with a discrete complex amplitude, we present a tunable pupil filter to achieve and manipulate the focused vector fields with ultra-long depth of focus. The filter consists of a polarization rotator with two /2 wave plates and a discrete complex amplitude filter with six zones. Amplitude transmissions of these zones are different and increase along the radial direction. And every two adjacent transmitted zones have the opposed phases 0 and . With optimized cylindrical polarization (0 =52) and discrete amplitude, the generalized cylindrical vector field can be tightly focused into a three-dimensional (3D) flat-top field with an extended depth of focus (～10 ) by a high numerical aperture lens. For the main outermost zone and the other five inner zones, we analyze the intensity distributions of the three polarized components and the total polarized component in the focal region. We find that the axially and azimuthally polarized components are the major contributors. The outermost zone offers the central field of the focused field while the other five zones affect the side lobe more obviously. Through adjusting the included angle between the double wave plates, we can change the polarization states of the incident vector field and alter the structures of the focused fields among the 3D flat-top focused field, needle-like field, tube-like field and the other fields with intermediate form. Result obtained is superior to that of the past research for the adjustable freedom between these forms, and it reveals the dynamic relation between the evolved vectorial form of incident field and the vector structure of the focused field. Our work paves a way to achieve the controlled dynamical focused field with a long depth of focus. The needle-like field, tube-like field and the well-matched 3D flat-top focused field will meet the demand of applications in optical microscope, optical micro-manipulating, optical micromachining and so on.
Generation of bright squeezed light at 1.5 m telecommunication band and its Wigner function reconstruction
Authors: Sun Zhi-Ni  , Feng Jin-Xia  , Wan Zhen-Ju  , Zhang Kuan-Shou  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

The squeezed light at 1.5 m telecommunication band has been considered as an important resource of continuous variable (CV) practical fiber-based quantum information research because it is the lowest loss in fiber. A bright phase quadrature squeezed light for continuous variable at 1.5 m is demonstrated from a semi-monolithic degenerate optical parametric amplifier (DOPA) based on a periodically poled KTiOPO4 (PPKTP) crystal. The laser source is a continuous wave (CW) single-frequency fiber laser at 1.5 m, which is sent through a ring mode cleaner (MC) as a preliminary spatial and noise filter. And then the main portion of the output from the MC is used for external-enhanced second harmonic generation to obtain a CW single-frequency low noise laser at 780 nm that acts as the pump of the DOPA. The residual light of the output from the MC at 1.5 m is used as the injected signal light of the DOPA and the local oscillator (LO) of a balanced homodyne detector (BHD) system. The DOPA is built by using a type-I PPKTP crystal and a piezo-actuated output coupler and works in double-resonance case with a threshold power of 230 mW. When the DOPA is operating in the state of amplification, the output down-conversion field should be a bright phase quadrature squeezed light, where the relative phase between the pump and the injected signal is locked to 0. A 4.7 dB bright phase quadrature squeezed light is measured by the BHD system with the pump light of 110 mW and the injected signal of 3 mW, where the relative phase between the down-conversion field and the LO is locked to 0. Our measurement is limited by the optical losses and the detection efficiency. We have taken into account the detection efficiency of 86.6%, and the actual squeezing of the squeezed light being 6.3 dB. Moreover, because it is so crucial a process for CV quantum information system that the transmission and evolution of the CV squeezed states in the fiber may reappear in all information of the quantum states in the phase space, then the bright squeezed light is detected by a BHD system in the time domain, and its Wigner quasi-probability distribution function can be reconstructed by using a quantum tomographic technique. Furthermore, the bright squeezed state at 1.5 m is an ideal source for fiber-based long-distance quantum information because of its stability and bright mean field.
Quantum phase transition in arrays of dissipative cavities with two-photon process
Authors: Xiong Fang  , Feng Xiao-Qiang  , Tan Lei  ,   Institute of Theoretical Physics, Lanzhou University, Lanzhou 730000, China
Published: December 2020

In this paper, we employ a new kind of quasi-boson approach and the mean field theory to study analytically the Hamiltonian of an array of cavities with a three-level atom embedded in each cavity in the process of two-photon resonant transition under the influence of a bosonic bath. The superfluid order parameter of the system is obtained analytically and then analyzed numerically to investigate the effects of dissipation on the quantum phase transition from the superfluid to the Mott-insulator phase. It is shown that when the two-photon resonance is achieved one can have the superfluid phase at (ZJ/)= (ZJ/)c' 0.34 in the related ideal case. Furthermore, the system while in the two-photon resonant process has a larger dissipation rate as compared with that in the one-photon resonant process, thus leading to the suppression of the long-range coherence time and enhancement of the critical hopping rate for restoring coherence.
Performance of Yb-doped silicate glass with thermal bleaching
Authors: Xiong Zhong-Long  , Wu Yan  , Jing Rui-Ping  , Ma Chong  , Long Wei-Hui  , Zhang Chao-Jun  , Cheng Yong-Jin  ,   College of Mathematics and Physics, China University of Geosciences (Wuhan), Wuhan 430074, China
Published: December 2020

