bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental optimal design on BaY2ZnO5: Tm3+/Yb3+ phosphor and its up-conversion luminescence property
Authors: Sun Jia-Shi  , Li Xiang-Ping  , Wu Jin-Lei  , Li Shu-Wei  , Shi Lin-Lin  , Xu Sai  , Zhang Jin-Su  , Cheng Li-Hong  , Chen Bao-Jiu  ,   Department of Physics, Dalian Maritime University, Dalian 116026, China
Published: December 2020

To obtain a maximal blue up-conversion luminescence of Tm3+/Yb3+ co-doped BaY2ZnO5 phosphors, orthogonal experimental design combined with quadratic general rotary unitized design method is employed to optimize the Tm3+ and Yb3+ ions doping concentration. Two sets of BaY2ZnO5:Tm3+/Yb3+ phosphors are synthesized by the traditional high temperature solid reaction method. The doping concentration ranges of Tm3+ and Yb3+ are first narrowed by orthogonal experimental design, and then quadratic general rotary unitized design is performed and one regression equation is established based on the experimental results from the latter design. The theoretical maximum value of the blue up-conversion luminescence intensity and the optimal Tm3+ and Yb3+ doping concentrations are obtained by genetic algorithm. The optimal sample is synthesized and its crystal structure and up-conversion luminescence properties are investigated. It is found that the blue up-conversion luminescence originates from three photon processes under 980 nm excitation. Temperature dependent up-conversion luminescence spectra of the optimal sample show that the blue up-conversion luminescence intensity declines with increasing temperature, implying the occurrence of thermal quenching of up-conversion luminescence. The calculated excitation energy is about 0.602 eV.
Defect induced asymmetric soliton transmission in the nonlinear circuit
Authors: Liu Hao-Hua  , Wang Shao-Hua  , Li Bo-Bo  , Li Hua-Lin  ,   Institute of Acoustics, Key laboratory of Modern Acoustics of Ministry of Education, Nanjing University, Nanjing 210093, China
Published: December 2020

Electrical diode, the first device to rectify the current flux, has significantly revolutionized fundamental science and advanced technology in various aspects of our routine life. Motivated by the one-way rectification effect, considerable effort has been dedicated to the study of the unidirectional transmission in other physical systems for the potential applications, such as the acoustic diode, thermal diode, etc. The nonlinear LC circuit, which has unique advantages in the measurement of energy with which the voltage and current can be achieved by digital oscilloscope conveniently, provides a simple and effective way of studying the nonlinear wave propagation in a dispersive medium. In this paper, we design a defective LC nonlinear circuit deliberately to realize asymmetric transmission of energy, and the energy carrier is nonlinear wave which is so-called soliton, instead of the linear wave in the pass band. The defect-induced localized wave is a kind of intrinsic bound-state wave mode that is evanescent away from the defect site but vibrates around the site with an intrinsic frequency fr. In the LC circuit, when the defect is close to the driver, with the frequency of driven signal in the forbidden band of system approaching to the intrinsic resonance frequency fr of the defect, the resonance induced by the defect enables the circuit to turn on, which is relevant to but somewhat different from what was uncovered by Leon et al. about the intrinsic instability of evanescent waves stirred up directly by a boundary drive. On the other hand, the system acts like an insulator, for the defect is far away from the drive. The defect changes the homogeneity of the line, which allows the soliton to be released in one direction by the local resonance, with the driver being at a lower amplitude. As a result, the introducing of defects significantly improves conversion efficiency from the driver energy into the soliton. To further understand this phenomenon in the defective LC nonlinear circuit, we numerically investigate the relationship among transmission energy, defect coefficient and driver amplitude. Finally, the combined defects are also considered to further adjust the LC nonlinear circuit.
High sensitive scheme for methane remote sensor based on tunable diode laser absorption spectroscopy
Authors: Ding Wu-Wen  , Sun Li-Qun  , Yi Lu-Ying  ,   State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, Tsinghua University, Beijing 100084, China
Published: December 2020

