bluuebunny/crossref_metadata_2025 huggingface dataset:
Spiral spectrum analysis and application ofcoherent synthetic vortex beams
Authors: Peng Yi-Ming , Xue Yu , Xiao Guang-Zong , Yu Tao , Xie Wen-Ke , Xia Hui , Liu Shuang , Chen Xin , Chen Fang-Lin , Sun Xue-Cheng ,   School of Physics and Electronics, Central South University, Changsha 410083, China,   College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The vortex beam is a ring-shaped beam whose center intensity or axial intensity is zero in the propagation direction and whose phase has a spiral rising or falling gradient distribution, which is also called a dark hollow beam. Vortex beams have important applications in free-space optical communication, optical micromanipulation, quantum information processing, optical measurement, super-resolution imaging, laser processing, and material processing. In recent years, with the in-depth research on vortex beams, the application requirements for high-power vortex beams also increase. High-power and high-quality vortex beam can be obtained by coherent combining technology. However, the spiral spectrum characteristics of the vortex beam generated by coherent combining technology need further exploring. In this paper, based on the theory of spectral analysis, we derive the position and magnitude of the spiral phase spectral component of the coherent synthetic vortex beam. The numerical results verify the correctness of the theoretical derivation. Based on the above spectral analysis theory, the mode purity of the target synthesis topology charge can be used as the evaluation function to evaluate quality and optimize the parameters for the coherent synthetic vortex beam, and then to quantitatively guide the coherent synthesis of the vortex beam. The results show that with the increase of the number of sub-beams and the radius of the beam waist of the source plane, the reduction of the radius of the bundle ring and the mode purity of the target synthesis topology charge can be improved, and then we can obtain the high-quality vortex beam. This is consistent with the conclusion obtained by using traditional evaluation functions such as power in the bucket. The spiral spectrum analysis of the coherent synthetic vortex beam not only makes up for the lack of evaluation of the spiral phase synthesis effect by the traditional evaluation function, but also has certain reference significance for understanding the nature of the coherent synthesis technique.
Nonlinear evolution of stimulated scattering near 1/4 critical density
Authors: Wu Charles F. , Zhao Yao , Weng Su-Ming , Chen Min , Sheng Zheng-Ming ,   Key Laboratory for Laser Plasmas, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China,   Key Laboratory of High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences, Shanghai 201800, China,   Tsung-Dao Lee Institute, Shanghai 200240, China
Published: December 2020

Based on particle-in-cell simulations, the propagation of intense long pulse lasers in non-uniform plasma, and particularly, the formation of plasma density cavities caused by the nonlinear evolution of stimulated Raman scattering (SRS) near the quarter critical density, and its effects on parametric instabilities have been studied. It is found that the stimulated Raman scattering instability developed near the quarter critical density leads to the trapping of scattered light and subsequent formation of a local electromagnetic solitary wave. Its amplitude increases with the development of the SRS instability, which pushes surrounding electrons and ions to form a quasi-neutral density cavity. When the first density cavity is formed, the plasma density evolves in such a way that more density cavities are formed during the laser interaction and subsequently the plasma is split into a few discontinuous portions. This new density profile finally tends to suppress the development of both SRS and the stimulated Brillouin scattering (SBS) instabilities considerably.
Analysis of broadening mechanism of ionospheric echo spectrum and spectrum sharpening method
Authors: Luo Huan , Xiao Hui ,   Air Force 95519 Army of PLA, Zunyi 563000, China,   Aerospace Early Warning Equipment Department, Air Force Early Warning Academy, Wuhan 430019, China
Published: December 2020

High-frequency sky wave detection equipment must rely on the ionosphere as the propagation medium in the early warning and sea state remote sensing tasks. The ionosphere is time-varying and unstable, which will change the characteristics of the high-frequency electromagnetic wave propagating through it, resulting in the broadening of the echo spectrum, thus seriously affecting the detection of targets and the inversion of sea state parameters. The reason and mechanism of the echo spectrum expansion are analyzed in detail from the dispersion effect, phase contamination and multimode propagation. The bandwidth of the dispersion effect is different from that of the high frequency detection equipment. When the bandwidth of the sky wave equipment is 3–30 MHz, the bandwidths of the dispersion effect are 41.6–57.4 kHz and 0.17–10.8 MHz. The multi-quasi-parabolic ionospheric model is used to discuss the frequency selection measures to avoid multimode propagation. The modulation process of ionospheric contamination to echo is studied theoretically. It is shown that the non-linear phase contamination will cause the energy of echo to diffuse in frequency domain and to be unable to accumulate. To solve the problem of phase contamination which is difficult to solve in practice, a contamination correction method without estimating the instantaneous frequency of the echo is proposed. In the method the consistency principle of signal subspace and signal frequency vector expansion space is used, and therefore the phase contamination term can be well estimated. Based on the real data, the contamination correction results from the proposed method, phase gradient autofocus method, maximum entropy spectral analysis method and time-frequency processing method are given. The results show that the new method is a better method and can effectively sharpen the broadened echo spectrum.
Dual-band acoustic topological insulator based on honeycomb lattice sonic crystal
Authors: Jia Ding , Ge Yong , Yuan Shou-Qi , Sun Hong-Xiang ,   Faculty of Science, Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

