bluuebunny/crossref_metadata_2025 huggingface dataset:
A new algorithm for polarization information restoration with considering the property of optoelectronic polarimeter
Authors: Liu Jing  , Jin Wei-Qi  , Wang Xia  , Lu Xiao-Tian  , Wen Ren-Jie  ,   MOE Key Laboratory of Optoelectronic Imaging Technology and System, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

The property of optoelectronic detector indicates that the response between incident light intensity and output digital number is non-linear. For imaging polarimeter, if light intensity is directly substituted by digital number when restoring polarization information from polarization images, the restored polarization information will apparently deviate from the true scene polarization information. This deviation makes the quantitative application of polarization information meaningless. To solve this problem, in this paper we propose a new algorithm for restoring the polarizaiton information with considering the property of polarimeter of the detector. Firstly, theorical correction equation of polarization information restoration are proposed for division-of-time polarimeter and for simultaneous polarimeter respectively. And then, specific implementation and polarization imaging test experiment are carried out. For divison-of-time polarimeter, we firstly test the property of the detector, and then use the tested parameter and the proposed restoration equation to restore polarizaiton information from the data of polarzation imaging test experiment. The degree of linear polarization (DoLP) restored with digital number directly changes from 0.932 to 0.753 when changes from 1.0 to 1.5. The DoLP restored with correction equation proposed in this paper varies from 0.932 to 0.926, which approaches to the ture scene DoLP value 1.0. For simultaneous polarimter, the instrument matrixes of the polarimeter are calibrated first under different setting values, and then the calibrated instrument matrixes are used to restore poliarzation information from the data of polarization imaging test experiment. The DoLP restored with digital number directly changes from 1.3763 to 1.1582 when changes from 1.0 to 1.5, which exceeds the possible DoLP range from 0 to 1.0. The DoLP restored with correction equation proposed in this paper varies from 0.8428 to 0.8683, which approaches to the ture scene DoLP value 1.0. Experimental result shows that the property of polarimeter has an apparent effect on the restored polarization information, and that the polarizaiton information restoration error increases with setting deviation from 1.0. With the restoration algorithm proposed in this paper, the restored polarization information can steadily approach to the scene polarization information with acceptable slants small. The poroposed polarization restoration algorithm with considering property establishes a theoretical foundation for the future study of polarimeter and its quantitative application.
Continuous-wave single-frequency 589 nm yellow laser generated from sum frequency of single-block non-planar ring cavity laser in periodically poled KTiOPO4 crystal
Authors: Xie Shi-Yong  , Zhang Xiao-Fu  , Yang Cheng-Liang  , Le Xiao-Yun  , Bo Yong  , Cui Da-Fu  , Xu Zu-Yan  ,   School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China;,   State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   Research Center for Laser Physics and Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Continuous-wave single-frequency 589 nm yellow laser can be used in laser cooling of sodium atoms. Besides, the interaction between 589 nm laser and sodium atoms can be studied by resonance fluorescence, which provides an important basis for the sodium guide star in the adaptive optics. In this paper, single frequency 589 nm yellow light is generated by sum frequency of single-block non-planar ring cavity 1064 nm and 1319 nm laser in periodically poled KTiOPO4 crystal. The geometric parameters of single-block non-planar Nd:YAG crystal and magnetic field intensity are optimally designed by simulation calculation through using Jones matrix. The output powers 1080 mW and 580 mW are obtained for continuous-wave single-frequency 1064 nm and 1319 nm laser in the experiment, respectively The two fundamental beams are expanded to be the same as perfectly as possible in size and are focused into a spot with a size of about 60 m by an achromatic lens. The sum-frequency generation takes place in a 1 mm2 mm20 mm phase-matched type-I periodically poled KTiOPO4 crystal with a matching temperature of 55℃ and polarization period of 12.35 m The crystal is anti-reflection coated for all three wavelengths (1064 nm, 1319 nm and 589 nm). A 14.8 mW output of 589 nm laser is obtained with beam quality factor M2=1.14 and the corresponding sum-frequency efficiency is 0.9%. The influence of periodically poled KTiOPO4 temperature on the sum-frequency efficiency is studied and the temperature acceptance bandwidth is measured to be 1.5 degrees The wavelength of 589 nm yellow light can be tuned to the sodium atom D2a absorption line by changing the temperature of 1064 nm Nd:YAG crystal and 0.164 pm of tuning accuracy is reached. The whole laser system is stable and reliable, so it provides a practical and effective technical means to obtain the continuous-wave single-frequency 589 nm laser, for it is relatively simple and easy to implement.
Several dynamic models of a large deformation flexible beam based on the absolute nodal coordinate formulation
Authors: Zhang Xiao-Shun  , Zhang Ding-Guo  , Chen Si-Jia  , Hong Jia-Zhen  ,   School of Sciences, Nanjing University of Science and Technology, Nanjing 210094, China;,   Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, China;,   Department of Engineering Mechanics, Shanghai Jiaotong University, Shanghai 200240, China
Published: December 2020