Methane is an important raw material for various petrochemicals in industrial fields and as also a clean fuel in daily life. However, as an inflammable and explosive material, methane leak can lead to disastrous consequences such as fire and explosion. Furthermore, as a kind of greenhouse gas, methane has stronger influence on global warming than carbon dioxide. In this paper, we present a new high sensitive scheme for methane remote sensing, which can facilitate detection and location of methane leakage. And the 2v3 band (near 1653.7 nm) of methane is chosen as the target transition which is free from the absorption of the other molecule in atmosphere. A tunable distributed-feedback diode laser is adapted to scan across the target transition. A Fresnel lens with a diameter of 150 mm is employed to collect the ambient backscattering light from natural features such as the buildings. The first harmonic signal is used to normalize the second harmonic signal to remove the influence introduced by the unknown reflectance factor of the actual target, therefore no retro-reflector is needed. Traditional tunable diode laser absorption spectroscopy (TDLAS) method has difficulty in locating the second harmonic signal peak position in low concentration conditions because of low signal-noise-ratio (SNR). To improve the SNR especially in low concentration environment, a scheme named baseline-offset TDLAS is presented in the paper, in which a reference cell filled with standard methane sample is inserted into the measuring optical path. The reference cell can also be used to calibrate the sensor. Furthermore, the reference cell can be used to lock the central frequency of the diode laser to the absorption peak position to monitor concentration fluctuation continuously. In the peak-locking mode, the sensor demodulates the third harmonic signal as error signal to control the injection current of the laser source with PID control. Moreover, one advantage of peak-locking mode is that the measurement frequency is about two orders of magnitude higher than the traditional TDLAS method. With baseline-offset TDLAS, the remote sensor described in this paper obtains SNRs as high as 19 and 16 at a stand-off distance of 10 m and 20 m, respectively. With such a high SNR, there is no necessity for complex algorithm in absorption peak position location. By defining the standard deviation of the measuring concentration as the detection limit, experimental results show that the proposed methane remote sensor has detection limits of 5 ppm m at a distance of 10 m and 16 ppmm for 20 m, respectively, while measuring the ambient methane. In peak-locked mode, the experimental system has a detection limit of 22 ppmm at a distance up to 37 m and can monitor rapid concentration fluctuation in.
Experiment on similarity between wake flow field and electromagnetic scattering characteristic of the hypersonic model
Authors: Ma Ping  , Shi An-Hua  , Yang Yi-Jian  , Yu Zhe-Feng  , Liang Shi-Chang  , Huang Jie  ,   China Aerodynamics Reasearch and Development Center, Mianyang 621000, China
Published: December 2020

The plasma sheath and wake flow of the hypersonic vehicle can affect the electromagnetic scattering characteristics of the reentry targets when they pass through the earth atmosphere at high speed. In order to study the similarity between the wake and the characteristic of the model launched at high velocity, the simulation experiments on the electromagnetic scattering characteristics of the spherical models made of Al2O3 and their wakes are carried out under the same binary scaling parameters in the ballistic range. The models are launched by the two-stage light-gas gun. The diameters of the models are 8 mm, 10 mm, 12 mm and 15 mm, respectively, while the pressures of the target chamber are 6.3 kPa, 5.0 kPa, 4.2 kPa and 3.3 kPa, respectively. The shock standoff distance is obtained by the shadow graph system. The electron density distribution of the wake is measured by the electron density measurement system. The RCS distribution of the wake and the model are acquired by X band monostatic radars, whose visual angle is 40. The results show that the shock standoff distance gradually increases with the increasing of the model dimension under the conditions of the same velocity and binary scaling parameters. The wake electron densities of different models are similar in their variation trends and orders of magnitude. The wake flow field of the different models with high velocity are the same as the results predicted by the double scale laws. The RCS distributions and total RCS of the wake of the models are different from each other. The electromagnetic scattering properties of the wake flow field of the various models do not conform with the predicted results obtained from the double scale law. The electromagnetic scattering energy is distributed over the regions of the models made up of aluminium oxide and the wake zones. There appears to be one center of the electromagnetic scattering energy in the area of the model coated with flow field, while several centers emerge in the region of the wake. The measuring signals of the RCS of the models show a random distribution, because the amplitude variation of the RCS and the frequency change of the RCS are random. The total RCS of the model increases with the increase of the model dimension, but the variation range of ripple frequency decreases with the increase of the model dimension.
Determination of the hyperfine coupling constants of the 5D5/2 state of 85Rb atoms by using high signal-to-noise ratio electromagnetically-induced transparency spectra
Authors: Yang Guang  , Wang Jie  , Wang Jun-Min  ,   Institute of Opt-Electronics, Shanxi University, Taiyuan 030006, China;,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Taiyuan 030006, China
Published: December 2020

We report the hyperfine splitting measurement of the 85Rb 5D5/2 state by electromagnetically induced transparency spectroscopy with high signal-to-noise ratio in the 85Rb 5S1/2-5P3/2-5D5/2 ladder-type system (m 780 nm + 776 nm). The frequency calibration is performed by employing a phase-type electro-optic modulator with a confocal Fabry-Perot cavity. From the measured hyperfine splittings among the manifolds of (F=5), (F=4) and (F=3) of the 85Rb 5D5/2 state, we determine the magnetic dipole hyperfine coupling constant (A= (-2.222 0.019) MHz) and the quadrupole coupling constant (B= (2.664 0.130) MHz) of 5D5/2 state of 85Rb atoms.
Vibration states and entropy of adsorbed hydrogen molecules
Authors: Wang Xiao-Xia  , Liu Xin  , Zhang Qiong  , Chen Hong-Shan  ,   College of Physics and Electronic Engineering, Northwest Normal University, Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, Lanzhou 730070, China
Published: December 2020