Based on honeycomb-lattice sonic crystals with gear-like scatterers, we study and design a pseudospin-dependent dual-band acoustic topological insulator. Compared with cylindrical scatterers with only a single tunable structure parameter (radius), there exist four tunable parameters for the gear scatterer, which enables the sonic crystal to realize four-fold accidental degeneracy at two different frequencies simultaneously. By changing structure parameters of the gear-like scatterers, we can obtain topological phase transitions between two sonic crystals. Based on this, we design acoustic topological waveguides based on two honeycomb-lattice sonic crystals with different topological phases, and introduce two kinds of defects (a lattice disorder and a bend) into the topological waveguide near the domain wall. Numerical simulations show that pseudospin edge states almost immune to two types of defects and can pass through the topological waveguides with negligible backscatterings. Compared with the results for the topological waveguide without defects, the measured transmission spectra are almost unchanged with the two types of defects, which further experimentally verify the robustness of pseudospin-dependent edge states. Additionally, by keeping the structure of the sonic crystals unchanged, we can also obtain another four-fold accidental degenerate Dirac point and the corresponding topological sound phase transitions in the high-frequency region. The simulations show that there also exists a pair of edge states in the overlapped bulk bandgap of the two sonic crystals in the high-frequency region. It is worth noting that the tiny gap between two edge states is larger than that in the low-frequency region, which may arise from the greater difference between the distributions of pressure eigenfunction of two sonic crystals. The proposed dual-band acoustic topology insulator has potential applications in multi-band sound communication and sound information processing.
Fractional order model and Lump solution in dusty plasma
Authors: Sun Jun-Chao , Zhang Zong-Guo , Dong Huan-He , Yang Hong-Wei ,   College of Mathematics and System Science, Shandong University of Science and Technology, Qingdao 266590, China,   School of Mathematics Statistics, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
Published: December 2020

In recent years, the dust plasma research plays an important role in the field of space, industry, and laboratory. In this paper, starting from the control equations of the double temperature dust plasma, we derive the (2+1)-dimensional Kadomtsev-Petviashvili (KP) equation to describe the double temperature dust plasma sound waves by using the multi-scale analysis, and reduce it by using the perturbation method. Then by using the semi inverse method and fractional variational principle, the (2+1)-dimensional KP equation is introduced into the time-space fractional KP equation (TFS-KP). The fractional KP equation has potential applications in describing physical phenomena in practical problems. Furthermore, based on the symmetrical analysis method, by which lie discussed the time fractional KP (TF-KP) equation of the conservation law, the dual temperature dust plasma acoustic conserves quantity. Finally, based on the bilinear method, the lump solution of fractional KP equation is obtained. The existence of this solution indicates the rogue waves existing in double temperature dusty plasma. The influence of fractional order on rogue wave is also analyzed.
Recent progress on Ⅳ-Ⅵ compound semiconductor heterojunction two-dimensional electron gas
Authors: Ma Song-Song , Shu Tian-Yu , Zhu Jia-Qi , Li Kai , Wu Hui-Zhen ,   Department of Physics, State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Semiconductor heterojunctions play a crucial role in exploring novel physics and developing advanced devices. Due to the characteristic electronic band structure, such as the narrow bandgap and the large spin-orbital interaction, the Ⅳ-Ⅵ compound semiconductor heterojunctions are not only of great importance to infrared detectors, but also arouse extensively concern in the frontier fields of physics, like topological insulators (TIs) and spintronics. Most excitingly, the two-dimensional electron gas (2DGE) with high electron density and high mobility is revealed at the interface of the typical Ⅳ-Ⅵ compound semiconductor CdTe/PbTe heterojunction, the formation of which is attributed to the unique twisted interface of the Ⅳ-Ⅵ compound semiconductor heterojunctions. Further researches demonstrate that the 2DEG system boasts prominent infrared photoresponse and is of Dirac fermion nature. This review presents the major progress in Ⅳ-Ⅵ compound semiconductor heterojunction 2DEG in the past decades. First, the formation mechanism of the twisted heterojunction 2DEG is discussed based on both theoretical and experimental results. By molecular beam epitaxy the novel lattice-mismatch heterostructure CdTe/PbTe with sharp interface was obtained and first-principle calculations revealed that the alternately changed atomic layer spacing played a crucial role in the formation of 2DEG. High resolution transmission electron microscope image of the interface clearly demonstrated the twisted interfacial structure and showed that the interfacial Te-sharing bonding configuration provided the excessive electrons. Second, we show the transport properties of the 2DEG under the condition of low temperature and high magnetic field, and the unambiguous π Berry phase of quantum oscillations indicate that the 2DEG is of Dirac fermion nature and demonstrate its potential for realizing two-dimensional TI and spintronic device. Moreover, the 2DEG exhibits quite high mobility, making it candidate for high electron mobility transistor. At last, the high-performance mid-infrared photodetector is displayed, which is built based on the typical Ⅳ-Ⅵ compound semiconductor CdTe/PbTe heterojunction. The most exciting feature of the detector is that it is able to achieve high-speed response with satisfying detectivity while working at room temperature, which could be a complementation to state-of-art mid-infrared photodetectors. In summary, the Ⅳ-Ⅵ compound semiconductor heterojunctions are of great significance not only in fundamental physics but also in device applications, and this review could provide the researchers with the main results in the field.
Experimental optimal design of Er3+/Yb3+ co-doped Ba5Gd8Zn4O21 phosphor and red upconversion luminescence properties
Authors: Zhao Yue , Yang Fan , Sun Jia-Shi , Li Xiang-Ping , Zhang Jin-Su , Zhang Xi-Zhen , Xu Sai , Cheng Li-Hong , Chen Bao-Jiu ,   College of Science, Dalian Maritime University, Dalian 116026, China
Published: December 2020