A series of Yb-doped silicate glasses with the composition of 60 SiO2-12 Al2O3-28 CaO-1.0 mol% Yb2O3 are prepared by a conventional melting method under normal processing conditions. These glasses are divided into two groups. One group experienced a total dose 3 kGy radiation under a Co60 radiation source, and the other group is pristine. The absorption spectra as well as the near-infrared (NIR) luminescence spectra of the glasses (pristine Ybc, irradiated Ybc, heat bleaching Ybc) are investigated. Theoretically, effects of gamma-ray radiation exposure would lead to the formation of color centers in the glass samples. Such radiation-induced color center defects cause a strong broad optical absorption band with widths from 300 to 900 nm, and its tail extends into the NIR region. In this experiment the absorption coefficient of the glass is measured by a ultraviolet-visible spectrophotometer named Lambda35, and the NIR spectrum is measured by a Zolix grating spectrometer named Omni-. Furthermore, a special test system is set up to test the NIR spectrum of the glass at high temperatures. Experimental results show that the absorption coefficient of the glass after irradiation increases significantly in the visible region. The absorption coefficients of the glasses (pristine Ybc, irradiated Ybc) at 400 nm are 0.93 cm-1 and 2.9 cm-1 respectively. With a certain temperature treatment, the absorption coefficient of the irradiated glass is 1.89 cm-1 at 400 nm. Compared with the absorption coefficient obtained before, it is decreased by 35%. The NIR intensities of the glasses (pristine Ybc, irradiated Ybc, heat bleaching Ybc) are 588, 261 and 436 (arbitrary units) respectively. It may be due to the color center defects produced by radiation, that have decomposed under a certain temperature treatment. As a result, this method greatly improve the optical performance of the glass. So thermal bleaching phenomenon will happen in the irradiated glass that experiences in a certain temperature treatment. Finally, results obtained in this paper may provide a theoretical basis for studying the anti-radiation of optical glasses.
Velocity analysis for collapsing cavitation bubble near a rigid wall under an ultrasound field
Authors: Guo Ce  , Zhu Xi-Jing  , Wang Jian-Qing  , Ye Lin-Zheng  ,   School of Mechanics and Power Engineering, North University of China, Taiyuan 030051, China
Published: December 2020

