bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and numerical simulation demonstration of multi-functional holographic phase plate for large depth of field single molecular localization microscopy
Authors: Li Si-Wei  , Wu Jing-Jing  , Zhang Sai-Wen  , Li Heng  , Chen Dan-Ni  , Yu Bin  , Qu Jun-Le  ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

The development of nanoscale single-molecule localization and tracking technology for multiple bio-molecules in intact cells has important significance for studying the dynamic process in life process. Since most of cells are several microns in depth, but the focal depth of traditional optical microscopes are less than one micron, the limited depth of field is the main drawback of conventional single molecular localization microscopy that prevents observation and tracking of multiple molecules in intact cells. In this paper, based on the wavefront coding technique, a new type of holographic phase plate with high efficiency is proposed and designed to extend the depth of field of single molecular localization microscopy, which combines the distorted multi-value pure-phase grating (DMVPPG) with the double-helix point spread function (DH-PSF). The DMVPPG can be used to realize multiplane imaging of several tens of layers of a sample in a single detection plane. And the DH-PSF is an engineered point spread function which encodes the lateral and axial position with high precision of a molecule in the center of its two lobes and the angle between them respectively. Using the combined holographic phase plate, the molecules in dozens layers of a whole cell can be simultaneously imaged on the same detection plane with DH-PSF. Not only can the axial resolving power be improved, but the imaging depth can also be extended without scanning. Adding such a holographic phase plate to the imaging path, the limited imaging depth problem in single-molecule-localization microscopy can be solved without sacrificing the localization accuracy. The proposed new type of holographic phase plate can also be implemented with a spatial light modulator. In the following numerical simulation experiments, the designed holographic phase plate is composed of 600×600 pixels with a pixel size of 10 μm. The distance between two adjacent focal planes is designed to be 0.5 μm. Such a holographic phase plate is placed on the Fourier transform plane of the detection light path. When an emitter is located on the focal plane, it can be imaged as two lobes without rotation in a center area of the field of view. If an emitter is -6 μm away from the focal plane, the DH-PSF appears in the upper-left area of the field of view. Simulation results demonstrate that a total of 25 sample layers can be simultaneously imaged on the single detection plane and the 12 μm detection range can be achieved, thus proving the feasibility of this method.
A method of calculating and analyzing wear rate of materials under fretting condition
Authors: Yang Xiao-Li  , Wang Bin-Rong  , Hu Hai-Yun  ,   School of Physics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Fretting phenomena exist widely in structural engineering. In recent years, it has attracted more attention from scientists and technicians. In order to study the fretting wear in depth, we establish a new method of calculating the wear rate of material in vibratory environment. Firstly, according to the characteristics of friction pair and fretting wear process in fretting friction system, the asymmetric double potential well model is proposed and the potential energy function of the model is given. The transfer of particles between the two kinds of materials during the fretting is regarded as the motion of the particles in the two potential wells which are asymmetrical, and the particle motion equation in the potential well is established. Furthermore, considering the characteristics of the randomness, time-varying and irreversibility of particle motion in fretting friction system, a theoretical model is established by using the non-equilibrium statistical theory, which is based on the particle equation motion, combined with the Langevin equation in random theory and the Foker-Planck equation in the non-equilibrium statistical theory. The probability density distribution function of particles moving from the interior of the material to the material surface at any time is obtained. A method of calculating the wear rate is proposed by integrating the probability density distribution function. Secondly, by calculating the wear rate of the friction pair which consists of metal materials Mg and Fe, we obtain the potential energy function of the asymmetric double potential well model as the different surface energies of both materials. Furthermore, the probability density distribution function of particles moving in this friction pair is calculated. Then, the change of wear rate with wear time and width of potential well is derived, and the effect of normal force on wear rate is further analyzed. The results of calculation and analysis show that the wear rate of material decreases with the decrease of the width of the potential well in the friction pair system, decreases with the increase of wear time and increases with the increase of the normal force of the load, and the surface of the relatively soft material in the friction pair system is more likely to wear off. Finally, the conclusions of the theoretical model accord with the experimental results, illustrating the applicability of the theoretical model.