In order to obtain the Er3+/Yb3+ co-doped Ba5Gd8Zn4O21 up-conversion phosphor material with maximum red luminous intensity, three steps are adopted as follows. Firstly, the uniform design in the experimental optimal design is used to find the reasonable doping concentration of Er3+/Yb3+. Secondly, according to the quadratic general rotary unitized design, the regression equation of the red luminescence intensity of Er3+/Yb3+ co-doped Ba5Gd8Zn4O21 under 980 nm and 1550 nm excitations is established. Finally, the optimal solution of the regression equation is obtained by genetic algorithm. The Ba5Gd8Zn4O21:Er3+/Yb3+ phosphors are prepared by a high-temperature solid-phase method. The crystal structure for each of the prepared phosphors is analyzed by X-ray diffraction, and it is confirmed that the prepared phosphor samples of Ba5Gd8Zn4O21 are all in pure phase. Using the 980 nm laser as an excitation source, the relationship between the red up-conversion luminescence intensity of the optimal sample and the operating current of the laser is studied. It is found that the red luminescence is emitted through a double-photon process by the formula fitting analysis. Using the 1550 nm laser as the excitation source, it is found that red luminescence is emitted through a three-photon process. The up-conversion emission spectrum of the optimal sample with respect to temperature is measured and discussed, and it is found that the red up-conversion luminescence intensity of the sample is weakened as the temperature increases. The optimal samples are compared with the commercial phosphors of NaYF4:Er3+/Yb3+ under the 980 nm and 1550 nm excitation respectively, the luminescence intensity of the optimal sample is much stronger than that of the commercial phosphor of NaYF4:Er3+/Yb3+. Moreover, under the same power density excitation, the red up conversion luminescence intensity of the optimal sample at 980 nm is stronger than that at 1550 nm.
Ab initio calculation of electronic state structure of TiAl
Authors: Zhang Shu-Dong , Wang Chuan-Hang , Tang Wei , Sun Yang , Sun Ning-Ze , Sun Zhao-Yu , Xu Hui ,   School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China
Published: December 2020

The potential energy curves (PECs) of the low-lying electronic states of TiAl are calculated with the complete active space self-consistent field (CASSCF) method combined with the N-electron valence perturbation theory (NEVPT2) approximation. The complete active space is mainly composed of the (3s23p1) valence orbital of Al and (3d24s2) valence orbital of Ti. Moreover, the valence splitting all-electron basis set def2-nZVPP (n = T, Q) proposed by Karlsruhe group is used in the calculation. On the basis of confirming that the ground state of TiAl is a quadruple state, the PECs of the ground state and the lowest two excited states of TiAl are obtained in a range of nuclear distance R of 0.200–0.500 nm, and the electronic states are identified. It is found that there is a “break” of the electronic structure near R = 0.255 nm. In the R > 0.255 nm region, the ground state and the two excited states are X4Δ, A4Π and B4Γ respectively; in the R < 0.255 nm region, the ground state is still X4Δ, but the two excited states become A'4Φ and B'4Π, and the degeneracy of the excited state tends to be eliminated. Based on the PECs of TiAl obtained by the dynamic correlation correction with NEVPT2, the characteristic parameters of three low-lying quadruple electronic states (such as equilibrium nuclear distance, binding energy, adiabatic excitation energy) and transition dipole moment, are obtained, and these parameters are used to explain the reason why the electronic transition spectrum of TiAl is not observed experimentally. The characteristic of “break” in the electronic state structure also provides a meaningful reference for analyzing and understanding the brittleness of TiAl alloy at room temperature.
Reference-frame-independent measurement-device-independent quantum key distribution under reference frame fluctuation
Authors: Gu Wen-Yuan , Zhao Shang-Hong , Dong Chen , Wang Xing-Yu , Yang Ding ,   Information and Navigation College, Air Force Engineering University, Xi’an 710077, China,   State Key Laboratory of Cryptology, Beijing 100878, China,   College of Information and Communication, National University of Defense and Technology, Xi’an 710006, China
Published: December 2020