Acoustic cavitation bubble and its production extreme physics such as shockwaves and micro-jets on a solid wall have attracted great interest in the application of ultrasound (e.g., ultrasonic medical, ultrasonic cleaning, and ultrasonic machining). However, the prediction and control of micro-jets induced by ultrasonic field have been a very challenging work, due to the complicated mechanisms of collapsing of cavitation bubbles. In order to determine the interaction of micro-jet with the key parameters that influence the acoustic cavitation, the dynamics of bubble growth and collapse near a rigid boundary in water is investigated. Using the method of mirror image, a revised bubble dynamics equation in radial oscillation for a bubble near a plane rigid wall is derived from the double-bubble equation (the Doinikov equation). In the present equation, the gas inside the bubble is assumed to be the van der Waals gas, and the weak compressibility of the liquid is also assumed. The revised equation is then employed to simulate numerically the dynamical behaviors of a bubble, using the fourth-order Runge-Kutta method with variable step size adaptive control. Numerical simulations of the motion characteristics and collapse velocities of a bubble near a rigid boundary or a free boundary have been performed, under various conditions of initial bubble radius, spacing between the center of the bubble and the wall, acoustic pressure and ultrasonic frequency, in order to explain the effects of these key parameters on the acoustic cavitation intensity. It is shown that, compared with free boundary, the effect of rigid boundary on the bubble plays a significant role in suppressing the bubble oscillation. The intensity of bubble collapsing is reduced as the increase of the initial bubble radius and ultrasonic frequency, and increased by enlarging the spacing between the center of the bubble and the wall. There exists an optimal acoustic pressure (almost 3.5 times bigger than the ambient pressure), at which the collapse of a bubble near a rigid wall can be the most violent. Furthermore, the relationship between the collapse velocity of a bubble near a rigid boundary and its micro-jet is described. Results demonstrate that the velocity of micro-jet is dependent on that of bubble collapse, and it can be controlled by adjusting the velocity of bubble collapse indirectly. Calculation results of the micro-jet in this paper are compared with some numerical and experimental results given in the literature and good apparent trends between them are obtained. These results will give important implications for further understanding the dynamics of cavitation bubble on a solid wall induced by the ultrasonic field and its different requirements in engineering applications.
Ion extraction experiment for electron cyclotron resonance ion source with different magnetic topology
Authors: Jin Yi-Zhou  , Yang Juan  , Feng Bing-Bing  , Luo Li-Tao  , Tang Ming-Jie  ,   School of Astronautics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Electron cyclotron resonance ion source (ECRIS) for space propulsion requires to be compact and efficient. In this work, ECRIS, which generates magnetic field through permanent magnets, is compact and heats electrons by microwave in magnetic field to induce ionization collision and produce plasma. In ECRIS, magnetic field is crucial in gas discharge, plasma confinement and transport. Due to the complex interaction among the processes, including plasma generation, wave transmission and ion extraction, the effects of magnetic field on the performance of ECRIS are complex. In this paper, the effects of magnetic field topology on the performance of the ECRIS are studied experimentally. Argon is discharged by microwaves in four types of ion sources, different in the magnet positions and the ion beam extracted. The gas flow rate varies from 30 to 210 g/s, the microwave power from 10 to 20 W and the extracting voltage form 500 to 1500 V. The properties of the ion sources are analyzed by comparing their extracted ion beams, propellant utilization efficiency, discharge loss and stability. Results show that the maximum ion beam, the highest gas utilization efficiency and the minimum discharge loss are respectively 160 mA, 60%, and 120 WA-1. Each ion source presents more than one mode, determined by the microwave power and the gas flow rate, and affected by the extracting voltage. The microwave power and the gas flow rate at which the ion source mode changes relative to the position of the magnets. Finally, the influences of magnetic topology on the performance of the ion source are summarized and analyzed. It is concluded that inside this kind of ECRIS, the magnetic field featured by a wide electron cyclotron resonance (ECR) zone, and the narrow gap between the ECR zone and the screen grid will increase the extracted ion beam at the same level of the input power and the gas supply. But it is difficult to achieve high gas utilization efficiency in the ion source with such a structure. By keeping the ECR zone close to the power entrance, the gas inlet will significantly decrease the threshold for the power and gas consumption to sustain the high current mode. But the discharge loss in the ion source of such a structure is huge. Elaborate considerations should be taken to balance the magnitude of the extracted ion beam and the efficiency. These results may improve the understanding of the working process of this type of ECRIS and help the design processes.
Optimization design of laser X-ray radiography for density diagnosis in compressed matter
Authors: Zhang Tian-Kui  , Han Dan  , Wu Yu-Chi  , Yan Yong-Hong  , Zhao Zong-Qing  , Gu Yu-Qiu  ,   Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China;,   Shanghai Jiao Tong University, IFSA Collaborative Innovation Center, Shanghai 200240, China
Published: December 2020