Temperature dependent excitonic transition energies and linewidths of monolayer MoS2 probed by magnetic circular dichroism spectroscopy
Authors: Wu Yuan-Jun  , Shen Chao  , Tan Qing-Hai  , Zhang Jun  , Tan Ping-Heng  , Zheng Hou-Zhi  ,   State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China;,   College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 101408, China
Published: December 2020

Layered transition metal dichalcogenides (TMDs), as a new class of two-dimensional material, have received wide attention of scientific community due to their peculiar electronic and optical properties. Monolayer TMDs such as MoS2, MoSe2, WS2 and WSe2 are semiconductors with band gap energies in the visible and near-infrared region, which promises the applications in logic nano-devices, ultra-high speed photoelectric detectors and nano-lasers. Temperature has strong influences on the electronic and optical properties of semiconductors, and their applications in photonic and optoelectronic devices. Thus, the research on the temperature dependence of the energy band of monolayer TMDs is important and meaningful. Monolayer MoS2, as a prototype of TMDs, displays a weak absorption line with a strong background in original reflection or absorption spectra. The strong background has a tremendous influence on the determination of excitonic transition energy and linewidth. In this work, we adopt the reflection magnetic circular dichroism (MCD) spectroscopy in which reflection spectra and MCD spectra can be simultaneously obtained. We demonstrate that the background disturbance is eliminated in the MCD spectra, in contrast to the reflectivity spectra. And we discuss the optimization of our home-built experimental setup in detail. Through the elaborate analysis of the MCD theory, we demonstrate that the excitonic transition energy and linewidth can be directly and accurately extracted from the MCD spectrum. We perform the reflection MCD measurements on monolayer MoS2 in a temperature range of 65–300 K. The transition energies and linewidths of A and B excitons of monolayer MoS2 are extracted, respectively. Those functional parameters that describe the temperature dependence of the energy and linewidth of both excitonic transitions are evaluated and analyzed. We find that the broadening of the linewidth is related to the LO phonon scattering, and the linewidth of A exciton is clearly narrower than that of B exciton. The linewidth difference between A and B excitons might result from the stronger inter-valley coupling of B exciton. Our results indicate that MCD spectroscopy, as a modulated spectroscopy by magnetic fields, provides an easy tool to determine the features of monolayer excitons.
Thermocapillary migration characteristics of self-rewetting drop
Authors: Ye Xue-Min  , Zhang Xiang-Shan  , Li Ming-Lan  , Li Chun-Xi  ,   Key Laboratory of Condition Monitoring and Control for Power Plant Equipment, North China Electric Power University, Baoding 071003, China
Published: December 2020

The thermocapillary migration characteristics of a self-wetting drop on the non-uniformly heated, horizontal, solid substrate are investigagted by numerical simulation. Based on the lubrication theory, an evolution equation for the height of the two-dimensional drop is established. The substrate underlying the drop is subjected to a temperature gradient which induces surface tension gradient-driven drop deformation and migration. The self-rewetting fluid has non-monotonic dependence of the surface tension on temperature with a well-defined minimum, and the position of the minimum corresponding to the temperature on the substrate is called the critical point. The effect of the relationship between the critical point and the drop position on drop dynamics is analyzed.
With the temperature sensitivity coefficient of three interfaces under the same condition, the substrate is illustrated with constant wettability. The direction of drop migration will alter as the initial drop location moves to the left relative to the critical point position, resulting from the variation of the interplay among thermocapillary, gravity, and capillarity forces within the drop. But the drop always migrates toward the high interfacial tension region due to the thermocapillary force.
In the presence of substrate wettability variations, the drop migrates toward the low temperature region no matter where the drop is placed relative to the critical point. This is due to the fact that the deterioration of substrate wettability on the right side of the drop prevents the drop from migrating toward the hot region. Under the critical point being on the left or within the drop, as the initial drop location moves to the left relative to the critical point position, the enhancement of the thermocapillary force toward the left leads to increased moving speed of the left contact line and increased spreading area. When the critical point is positioned on the outer right side of the drop, the speed of the left contact line sharply decreases at t=6103, caused by the suddenly deteriorating substrate wettability.
Hence, it is effective to manipulate the self-wetting drop movement by regulating the relationship between the critical point and the initial drop location. To inhibit the migration of the drop toward the cold region, the drop should be placed on the right side of the critical point.