Reference-frame-independent measurement-device-independent quantum key distribution is adopted to avoid aligning the reference frames in realistic setup, which can guarantee the system security against the slow drift of reference frame. However, the relative motion of reference frame including deviation and fluctuation can influence the performance of reference-frame-independent measurement-device-independent quantum key distribution in practical experimental demonstration. In this paper, taking finite effect into consideration, the performance of reference-frame-independent measurement-device-independent quantum key distribution with biased bases under reference frame deviation and fluctuation is presented to evaluate the effect of the relative motion of reference frame on our scheme, which makes the analysis conform to reality. Our simulation results imply that the key rates fluctuate periodically with the reference frame rotating, while declining with the reference frame fluctuation increasing.
An improved Kalman filter time scale algorithm for atomic clock noise variation
Authors: Song Hui-Jie , Dong Shao-Wu , Wang Xiang , Zhang Yu , Wang Yan-Ping ,   National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China,   Key Laboratory of Time and Frequency Primary Standards, Chinese Academy of Sciences, Xi’an 710600, China,   School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Kalman filter time scale algorithm is a method of real-time estimating atomic clock state. It is of great practical value in the time-keeping work. Reliable Kalman filter time scale algorithm requires a reliable atomic clock state model, a random model and a reasonable estimation method. However, it is difficult to construct accurate state model when the noises of atomic clock change. The random model is generally based on the prior statistical information about atomic clock noises, and the prior statistical information may be distorted. In the process of time scale calculation, the noises of atomic clocks need estimating in the Kalman filter time scale algorithm, which is quantified according to the intensity of the noise. With the change of the external environment or aging of atomic clock, the noise intensity may change, resulting in the disturbance of atomic clock state estimation in the Kalman filter time scale algorithm, which further affects the accuracy and stability of the time scale. On the other hand, the error of the noise intensity estimation of atomic clocks will also affect the performance of time scale. Therefore, it is necessary to control the disturbance caused by the variation of noise intensity or the estimation error of noise intensity. In this regard, an adaptive factor is introduced to improve the Kalman filter time scale algorithm, and another adaptive factor is introduced into the state prediction covariance matrix in Kalman filter time scale algorithm. And the values of the two adaptive factors are calculated in real time by using statistics to control the growth of the state prediction covariance. The disturbance of state estimation of atomic clock is reduced, and the accuracy and stability of time scale are improved. In this paper, the sampling interval of simulated data and the measured data are 300 s and 3600 s respectively. The simulated data and measured data are used to calculate the overlapping Allan deviations of the time scale. The results show that the improved Kalman filter time scale algorithm can improve the stability of the sampling time more than 14400 s compared with classical Kalman filter time scale algorithm, and affect the stability of the sampling time less than 14400 s. The degree of influence is related to the weight algorithm of atomic clock. The measured data in this paper are treated by the “predictability” weighting algorithm, which guarantees the long-term stability of time scale. So the simulated data and measured data show that compared with classical Kalman filter time scale algorithm, the improved Kalman filter clock time scale algorithm can improve the accuracy and the long-term stability of time scale.
Group III monochalcogenide of single-layered haeckelites structure MX (M = Al, Ga, In; X = S, Se, Te)
Authors: Liu Hui-Ying , Wang Shu-Shen , Lin Heng-Fu ,   Hubei Province Key Laboratory of Systems Science in Metallurgical Process, State Key Laboratory of Refractories and Metallurgy, International Research Institute for Steel Technology, Wuhan University of Science and Technology, Wuhan 430081, China
Published: December 2020

Single-layered III-VI compounds have potential applications in many fields, such as highly sensitive photodetectors, field effect transistors, and electrochemical sensors, due to their wide range photosensitivities and excellent electronic properties. This paper presents a new two-dimensional tetragonal allotrope (called haeckelites structure) of single layered group III monochalcogenides MX (M = Al, Ga, In; X = S, Se, Te), which are constructed from the square and octagon rings. The first-principles calculations are performed using the Vienna ab initio simulation package (VASP) based on density functional theory (DFT). The cohesive energy of the haeckelite structure MX is positive and a little smaller than that (0.07—0.10 eV) of the hexagonal MX. The phonon spectra for the haeckelites structure MX have basically no imaginary frequencies in the whole Brillouin zone. The calculated binding energy and phonon spectrum show that these structures are energetically and dynamically stable. For all the compounds, the charge density isosurfaces show that most electrons are localized at the positions of X and M atoms, indicating that the M—X bond is ionic and M—M bond is covalent. All of haeckelite structure MX are indirect bandgap semiconductors, and their band gap sizes decrease with the X atom changing from S to Se to Te. For example, the band gaps of InS, InSe, and InTe are 2.42, 2.07, and 1.88 eV, respectively. The calculation results show that these materials have a wide band gap range from 1.88 to 3.24 eV. We find that the band gaps of AlS, AlSe, and GaS are relatively large with the values of 3.08, 3.03, and 3.24 eV, respectively. This may make them suitable for optically transparent devices. The band structures of GaSe, InS, InSe, and InTe can be further modulated by the biaxial strains. Their band gaps decrease linearly with the strain increasing. The band gap of AlS and AlSe both first increase and then decrease with the strain increasing.
Modification of method of sampling radiation source particle in spherical geometry
Authors: Xu Yu-Pei , Li Shu ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