The shock wave driven by laser is an important tool for investigating equation of state and can provide the state of compressed matter. The X-ray source, generated by the short-pulse intense laser interaction with the solid target, has the properties of short pulse, small spot, high yield and tunable energy. Therefore the X-ray source is the first chosen as a backlighter for the diagnosis of dynamic process. The model of the X-ray radiography is established by Monte Carlo code Geant4. The density distribution in an object is obtained by hydrodynamic code Multi-1D and the laser parameters are obtained by the XGIII laser facility. Under the condition of one-dimensional density the object in the shape of rectangular solid, three evaluation criterions, root mean square, peak value and ratio of rise gradient, are defined for evaluating density results. The signal-to-noise, spatial resolution, and contrast of radiography results have been optimized. First, the signal-to-noise has been optimized and the optimization magnification is 5.6 with the photon yield 1012. Second, the spatial resolution according to different spot X-ray source has been simulated by designing resolution plate radiography. Third, in the condition of same magnification, the influence of source yield on radiography result has been analyzed. Fourth, the radiography results of different X-ray energy have been simulated. The optimization energy for radiography requests that the penetrability ratio is greater than 1.5 and the photon count in pixel after penetrating the compressed matter is greater than 3000. And the optimum criteria make sure that the radiography images simultaneously have high contrast and high signal-to-noise. The radiography of one-dimensional density object in the shape of cylinder has been simulated. The Abel inversion algorithm is established based on Radon inversion. The inversion result accords well with the designed density distribution in simulation at the request of the radius of X-ray source less than 5 m. The inversion result basically accords with the designed density distribution in simulation at the request of the radius of X-ray source less than 15 m. This work will contribute to the measurement experiments on the compressed matter achieved by laser-driven-shock and provide the reference for the optimization of radiography based on X-ray.
Refractive index of Z-cut quartz under magnetically driven quasi-isentropic compression
Authors: Zhang Xu-Ping  , Luo Bin-Qiang  , Chong Tao  , Wang Gui-Ji  , Tan Fu-Li  , Zhao Jian-Heng  , Sun Cheng-Wei  , Liu Cang-Li  ,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China;,   China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The refractive index of Z-cut quartz under magnetically driven quasi-isentropic compression is researched by using the pulsed power generator CQ-4. Its velocities of interface between the aluminum panel and the window are measured by a four-channel dual laser heterodyne velocimeter, which is operated at an incident laser wavelength of 1550 nm. The history profile of magnetic pressure on the electrodes is obtained by a backward integration calculation of the aluminum/LiF interface velocity. And then the pressure history profile is used in the LS-DYNA simulation to get the true particle velocity of the aluminum/quartz interface. Combining with the apparent particle of aluminum/quartz interface which is obtained from experiments, a continuous index of refraction in Z-cut quartz has been obtained at up to a pressure of 14.55 GPa as the longitudinal stress is gradually increased to its elastic limit. The relation between the apparent particle and true particle velocities can be fitted by a polynomial, and the required derivative obtained by differentiation of that polynomial. Refractive index determined from the linear fitting parameters is n=1.087 ( 0.008)+0.4408 /0, which agrees well with the previous shock results. Results from polarizability analysis suggest that the temperature and loading path should have less effect on the refractive index of Z-cut quartz within its elastic limit.
Static subminiature snapshot imaging polarimeter using spatial modulation
Authors: Cao Qi-Zhi  , Zhang Jing  , Edward DeHoog  , Lu Yuang  , Hu Bao-Qing  , Li Wu-Gang  , Li Jian-Ying  , Fan Dong-Xin  , Deng Ting  , Yan Yan  ,   College of Physics and Electronic Engineering, Guangxi Teachers Education University, Nanning 530023, China;,   Key Laboratory of Environment Change and Resources Use in Beibu Gulf (Guangxi Teachers Education University), Ministry of Education, Guangxi Key Laboratory of Earth Surface Processes and Intelligent Simulation, Guangxi Teachers Education University, Nanning 530001, China;,   Institute of Space optics, Xi'an Jiaotong University, Xi'an 710049, China;,   Optical Engineering and Analysis LLC, 1030 Loma Ave, Long Beach, California 90501, USA
Published: December 2020

The spatially modulated snapshot imaging polarimeter can acquire the image and two-dimensional state of polarization using the spatial carrier fringe to encode the full Stokes vectors in a single interference image. It can be used in space exploration, earth observation and detection of biological medicine, land surface and oceans. In an earlier publication, we demonstrated by theoretical analysis that the spatially modulated snapshot imaging polarimeter using modified Savart polariscopes (MSPSIP) is comparable in carrier frequency, signal-to-noise ratio, and spatial resolution to a spatially modulated snapshot imaging polarimeter using conventional Savart polariscopes. In this investigation, the numerical simulation is used to demonstrate theoretical analysis and the feasibility of MSPSIP. Moreover, a geometric ray model is developed to explain the principle and scheme of MSPSIP and derive the expressions of interference intensities. Moreover, a laboratory experiment is conducted to demonstrate the validity of MSPSIP. In addition, we analyze that the interference intensity varies with the direction of polarization analyzer. This investigation enriches the study on MSPSIP and provides a theoretical and practical guidance for study, design, modulation, experiment and engineering of MSPSIP. Furthermore, the MSPSIP operates based on the principle of encodeding polarization information within the spatial modulation of the image. This unique technology allows all Stokes parameters to be simultaneously recorded from each spatial position in an image with a single integration period of the imaging system. The device contains no moving parts and requires no scanning, allowing it to acquire data without the motion artifacts normally associated with scanning polarimeter. In addition to having snapshot imaging and static (no moving parts) capabilities, image processing is simple, and the device is compact, and miniature. Therefore, we believe that MSPSIP will be useful in many applications, such as remote sensing and bioscience.
Spherical Dirac equation on the lattice and the problem of the spurious states
Authors: Zhao Bin  ,   School of Physics and Nuclear Energy Engineering, International Research Center for Nuclei and Particles in the Cosmos, Beihang University, Beijing 100191, China
Published: December 2020