Simultaneous measurement of magnetic field and temperature based on photonic crystal fiber with eliminating cross-sensitivity
Authors: Wu Qian  , Zhang Zhu-Yu  , Guo Xiao-Chen  , Shi Wei-Hua  ,   College of Electronic and Optical Engineering, College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
Published: December 2020

Measurement of magnetic field is very important in many fields, such as industrial manufacture, marine environmental monitoring, medical testing, etc. However, there is a cross sensitivity between the measurement of magnetic field and the fluctuation temperature in the environment. So how to accurately measure the magnetic field and the temperature simultaneously by eliminating the cross-sensitivity has been an urgent problem. In recent years, photonic crystal fiber (PCF) sensor has been widely used due to its particular advantages, such as high sensitivity, small size and its flexibility of filling various sensitive media into the air hole. So the PCF provides a new idea for designing the high-sensitivity magnetic sensor. In this paper, a new PCF sensing structure based on the mixed effects of directional resonance coupling and surface plasmon resonance (SPR) is proposed. In the cladding of the PCF, one air hole infiltrated with the magnetic fluid (MF) forms a defect core and is used as a directional coupling channel. When the wave vector matching condition is satisfied in the directional coupling channel, the power is transferred from the fiber core region to the clad defect core at a particular wavelength, and a loss peak is generated in the transmission spectrum. The MF has its unique magneto-optical effect. This is because its refractive index changes with external magnetic field. So the loss peak can be shifted with the magnetic field at a fixed temperature. Another air hole coated with a gold nano film and infiltrated with the methylbenzene is used as the SPR channel. So plasmon modes are excited, and the resonance peak occurs when the real part of the effective index of the core mode is equal to that of the SPR mode at a particular wavelength. The resonance peak can also be shifted with the index of the methylbenzene at changed temperature. The simulation and numerical analysis of the magnetic field and temperature sensing characteristics of the structure are carried out, and the structure parameters of PCF are optimized by COMSOL Multiphysics through using the finite element method under the boundary condition of perfectly matched layer. In a magnetic field range of 90-270 Oe and in a temperature range of 25-60 ℃, the highest magnetic field sensitivity and temperature sensitivity are respectively 1.16 nm/Oe and -9.07 nm/℃, each with a good linearity in the sensing structure. To eliminate the cross sensitivity between the temperature and magnetic field, a sensitivity coefficient matrix is established. As a result, the highly sensitive double-parameter detection of magnetic field and temperature is realized. Moreover, this sensing structure can be used in an extensive range, which has a certain potential value and practical significance.
Quantum coherence measurement with femtosecond time-resolve two-dimensional electronic spectroscopy: principles, applications and outlook
Authors: Weng Yu-Xiang  , Wang Zhuan  , Chen Hai-Long  , Leng Xuan  , Zhu Rui-Dan  ,   Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Two-dimensional electronic spectroscopy is a kind of nonlinear optical spectroscopy with both high time resolution and high frequency resolution. It can be used to observe the complex dynamics of a condensed molecular system. Meanwhile it is a very powerful tool to study the coherence between the electronic states or electronic and vibration states. In 2007, Flemming's group reported the long-lived quantum coherence observed in the energy transfer process in the light-harvesting antenna protein complex Fenna-Matthews-Olson at 77 K by means of two-dimensional electronic spectroscopy. Though it has been proved not to arise from the pure electronic coherence later, this discovery has greatly stimulated the exploration of the coherent energy transfer pathways possibly existing in the natural and artificial photosynthetic systems, and this is still a very active area nowadays. Here in this paper we briefly review the principle and set-up of the two-dimensional electronic spectroscopy, and also some of its applications in investigating coherent energy transfer in the photosynthetic and artificial systems, aiming to bring this novel spectroscopic tool into a wider application.
Quantum phase gate on a single superconducting Λ-type three-level and two superconducting resonators
Authors: Liu Chao  , Wu Yun-Wen  ,   College of Physics, Mechanical and Electrical Engineering, Jishou University, Jishou 416000, China
Published: December 2020

Quantum phase gate is a necessary quantum component for quantum coding and quantum computing. Compared with the traditional gate circuit, quantum phase gate has the characteristics of unitarity and reversibility. Therefore, we construct a model of mutual coupling between a single Λ -type three-level atom and two superconducting resonators, which is connected by a capacitor. By separately controlling the disconnection time and connection time of the two superconducting resonators in the model as well as by controlling the magnetic flux of the superconducting quantum interference device (SQUID) to make a certain transition energy level of the Λ -type three-level atom equal the relevant resonance energy level, the interaction between the two levels can be achieved and the system can be manipulated. Afterwards, we propose four control schemes for implementing the controlled-Z gate through a three-step operation, and two operation schemes for implementing swap gate through a four-step operation. At the same time, the numerical simulations of fidelity are implemented for the first operation scheme for controlling the Z-gate. The results of fidelity discussion show that the fidelity of this scheme is 96.67% through the running time of 20.83 ns, thus it proves that this scheme is theoretically feasible. The increase in the three attenuation parameters, i.e., attenuation rate, relaxation rate, and phase shift ratio, will reduce the fidelity of the system, while the increase in coupling strength will cut down the time of system operation, thus reducing the influence of attenuation parameters and improving the system fidelity.In this paper we present a quantum phase gate scheme in which two superconducting resonators and a Λ -type three-level atom are coupled with two capacitors. Since the experimental setup is simplified, it is important to reduce the coherence between devices. In addition, the solution has no restriction on the strength of the classic pulse principally, through which the system operates faster and the fidelity of the phase gate is improved effectively.
