bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetotransport in antidot arrays of three-dimensional topological insulators
Authors: Jing Yu-Mei  , Huang Shao-Yun  , Wu Jin-Xiong  , Peng Hai-Lin  , Xu Hong-Qi  ,   Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices, and Department of Electronics, Peking University, Beijing 100871, China;,   Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences(BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
Published: December 2020

Three-dimensional topological insulators are a new kind of quantum matter featured with gapless Dirac-like energy-dispersive surface states in the insulating bulk band gaps. However, in experiment, it is difficult to study quantum interference effect of surface states due to considerable contribution from bulk carriers in thick bulk material. To suppress such a bulk state contribution, nanostructures, such as ultra-thin films, nanowires and nanoribbons, have been employed in the study of quantum interference effects of the surface states. Here, we report on a magnetotransport measurement study of nanoscaled antidot array devices made from three-dimensional topological insulator Bi2Se3 thin films. The antidot arrays with hundreds of nanometers in diameter and edge-to-edge distance are fabricated in the thin films by utilizing the focused-ion beam technique, and the magnetotransport properties of the fabricated devices are measured at low temperatures. The results of the magnetotransport measurements for three representative devices, denoted as Dev-1 (with no antidot array fabricated), Dev-2 (with an antidot array of a relatively large period), and Dev-3 (with an antidot array of a relatively small period), are reported in this work. Weak anti-localization indicated by a sharp peak of conductivity at zero magnetic field is observed in all the three devices. Through theoretical fitting to the measurement data, the transport parameters in the three devices, such as spin-orbit coupling length Lso, phase coherence length L, and the number of conduction channels , are extracted. The extracted Lso value is tens of nanometers, which is consistent with the presence of the strong spin-orbit interaction in the Bi2Se3 thin film. The extracted L value is hundreds of nanometers and increases exponentially with temperature decreasing. It is found that the magnetotransports in Dev-1 and Dev-2 are well characterized by the coherent transport through a single conduction channel. For Dev-3, the magnetotransport at low temperatures is described by the coherent transport through two independent conduction channels, while at elevated temperatures the magnetotransport is dominantly described by the transport through one single conduction channel. Unlike the case where the transport occurs dominantly through a single conduction channel, the transport through two independent conduction channels in Dev-3 implies that at least one surface channel is present in the device.
Properties of band gaps in phononic crystal pipe consisting of expansion chambers with extended inlet/outlet
Authors: Zhang Zhen-Fang  , Yu Dian-Long  , Liu Jiang-Wei  , Wen Ji-Hong  ,   Laboratory of Science and Technology on Integrated Logistics Support, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Noise reduction is an interesting and important subject in the piping systems of many applications, in order to suppress noise in the pipe, many significative researches have been done. In recent years, the acoustic wave propagation in the phononic crystal pipe has received increasing attention. The characteristic band gaps in phononic crystal pipe can forbid wave to propagate within the band-gap frequency range, which provides a new way to control the noise in piping system. In this paper, the acoustic properties of phononic crystal pipe consisting of expansion chambers with the extended inlet/outlet are investigated theoretically and numerically. By combining the two-dimensional mode matching method and the transfer matrix method, the band structure and transmission loss, especially the band-gap properties of the phononic crystal structure are presented. The obtained results exhibit excellent agreement with the results from the finite element method. Then, this theoretical method is compared with the one-dimensional plane wave method, and it is found that the results from the proposed method are more accurate within the studied frequency range. Further, the effect of modal order in the band-gap frequency range is analyzed, which shows that the mode matching method has a good convergence.The wave scattering and resonance of the chamber will induce the Bragg and locally-resonant band gaps in the periodic pipe, respectively. Further analysis on the transmission coefficient in a band gap is conducted. It shows that the transmission coefficient decays exponentially with the periodic number increasing, which demonstrates that the suppression of the wave propagation in phononic crystal pipe is caused by the band-gap rather than the impedance mismatch. Then the effects of variable parameters including the lattice constant and the length of the insertion on the location and width of the band gaps are investigated. The results show that the lattice constant mainly controls the Bragg band gaps and the length of the insertion exerts a significant influence on the locally-resonant band gaps. Finally, the coupling behaviors of band gaps are studied to expand their widths. It is found that the Bragg band gaps can be coupled with the locally-resonant band gaps via changing the lattice constant and the length of the insertion, which can give rise to wider band gaps. Furthermore, the coupling between two locally-resonant band gaps is proposed by changing the length of the insertion, which also produces wider band gaps.This study can provide new ideas for designing the phononic crystal pipe to suppress the noise in piping system.
Potential energy curves and transition properties for the ground and excited states of BH+ cation
Authors: Luo Hua-Feng  , Wan Ming-Jie  , Huang Duo-Hui  ,   College of Chemistry & Chemical Engineering, Yibin University, Yibin 644007, China;,   Computational Physics Key Laboratory of Sichuan Province, Yibin University, Yibin 644007, China
Published: December 2020