With the development of space technology, flexible appendages such as lightweight manipulators and satellite antennas, often appear in spacecrafts. Usually, the large overall motion of the flexible appendage will bring about large deformation problem. And there is a strong nonlinear coupling between the large overall motion and deformation of the flexible appendage, which brings about a large challenge to the precise control of the spacecraft. Dynamics of a rotating flexible planar beam with large deformation is investigated in this paper. A new nonlinear dynamic model of a flexible beam with large deformation is established based on an absolute node coordinate formulation (ANCF). The longitudinal and bending deformations of the flexible beam are both considered in the model. The longitudinal strain energy and bending strain energy of the beam can be calculated by using Green-Lagrangian strain tensor and the exact expression of the flexible beam curvature, respectively. A new concise expression of the bending deformation energy can be obtained by using the Lagrange identical equation. The new elastic force model is derived from the new expression of the deformation energy. The dynamic equations of the present model can precisely deal with the large deformation problem of flexible beams. Then, simulation results from three dynamic models, including the ANCF model, the high order coupling model (HOC model), and the BEAM188 model in ANSYS, are compared to prove the validity of the ANCF model proposed in this paper. And we can also find the deficiency of the HOC model from the simulation. Further study shows that the new generalized elastic force model can be simplified properly. Two simplified models are presented in this paper. The applicabilities of the simplified models are pointed out from the viewpoints of computational efficiency and accuracy. A dimensionless parameter denoted as is introduced to describe the extent to which a flexible beam pendulum undergoing free falling motion is deformed. The deformation of the flexible beam increases as increases. Considering the calculating efficiency of the dynamic model, when is small, simplified model I is chosen preferentially; when is big, simplified model Ⅱ is adopted preferentially.
Manipulation of lattice vibration by ultrafast spectroscopy
Authors: Wang Jian-Li  , Guo Liang  , Xu Xian-Fan  , Ni Zhong-Hua  , Chen Yun-Fei  ,   Jiangsu Key Laboratory for Design and Manufacture of Micro/Nano Biomedical Instruments, Southeast University, Nanjing 211189, China;,   School of Mechanical Engineering, Purdue University, West Lafayette 47907, USA
Published: December 2020

The ultrafast pump-probe spectroscopy allows us to make movies of the dynamics of the carriers and vibrational excitations on the timescales shorter than the typical scattering time. In general, the temporal evolution of the reflectivity change is comprised of the oscillatory and the non-oscillatory components. The former corresponds to the coherent lattice vibration, while the latter is related to the complex cooling process of the hot carriers. To investigate the dynamics of the hot carrier and the lattice vibration, it is necessary to decouple the two parts in the detected signal. Comparatively, the manipulation of the coherent lattice vibration is easier in spite of its super-high frequency and subatomic vibration amplitude. In this work, the behavior of the coherent lattice vibration in Bi2Te3 single crystalline film with a thickness of 100 nm is studied by using the double pump-single probe ultrafast spectroscopy. Firstly, the coherent lattice vibration with the subatomic amplitude and a frequency of about 1.856 THz is simulated by a femtosecond pump pulse, and its damped oscillation signal is detected by the reflectivity change of a probe pulse. Compared with the Raman spectrum, this vibration is confirmed to be the coherent optical phonon with A1g1 symmetric vibration mode. To manipulate this lattice vibration, a pulse shaper is then installed in the pump-beam arm to generate double pump pulses with the different separation times and the intensity ratios. The resulting reflectivity change is found to be a superposition of the pulse train: the oscillation amplitude is enhanced when the separation time is matched to the period of the oscillation; if the separation time is the odd times the half-period of the oscillation, the A1g1 vibration mode can be completely cancelled out after adjusting the intensity ratio. Finally, by maintaining the same intensity ratio, the amplitudes of the oscillation signals after the second pump pulse are measured with different separation times. The results agree well with the theoretical predictions: the amplitude of the oscillation after the second pump pulse shows a cosine function of separation time with a period of about 1080 fs, which is the twice the period of the oscillation illuminated by a single pump pulse. This work suggests that the lattice vibration can be optically manipulated, thus provides an effective way to disentangle the lifetimes of the phonons and the interactions with the excited carriers in the ultrafast energy relaxation process in semiconductor, which is extremely important for a number of interesting phenomena such as the non-thermal melting and the insulator-to-metal transition.
Large enhanced perpendicular magnetic anisotropy and thermal stability in Ta/CoFeB/MgO films with excess boron
Authors: Chang Yuan-Si  , Li Gang  , Zhang Ying  , Cai Jian-Wang  ,   State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The discovery of perpendicular magnetic anisotropy(PMA) in Ta/CoFeB/MgO film and the demonstration of high performance perpendicular magnetic tunnel junction(p-MTJ) based on this material system have accelerated the development of the next-generation high-density non-volatile memories and other spintronic devices. Currently it is urgently needed to improve the interfacial PMA and thermal stability of the CoFeB/MgO system for practical applications. So far, the perpendicularly magnetized CoFeB/MgO films and the corresponding p-MTJs have been extensively explored with the B content of the CoFeB layer mostly fixed at about 20 atomic percent. In this paper, four sets of multilayered films Ta/(Co0.5Fe0.5)1-xBx/MgO(x=0.1, 0.2, 0.3) and MgO/(Co0.5Fe0.5)0.7B0.3/Ta with different CoFeB thickness are deposited on thermally oxidized Si substrates by magnetron sputtering at room temperature, and subsequently they are annealed in high vacuum at different temperatures ranging from 573 to 623 K. The room temperature magnetic properties of the annealed samples are characterized by using vibrating sample magnetometer and superconducting quantum interference device magnetometer.
With normal B content of 20% for the CoFeB layer, the Ta/CoFeB/MgO structure annealed at 573 K shows perpendicular magnetization when the CoFeB layer is no thicker than 1.2 nm. As the B content decreases to 10%, it has been found that PMA is achieved only in the sample with a 0.8 nm CoFeB layer under the same annealing condition. The result shows that the interfacial PMA appreciably falls off when the B content is reduced by half. On the other hand, when the B content of the CoFeB layers increases from 20% to 30%, the Ta/CoFeB/MgO structure annealed at 573 K exhibits PMA with the CoFeB layer as thick as 1.4 nm and the interfacial PMA(Ks) increases from 1.710-3 Jm-2 to 1.910-3 Jm-2 together with slightly improved thermal stability. Most remarkably, the MgO/CoFeB/Ta structure with 30% B shows optimum annealing temperature of about 623 K, at which Ks reaches 2.010-3Jm-2 and PMA is realized in the samples with the CoFeB thickness up to 1.5 nm. In contrast, the same structure with 20% B is magnetically destroyed completely under this annealing temperature. The present results suggest that the CoFeB layer with excess B can effectively improve the perpendicular magnetic properties and thermal stability for the Ta/CoFeB/MgO system, and one should take into account the B content effect to optimize the spintronic devices based on the perpendicularly magnetized CoFeB/MgO system.
Research on dual energy grating based X-ray phase contrast imaging
Authors: Rong Feng  , Xie Yan-Na  , Tai Xue-Feng  , Geng Lei  ,   School of Electronics and Information Engineering, Tianjin Polytechnic University, Tianjin 300387, China;,   Tianjin Key Laboratory of Optoelectronic Detection Technology and System, Tianjin Polytechnic University, Tianjin 300387, China
Published: December 2020