Propagation characteristics of pseudo-Scholte waves at the interface between finite-thickness fluid layer and quasi-saturated porous half-space
Authors: Qiu Hao-Miao  , Xia Tang-Dai  , He Shao-Heng  , Chen Wei-Yun  ,   Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China;,   MOE Key Laboratory of Soft Soils and Geo-environmental Engineering, Zhejiang University, Hangzhou 310058, China;,   Institute of Geotechnical Engineering, Nanjing Tech University, Nanjing 210009, China
Published: December 2020

The propagation of interface waves at the interface between a fluid-saturated porous medium and a fluid has been extensively investigated in the last three decades due to its various and wide applications in several fields including earthquake engineering and materials testing. Although the sea floor is usually covered with porous marine sediment, the previous interface wave theories are rarely used for submarine acoustic problems for the following reasons. 1) In addition to hard porous media, unconsolidated soft porous media exist widely in the seabed, which are seldom considered in previous studies. 2) The depth of seawater is limited, and in many cases it cannot be regarded as a half-space. 3) The fluid-saturated porous medium model cannot describe the effect of a small number of bubbles caused by decomposition of organic matter in the sediment. Hence, the present paper focuses on the low-frequency pseudo-Scholte waves at the interface between an overlying fluid layer of finite thickness and a quasi-saturated porous half-space. The overlying fluid is assumed to be ideal compressible water and the quasi-saturated porous media are assumed to be sandstone and unconsolidated sediment and modeled by Biot theory. A fluid equivalent model is used to analyze the effects of the bubbles in the pores. Based on the boundary conditions, the closed-form dispersion equations of far-field interface waves are derived by using classical potential function method. The velocity and attenuation of pseudo-Scholte wave are determined by Newton iteration in a reasonable rooting interval. The analytical expressions of the displacement field and fluid pressure distribution caused by pseudo-Scholte waves are also derived. Then, based on the derived theoretical formulation, the numerical examples of calculations are presented. Our calculation results show that the stiffness of porous medium significantly affects the mode, phase velocity, displacement and fluid pressure distribution of interface waves; the phase velocity of the pseudo-Scholte wave in the finite-thickness fluid/fluid-saturated porous half-space is related to the ratio of the wavelength to the thickness of the fluid layer; the phase velocity of the shear wave is insensitive to a small number of bubbles dissolved in the pores, but the existence of bubbles has a significant influence on the phase velocity of the compressional wave and the pseudo-Scholte wave. Furthermore, the existence of bubbles can significantly affect the distribution of the pore pressure.
40Ca+ optical frequency standards with high accuracy
Authors: Guan Hua  , Huang Yao  , Li Cheng-Bin  , Gao Ke-Lin  ,   State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China;,   Key Laboratory of Atomic Frequency Standards, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China;,   Center for Cold Atom Physics, Chinese Academy of Sciences, Wuhan 430071, China
Published: December 2020

With the development of the technologies in the lasers and the manipulation of cold atoms, the high precision optical frequency standards have been extensively studied and built in recent years. These high precision frequency standards may play an important role in establishing the new time reference, promoting the researches in the fundamental fields, fulfilling the national strategic needs, etc. In this paper, the research progress of high accuracy 40Ca+ optical frequency standard in Wuhan Institute of Physics and Mathematics (WIPM) of Chinese Academy of Sciences is presented. A new ULE super cavity is adopted for stabilizing the frequency of 729 nm clock laser, and the stability of the laser is improved now to 2×10-15 in a duration of 1-100 s. By controlling the external fields and other environmental influences, especially suppressing the micromotion effects of the trapped ion, the uncertainty of the optical frequency standard based on a single 40Ca+ is reduced to 5.5×10-17. The stability of 5×10-17 in a duration of 20000 s is achieved via the comparison between two 40Ca+ optical frequency standards. Several precision measurement experiments are performed, based on the high precision 40Ca+ optical frequency standard. The absolute value of the clock transition frequency of the 40Ca+ optical frequency standard is measured second time, using an optical comb referenced to a hydrogen maser which is calibrated via GPS referenced to UTC (NIM)) using the precise point positioning data-processing technique. The frequency offset of UTC (NIM) relative to the SI second can be evaluated through BIPM circular-T reports, and the newly measured value of m 4s 2S1/2-3m d 2D5/2 transition is adopted by CCTF-20, thus updating the recommended value of 40Ca+ optical clock transition. Besides the absolute frequency measurement, the magic wavelengths of 40Ca+ optical clock transition are measured precisely, and this work is a milestone for establishing all-optical trapped-ion clocks. The lifetime of the m 3 d 2D3/2 and m 3 d 2D5/2 state in 40Ca+ are precisely measured, too. The work mentioned above contributes to the researches of the precision measurements based on cold atomic systems.