Sampling of radiation source particles is important for obtaining a correct result in the thermal radiative transfer simulation with implicit Monte Carlo. When conducting the implicit Monte Carlo simulation of spherical geometry, temperature in a cell (a spherical shell) is generally treated as a spatially independent value. That means that the particles of radiative source are uniformly distributed in a spherical shell. In some cases where the gradient of temperature inside a cell is relatively small, the treatment does not cause too many errors. However, when the opacity of material becomes large enough or the spherical shell becomes thick enough, the temperature of thermal wave head will change sharply and there will be a great temperature gradient even in a single spherical shell. The treatment will make the thermal radiation propagate much faster than the practical one, which is unacceptable in physics. We investigate the physical and numerical reasons for this violation, finding that the simulation results strongly rely on the separation of cell and that the thermal wave propagates faster with the cell number decreasing. In order to yield an accurate result, the cell number has to increase up to a large enough value. Unfortunately, more cells need more particles to reduce the numerical variance, and more particles will cost more computation time and thus causing the simulation efficiency to lower. In our work, temperature is not treated as a constant in space any more. Instead, it is treated as a linear function in a cell. Based on a new temperature function and radiative energy density distribution, a probability density distribution function of emitting position of radiation source particle in spherical geometry is obtained. Then two new spatial sampling methods are proposed and the sampling procedures of radiation source particle are designed. To verify our new sampling methods, we test several typical thermal radiative problems and compare the result with a reference solution. Numerical experiments show that both two new sampling methods can correct the errors of thermal radiative propagation speed and overcome the difficulty that simulation result is strongly dependent on cell number. In addition, both new sampling methods can obtain an accurate result even with less cells and less particles, which can saves plenty of computation time and improves the simulation efficiency.
Quantum entanglement in coherent feedback system based on the cascaded four wave mixing processes
Authors: Zhong Yin-Yin , Pan Xiao-Zhou , Jing Jie-Tai ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Based on the cascaded four wave mixing processes, a coherent-feedback control system is constructed by utilizing a linear beam splitter as the feedback controller. Considering the loss of optical propagation in the coherent feedback loop and the absorption effect of Rb vapor cells to beams, we theoretically investigate the entanglement properties of this system under different feedback ratio, gain and phase by calculating the covariance matrix of system and applying the positivity under partial transpose (PPT) criterion to all possible bipartitions. The result shows that the genuine tripartite entanglement exists in the coherent feedback control system, but the entanglement structure of system will be destroyed by the excessive feedback. In addition, when the phase is π, we find that the tripartite entanglement can be enhanced by changing the gains and the reflectivity of the beam splitter in the range of 0.1 to 0.4. The results pave the way for manipulating multipartite entanglement by coherent feedback control and have potential application in quantum communication.
Intersystem crossing of 2-Methlypyrazine studied by femtosecond photoelectron imaging
Authors: Bumaliya Abulimiti , Ling Feng-Zi , Deng Xu-Lan , Wei Jie , Song Xin-Li , Xiang Mei , Zhang Bing ,   College of Physics and Electronic Engineering, Xinjiang Normal University, Urumqi 830054, China,   State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
Published: December 2020

The ultrafast nonadibatic relaxation dynamics of the excited state of 2-methylpyrazine has been studied by using femtosecond time-resolved photoelectron imaging and femtosecond time-resolved mass spectrometry. The first excited state S1 of 2-methylpyrazine was excited by 323 nm pump light, and the excited state deactivation process is detected by 400 nm probe light. The lifetime of S1 state 98 ps is obtained by time-resolved mass spectroscopy. The intersystem crossing from the S1 state to the T1 state is observed on real time. The relaxation dynamics of S1 state of 2-methlypyrazine is different from that of pyrazine, the results show that the intersystem crossing process between S1 and T1 is the main relaxation channel of S1 state of 2-methlypyrazine, but the internal conversion process between S1 and S0 is also a main relaxation channel of S1 state. By using the advantages of femtosecond time-resolved photoelectron imaging, the photoelectron angular distribution at different pump-probe time delay was obtained experimentally. From the photoelectron angle distribution combined with photoelectron kinetic energy distributions, we tried to observe the field-free nonadiabatic alignment. However, due to the fact that the molecular symmetry of 2-methylpyrazine is lower than that of pyrazine, it is more challenging to observe the phenomenon of molecular nonadiabatic alignment with lower symmetry. Therefore, it is fail to observe nonadiabatic alignment feature of 2-methylpyrazine in this experiment. This work provides a clearer physical picture for S1 state nonadibatic relaxation dynamics of 2-methylpyrazine.
Optical properties and microstructure of two Ge-Sb-Se thin films
Authors: Pan Lei , Song Bao-An , Xiao Chuan-Fu , Zhang Pei-Qing , Lin Chang-Gui , Dai Shi-Xun ,   Faculty of Electrical Engineering and Computer Science, Ningbo University, Ningbo 315211, China,   Zhejiang Key Laboratory of Photoelectric Detection Materials and Devices, Ningbo University, Ningbo 315211, China,   Advanced Technology Research Institute, Ningbo University, Ningbo 315211, China
Published: December 2020