There exist some problems in a grating-based X-ray differential phase contrast imaging system, such as complex imaging system, low imaging efficiency and high requirements for step precision. The phase information extraction method of imaging system has been developed into an existing two-stepping phase shift method from the original phase stepping method, which improves the imaging efficiency and reduces the imaging radiation dose and imaging time. However, the method of two-stepping phase shift still needs to move the grating, and the requirement for accuracy of the step position is also very high. According to the problems mentioned above, in this paper we propose a dual energy multi-line X-ray source and a dual energy analysis grating. The dual energy multi-line X-ray source can emit two different levels of X-ray structure light, which can replace the X-ray source and source grating. The dual energy analysis grating is composed of two different types of scintillator materials, which are in staggered distribution. One is scintillator material that can transform high energy X-ray into visible light, and the other one can convert low energy X-ray into visible light. The dual energy analysis grating can replace traditional analysis grating and the conversion screen of X-ray CCD detector. By using the dual energy multi-line X-ray source and dual energy analysis grating in grating-based X-ray differential phase contrast imaging system, a dual energy grating-based X-ray phase contrast imaging system is proposed in this paper. In addition, in this paper we show the structure and imaging principle of the imaging system. The imaging system can achieve high and low energy X-ray imaging without moving grating. Two levels of X-ray imaging are equivalent to the analysis grating displacement π phase, which is in line with the traditional two-stepping method of two image phase shift requirements. Therefore, after the normalization processing of the two kinds of energies, the phase information can be extracted by the traditional two-stepping phase shift method. In order to validate the correctnesses of the imaging principle of the proposed imaging system and extraction method of phase information, the imaging system is simulated. The simulation is performed on the assumption that an X-ray beam passes through a polymethyl methacrylate sphere as a phase specimen, and the method is adopted by using the proposed dual energy X-ray about left and right lumbar imaging to extract phase information. The simulation result shows that the imaging system can realize normal imaging, and the first-order derivative distribution of the sphere phase extracted by the dual energy X-ray method is consistent with the experimental result.
Irradiation-induced modifications in the mechanical properties of borosilicate glass
Authors: Wang Tie-Shan  , Zhang Duo-Fei  , Chen Liang  , Lü Peng  , Du Xin  , Yuan Wei  , Yang Di  ,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
Published: December 2020