The entropy and enthalpy changes upon absorption determine the equilibrium adsorption states, the adsorption/desorption kinetics, and the surface reaction rates. However, it is difficult to measure experimentally or calculate theoretically the entropy of adsorption state. Hydrogen is considered as the most promising candidate to solve the global energy problems, and the storage by adsorption on light porous solids constitutes a main avenue to research field. An ideal storage system should be able to operate under ambient conditions with high recycling capacity and suitable uptake-release kinetics. The entropy of adsorbed H2 molecules is of great significance for determining the optimum conditions for hydrogen storage and for designing the storage materials. To the best of our knowledge, however, the only report on the entropy of the adsorbed H2 molecules is that adsorbed on alkali-metal exchanged zeolites at temperatures around 100 K. Due to different assumptions of the entropy changes, the values of the optimum enthalpy H reported in the publications cover a wide range. In this paper, the adsorption states, vibrational modes, and the entropies of H2 molecules adsorbed on (MgO)9 and (AlN)12 clusters are studied by using first principal method. The computation is performed by the second-order perturbation theory (MP2) with the triple zeta basis set including polarization functions 6-311G(d, p). The very-tight convergence criterion is used to obtain reliable vibration frequencies. Analysis shows that six vibrational modes of the adsorption complexes can be attributed to the vibration of H2 molecule. For these normal modes, the amplitudes of the displacements of cluster atoms are usually two orders smaller than those of the hydrogen atoms. As the vibrational frequency is inversely proportional to the square root of the mass, the zero-point energy has an important influence on the adsorption energy. The ZPE correction exceeds half of the adsorption energy, and the adsorption on the anions is not stable after including the correction. Under the harmonic approximation, the normal vibration modes are independent, so the entropy of adsorbed H2 molecules can be calculated by using the vibrational partition function based on the vibrational frequencies. The results indicate that the entropy values depend mainly on the two lowest in-phase vibrational frequencies and it is not directly related to the adsorption strength but determined by the shape of the potential energy surface. In a temperature range of 70350 K and at a pressure of 0.1 MPa, there is a good linear correlation between the entropy of adsorbed H2 and the entropy of gas-phase. The entropy of H2 decreases about 10.2R after adsorption.
Efficiency analysis of 808 nm laser diode array under different operating temperatures
Authors: Song Yun-Fei  , Wang Zhen-Fu  , Li Te  , Yang Guo-Wen  ,   State Key Laboratory of Transient Optics and Photonics, 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;,   Xi'an Lumcore Optoelectronics Technologies Co., Ltd, Xi'an 710077, China
Published: December 2020

The 808 nm high-efficiency laser diodes have many advantages, such as high output power, high reliabilities, compact sizes, which are widely used in many areas, such as industry, communication, science, medicine and biology. In order to improve the power conversion efficiencies of 808 nm laser diodes, the following requirements must be considered, such as loss of joule heating, loss by the carrier leakage, spontaneous radiation loss below the threshold current, loss by interface voltage defect, internal losses including free-carrier absorption loss and scattering loss. These losses above are closely related to the operating temperature of laser diode. In this paper, power conversion efficiency analysis is demonstrated from the aspects of the output power, threshold current, slope efficiency, voltage, and series resistance at different temperatures.. This is the first time that the detailed study has been carried out under various temperatures (up to the lowest temperature of -40℃). And the detailed study above can be of benefit to designing the wafer epitaxial structure.
High-power 808 nm laser diode arrays are mounted on conduction cooled heatsinks. And the laser chips have 47 emitters with 50% in fill factor, 100 m stripe in width and 1.5 mm in cavity length. The asymmetric broad waveguide epitaxial structure with lower absorption loss in p-type waveguide and cladding layer is designed in order to reduce the internal losses. The device performances are measured under operating temperatures ranging from -40℃ to 25℃ including the output power, threshold current, slope efficiency, series resistance, voltage, etc. Then the power conversion efficiency of 808 nm laser diode arrays are demonstrated from the output characteristics at different operating temperatures.
With temperature decreasing, the series resistance gradually increases. The loss of joule heating ratio rises from 7.8% to 10.3%. In that case, the high series resistance is the major factor to prevent the efficiency from further improving at a low temperature of -40℃. As temperature decreases from 25℃ to -40℃, the carrier leakage ratio is reduced from 16.6% to 3.1%, the carrier leakage is the dominant factor for increasing efficiency, which means that it is necessary to optimize the epitaxial structure in order to reduce the carrier leakage at the room temperature. Comparing the two different work temperatures from -30℃ to -40℃, the carrier leakage ratio only changes 0.1%, which implies that the carrier leakage could be ignored under the low temperature. Meanwhile, as temperature decreases from 25℃ to -40℃, the power conversion efficiency increases from 56.7% to 66.8%.
Experimental study on two-photon fluorescence and coherent anti-Stokes Raman scattering microscopy
Authors: Hou Guo-Hui  , Luo Teng  , Chen Bing-Ling  , Liu Jie  , Lin Zi-Yang  , Chen Dan-Ni  , 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