Physical characteristics of ion extraction simulation system based on gas discharge plasma jet
Authors: Chen Jian  , Liu Zhi-Qiang  , Guo Heng  , Li He-Ping  , Jiang Dong-Jun  , Zhou Ming-Sheng  ,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China;,   College of Mechanical Engineering, North China University of Science and Technology, Tangshan 063210, China
Published: December 2020

In an atomic vapor laser isotope separation process, the required isotope atoms are ionized selectively by a pulsed laser with a specific narrow line width, and then the produced isotope ions are extracted to the collected plates under an externally applied electromagnetic field. In the whole ion separation process, the ion extraction sub-process is one of the most important physical processes. Previous studies have shown that the key parameters of the laser-induced plasma, e.g., the initial electron number density and temperature, have a significant influence on the ion extraction features. In an actual isotope separation process, a specifically designed laser is necessary to produce the required isotope ions, which, however, leads the whole facility to have a very complicated structure, high capital cost, and especially, very narrow window of the key plasma parameters. These will, to some extent, limit a more in-depth investigation of the influences of the key plasma parameters on the ion extraction characteristics.
In this paper, an ion extraction platform (ion extraction simulation experimental platform-2015, IEX-2015) is developed on the basis of a gas discharge plasma jet driven by a kilo-hertz high-voltage power supply. And an argon plasma collisional-radiative model is established to measure the electron temperature and number density in the plasma jet region. The experimental results show that the power input and driving frequency of the power supply and the argon mass flow rate can all affect the electron temperature and electron number density. The measured variation ranges of the electron number density and temperature are 109-1011 cm-3 and 1.7-2.8 eV, respectively, under a chamber pressure on the order of 10-2 Pa, which are close to the parameter levels in the actual ion extraction process. Subsequently, the preliminary ion extraction experiments are conducted under different extraction conditions including different externally applied voltages, different electrode distances and different plasma densities. The experimental results are also qualitatively consistent with those in an actual ion extraction process. The preceding preliminary experimental results show that it is feasible to conduct the ion extraction simulation study on IEX-2015. This is very helpful for systematically studying the ion extraction characteristics under different operating conditions in our future research.
Theoretical study on magnetoelectric effect in multiferroic tetragonal BiMnO3
Authors: Yuan Ye  , Tian Bo-Bo  , Duan Chun-Gang  ,   Key Laboratory of Polar Materials and Devices, Ministry of Education, School of Information Science Technology, East China Normal University, Shanghai 200241, China
Published: December 2020

Perovskite BiMnO3 with ferroelectric and ferromagnetic ordering simultaneously, as a kind of multiferroics, can be expected to have the coupling between the magnetic and dielectric properties as well as their control by the application of electric fields. This advantage can make BiMnO3 a good candidate for an artificial synapse material. Under the framework of the density functional theory, in this paper we adopt the generalized gradient approximation (GGA+U) plane wave pseudopotential method to calculate the ferroelectricity double-well potential curves and magnetic moments of Mn of tetragonal BiMnO3, with 0.18% and 4% strain exerted in its x-y plane. The results show that the magnetic moment of Mn monotonically increases from paraelectric state to ferroelectric state. It means that the ferromagnetic property of tetragonal BiMnO3 can be controlled by the intensity of polarization. The greater the stress, the greater the range of magnetic moment is. This would imply that the multiferroic artificial synapse device based on BiMnO3 can bring another degree of freedom into designing the complex cognitive systems of artificial intelligence in the future.
All-optical imaging and tracking technology for rectilinear motion targets through scattering media
Authors: Jia Hui  , Luo Xiu-Juan  , Zhang Yu  , Lan Fu-Yang  , Liu Hui  , Chen Ming-Lai  ,   Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Light scattering is a main factor that restricts optical transmission and deteriorates optical imaging performance. All-optical imaging for moving targets through complex scattering media is one of the most challenging techniques. In this paper, a method for real-time tracking of moving targets through scattering medium is presented by utilizing optical memory-effect and autocorrelation of speckle difference. In the experiment on imaging through a scattering medium, an object is hidden at a distance u behind a highly scattering medium. The object is illuminated by a spatially incoherent pseudothermal light source. The light is diffused through the scattering medium. Camera placed at a distance u0 on the other side of the medium records the pattern of the scattered light. According to the theory of optical memory-effect, the process of scattering imaging is a convolution process of point spread function (PSF) and object. In the procedure of object moving, the scattered signals from two frames are captured. The background noise could be removed by subtracting the two captured image. Then, the autocorrelation operation calculates the speckle difference, and hidden targets can be effectively reconstructed with the phase retrieval algorithm. The experiment demonstrates the imaging of targets with different speeds. The results have shown that the faster the speed, the worse the imaging quality is. High-speed moving objects can be imaged by using a high frame rate camera to reduce the exposure time or by disambiguating the speckle pattern. In subsequent experiments, the distance of the target movement is calculated with the magnification of the system. The collected two frames of speckle must be within the same memory effect angle. Only in this way can the calculation accuracy of the motion distance be guaranteed. With the moving of the target, the cross-correlation information of the target appears at different positions of the speckle difference autocorrelation map. Finally, according to the cross-correlation of the target at different locations, the real-time tracking of the moving target can be realized. Due to the Gaussian distribution of the laser beam, the cross-correlation intensity of the speckle difference autocorrelation map decreases with the object moving further. Therefore the target moving range is limited by the laser beam diameter, intensity distribution and camera field angle. It is verified experimentally that the imaging and tracking of moving targets which are hidden behind the ground glass can be achieved successfully by using this method. This kind of imaging and real-time tracking technology for targets moving through the scattering medium has important potential applications in biomedicine and other fields.