Understanding the evolutions of the mechanical properties of borosilicate glasses under irradiation is crucial for evaluating their performances after long-term interaction with the irradiation environment in the disposal of high level nuclear waste.The variations of the mechanical properties of borosilicate glasses,induced by irradiation have been extensively studied.However,the mechanisms of variations in mechanical properties,induced by irradiation have not been clarified yet,especially when considering the effects of electronic and nuclear processes,respectively.To clarify this issue,a commercial borosilicate glass is investigated through an external irradiation of 5 MeV Xe ions and 1.2 MeV electrons in this paper.The nano-indentation test is used to study the changes of the hardness and modulus.The microstructure evolutions of Xe ion irradiated borosilicate glasses are characterized by Fourier transform infrared (FTIR) spectroscopy to discuss the mechanisms in the evolutions of mechanical properties.The nano-indentation results indicate that the hardness is reduced by 24%,and the modulus is lessened by 7.4% after the glass has been irradiated by Xe ions.Both the hardness and modulus variations reach their stable states when the total deposited energy is around 6.61021 keV/cm3.Although hardness and modulus are also observed to decrease by about 4.7% and 2.9%,resepectively, when the total deposited energy reaches approximately 1.41022 keV/cm3 after the glass has experienced the electron irradiation,the results still emphasize that the nuclear energy deposition is the major factor for the evolutions of the hardness and modulus of the borosilicate glass under ion irradiation.The decreases of hardness and modulus after the glass has experienced ion irradiation can be attributed to the deformation of glass network and volume expansion, which are induced by reducing the average ring size and transforming from[BO4] to[BO3] units.By considering the recovery resistance,it is found that the toughness of the borosilicate glass is significantly strengthened,and therefore the mechanical properties of the borosilicate glass are enhanced after the glass has been irradiated by Xe ions.Compared with the results after ion irradiation,the mechanical properties have negligible changes after electron irradiation.The present work is important for understanding both the irradiation effects on the hardness/modulus and the variations in the mechanical properties during the high level waste disposal.
Structure of NO dimer multilayer on Rh(111)
Authors: Wang Chen-Chao  , Wu Tai-Quan  , Wang Xin-Yan  , Jiang Ying  ,   Department of Applied Physics, China Jiliang University, Hangzhou 310018, China
Published: December 2020

Molecular self-assembly is the spontaneous organization of molecules under thermodynamic equilibrium conditions into well-defined arrangements via cooperative effects between chemical bonds and weak noncovalent interactions. Molecules undergo self-association without external instruction to form hierarchical structures. Molecular self-assembly is ubiquitous in nature and has recently emerged as a new strategy in chemical biosynthesis, polymer science and engineering. NO monomer is apt to be absorbed on the surfaces of some metals such as Ir(111), Ni(111), Pd(111), Pt(111), Rh(111) and Au(111), and the interactions of NO monomer with the metal surfaces have been extensively studied. When NO monomer is weakly adsorbed on the noble-metal surface, it cannot be reduced completely but forms a stable structure, which is named NO dimer. The first-principle technique is employed to determine the structures of NO dimer ((NO)2) molecular chains and monolayers on virtual Rh(111), as well as (NO)2 monolayer and multilayer on Rh(111). First, (NO)2 monomers are assembled into two stable molecular chains on the virtual Rh(111) surface, whose bind energies are 0.309 and 0.266 eV, respectively. The molecular chains are self-assembly systems, in which (NO)2 monomers are parallel and ordered, and the O atoms and N atoms are shown to be of (100) and (111) structures, respectively. Then, the two molecular chains are assembled into two stable monolayers (denoted as M1 and M2) on the virtual Rh(111)-(13), and the coverage is 1.00 ML. In the M1 monolayer, the angle between the NN bond of (NO)2 monomer and the substrate is in a range of 70-90, and in the M2 monolayer, the NN bond is parallel to the substrate.In the adsorption system of M2/Rh(111), (NO)2 molecules can be adsorbed on the top as well as the hcp and fcc hollow sites. When (NO)2 molecules are adsorbed on the top site, the adsorption system is best described by the electron structure Rh+0.14N0=O-0.14, and when (NO)2 molecules are absorbed on the two hollow sites, the adsorption system is described by the electron structure Rh+0.34N-0.18=O-0.16. Therefore, (NO)2 molecules are more apt to be adsorbed on the two hollow sites than on the top site. In the adsorption systems of M1+M2/Rh(111) and M1+(M1+M2)/Rh(111), (NO)2 molecules are adsorbed vertically on the two hollow sites, the NN bond is parallel to the substrate in the first monolayer, and the angle between the NN bond and the substrate is in a range of 70-90 in the second and third monolayers. The interaction between the neighbor monolayers is about 0.01 eV, and the thickness of the vacuum layer is 0.31 nm0.02 nm.
Structural and photoelectrical properties of AZO thin films improved by Ag buffer layers
Authors: Cheng Jing-Yun  , Kang Chao-Yang  , Zong Hai-Tao  , Cao Guo-Hua  , Li Ming  ,   School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo 454000, China
Published: December 2020