Two-photon excitation fluorescence (2PEF) and coherent anti-Stokes Raman scattering (CARS) are both third-order nonlinear optical processes, but for a long time, the true relationship and differences between them are not clearly understood. For decades, the second harmonic generation has been studied in conjunction with two-photon excitation fluorescence, so it was thought that the latter was a second-order nonlinear optical process. In order to make the two nonlinear interaction processes clear enough, the two nonlinear interaction processes are worthy to study at the same time. In this paper, firstly, we give the relationships between the 2PEF, CARS signal and their third-order nonlinear susceptibility, respectively; secondly, we use our own near infrared super-continuum CARS microscopy system to study both processes. In doing so, we describe the relationship between their third-order nonlinear susceptibility and the signal. The reconstructed images derived from CARS and those derived from 2PEF differ significantly when imaging the same 1.01 $\muup$m fluorescence polystyrene beads. If the lateral spatial resolution of the CARS imaging system is larger than the fluorescence polystyrene beads, the measured size cannot be used to calculate the real spatial resolution of the CARS system. However, the resolution of the 2PEF microscopy system can be obtained through the de-convolution of the 2PEF image, which is approximately equivalent to the current resolution of the CARS imaging system, which is measured using 280 nm polystyrene beads. The images of 280 nm polystyrene beads and 190 nm fluorescent polystyrene beads also exhibit differences between the two samples and the environment around them, respectively. This means that although CARS and 2PEF are both third-order nonlinear optical processes, they have their own properties. In particular, CARS is a third-order nonlinear optical oscillation process which is caused by the phasing match condition, but 2PEF is not influenced by the phasing match condition. The phase matching condition is responsible for the differences around the sample in the images of the 280 nm pure polystyrene beads, but not for the 190 nm fluorescent polystyrene beads. The de-convolution results for the 1.01 $\muup$m fluorescence polystyrene beads and the 280 nm pure polystyrene beads are very similar, so we can use the de-convolution results for 2PEF by the 1.01 $\muup$m fluorescence polystyrene beads to approximate the current measure condition and the resolution of the CARS imaging system. If we want to gain a more accurate resolution from the CARS imaging system, the spherical sample should be smaller than the lateral spatial resolution of this system.
Image restoration and enhancement based on phase conjugation of optical parametric amplification
Authors: Wang Cong  , Yang Jing  , Pan Xiu-Juan  , Cai Gao-Hang  , Zhao Wei  , Zhang Jing-Yuan  , Cui Da-Fu  , Peng Qin-Jun  , Xu Zu-Yan  ,   Key Laboratory of Solid State Laser, Key Laboratory of Functional Crystal and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100190, China;,   Department of Physics, Georgia Southern University, Statesboro, GA 30460, USA
Published: December 2020

It is well known that the weak optical image can be amplified based on the optical parametric amplification (OPA), and the distorted wave-front can be recovered by the optical phase conjugation (OPC) method. In this paper, weak infrared images, which are barely recognizable after the propagation through the milk emulsion, are restored and optically amplified based on phase conjugation of OPA.The OPC property of OPA is demonstrated with a type-II phase matched nonlinear optical crystal KTiOPO4 (KTP). The near-infrared image at 1064 nm is the input of OPA as the signal beam, and a 10 Hz, mJ-level, 21 ps 532 nm laser is used as the pump beam. When the spatial and temporal overlap are achieved, the attenuated optical image is amplified. Due to the difference in polarization, the idler beam of the OPA is selected and detected with the CCD and the blurred image is restored by the re-entry of the turbid media.The resolution of restored image is 12 lines/mm, which has achieved a theoretical limit. Moreover, by combining the optical gain of the OPA process, over 17 dB image amplification is obtained, which is the highest for the OPC-based image restoration in turbid media to our knowledge. The significant improvement in image quality is also demonstrated by 160% increase of the peak signal-to-noise ratio. By taking advantage of tunability of the OPA, the operational wavelength of this technique can be extended to an optical therapeutic window, which is suitable for noninvasive image restoration, enhancement and detection.
Dynamical behaviors of Sn micro-sphere particles under shock wave action
Authors: Zhao Xin-Wen  , Li Xin-Zhu  , Zhang Hang  , Wang Xue-Jun  , Song Ping  , Zhang Han-Zhao  , Kang Qiang  , Huang Jin  , Wu Qiang  ,   Laboratory for Shockwave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