Multipoint Cauchy method (MCM) is presented to investigate the refractive index and dispersion for each of Ge20Sb15Se65 and Ge28Sb12Se60 chalcogenide thin films at any wavelength in the transmission spectrum based on the regional approach method and Cauchy fitting. We theoretically calculate and compare the refractive index and dispersion curves obtained by using six different models. The results show that the most accurate results are obtained by the MCM. Two Ge—Sb—Se films are prepared by magnetron sputtering experimentally, and transmission spectrum curves are measured by Fourier infrared spectrometer, the noise is removed by segmental filtering and then the refractive index, dispersion, absorption coefficient, and optical band gap of the two films ina range of 500–2500 nm are obtained by the MCM. The results show that the refractive index of Ge28Sb12Se60 film is larger than that of Ge20Sb15Se65 film, which is caused by the higher polarizability and density of the former. The refractive indexes of both films decrease with wavelength increasing, so the long waves travel faster than short waves in the two films. The optical band gap of Ge28Sb12Se60 film (1.675 eV) is smaller than that of Ge20Sb15Se65 film (1.729 eV), and the corresponding wavelengths of the two are 740.3 nm and 717.2 nm. Finally, the microstructures of the two films are characterized by Raman spectra, and the reasons why the two chalcogenide films have different optical properties are explained from the bonding properties between the atoms.
Data traffic capability of double-layer network based on coupling strength
Authors: Ma Jin-Long , Du Chang-Feng , Sui Wei , Xu Xiang-Yang ,   School of Information Science and Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China,   Science and Technology on Communication Networks Laboratory, Shijiazhuang 050081, China
Published: December 2020

The two-layer network model offers us a new viewpoint to observe the traffic dynamics of multilayer network systems. An efficient coupling mechanism is of great importance for alleviating the traffic congestion on two-layer networks. In order to reduce the network congestion and improve network transmission performance, the coupling mechanism between two layers of network and three coupling methods, which are random coupling, disassortative coupling and assortative coupling, are studied based on degree correlation. The packet transmission process is analyzed with both the shortest path routing strategy and degree-based weight routing strategy. The influences of the coupling mode and its corresponding routing strategy on the traffic capacity of the two-layer network are studied. In this paper, two scale-free networks are used to construct the two-layer network for simulation experiments. The network scale is in a range from 200 to 2400 with the value of average degree being 8. We focus on the traffic dynamics of two-layer network, and analyze the relationship between the traffic capacity and the three coupling modes, which are random coupling, disassortative coupling and assortative coupling, under the constraints of the shortest path routing strategy and the weight-based routing strategy. According to the characteristics of the coupling connection between the two layers of network, the best coupling method which is suitable for a certain routing strategy should be investigated. The suitable coupling connection between the two layers can effectively increase the traffic capacity. Both numerical result and analytical result show that the packet generation rate, average transmission time, and average throughput can be obviously improved under the shortest path routing strategy with the disassortative coupling method. When the degree-based static weight routing strategy is used, the traffic performance parameters such as packet generation rate, average transmission time, and average throughput can reach the optimal values with the assortative coupling method. It makes the traffic flow uniform that the routing strategy is chosen with the most suitable coupling method on the two-layer network, and the network traffic capacity may be effectively enhanced. More generally, the results indicate that the coupling modes can give rise to traffic behavior that relies subtly on the routing strategy on the two-layer network. Our work may shed some light on the design and optimization of some real traffic or communication networks.
Redox-enhanced solid-state supercapacitor based on hydroquinone-containing gel electrolyte/ carbon nanotube arrays
Authors: Ye An-Na , Zhang Xiao-Hua , Yang Zhao-Hui ,   Jiangsu Key Laboratory of Thin Films, Center for Soft Condensed Matter Physics and Interdisciplinary Research, School of Physical Science and Technology, Soochow University, Suzhou 215006, China
Published: December 2020