In order to obtain more excellent photoelectric properties of transparent conductive film, a series of high-quality AZO thin films and AZO/Ag/AZO thin films with various thickness values of Ag buffer layers are prepared on glass substrates by the radio frequency magnetron sputtering method at room temperature. The phase and surface morphologies of films are characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. The technology of Hall effect measurement and ultraviolet, visible spectrophotometer are employed to investigate the photoelectric properties of films. The electrical properties (including sheet resistance, sheet concentration and mobility) of films are also determined by using non isothermal technique to explore their thermal stability performances. The results indicate that the thickness values of Ag buffer layers have a large influence on the crystalline structures and photoelectric properties of AZO thin films. The XRD results show that with the increase of the thickness of Ag, the diffraction peak of Ag (111) is gradually enhanced, the ZnO (002) diffraction peak is gradually weakened, and the preferred orientation of ZnO (002) crystal plane is weakened. AFM test indicates that the change of Ag layer thickness has a great influence on the surface growth mode of the upper layer AZO thin film. When the Ag layer thickness is less than 5 nm, AZO thin film surface is rough and the grain size is smaller. When the Ag layer thickness is larger than 10 nm, the continuous surfaces of multilayer films begin to be shaped, directly affecte the photoelectric properties of the films. Hall effect measurement and transmittance test show that with the increase of Ag layer thickness, the transmission of AZO/Ag/AZO multilayer film gradually decreases, and also the resistance gradually decreases. When the thickness of Ag layer is 10 nm, AZO(30 nm)/Ag(10 nm)/AZO(30 nm) thin film gains a best figure of merit of 1.5910-1 -1 an average transmittance of 84.2% and a sheet resistance of 0.75 /sq. Hall effect measurement versus temperature indicates that AZO film without an Ag layer proves to be subjecte to the regular change of semiconductor resistance with temperature. When adding an Ag layer, the trend of the relationship of resistance with temperature presentes the characteristic of that metal resistance relating to temperature. Moreover, the sheet concentration of AZO with Ag layer is higher than that of AZO. The highest sheet concentration and the excellent thermal stability are obtained on AZO/Ag (10 nm)/AZO. The changes of the mobility of AZO under different temperatures turn out to be poorly stable. However, when adding an Ag layer, the better stability of AZO/Ag/AZO can be obtained. In conclusion, the photoelectric properties of films own excellent thermal stabilities with optimum thickness of Ag layer.
Study of three-dimensional nonlinear backward-wave interaction model and numerical simulation for helical traveling wave tube
Authors: Hu Yu-Lu  , Hu Quan  , Zhu Xiao-Fang  , Li Bin  , Qiu Hai-Jian  , Gao Luan-Feng  ,   National Key Laboratory of Science and Technology on Vacuum Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China,   National Key Laboratory of Science and Technology on Vacuum Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

The wide band high power traveling wave tubes (TWTs) employed in radar, communication systems, etc. are always facing the backward wave oscillation (BWO) problem. However, it takes much time and computer resource to simulate BWO by the large electromagnetic software. Thus, several parametric models are developed to solve the problem faster. Most of those models do not discuss the saturated oscillation power. In this paper, a three-dimensional (3D) nonlinear backward-wave interaction model is presented, by which the BWO phenomenon can be accurately studied in TWTs and the oscillation power is also analyzed. This model is established with the equation of 3D excitation fields combined with 3D motion equations and 3D space charge force. The oscillation frequencies and the start-oscillation lengths are calculated by one-dimensional (1D) and 3D models, respectively, and they are carefully compared in the cases of with and without the space charge force, indicating that the space charge force in 1D model is much weaker than in 3D model. The reason for that is the model of current density for space charge model in 1D model is supposed to be proportional to particle radius, but the one in 3D model is almost uniform, which is indicated by 3D beam trace distribution analysis. The BWO saturated powers and the oscillation frequencies are studied by this nonlinear 3D backward-wave interaction model. The simulation results show that the BWO saturated power increases as the beam-wave interaction length extends before many trajectories intercept the helix. While the oscillation frequencies decrease, the large saturated power supplies more energy to the beam at the very beginning in beam-wave interaction starting region. Then the BWO suppression induced by the magnetic field effect of the beam ripple is also under consideration. As the magnetic force increases, not only some cross area of interaction beam is suppressed, but also the interaction impedance of -1 space harmonic decreases. So increasing magnetic field strength can obviously reduce BWO, while the effect on forward wave interaction should be balanced. Finally, a Ka-band tube is used to validate the 1D and 3D nonlinear backward-wave interaction models. The BWO frequencies at different voltages are compared among the experimental results and the calculations by 1D and 3D models. The results from the 3D model in the test voltage range are 4.8% lower than the experimental data, while the difference from the results of the 1D model is 6.7%. The 3D model seems to be more accurate than the 1D model.
Photodissociation dynamics of organic molecules in condensed phase by femtosecond transient grating spectroscopy
Authors: Wu Hong-Lin  , Song Yun-Fei  , Wang Yang  , Yu Guo-Yang  , Yang Yan-Qiang  ,   National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Chengdu 610200, China;,   Qingdao Research Center for Advanced Photonic Technologies, Laser Institute of Shandong Academy of Sciences, Qingdao 266000, China
Published: December 2020