In these decades, the turbulence mixing of micro-ejecta particles and gas has attracted considerable attention because it has great influence on inertial confinement fusion and some technologies of optical detection. It is significantly important for studying the evolution of micro-ejecta by investigating the influence of particle size and the transporting progress. In this paper, we experimentally investigate the micro-ejecta dynamical behaviors when a strong shockwave acts on Sn micro-sphere particles with different sizes of 0.1 μm, 1 μm, 5 μm and 10 μm. A strict experiment is carried out, in which a thin Ta flyer is accelerated by TNT explosion to load the Sn particles, and the velocity variation of ejecta particles transported in air is measured by the displacement interferometer system for any reflector. The results show that the tip-velocity of the micro-ejecta is very sensitive to the initial size of particle, where the larger size results in increased velocity. By analyzing the results of each case in detail, we discover that the formation of micro-ejecta is caused by the interaction between shockwave and the gap structure among several particles, where the larger gap structure induces faster ejecta tip-velocity. To verify this explanation, the effects of particle size on the ejecta tip-velocity is examined by simulating the cases of 5 μm and 10 μm in particle size through three-dimensional smooth particle hydrodynamics method. The simulated tip-velocity results are in good agreement with the corresponding experimental results. However, the scenario is different when the particle size is smaller than 1 μm, where the experimentally measured tip-velocity of 0.1 μm size particle is nearly the same as that of 1 μm size particle. We attribute this to the fact that the gap structure is too small to affect the micro-ejecta progress and the micro-ejecta is mainly caused by the large scale defects accumulated by a huge number of particles. Furthermore, by comparing with the experimentally measured velocity decay, we also estimate the size distribution of ejecta particles by simulating the decelerating processes of different-sized particles with different initial velocities in gas. This paper is helpful in comprehending in depth the micro-ejecta process caused by the shockwave acting on micro particles, and also in designing such experiments accurately.
Fine flow structure and mixing characteristic in supersonic flow induced by a lobed mixer
Authors: Zhang Dong-Dong  , Tan Jian-Guo  , Li Hao  , Hou Ju-Wei  ,   Science and Technology on Scramjet Laboratory, National University of Defense Technology, Hunan Changsha 410073, China
Published: December 2020

In a supersonic suction type of mixing layer wind tunnel, by employing nanoparticle-based planar laser scattering (NPLS) method, contrast experiments are carried out with the emphasis on the fine flow structures of planar mixing layer and the mixing layer induced by triangular lobed mixer. The normal-shock equation, isentropic equation and sound speed relationship are utilized to calculate the flow parameters. The calculated Mach numbers are 1.98 and 2.84 for upper and lower airstreams respectively with a convective Mach number of 0.2. The NPLS images clearly shows the Kelvin-Helmholtz vortices, streamwise vortices, shock waves and the pairing processes of large-scale vortex structures. The unsteady properties of development and evolution for large-scale vortices are obtained by contrasting the NPLS images at different times. Also, it has been demonstrated by the present experimental investigation that in supersonic mixing layer with low convective Mach number, the small shock waves are still existing. These small shock waves that occur have negative effects on the mixing process. It is because the convection flow process of upper and lower airstreams is non-isentropic, causing the total pressure to lose. Based on the NPLS results, flow structures and mixing characteristics are analyzed quantitatively by using fractal and intermittency theory. The results show that the mixing efficiency increases obviously with the introducing of large-scale streamwise vortices. The nibbling of vortex clusters induced by large-scale streamwise vortices obviously increases the interface area of mixing. Meanwhile, compared with planar mixing layer, larger spanwise structures roll up in triangular lobed mixing layer, leading to more entrainment of upper and lower airstreams. In the present investigation of supersonic planar mixing layer, the value of fractal dimension of fully turbulent region is stable at 1.55-1.6. Whereas the value of fractal dimension for triangular lobed mixing layer reaches 1.88 at the flow field far away downstream, which breaks through the value of fully developed turbulence for planar mixing layer. Besides, in triangular lobed mixing layer, the shear action between streamwise vortices and spanwise structures plays a leading role in promoting mixing. The mixing flow shows the property of apparent crushability and three-dimensional behavior, which plays a positive role in promoting mixing at a scalar level. The analysis of intermittency indicates that the interaction between streamwise and spanwise vortices dominates the mixing characteristics, and due to the entrainment of streamwise vortices, the mixing region induced by triangular lobed mixer becomes larger, and more fluids are engulfed into the mixing region to complete the mixing process.
Formation of periodic ripples on silicon surface ablated by femtosecond laser
Authors: Li Zhi-Ming  , Wang Xi  , Nie Jin-Song  ,   State Key Laboratory of Pulsed Power Laser Technology, Electronic Engineering Institute, Hefei 230037, China
Published: December 2020