With the development of radioactive ion beam facilities, the study of exotic nuclei with unusual N/Z ratio has attracted much attention. Compared with the stable nuclei, the exotic nuclei have many novel features, such as the halo phenomenon. In order to describe the halo phenomenon with the diffused density distribution, the correct asymptotic behaviors of wave functions should be treated properly. The relativistic continuum Hartree-Bogoliubov (RCHB) theory which provides a unified and self-consistent description of mean field, pair correlation and continuum has achieved great success in describing the spherical exotic nuclei. In order to study the halo phenomenon in deformed nuclei, it is necessary to extend RCHB theory to the deformed case. However, solving the relativistic Hartree-Bogoliubov equation in space is extremely difficult and time consuming. Imaginary time step method is an efficient method to solve differential equations in coordinate space. It has been used extensively in the nonrelativistic case. For Dirac equation, it is very challenging to use the imaginary time step method due to the Dirac sea. This problem can be solved by the inverse Hamiltonian method. However, the problem of spurious states comes out. In this paper, we solve the radial Dirac equation by the imaginary time step method in coordinate space and study the problem of spurious states. It can be proved that for any potential, when using the three-point differential formula to discretize the first-order derivative operator, the energies of the single-particle states respectively with quantum numbers and - are identical. One of them is a physical state and the other is a spurious state. Although they have the same energies, their wave functions have different behaviors. The wave function of physical state is smooth in space while that of spurious state fluctuates dramatically. Following the method in lattice quantum chromodynamics calculation, the spurious state in radial Dirac equation can be removed by introducing the Wilson term. Taking Woods-Saxon potential for example, the imaginary time step method with the Wilson term is implanted successfully and provides the same results as those from the shooting method, which demonstrates its future application to solving the Dirac equation in coordinate space.
Molecular structure and properties of sulfur dioxide under the external electric field
Authors: Yang Tao  , Liu Dai-Jun  , Chen Jian-Jun  ,   College of Chemical Engineering, Sichuan University, Chengdu 610044, China
Published: December 2020

SO2 is not only an important resource but also a notorious air pollutant, so it has attracted increasing attention nowadays. This paper focuses on the influence of external electric field on SO2. In order to obtain more reliable results, the density functional theory B3P86 method is chosen to calculate the values mentioned below. The ground states of SO2 molecule under different strong electric fields ranging from -0.04 a.u. to 0.04 a.u. are optimized by density functional theory B3P86 method with 6-311++g(3d,p) basis sets. The geometric parameters, charge distributions, total energies, dipole moments, the highest occupied molecular orbital (HOMO) energies, the lowest unoccupied molecular orbital (LUMO) energies, energy gaps of SO2 under different external electric fields are obtained, respectively. On the basis of optimized configuration, the excitation energy, transition wavelength and oscillator strength in the same intense external electric field are calculated by the time dependent density functional theory (TD-B3P86) method.#br#The calculated values for geometric parameters of SO2 without external electric field agree well with the available experimental data and other theoretical results. The geometric parameters and charge distribution of SO2 strongly depend on the intensity and direction of external electric field. The total energy of SO2 in the considered range of external electric field first increases and then decreases. On the contrary, the dipole moments of SO2 in different external electric fields ranging from -0.04 a.u. to 0.04 a.u. first decrease and then increase. When the external electric field is -0.04 a.u., the total energy and symmetry of SO2 both reach the maximum values. With the change of external electric field, the LUMO energy first increases and then decreases. The HOMO energy is found to decrease through the variation of the external field. The energy gaps of SO2 are proved to first increase, and then decrease with the variation of external electric field. Through studying the energy gaps of SO2, it is found that the external electric field can affect the chemical reactivity of SO2. The excitation energies, transition wavelengths and oscillator strengths are very complicated with the change of the external electric field. The excitation properties of SO2 molecule are seriously affected by the external electric field.
Design and verification of an electronically controllable ultrathin coding periodic element in Ku band
Authors: Yang Huan-Huan  , Yang Fan  , Xu Shen-Heng  , Li Mao-Kun  , Cao Xiang-Yu  , Gao Jun  ,   Department of Electronic Engineering, Tsinghua University, Beijing 100084, China;,   School of Information and Navigation, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

The coding periodic element is able to achieve coded reconfigurable electromagnetic (EM) responses by loading controllable electronic devices. In this work, an electronically controllable ultrathin planar periodic element structure in Ku band is implemented with one PIN diode. When the PIN diode turns ON or OFF by applying a proper biasing voltage, the resonant property of the element changes correspondingly, and hence a 180° phase difference between the two states is obtained. By optimizing the geometrical parameters, the reflection loss less than 0.5 dB is achieved by the proposed element. Therefore, using a proper biasing voltage control network, the PIN diodes of the proposed elements in a periodic arrangement are set at different states, which may be denoted by a binary string with "1"s or "0"s, and the whole array of elements operates as a binary coding periodic structure and exhibits controllable EM functionalities. In order to verify the coding property of the proposed element, the general principle for the biasing circuit design is given. An optimized biasing circuit is thoroughly studied using both field distribution analysis and equivalent circuit theory. Simulated results show that the specially designed biasing hardly affects the element reflection performance. Finally, a group of element prototypes are fabricated with welded PIN diodes and measured using the standard waveguide test method. The difference in mirror image between the waveguide test and the desired periodic arrangement is also discussed. The experimental results validate that the proposed element successfully achieves good coding EM performance by controlling its biasing voltage. The reflection loss of the element is very low, and well distributed phase difference between the two element states is observed. The simulation and experiment results agree well, and the deviation between them is analyzed in detail. The proposed element possesses distinctive favorable features such as coded controllable EM functionalities, simple structure and ultrathin profile, thus exhibiting the promising prospects in tunable stealth surface, agile antennas, and many other applications.
Characteristics of Raman spectrum from stand-off detection
Authors: Zhang Li  , Zheng Hai-Yang  , Wang Ying-Ping  , Ding Lei  , Fang Li  ,   Laboratory of Environmental Spectroscopy, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