In condensed phase, the dissociation mechanism of molecule is different from that of isolated molecule due to the effect of interaction between molecules. How to effectively trace the reaction process and products in condensed phase is a technical problem which needs to be solved urgently. In this paper, femtosecond transient grating spectroscopy is used to investigate dissociation dynamics in condensed phase. Transient grating spectroscopy, as a coherent spectral technique, has some advantages such as high signal-noise ratio and free background, thus it can identify trace numbers of reaction products in dissociation. The investigation about model molecules such as iodomethane and nitromethane demonstrates that the transient grating technique can observe relaxation in electronic excited state and also has ability to track reactants, products, and vibration of molecule or perssad. The dissociation dynamics in condensed phase material is significant for understanding the reaction mechanism in the fields of biochemistry and detonation. Thus the femtosecond transient grating has a wide application prospect in these fields. In addition, the transient grating technique, as a non-contact diagnostic approach, can be easily adapted to high temperature and high pressure conditions, etc. Thus, the transient grating technique also has a potential value in the fields of phase transform dynamics and high pressure synthesis, etc.
Acoustic manipulation of particles by a resonant one-dimensional grating in air
Authors: Huang Xian-Yu  , Cai Fei-Yan  , Li Wen-Cheng  , Zheng Hai-Rong  , He Zhao-Jian  , Deng Ke  , Zhao He-Ping  ,   College of Physics and Mechanical and Electrical Eengineering, Jishou University, Jishou 416000, China;,   Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
Published: December 2020

It is well known that acoustic wave carries momentum and energy. An object in a sound field, which absorbs or reflects sound energy, can be subjected to the acoustic radiation force (ARF), and thus can be manipulated in the contactless and noninvasive manners. This effect has potential applications in the fields of environment monitoring, microbiology, food quality control, etc. Obtaining a tunable trapping or pushing ARF should enable the design of an incident beam profile. However, the conventional acoustic manipulation system with plane wave, standing waves or Gaussian beams, which is usually generated directly by acoustic transducer, cannot be redesigned easily, nor can the corresponding ARF be modulated efficiently. Phononic crystals, which are artificial periodic structure materials, exhibit great advantages in modulating the propagation and distribution of acoustic wave compared with conventional materials, and thus have potential applications in tunable particle manipulation. Here, we present a theoretical study of the ARFs exerted on a cylindrical polystyrene foam particle near the surface of a one-dimensional (1D) grating in air. By using the finite element method (FEM) to investigate the transmission spectra and field distribution of the 1D grating and the FEM combined with momentum-flux tensor to obtain the ARF on the particle, we find that there are two resonance modes in the 1D grating, which origin from the coupling between the diffractive waves excited from the export of periodic apertures and the Fabry-Perot resonance mode inside the apertures. In addition, it can be seen from field distribution that in the first resonant mode, the resonance wavelength is approximate to the period of grating, and the enhanced spatial confinement of acoustic wave is located at the surface of the plate besides in the aperture. In the second resonant mode, the corresponding wavelength is more than twice the period of grating, and the enhanced spatial confinement of acoustic wave is mainly located in the aperture. Moreover, due to the gradient field distribution at the surface of slits and plate in these resonance modes, particles at the surface can be under the action of tunable negative ARFs. In the first resonance mode, the particle can be trapped on the surface of grating. While in the second resonance mode, the particle can be trapped in the aperture, and the amplitude of ARF of this mode is far smaller than that of the first mode. Thus, this system in the first resonance mode may have potential applications in air acoustic manipulation, aligning, and sorting micro-particles.
Influence of hydroxyls at interfaces on motion and friction of carbon nanotube by molecular dynamics simulation
Authors: Li Rui  , Mi Jun-Xia  ,   School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Understanding how the groups at interface influence the friction of carbon nanotubes can provide reference for their applications. In this paper, we investigate the influences of hydroxyls on motion and friction of carbon nanotube on graphite substrate by molecular dynamics simulation. The simulation cases include the ideal vertical carbon nanotube on the ideal graphite substrate, the ideal vertical carbon nanotube on the graphite with hydroxyls on the top layer, the carbon nanotube and the graphite both with hydroxyls on the surface. The results show that the lateral force of carbon nanotube changes when hydroxyls are introduced into the interfaces. If hydroxyls are only on the graphite, the fluctuation of lateral force increases obviously. The reason can be attributed to the increase of atomic surface roughness. Moreover, due to the small contact area between vertical aligned carbon nanotube and substrate, the mean friction becomes raised with hydroxyl content increasing, which is different from the conclusion obtained from silicon tip sliding on graphene with hydrogen on the surface. In that case, owing to the large contact area, the mean friction of tip reaches a maximum value at hydrogen content in a range between 5 and 10% because of the competition between the increase in the number of hydrogen atoms and the weakening of the interlock due to the increase in separation of tip from substrate. Hydrogen bond and Coulomb force appear between interfaces when hydroxyls are both on carbon nanotube and on graphite, which significantly increases friction force on carbon nanotube. And slip interfaces translate rapidly from between carbon nanotube and graphite into between graphite layers. Like the case with hydroxyls only on the graphite, the sliding of carbon nanotube perpendicular to the initial velocity also occurs when carbon nanotube and graphite are both with hydroxyls. This phenomena can be explained as the fact that the introduction of hydroxyls breaks the equilibrium of the force on the carbon nanotube in the Y direction. Moreover, the random distribution of hydroxyls causes the random motion of the carbon nanotube.
Single photon transport by a quantized cavity field driven cascade-type three-level atom in a dissipative coupled cavity array
Authors: Shi Yong-Qiang  , Kong Wei-Long  , Wu Ren-Cun  , Zhang Wen-Xuan  , Tan Lei  ,   Institute of Theoretical Physics, Lanzhou University, Lanzhou 730000, China
Published: December 2020