The formation mechanism of low-spatial-frequency laser-induced periodic surface structure (LSFL) on single-crystalline silicon irradiated by single femtosecond-laser pulse (pulse duration =150 fs and central wavelength =800 nm) in air is investigated theoretically based on the interference theory of Sipe-Drude model and surface plasmon polariton (SPP). In order to account for transient intrapulse changes in the optical properties of the material due to the excitation of a dense electron-hole plasma, we model the maximum of the electron density as a function of laser fluence by solving the generally accepted two-temperature equation and Drude model. The results show that both theories are applicable to explaining the LSFL formation on the high-excited silicon. In the Sipe-Drude theory, the factor (k) is used to describe the efficacy with which the surface roughness at position k leads to inhomogeneous absorption of radiation. We find that the value of (k) first increases until reaching a maximum at an electron density of 61021 cm-3 and then decreases with the laser fluence increasing. When the incident laser fluence is 0.38 J/cm2, which is the threshold for excited plasma, the period reaches a minimum value in a small range of the top. Besides, the law of period is calculated according to the relationship between the (k) and period. In the SPP theory, the ripple period on the highly excited silicon increases with the laser fluence increasing. Comparing the scopes of application of two theories, the Sipe-Drude theory is found to be suitable for the analysis of more extensive periodic surface structures, while the SPP theory is applicable only for the case that laser fluence is close to the damage threshold. Moreover, our results are capable of explaining that the delay direction of periodic ripples are always perpendicular to the incident laser polarization direction by using the Sipe-Drude theory. When laser fluence approaches to the damage threshold, the LIPSS period is calculated sightly to be below the laser wavelength. It also reveals that the periodic surface structures are approximately the same in the different polarization directions with the increase of incident angle. Taking into account a single pulse, the corrugation period decreases with the increase of angle of incidence in the S polarization direction. And under different polarizations, with the increase of incident angle, the changes of the ripple period show an opposite trend. The obtained dependence provides a way to better control the properties of the periodic structures induced by femtosecond laser on the surface of a semiconductor material, which is of great significance for understanding the formation of periodic structure of silicon surface, caused by femtosecond laser, and its application in the field of silicon materials processing.
Basic dynamic and scale study of quasi-spherical Z-pinch implosion
Authors: Zhang Yang  , Sun Shun-Kai  , Ding Ning  , Li Zheng-Hong  , Shu Xiao-Jian  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Unlike cylindrical Z pinch, a quasi-spherical implosion enables load plasma to implode inward spherically and concentrate its kinetic energy toward the center. This helps to improve the energy-transport efficiency and increase the shock-induced radiation intensity of the foam convertor, when the quasi-spherical implosion is used to drive a dynamic hohlraum (DH). In previous work, it has been proved that a spherical metal shell with an exact mass-distribution can implode spherically by the nonuniform magnetic field, whose magnitude increases with the load latitude, Bφ~cos-1θ. However, this ‘mass-redistribution’ method is hard to realize on the fast pulse power generator widely used in today's Z-pinch study. The rise time of the facility is only ~100 ns, and the load is wire arrays with typical weight about 1 mg/cm. We develop a method of gaining quasi-spherical implosion with wire arrays by adjusting their initial shape, and it proves feasible on the 1.5 MA Qiangguang-I facility. Recently, we try to realize the quasi-spherical dynamic hohlraum (QSDH) implosion on generator with higher current, such as the 4.5 MA Angara5-I or the 8 MA PTS facility, and to make a direct compare with its cylindrical equivalence. But first of all, a basic but relatively comprehensive study on the quasi-spherical implosion dynamics is necessary and useful for the future QSDH load design and optimization.#br#Comparing with the device for classical cylindrical Z-pinch implosions, the load and electrodes structures of quasi-spherical implosions are complex, which leads to distinct implosion dynamics and scale rules. In this paper, we develop a thin shell model for the quasi-spherical implosion, from which the movement equation, as well as the energy scale relation is derived analytically. It is found that under the same drive condition, the implosion velocity and total kinetic energy of cylindrical load are higher than those of quasi-spherical one. However, as we expected, the quasi-spherical implosion has larger kinetic energy density, which is important for the applications such as driving a dynamic holhraum. Besides the peak current, the kinetic energy of quasi-spherical implosion also depends on the initial size of the load. By increasing the initial radius and maximum latitude angle moderately, one can obtain higher kinetic energy and energy density of the implosion, which is crucial for the load design. The theoretical study is supported by simulation results. It is found that under a drive condition close to that of the ZR facility, a quasi-spherical load with an initial radius of 5 cm will reach a peak kinetic energy density of 3.2 MJ/cm, which is about 3 times those from the cylindrical ones.
Video saliency detection algorithm based on biological visual feature and visual psychology theory
Authors: Fang Zhi-Ming  , Cui Rong-Yi  , Jin Jing-Xuan  ,   Intelligent Information Processing Laboratory, Department of Computer Science and Technology, Faculty of Engineering, Yanbian University, Yanji 133002, China
Published: December 2020