Influence of interface structure on nanoindentation behavior of Cu/Ni multilayer film: Atomic scale simulation
Authors: Li Rui  , Liu Teng  , Chen Xiang  , Chen Si-Cong  , Fu Yi-Hong  , Liu Lin  ,   School of Automation, Chongqing University of Posts and Telecommunications, Chongqing 400065, China;,   School of Advanced Manufacturing Engineering, Chongqing University of Posts and Telecommunications, Chongqing 400065, China;,   Chongqing Pump Industry Co., Ltd, Chongqing 400030, China
Published: December 2020

The mechanical properties of metal multilayers change significantly when the modulation period decreases to a nanoscale. As is well known, the lattice misfit between Ni and Cu is~2.7%, it means that the coherent and semi-coherent interfaces can form between the Ni and Cu atomic layer. Hetero-twin interface Cu/Ni multilayer film with a modulation period of several nanometers and grown along the[111] direction is realized experimentally, and the mechanical properties change significantly due to the effect of interfaces. In this study, molecular dynamics simulations on Cu/Ni multilayers with coherent, coherent twin, semi-coherent, and semi-coherent twin interfaces under nanoindentation are carried out to study the deformation evolutions of different interfaces and the interactions between dislocation and interfaces. Furthermore, the influence of Cu/Ni interface on the mechanical property is investigated. The simulation results show that the different interface structures exhibit different strengthening and/or softening mechanisms at different indentation depths. The hardness values of the Cu/Ni multilayer films with four different interface structures are different, and the hardness of the coherent interface is larger than the semi-coherent interface's. The hardness values of the four interface structures reside between the pure Cu and pure Ni. For the coherent twin interface, with the increase of the modulation ratio, the strengthening effect of the twin interface is enhanced. The softening effect for the coherent interface is mainly attributed to the generation of parallel dislocations and their proliferation. While for the semi-coherent interface, the mismatched networks are formed at the Cu/Ni interfaces, the softening effect on the movable dislocation is mainly the repulsion of the mismatched network, while the strengthening effect on the movable dislocation is the hindrance of the mismatched dislocation network. The strengthening of the coherent twin interface is attributed to the limited effect of twin interface on the movable dislocation within the monolayer. Unlike the coherent twin interface, the strengthening effect of the semi-coherent twin interface is mainly due to the mutual repulsion between the arched dislocation, which is generated within the twin interface, and the mismatched network. Furthermore, the pinning effect of misfit dislocation network will impede the migration of twin interfaces and will also enhance the mechanical property of Cu/Ni multilayer film.
Characteristic parameters of optical wave and short-term beam spreading in oceanic turbulence
Authors: Wu Tong  , Ji Xiao-Ling  , Li Xiao-Qing  , Wang Huan  , Deng Yu  , Ding Zhou-Lin  ,   College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610068, China
Published: December 2020

In 2000, Nikishov et al. presented an analytical model for the power spectrum of oceanic turbulence, in which the stable stratification of seawater is assumed, i.e., the eddy diffusivity of temperature is equal to that of salinity, and the eddy diffusivity ratio is equal to unity. Until now, all previous studies on the light propagation through oceanic turbulence were based on the Nikishov's power spectrum model. However, the eddy diffusivity of temperature and eddy diffusivity of salt are different from each other in most of underwater environments. Very recently, Elamassie et al. established a more reasonable power spectrum model of underwater turbulent fluctuations as an explicit function of eddy diffusivity ratio. The characteristic parameters such as the spatial coherence length of optical wave in turbulent medium play an important role in characterizing the strength of turbulence, the phase correction techniques in light propagation, etc. In the present paper, based on the Elamassie's power spectrum model of oceanic turbulence, the analytical formulae of the wave structure function, the spatial coherence length of optical wave and the Fried parameter in oceanic turbulence are derived, and the correctness of each of these formulae is verified. It is shown numerically that the results obtained by using the Elamassie's power spectrum model are quite different from those obtained by using the Nikishov's power spectrum model. If the Nikishov's power spectrum model is adopted, the strength of turbulence is underestimated when oceanic turbulence is dominated by the temperature fluctuations, while the strength of turbulence is overestimated when oceanic turbulence is dominated by the salinity fluctuations. If the Elamassie's power spectrum model is adopted, it is shown that the Kolmogorov five-thirds power law of the wave structure function is also valid for oceanic turbulence in the inertial range, and 2.1 times the spatial coherence length of optical wave is the Fried parameter, which are in agreement with those in atmospheric turbulence. In addition, based on the Elamassie's power spectrum model, the semi-analytical formula of the short-term beam spreading of Gaussian beams is derived in this paper, and its correctness is also verified. It is shown that the difference in short-term beam spreading is very large, whether the stable stratification of seawater is assumed or not. The results obtained in this paper are very useful for applications in optical communication, imaging and sensing systems involving turbulent underwater channels.