In this paper, a new kind of quasi-boson method is used to eliminate the coordinates of the environment and redescribe the dissipative system by using an effective Hamiltonian; the localized mode and the interaction between cavities can be renormalized. Based on the quasi-boson approach, the single photon transport in one-dimensional coupled cavity array, with a driven cascade-type three-level atom embedded in one of the cavity, is investigated under the influence of the environment. The single-photon transmission and the reflection amplitudes are obtained analytically. And the additional effective potential induced by the interaction between the atom and the cavity is also derived. The effects of the controlling parameters on the reflection and transmission amplitudes are discussed with considering the dissipation. It is shown that the decay rates of the atoms and the cavity both reduce the reflection spectrum. But the dissipation of the atom has a significant influence on the reflection amplitude compared with the cavity decay under the same conditions. Due to the irreversible loss of energy, the photon number is non-conservative. Furthermore, the single-photon can be almost reflected by the three-level atom in the dissipative case when one adjusts the detuning and photon number of the quantized cavity field. The investigation will be of benefit to the realization of photon transport in a real experiment, which is also helpful for manipulating the photons in quantum information and quantum simulation.
A 100 Hz 3.31 J all-solid-state high beam quality Nd:YAG laser for space debris detecting
Authors: Fan Zhong-Wei  , Qiu Ji-Si  , Tang Xiong-Xin  , Bai Zhen-Ao  , Kang Zhi-Jun  , Ge Wen-Qi  , Wang Hao-Cheng  , Liu Hao  , Liu Yue-Liang  ,   Academy of Opto-Electronics, Chinese Academy of Sciences, Beijing 100094, China;,   National Engineering Research Center for DPSSL, Beijing 100094, China;,   Zhongkeheguang Applied Laser Technology Institute Company, Ltd. Tianjin 300304, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

With the rapid development of space technology, human activities into space are increasing, thereby producing lots of space debris. And the space debris impact is the major cause for the mechanical damage to the space crafts and the main factor affecting the service life; it even endangers the life safety of the astronauts working outside the spacecraft and pose a threat to the astronomical observation and studies. Thus, the monitoring and early warning of space debris are gradually attracting wide attention. Obviously, laser detection as a good-directivity and strong anti-jamming active detecting means has a unique advantage in terms of a round-the-clock detection. Therefore, the developing of debris-detecting laser beam source becomes the most direct and effective means for increasing the space debris detection accuracy. The laser detecting ability is restricted by the laser beam quality, the pulse energy and the repetition frequency at the same time. The beam quality could affect the ability to detect and recognize space target. The bigger the laser pulse energy, the higher the repetition frequency and the smaller the detectable debris, the stronger the detecting ability will be. A good detection effect could be achieved at 80-100 Hz laser pulse repetition frequency. A further increase of the repetition frequency will greatly increase the difficulty and cost accordingly but the improvement of the detection performance is not obvious at all. Thus, repetition frequency around 100 Hz becomes the best choice for laser space debris detection. Based on the laser diode side-pumped rod-shaped amplifier, a high-repetition-frequency and high-beam-quality of joule level Nd:YAG nanosecond laser for space debris detection is developed in this work. The laser adopts MOPA structure, mainly including single longitudinal mode, pre-amplifier unit, SBS phase-conjugate beam control unit and energy extraction unit. In the energy extraction unit, beam splitting-amplifying-combining is adopted for reducing the thermal effect on beam quality by reducing the working current of the amplifier. Under the condition of 100 Hz high repetition frequency and 10.73 J single pulse energy injected by the single longitudinal mode seed, 3.31 J output energy is gained. The output laser beam has a 4.58 ns pulse width, far field beam spot of 2.12 times the value of the diffraction limit, and 0.87% energy stability (RMS).
Temperature and pressure calculation of porous materials
Authors: Chen Jun-Xiang  , Yu Ji-Dong  , Geng Hua-Yun  , He Hong-Liang  ,   National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China
Published: December 2020