In order to solve the problems of video saliency detection and poor fusion effect, a video saliency detection model and a fusion model are proposed. Video saliency detection is divided into spatial saliency detection and temporal saliency detection. In the spatial domain, inspired by the properties of visual cortex hierarchical perception and the Gestalt visual psychology, we propose a hierarchical saliency detection model with three-layer architecture for single frame image. The video single frame is simplified layer by layer, then the results are combined to form a whole consciousness vision object and become easier to deal with. At the bottom of the model, candidate saliency regions are formed by nonlinear simplification model of the characteristic image (dual color characteristic and luminance characteristic image), which is in accordance with the biological visual characteristic. In the middle of the model, the candidate regions with the strongest competitiveness are selected as the local salient regions according to the property of matrix minimum Fresenius- norm (F- norm). At the top level of the model, the local salient regions are integrated by the core theory of Gestalt visual psychology, and the spatial saliency map is obtained. In the time domain, based on the consistency assumption of a moving object in target location, motion range and direction, the optical flow points detected by Lucas-Kanade method are classified to eliminate the noise interference, then the motion saliency of moving object is measured by the motion amplitude. Finally, based on the difference between the visual sensitivity of dynamic and static information and the difference in visual sensitivity between color information and gray information, a general fusion model of time and spatial domain salient region is proposed. The saliency detection results of single frame image and video sequence frame image are represented by the gray color model and the Munsell color system respectively. Experimental results show that the proposed saliency detection method can suppress the background noise, solve the sparse pixels problem of a moving object, and can effectively detect the salient regions from the video. The proposed fusion model can display two kinds of saliency results simultaneously in a single picture of a complex scene. This model ensures that the detection results of images are so complicated that a chaotic situation will not appear.
Sensitivity analysis and validation of detonation computational fluid dynamics model
Authors: Liang Xiao  , Wang Rui-Li  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   College of Mathematics, Shandong University of Science and Technology, Qingdao 266590, China
Published: December 2020

Verification, validation and uncertainty quantification (V&V&UQ) is a method of assessing the credibility of physical model and quantifying the confidence level of numerical simulation result in complex engineering. Verification is used to answer the question whether the physical model is well solved or the program is implemented correctly, and it will give the ranges of error and uncertainty. Validation is used to answer the question whether the physical model reflects the real world or the confidence level of the physical model. This article deals with the detonation computational fluid dynamics model, and analyses the uncertainty factor in modeling, then presents the key factor which affects the accuracy of the simulation result. Due to the complexity of the explosive detonation phenomenon, there are a huge number of uncertainty factors in the detonation modeling. The sensitivity analyses of these uncertainty factors are utilized to distinguish the main factors which influence the output of the system. Then uncertainty quantification is conducted in these uncertain factors. After comparing the simulation result with the experiment data, the adaptation of the model is validated. This procedure is applied to the cylindrical test with TNT explosive. From the result, we can see that the parameters in the JWL EOS are calibrated and the accuracy of the model is validated. By the way, through conducting the uncertainty quantification of this system, we obtain that the expectation and standard deviation of detonation pressure for TNT are 1.6 and 2.2 GPa respectively. Detonation velocity and position of the cylindrical wall accord well with the experiment data. That means that the model is suited in this case. This technique is also extended to the detonation diffraction phenomenon. We can conclude that simulation result is greatly affected by the scale of the cell. From these examples, we can infer that this method also has a wide application scope.
Recent progress of the application of surface plasmon polariton in quantum information processing
Authors: Li Ming  , Chen Yang  , Guo Guang-Can  , Ren Xi-Feng  ,   Chinese Academy of Sciences Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China;,   Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Surface plasmon polariton has attracted more and more attention and has been studied extensively in the recent decades, owing to its ability to confine the electro-magnetic field to a sub-wavelength scale near the metal-dielectric interface. On one hand, the tightly confined surface plasmonic modes can reduce the size of integrated optical device beyond the diffraction limit; on the other hand, it provides an approach to enhancing the interaction between light and matter. With the development of experimental and numerical simulation techniques, its investigation at a quantum level has become possible. In the recent experiments, scientists have realized quantum interference between single plasmons in a nanoscale waveguide circuit and achieved the strong coupling between photons and single molecules by using plasmonic structure, which demonstrates its superiority over the traditional optics. Here, we review the theoretical and experimental researches of surface plasmon polariton in the field of quantum information processing. First, we introduce the experiments on the basic quantum properties of surface plasmons, including the preservation of photonic entanglement, wave-particle duality and quantum statistical property. Second, we review the research work relating to the generation, manipulation and detection of surface plasmons in a quantum plasmonic integrated circuit. Then, we present the research of the interaction between surface plasmons and single quantum emitters and its potential applications. Finally, we make a discussion on how the intrinsic loss affects the quantum interference of single plasmons and the coupling between quantum emitters. The collision and combination of quantum optical and plasmonic fields open up possibilities for investigating the fundamental quantum physical properties of surface plasmons. It can be used to make ultra-compact quantum photonic integrated circuits and enhance the interaction strength between photons and quantum emitters.
Sub-diffraction-limit fabrication of sapphire by femtosecond laser direct writing
Authors: Gao Si  , Wang Zi-Han  , Hua Jian-Guan  , Li Qian-Kun  , Li Ai-Wu  , Yu Yan-Hao  ,   College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
Published: December 2020