By introducing redox active substances into electrolyte, the energy density can be effectively increased without reducing the power density. Considering the influence of ionic conductivity and environmental safety, we introduce the redox small molecule hydroquinone (HQ) into the PVA/H3PO4 gel electrolyte, which then will recombine with the carbon nanotube arrays (ACNT) possessing high specific surface area and vertical orientation structure. The symmetrical “sandwich” type redox-enhanced solid-state super capacitor is then designed and prepared. We systematically study the effects of oriented structure and pore space on the electrochemical properties of the ACNT@PVA@HQ device and charge storage mechanism. With the addition of hydroquinone (0.1%, mol%), the specific capacitance of ACNT@PVA@HQ composite device increases 6.4 times compared with that of the ACNT@PVA, and maintains the extremely high rate performance and cyclic stability. When the current density increases 10 times, the specific capacitance of the device still possesses 85% of the original value. The energy storage mechanism is mainly ascribed to a diffusion-control behavior at a low scan rate while it will change into a capacitive behavior at a high scan speed. Furthermore, we prepare highly densified oriented carbon nanotube arrays (DACNT) by solvent evaporation, enhancing the mechanical stability of carbon nanotube arrays and improving the specific capacitance and energy density of the devices. Compared with the specific capacitance of ACNT and random carbon nanotube (CCNT), that of DACNT@PVA@HQ device under the current density of 11.1 mA·cm–2 increases up to 385 mF·cm–2 (1674 mF·cm–3), which is 6.6 times higher than that of the CCNT@PVA@HQ device and 18 times higher than that of the ACNT@PVA device. The maximum energy density can finally reach as high as 0.06 mW·h·cm–2 (0.26 mW·h·cm–3), which is much better than those of many other reported CNTs-based devices. The oriented structure of the arrays effectively shortens the ion migration path of the device, achieving a good rate performance and lower internal resistance. This new type of redox-enhanced solid-state supercapacitor not only has excellent electrochemical energy storage properties, but also meets the requirements for environmental protection and safety. This design provides a new idea for developing the new energy devices in the future, which has a good prospect in practical applications.
Polarization and phase transition behavior of PbLa(Zr, Sn, Ti)O3 antiferroelectric ceramics under pulse electric field
Authors: Xu Ran , Feng Yu-Jun , Wei Xiao-Yong , Xu Zhuo ,   Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, School of Electronic Science and Engineering, Faculty of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

In real applications, antiferroelectric (AFE) ceramics are usually subjected to a pulse electric field with fast rising or falling speed. In the measurement of hysteresis loop at low frequency, the applied electric field has a low changing rate. Thus, the obtained results cannot reveal the polarization nor phase transition of AFE ceramics in real applications. In the present work, a platform to measure the pulse hysteresis loop is developed and the polarization and phase transition of Pb0.94La0.04[(Zr0.52Sn0.48)0.84Ti0.16]O3 (PLZST) AFE ceramics under pulse electric field on a μs scale are investigated. The obtained results indicate that the phase transition can be induced by pulse electric field. However, the maximum polarization decreases, the forward transition field increases and the backward one decreases, resulting in the variation of energy storage performance. Thus, the hysteresis loop at low frequency cannot reveal the performance of AFE ceramics under the action of a pulse electric field. The pulse hysteresis loop is of great significance in real applications.
Technique of detecting optical components based on coherent modulation imaging
Authors: Ge Yin-Juan , Pan Xing-Chen , Liu Cheng , Zhu Jian-Qiang ,   Key Laboratory of High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China,   National Laboratory on High Power Laser and Physics, Chinese Academy of Sciences and China Academy of Engineering Physics, Shanghai 201800, China,   School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
Published: December 2020

As one of the coherent diffractive imaging (CDI) techniques, coherent modulation imaging (CMI) is a lensless phase imaging technology with diffraction limited resolution in theory. Unlike multiple measurement phase retrieval algorithms, the CMI can achieve fast convergence speed with single-shot measurement by introducing a pre-characterized random phase modulator. Besides, it has simple structure without reference wave based on iterative engine. Despite the fact that the matured phase imaging can be used to implement the on-line wave diagnostics of laser pulse, in this work we accurately measure the face-type of optical component with peak-to-valley value below 0.5λ (λ = 632.8 nm) by using the CMI for the first time. In order to verify its measurement capability, 10 quartz windows with a diameter of 80 mm and PV value between 0.1λ and 0.5λ are repeatedly measured. Compared with the results of commercial interferometer, the root mean square error (Root MSE) of the peak-to-valley (PV) ratio of the results of the CMI is 0.0305λ, and the Root MSE of the root mean square (RMS) is 0.00522λ. The measurement accuracy of PV ratio and RMS can reach 0.1λ and 0.01λ respectively. In addition, the parallel flat with PV ratio = λ/20 is measured and analyzed with CMI, and its noise level is also analyzed. Considering that the potential improvement of CMI is available in the future, the CMI is expected to become a new technique for optical metrology with high precision, which is different from interferometry.
Effect of atmospheric turbulence on orbital angular momentum crosstalk of focused vortex beams
Authors: Yan Jie-Lin , Wei Hong-Yan , Cai Dong-Mei , Jia Peng , Qiao Tie-Zhu ,   Institute of Physics and Optoelectronics Engineering, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