Porous material contains a large number of pores, and once the pore space collapses, it changes into a dense material with the great increase of temperature because of the energy deposition by porosity collapsing. In the process of shock compression, the temperature is extremely increased, which influences the thermodynamic state of porous material significantly. Therefore, the calculation of temperature is important for the shock compression of porous material, yet it has not been solved well in the literature. In this paper, based on the study of Grneisen general function v(v), the Debye temperature function of solid material is extended to the region of porous material, and the equivalent Debye temperature function (v) of porous material is formulated, from which the isentropic temperature function Ts(v) of porous material is obtained. Furthermore, a computation model is established, in which the isentropic work of porous is assumed to be equal to that of compact material under the same pressure at 0 K. With this model, the isentropic pressure function ps(v) of the porous material is acquired. Hence, the reference equation for calculating temperature and pressure of porous material, i.e., Ts(v) and ps(v), is completed. To demonstrate this method, the p-v and T-v curves of the Hgoniot state of porous copperare computed, and the values of porosity are m 1.13, 1.22, 1.41, 1.56 and 1.98, respectively. The calculated results are in good agreement with the experimental data. A comparison with other calculation is also made, indicating a better reliability of the present method.
Influence of nano-scaled roughness on evaporation patterns of colloidal droplets
Authors: Zhang Yong-Jian  , Ye Fang-Xia  , Dai Jun  , He Bin-Feng  , Zang Du-Yang  ,   Shaanxi Key Laboratory of Surface Engineering and Remanufacturing, College of Mechanical and Materials Engineering, Xi'an University, Xi'an 710065, China;,   Key Laboratory of Space Applied Physics and Chemistry(Ministry of Education), School of Science, Northwestern Polytechnical University, Xi'an 710129, China
Published: December 2020

Evaporation of colloidal droplets often leads to various deposited patterns which are not only interesting but also provide a very simple and useful method to fabricate functional materials. The patterns induced by the evaporation can be tuned via several factors, among which the roughness of the substrate is an important one. However, the effect of nano-scaled roughness is scarcely studied and far from being fully understood. In this work, the evaporation and pattern formation of SiO2 colloid droplets are studied on smooth substrate and nano-rough substrate, respectively. The aim of this work is to clarify how the evaporation dynamics and patterns are influenced by nano-scaled roughness. The roughness of the substrate is analyzed by using a scanning electron microscope and an atomic force microscope, the evaporation process and pattern formation are monitored via an in-situ microscope observation. The obtained deposited patterns are analyzed by using stylus profiling. It is found that the evaporation of droplets is accompanied by an obvious coffee ring effect on smooth substrate and the deposition patterns are bowl-shaped. However, uniform thickness evaporation patterns are obtained through evaporation on rough substrate, moreover, the crack density increases obviously. The analysis shows that nano-roughness is able to inhibit the circumfluence of droplets along the substrate, which greatly weakens the compensation for capillary flow, leading to particles gathering at air-droplet interface and formulating a particle layer. This prevents the coffee ring effect, and eventually results in the formation of evaporation patterns with uniform thickness.
Positron wave interference and Klein tunnel during the production of pairs in the double-well potential
Authors: Wu Guang-Zhi  , Wang Qiang  , Zhou Cang-Tao  , Fu Li-Bin  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   Graduate School, China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

In this paper, the electron-positron creation process in a double well scheme is investigated. A series of simulations is conducted by solving the quantized Dirac equation numerically. Here the split operator scheme is used to solve the Dirac equation, and the Fourier analysis is adopted to study the evolution of the wave function. The evolution starts from the state that all the negative energy eigenstates are occupied. By projecting the time dependent wave function to the positive energy eigenstates, the distributions of electrons and positrons in coordinate space and momentum space would be calculated. The total number of the electrons and positrons can be obtained by integrating the momentum distributions, and the number of the positrons in different parts of coordinate space can be achieved by integrating the space distributions. At first the electron-positron is created at the double-well edge, and positrons are emitted from the edges of double-well potential and propagate out while the electrons are bounded by the barriers. It is found that when the positron waves from different double-well edges encounter in the double-well for the first time, there occurs no positron wave interference phenomenon. The wave interference emerges after the positron no indent wave is reflected by the barriers. At the same time, because of Klein tunneling the number of positrons outside the double well begin to surpass the positrons inside the double well. After a piece of time, the amplitude of interference wave would reach its peak, and then collapses since Klein tunneling. If the double-well potential meets the standing-wave conditions, a stationary wave would be found before the interference wave reaches its peak if the distance between the double wells is short, and a stationary wave would be found after the interference wave has reached its peak if the distance between the double wells is long. And the stationary wave occurs when the positron wave is reflected by the barriers for the second time. The occurring of the stationary wave would affect the pairs producing process by making the number of pairs fluctuate. Because of Klein tunneling, the wave packages close to the double-well would disappear first, and the others can last for a longer time when the standing-wave condition is fulfilled, but all of the stationary wave packages disappear in the double well finally. And there is barely no positrons left inside the double well to the end since Klein tunneling.