For developing a method to detect unknown or hazardous materials beyond safe distances, an experimental standoff detection system with using Raman scattering is established in laboratory. It consists of a pulsed laser with a wavelength of 532 nm as an excitation source, an optical assembly for light collecting and focusing with a 25 mm entrance aperture, a grating monochromator for dispersing scattering light, and a photomultiplier connected to an oscillograph for signal monitoring. The angle between the direction of incident laser beam and that of the scattering light collecting assembly is less than 2°. Raman signal intensities of ammonium nitrate, potassium nitrate and sodium nitrate in solid samples in a distance range from 2 m to 10 m are measured. The results are supposed to be comparable to those obtained in a distance range from 20 m to 100 m if a telescope of 250 mm diameter is used instead to collect Raman scattering light as in a usual standoff detection system. Some characteristics of Raman spectra are investigated, such as the spectrum features, the relationships between the amplitude of the highest Raman peak of ammonium nitrate and the intensity of the excitation light, the detection distance, the concentration of the sample and the normal direction of the sample surface. The Raman spectra of ammonium nitrate, potassium nitrate and sodium nitrate look similar: each of them has a highest peak in the vicinity of 1050 cm-1, small difference can be observed, and it can serve as a "signature" for discriminating between them. The experimental results demonstrate that the intensity of the characteristic Raman spectrum of ammonium nitrate is proportional to the excitation power, with approximate quadratic relationship, and tends to be inversely proportional to the square of the detection distance except that the detection distance is too short to ignore the influence of the focal length of light collecting optics on image size. In addition, the intensity of the characteristic Raman spectrum of ammonium nitrate decays approximately at an exponential rate with the decrease of its concentration. Finally, the intensity of the Raman signal of ammonium nitrate is approximately proportional to the cosine of the angle between the direction of the incident light and the surface normal. This relationship is similar to Lambert's cosine law that the radiant intensity observed from an ideal diffusely reflecting surface is directly proportional to the cosine of the angle. The last two phenomena imply that it may be particularly difficult to detect the substances of interest in a mixture on horizontal ground surface for Raman standoff detection system.
Effects of Gd3+/Y3+ codoping on the spectral properties of Nd:CaF2 crystals
Authors: Liu Jian  , Liu Jun-Fang  , Su Liang-Bi  , Zhang Qian  , Ma Feng-Kai  , Jiang Da-Peng  , Xu Jun  ,   School of Materials Science and Engineering, Tongji University, Shanghai 201802, China;,   Key Laboratory of Transparent and Opto-functional Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201809, China;,   School of Physics Science and Engineering, Institute for Advanced Study, Tongji University, Shanghai 200092, China
Published: December 2020

In the last few years, Nd3+ doped fluoride crystals have achieved some amazing laser performances by codoping buffer ions such as Y3+ and Gd3+ ions, which lead to the changing of local structure of Nd3+ ions. In this work, effects of doping concentration of Gd3+ and Y3+ ions on optical properties are discussed. The relationships between spectroscopic properties and the unit cells are also discussed. Nd, Y:CaF2 and Nd, Gd:CaF2 disordered crystals are grown by using temperature gradient technique (TGT). Among 0.5 at.%Nd, x at.%Gd(x=2, 5, 8, 10):CaF2 crystals, the crystal with Gd3+ of 2 at.% has the longest fluorescence lifetime (499 s). Increasing the concentration of Gd3+ up to 5 at.%, the crystal has a maximum absorption cross section of 1.910-20 cm2, and a maximum emission cross section of 1.910-20cm2. The crystal with Gd3+ of 8 at.%has a maximum emission bandwidth of 29.03 nm(FWHM). Among 0.6 at.%Nd, x at.%Y(x=2, 5, 8, 10):CaF2 crystal, the crystal with Y3+ of 5 at.%has the biggest absorption cross section (2.4110-20 cm2), and the biggest emission cross section (3.1710-20 cm2), when the concentration of Y3+ is 5 at.%. When the Y3+ concentration increases up to 10 at.%, the crystal has a longest fluorescence lifetime of 359.4 s and maximal emission bandwidth of 26 nm(FWHM).The different concentrations of codoping ions have different effects on the Nd:CaF2 crystals, for the formations of different optical centers. In order to study the effects of local structure around Nd3+ on the optical properties in a set of Nd:CaF2 single crystals with different codoping concentrations of Gd3+ and Y3+, the unit cell parameters are investigated by X-ray diffraction. With different concentrations of Gd3+ and Y3+ ions in Nd:CaF2 crystal, the local structure of Nd3+ changes, which leads to different optical properties. The relevant details will further be explained in this paper.
Seed electron production from O- detachment in high power microwave air breakdown
Authors: Wei Jin-Jin  , Zhou Dong-Fang  , Yu Dao-Jie  , Hu Tao  , Hou De-Ting  , Zhang De-Wei  , Lei Xue  , Hu Jun-Jie  ,   College of Communication System Engineering, The PLA Information Engineering University, Zhengzhou 450001, China
Published: December 2020