Sapphire has shown broad application prospects in military and medical fields, due to its high hardness, excellent corrosion resistance and high transmission in the infrared band. However, these characteristics have also brought about lots of difficulties in machining or chemical etching the material. Femtosecond laser processing with excellent characteristics including small heat-affected zones and high processing resolution ratio, has become an emerging field. Therefore, it has important application prospects and has found increasingly wide applications in the fields of material modification and high-quality fabrication of three-dimensional micro-nano structures and devices. In this paper, we propose a method in which femtosecond laser processing based on multi-photon absorption is used to process sapphire beyond the optical diffraction limit. In this work, femtosecond laser with a central wavelength of 343 nm is focused on the sapphire and the surface of sapphire is scanned with the high-precision piezoelectric positioning stages. Nano structures each with a width of about 61 nm are obtained, and the minimum space between the nano structures could be as short as about 142 nm. Further, the influences on the processing resolution from laser power and scanning speed are investigated and the generation mechanism for the nano-ripple structure is discussed. Finally, femtosecond laser processing on the sapphire with a resolution beyond the optical diffraction limit is achieved. This work provides a reference for processing the hard and brittle materials by femtosecond laser.
Propagation properties of nonuniform cosine-Gaussian correlated Bessel-Gaussian beam through paraxial ABCD system and generation of dark-hollow beam array
Authors: Zhu Jie  , Tang Hui-Qin  , Li Xiao-Li  , Liu Xiao-Qin  ,   School of Science, Guizhou Institute of Technology, Guiyang 550003, China;,   School of Physical Science and Technology, Central South University, Changsha 410083, China
Published: December 2020

Partially coherent beams with nonconventional correlation functions have been extensively studied due to their wide and important applications in free-space optical communication, particle trapping, image transmission and optical encryption. Here, we study the propagation of nonuniform cosine-Gaussian correlated Bessel-Gaussian beam (cGBCB) in detail. Analytical expressions for the cross-spectral density function of cGBCBs through paraxial ABCD system are derived based on the extended Huygens-Fresnel integral. By use of the derived formulae, the intensity distribution properties of a nonuniform cGBCB on propagation in free space are analytically investigated. Some numerical calculation results are presented and discussed graphically. It is found that when the root-mean-square correlation width δ and the parameter controlling the degree of coherence profiles β are appropriately chosen, the intensity distribution of the nonuniform cGBCB displays self-splitting properties during propagation. We point out that rather than a simple duplication, the self-splitting behaviour consists of a complex process in which the dark hollow pattern for cGBCB is gradually filled in the centre at first, then starts to split with increasing the propagation distance, and most impressively, an evolution process from a single dark hollow beam in the source plane to quadruple dark hollow profiles in certain propagation ranges can be realized. The influence of correlation function on the evolution properties of the intensity distribution is investigated, demonstrating that the values of parameters δ and β of the correlation function play a critical role in inducing the self-splitting effect for nonuniform cGBCB on propagation in free space. Therefore, it is clearly shown that modulating the correlation function of a partially coherent beam can alter the coherence length and the degree of nonuniformity, and thus provides an effective way of manipulating its propagation properties. We also find the evolution speed of the intensity distribution can be greatly affected by the topological charge n of the beam function and the parameter R controlling the hollow size of cGBCB in source plane, e. g. the intensity distribution evolves into quadruple dark hollow profiles more slowly with larger n or smaller R. As is well known, the dark-hollow intensity configurations are useful in many applications and have been extensively studied both theoretically and experimentally. Therefore, the results drawn in the paper develop an alternative way to realize dark-hollow beam array, and further pave the way for dark hollow beam applications in long-distance free-space optical communications.