Measurement of absolute gravity based on cold atom gravimeter at large tilt angle
Authors: Wu Bin  , Cheng Bing  , Fu Zhi-Jie  , Zhu Dong  , Zhou Yin  , Weng Kan-Xing  , Wang Xiao-Long  , Lin Qiang  ,   Center for Optics and Optoelectronics Research, College of Science, Zhejiang University of Technology, Hangzhou 310023, China;,   Institute of Optics, Department of Physics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

The tilt angle of a cold atom gravimeter (CAG) could have a significant influence on the measurement of absolute gravity. The measurement, manipulation, and compensation of the tilt for CAG need to be conducted in order to obtain a high-accuracy absolute gravity measurement. In this paper, firstly, the influences of tilt on absolute gravity measurement under four different conditions are analyzed theoretically by taking into account the position of vacuum system relative to Raman retro-reflection mirror. Then, the experimental investigation is carried out and it is found that the measured results agree well with the theoretical prediction curves. According to the analysis above, we design a scheme for absolute gravity measurement based on two inclinometers, mainly to solve the problem of long-term tilt drift of CAG especially in harsh measurement environment. In this scheme, a high-resolution inclinometer is used to record the tilt angle of Raman retro-reflection mirror, which is fixed on a passive vibration isolation platform. Besides, another inclinometer is utilized to monitor the tilt angle of vacuum chamber of the CAG. By doing so, the vibration noise can be suppressed and the tilt data can be measured with a high precision. Finally, the experimental verification of this proposal is carried out based on our homemade compact cold atom gravimeter, and the high accuracy absolute gravity measurement is realized in a complex workshop environment. Since the vibration noise of Raman mirror is improved by using the vibration isolation platform, the sensitivity of our CAG can reach 319 μGal √Hz. Besides, we measure the long-term changes of gravity with time and find that the experimental results are consistent with the curves calculated by theoretical tidal model. Moreover, due to the precise measurement and compensation for the tilt drift, the accuracy of our CAG is estimated at 12.3 μGal. In order to evaluate this system accuracy, a comparison between our CAG and the FG5 at the same measured site is made. The absolute gravity values determined by both gravimeters coincide with each other. In this paper, we provide a feasible scheme for measuring the absolute gravity in the complex environment. The experimental demonstration of this measurement scheme is performed thereby acquiring some valuable reference data for the practical use of CAG.
Numerical investigations of interactions between shock waves and triangular cylinders in magnetic field
Authors: Dong Guo-Dan  , Zhang Huan-Hao  , Lin Zhen-Ya  , Qin Jian-Hua  , Chen Zhi-Hua  , Guo Ze-Qing  , Sha Sha  ,   Key Laboratory of Transient Physics, Nanjing University of Science and Technology, Nanjing 210094, China;,   Beijing Institute of Electronic System Engineering, Beijing 100854, China
Published: December 2020

Magnetohydrodynamic (MHD) equations are solved by using the CTU+CT (corner transport upwind + constrained transport) algorithm which guarantees the divergence-free constraint on the magnetic field. The interactions between shock wave and heavy or light triangular cylinder are investigated in detail in the cases with and without magnetic field. In the cases of hydrodynamic (B=0 T) and MHD (B=0.01 T), the numerical results indicate that heavy and light triangular cylinders have quite different wave patterns and jet structures after being impacted by a planar incident shock wave. Specifically, a regular refraction and downstream R22 jet are formed in the heavy case, whereas an irregular refraction and upstream air jet are generated in the light case. In the hydrodynamic case, the Richtmyer-Meshkov (R-M) instability and Kelvin-Helmholtz (K-H) instability are induced by the incident shock wave. Hereafter, both heavy and light density interfaces begin to roll up with a series of interfacial vortex sequences. In addition, a main vortex ring is formed in the heavy case, while a vortex dipole passing through the downstream interface is generated in the light case. In the MHD case, both heavy and light density interfaces remain smooth and interfacial vortex sequences vanish. Furthermore, the main vortex ring formed in the heavy cases and the vortex dipole generated in the light cases disappear. Moreover, in the presence of a magnetic field, a detailed investigation demonstrates that Lorentz forces give rise to the transport of baroclinic vorticities to the Alfvn waves. As a consequence, the deposition of interfacial vorticities decreases and the rolling-up of interfaces is suppressed. In the end, the vorticities are transformed into two vortex sheets travelling away from the density interfaces, and the R-M instability and K-H instability are well controlled. The quantitative investigations reveal that for both heavy and light triangular cylinders, magnetic field can accelerate the upstream interface and decelerate the downstream interface, especially for the light triangular cylinder.