The existence of seed electrons is the precondition of air breakdown induced by high power microwave (HPM). Seed electrons are usually assumed to exist in background atmosphere when simulating the air breakdown triggered by HPM. However, this assumption may lead to some large errors especially in lower atmosphere where the number of electrons is very small. We establish a physical model of seed electron production from O- detachment collision with air molecules using the Monte Carlo method. A three-dimensional Monte Carlo program is developed to simulate this process. The average energies of O- and the average generation time of seed electrons under different electric intensities, frequencies, air pressures and breakdown volumes are obtained through simulation. The simulations show that the average generation time of seed electrons becomes longer with the increase of air pressure or the HPM frequency. The average seed electron generation time becomes shorter with the increase of electric intensity or breakdown volume. Finally, we simulate the processes of O- detachment collision with air molecules under the same experimental conditions. The comparative results show that the seed electron generation from O- detachment can explain the experimental results when the HPM frequency is low, while at higher frequencies, the average seed electron generation time becomes so long that it cannot correspond to the experimental value. Therefore some other mechanisms should be considered in the higher frequency case.
Femtosecond laser ablation of an aluminum target in air
Authors: Kang Xiao-Wei  , Chen Long  , Chen Jie  , Sheng Zheng-Ming  ,   Laboratory for Laser Plasmas, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

The dynamics of laser ablation of solid target with ultrashort intense laser pulses is not only fundamentally interesting, but also relevant to a few important applications such as microfabrication, laser propulsion, laser induced breakdown spectroscopy, etc. By use of time-resolved pump-probe shadowgraphic imaging technology, we study the dynamic process of laser ablation of a planar aluminum target in air. The incident laser pulses are from a Ti: sapphire femtosecond laser amplifier system with a duration of 50 fs, central wavelength of 800 nm, pulse energy varying between 4 mJ and 7 mJ. Time-resolved shadowgraphs of material ejection from the aluminum target are recorded at the time delay up to a few nanoseconds after laser irradiation. By changing the distance between the target and the focal point of the incident laser, we obtain the shadowgraphs of the target ejection under different laser spot sizes. When the laser spot size is relatively large say, over 1 mm, the irradiated target surface is ablated in the form of a planar shock. However, when the laser spot size is relatively small, the ejection appears in the form of a hemispherical blast wave. It is found that the hemispherical blast wave well conforms to the Sedov's blast wave theory. When the laser energy is relatively large, it is found that ionization of air has a great effect on laser ablation. Additional small ejections appear as columnar and hemispherical structures near the laser axis, which are superimposed on the large planar shock. These can be attributed to the following processes. Firstly, as the ionization of air occurs near the laser axis, effective heat transfer from air plasma to the aluminium target leads to enhanced target temperature. This leads to the formation of a columnar structure on a picosecond time scale. Secondly, the columnar ejection and air plasma expansion near the laser axis result in the decrease of air density and pressure, which leads to the formation of the hemispherical structure on a nanosecond time scale.
Microstructure characteristics of burning products of Ti-V-Cr fireproof titanium alloy by frictional ignition
Authors: Mi Guang-Bao  , Huang Xu  , Cao Jing-Xia  , Wang Bao  , Cao Chun-Xiao  ,   Aviation Key Laboratory of Science and Technology on Advanced Titanium Alloys, Beijing Institute of Aeronautical Materials, Beijing 100095, China
Published: December 2020