Vortex beams with orbital angular momenta with different mode numbers are mutually orthogonal to each other, which makes it possible to improve the information transmission efficiency in space optical communication system. Nevertheless, the implementation of this strategy is limited by the orbital angular momentum crosstalk caused by atmospheric turbulence. Focused Laguerre-Gaussian vortex beams are less affected by atmospheric turbulence due to their lager intensity density. Consequently, focused Laguerre-Gaussian vortex beams can be used as the carriers to reduce the orbit angular momentum crosstalk and increase the channel capacity of information transmission. In this paper, based on the spiral spectrum analysis theory, the analytical expression of spiral spectrum of focused Laguerre Gaussian beam propagating in anisotropic atmospheric turbulence is derived. The influences of turbulence and beam parameters on the received power of focused and unfocused Laguerre Gaussian beam are investigated via numerical calculations. Finally, the multi-phase screen method is used for verificating the simulation. The research findings are as follows. First, with the increase of transmission distance, turbulence intensity and topological charge, the receiving power of orbital angular momentum decreases, that is, the orbital angular momentum crosstalk turns more serious. Second, the larger the turbulence inner-scale, anisotropy index and beam wavelength are, the smaller the orbital angular momentum crosstalk is. Third, when the receiving aperture reaches a certain value, its influence on the orbit angular momentum crosstalk is very small. Fourth, different parameters have different effects on crosstalk, and the orbit angular momentum crosstalk of the focused vortex beam is less than that of the unfocused vortex beam. Therefore, in the vortex optical communication, the focused vortex beams can be used as the signal light to reduce the crosstalk between the orbit angular momentum modes, and thus improving the communication quality. These results have some theoretical reference values for reducing crosstalk in free-space optical communication.
Polar topological structures in ferroelectric materials
Authors: Tan Cong-Bing , Zhong Xiang-Li , Wang Jin-Bin ,   School of Physics and Electronic Science, Hunan University of Science and Technology, Xiangtan 411201, China,   School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China
Published: December 2020

Spin topologies, including flow-closure, vortex, meron, skyrmion and other spin configurations, are usually found in magnetic materials. The emergence of the topological structures will trigger a number of intriguing functionalities and physical properties. Recent studies have shown that the trival domain structures can be transformed into polar topological domain structures under certain boundary conditions, such as size-confining, interfacial coupling, and epitaxial strain. In this paper, we review the observations of polar topologies and their formation mechanism in ferroelectric nanoparticles, thin films, and superlattice films, and focus on the intriguing properties, including ferroelectric, piezoelectric, dielectric, and photoelectric performances, which arise from the formation of polar topologies. We also review the highlights of recent studies of the manipulations and evolutions of polar topologies under the external field loading in ferroelectric materials. Finally, the future research directions of polar topological structure and potential application directions are proposed.
Anonymous communication scheme based on quantum walk on Cayley graph
Authors: He Zhen-Xing , Fan Xing-Kui , Chu Peng-Cheng , Ma Hong-Yang ,   School of Sciences, Qingdao University of Technology, Qingdao 266033, China
Published: December 2020

Information security is the cornerstone and lifeblood of national security in the information society, and anonymous quantum communication is one of the important ways to protect information security. Using quantum walk randomness to effectively solve sensitive problems such as leakage of identity information. In this paper, an anonymous communication scheme based on quantum walks on the Cayley graph is proposed. First, both parties in the communication hide their identity information, and the sender Alice anonymously selects the receiver Bob through logic or operation. Secondly, the trusted third party and the communicating parties use the BB84 protocol to generate and distribute the security key. Alice encrypts the information sequence according to the security key to obtain the blind information; Bob uses the joint Bell state measurement and security key to sign and the trusted third party verifies the signature information. Third, the trusted third party calculates the position probability distribution function of Bob’s quantum walk via the Fourier transform, converts the position information corresponding to the maximum probability into a confirmation frame and sends it to Alice; Alice uses the quantum compression algorithm by decreasing dimensions to reduce the number of transmitted information bits(the length of the information bit can be reduced by up to 37.5%) and uses the security key to complete the information encryption and then transmit the information to the location indicated by the confirmation frame. Bob uses quantum walks to search the location node to obtain the transmission information and complete the anonymous quantum communication. Finally, the security analysis of the scheme is carried out, and the numerical simulation results of the Cayley graph of 200 nodes are given. At the 10-step walk, the maximal probability of the 6th node is 45.31%. According to the simulation results, the probability that Bob is eavesdropped on the specific location at his 10-step walk during the communication of this scheme is approximately 6 × 10–7%, so the receiver can avoid the identity information from the eavesdropping with a high probability, and the quantum network anonymity protocol is not broken.