Research progress of multiferroicity in Bi-layered oxide single-crystalline thin films
Authors: Zhai Xiao-Fang  , Yun Yu  , Meng De-Chao  , Cui Zhang-Zhang  , Huang Hao-Liang  , Wang Jian-Lin  , Lu Ya-Lin  ,   Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China;,   National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Room temperature multiferroics with a single phase is very rare, and magnetic elements doped Bi-layered Aurivillius oxides are an important family of room temperature single phase multiferroics. However, due to the lack of single crystalline samples, the multiferroic related researches of these materials are mostly based on polycrystalline bulk or thin film samples. And the multiferroic characterizations are performed mostly by using the bulk type of samples. Therefore the studies of the origin and mechanism of the multiferroicity of these materials are extremely difficult. Recently, multiple magnetic elements doped singlecrystalline thin films have been successfully prepared, which makes it possible to study the physics mechanism of the Bi-layered Aurivillius oxides of multiferroicity. The current study shows that most of the single-crystalline thin films exhibit in-plane orientated spontaneous ferroelectric polarization and very weak room temperature magnetism. Moreover, at low temperatures the single-crystalline films exhibit a second magnetic transition. The resonant inelastic X-ray scattering experiments indicate that the doped structure exhibits a changed crystal field split, which may enhance the weak ferromagnetism through Dzyaloshinskii-Moriya interaction. On the other hand, the polarized neutron reflectivity experiments reveal that the single-crystalline thin film possesses much weaker room temperature magnetism than the bulk sample, which indicates that the origin of the magnetism and the magnetoelectric coupling in the single-crystalline samples are different from those in the polycrystalline samples. The current study of the multiferroicity in the single-crystalline Bi-layered Aurivillius thin film opens the road to designing better multiferroic systems of the Aurivillius materials.
Noise transfer characteristics of Rydberg electromagnetically induced transparency
Authors: Jia Yue1\2  , Chen Xiao-Han1\2  , Zhang Hao1\2  , Zhang Lin-Jie1\2  , Xiao Lian-Tuan1\2  , Jia Suo-Tang1\2  ,   Institute of Laser Spectroscopy, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

The transfer mechanism from the amplitude noise of the coupling light to the phase noise of the probe light in a Rydberg electromagnetic induced transparency effect derived from a ladder-type system including 6S1/2↔6P3/2↔62D5/2 of Cs atoms is demonstrated by using Mach-Zehnder interferometer and balanced homodyne detection technology. In our experiments, the transmission signal of 852 nm probe light is measured by scanning the coupling light frequency nearby the transition from 6P3/2 to 62D5/2 Rydberg state, while the frequency of the probe light is locked at the resonance transition of the 6S1/2↔6P3/2. The relative phase stability of two arms of Mach-Zehnder interferometer, which is constructed with the first order diffraction light of probe light through an acoustic-optic modulator, is accomplished by the controlled piezoelectric ceramic with the PID feedback loop. The interferences between the probe light and the reference light of Mach-Zehnder interferometer under the different relative phases are observed. The interference spectrum of probe light is in good agreement with the theoretical simulation result of the ladder-type three-level system. Therefore, we study the transfer characteristics from the frequency noise of coupling light to the phase noise of probe light when coupling light frequency resonance happens at the transition 6P3/2↔62D5/2. We find the significant suppression of the phase noise of probe light at the higher frequency noise. Moreover, we observe the characteristics of the phase noise of the probe light varying with the power of the coupling light under the different detuning degrees of coupling light. In the red detuning side, the transferred phase noise of probe light decreases with the increase of coupling light power, which is different significantly from the scenario under the blue detuning condition. The ions produced in the ionization process of Rydberg atoms will form the local electric field that would cause the energy level of Rydberg states to shift. The investigation of the noise transfer between the coupling light and probe light in the Rydberg electromagnetically induced transparency effect is important for understanding the coherence mechanism of ladder-type system and the some potential applications, such as in Rydberg-atom-based electric field metrology.