Titanium fire in the aero-engine is a typical accident caused by ignition and burning of titanium alloy, which leads to a huge damage. Some articles wrote it as to turn pale at the mention of titanium. Fireproof titanium alloy, a new type of structural titanium alloy with fireproof function, has been developed to prevent titanium from fire hazard and to ensure safe and reliable service of aero-engine. In view of the lack of clear understanding of the microscopic mechanisms found currently for the structural functionality of fireproof titanium alloys, in this work, using frictional ignition technology in oxygen-rich environment (friction oxygen concentration method), associated with in-situ observation, SEM, EDS and XRD analyses, the microstructure characteristics of burning products of Ti-V-Cr fireproof titanium alloys are investigated and the element distribution law associated with microscopic mechanism during combustion reaction process is disclosed. Results show that Ti-V-Cr fireproof titanium alloys produce dazzling white light during combustion, with the typical flame characteristics of metal combustion. The generated products after burning are mainly TiO2, V2O5 and Cr2O3 oxides, in the form of dispersive particles and dense continuous body. The dispersive particles are in regular spheric shape, with a size of 10-50 m; the dense continuous products after burning presents divisional feature. After the combustion lasts 18 s, four distinct zones form from the alloy matrix to the combustion surface and they are in the sequence of transitional zone, heat-affected zone fusion zone, and combustion zone, with sizes of 40-50, 200-210, 60-70, and 18-21 m respectively. Further, some small granular shaped bulges exist in the transitional zone, in some fixed directions; in the heat-affected zone, a large number of V-based solid solution and some Ti-based solid solution form, and the titanium containing V-based solid solution is much higher than the needle-like precipitation phase in the matrix. In the fusion zone, there are some V-based solid solutions in most of Ti-based solid solution; while, the combustion zone mainly contains the mixed oxides of Ti, V, and Cr. The V-based solid solution in the heat-affected zone reduces the diffusion rate of titanium to the fusion zone, slowing the preferential reaction between titanium and oxygen in the combustion zone; while the generated mixed oxides of TiO2, V2O5, Cr2O3, etc. in the combustion zone and the solution of oxygen in titanium in the fusion zone jointly prevent the diffusion of oxygen to the alloy matrix, thus the Ti-V-Cr fireproof titanium alloys can have excellent fireproof functions.
Effect of Na substitution on the electronic structure and ion diffusion in Li2MnSiO4
Authors: Jia Ming-Zhen  , Wang Hong-Yan  , Chen Yuan-Zheng  , Ma Cun-Liang  ,   School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China;,   Key Laboratory of Advanced Technologies of Materials, Southwest Jiaotong University, Chengdu 610031, China
Published: December 2020

With the developments of electric vehicles, the portable electronics and the large-scale storage systems, the research of the Li-ion rechargeable battery has focused on its high gravimetric and volumetric capacity. As a potential cathode, the Li2MnSiO4 structure has been intensively studied, in which two lithium ions of per formula unit (f.u.) can be extracted, and it exhibits a high theoretical capacity of about 330 mAh/g. However the low intrinsic electron conductivity and the slow lithium diffusion prevent its further development. In this paper, we build three structures with different Na+ doping concentrations in Pmn21 symmetric Li2MnSiO4, the electronic properties and Li+ ion diffusion behavior are studied by using the first principle and considering the transition barrier of the Mn-3d. Within the GGA+U scheme, the pure Li2MnSiO4 structure is semiconducting with a large band gap (3.28 eV), which is primarily derived from Mn-3d and O-2p states. Because lithium and sodium ions in the same main group have similar chemical properties, all the doped Li2-xNaxMnSiO4 (x= 0.125, 0.25, 0.5) are still semiconducting with the analogous densities of state (DOSs) to the pure Li2MnSiO4, however the band gaps reduce to 3.23 eV, 3.19 eV and 3.08 eV, respectively. Thus Na+ substitution can improve the electron conductivity. In Li2MnSiO4, the Li+ ions have two major diffusion channels predicted by the climbing image-nudged elastic band (CI-NEB) method. Channel A is along the a-direction [100], and channel B is in the bc plane with a zigzag trajectory. In the migration process, each of all the structures has only one migration pathway of Li ions. In the doped structures, the volumes of the crystal structures are increased by 1.40%, 2.65% and 5.25% for Li2-xNaxMnSiO4 (x= 0.125, 0.25, 0.5), and thus enlarge the hopping distances. Along channel A, the longer Li-O bond makes the ionic diffusion channel wider, therefore Li2-xNaxMnSiO4 (x= 0.125, 0.25, 0.5) have lower activation barriers of 0.48, 0.52 and 0.55 eV than the pure Li2MnSiO4 (0.64 eV). However, in channel B, the strong Li-O bonds increase the activation barriers of Li ion migration. When the doping concentration is x=0.125, the Li+ ion migration effect is strongest. For the Li+ ion migration pathways, it is easier for Li ion to hop into the site near Na ion. It means that the crystal structures are stabler at the short Li-O bond site. Therefore, doping Na+ ions would be a feasible method to improve the electron conductivity and Li+ ion migration rate in Li2MnSiO4 of Pmn21 phase.