BH+ cation is one of the candidates for laser cooling. The potential energy curves (PECs) for nine electronic states (X2+, A2, B2+, a4, b4+, 32+, 22, 32, 42+) relating to the B+(1Sg)+H(2Sg), B+(3Pu)+H(2Sg), B(2Pu)+H+(1Sg), and B+(1Pu)+H(2Sg) dissociation channels of BH+ cation are obtained using highly accurate multi-reference configuration interaction (MRCI) plus Davidson correction. All-electron basis sets AV5Z-DK for H and ACV5Z-DK for B are used in PEC calculations for the -i-S states of BH+ cation, respectively. In complete active space self-consistent field (CASSCF) calculation, H(1s2s2p3s3p) and B(2s2p) are chosen as active orbitals, B(1s) is the closed shell; in the MRCI calculation, the core-valence (CV) correction is considered, i.e., B(1s) shell is used for CV correlation. Spin-orbit coupling effects are considered with Breit-Pauli operators. Spectroscopic constants are fitted using the Murrell-Sorbie function. Spectroscopic constants for the X2+, A2, and B2+ states are in excellent agreement with the available experimental data; spectroscopic constants for the b4+, 32+, 32, and 42+ states are reported. Two potential wells for the 32 and 42+ states are found. The maximum fitting error of all electronic states is only 3.407 cm-1. In addition, PECs for the A2 and B2+ states are crossed at about 2.7 . Then, the transition dipole moments (TDMs) for the A2 X2+, B2+X2+, 32+X2+, B2+ A2, 32 X2+ and b4+ a4 transitions are also obtained. The strength for the B2+ A2 transition is very weak. Based on the accurate PECs and TDMs, the Franck-Condon factors and spontaneous radiative lifetimes are calculated. A strongly diagonal Franck-Condon factor (f00) for the A2X2+ transition is obtained, which equals 0.9414. Spontaneous radiative lifetime for the A2 and B2+ states is also predicted. i.e., (A2)=239.2 ns and (B2+)=431.2 ns. When SOC effect is considered, the A21/2 and B21/2+ states avoid crossing in the Franck-Condon region (R is about 2.7 ). Calculated f00 for the A21/2 X21/2+ transition is 0.9430; spontaneous radiative lifetime for the A21/2 is 239.0 ns. Our calculated results indicate that the influence for laser cooling BH+ cation via the crossing between B2+ and A2 states can be ignored.
Miniaturization of physics system in Sr optical clock
Authors: Zhao Fang-Jing  , Gao Feng  , Han Jian-Xin  , Zhou Chi-Hua  , Meng Jun-Wei  , Wang Ye-Bing  , Guo Yang  , Zhang Shou-Gang  , Chang Hong  ,   Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, 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

The compactness and robustness of the vacuum setup are the major limitations to develop transportable and space-borne optical clocks. The first step in the engineering challenge is to reduce volume and weight with respect to a stationary system. In this paper, we present the realization of a miniaturized vacuum system by building two anti-Helmholtz coils inside the vacuum magneto-optical-trap (MOT) chamber. The built-in coils are specially designed to minimize the distance between the coils, and in this way it is possible to reduce the current needed to realize a typical magnetic gradient of 40 Gs/cm required for blue MOT. When the MOT coil current is 2 A, an axial magnetic field gradient of 43 Gs/cm is obtained in the center of the MOT, which is enough for the first stage Doppler cooling. This novel design allows us to reduce size, weight and power consumption with respect to a traditional laser cooling apparatus, and simultaneously avoid complicating the water cooling equipment. Our vacuum system has a size of 60 cm×20 cm×15 cm, about 1/10 of the original system in the laboratory. In addition, the circularly polarized Zeeman slowing laser is sent to counter propagating atomic beam, and atoms at a few hundred meters per second are now routinely slowed down to velocities of tens of meters per second. As a result, about 16.4% of the atoms are actually trapped into the blue MOT. The final temperature of the blue MOT is approximately 10.6 mK, and the internal diameter is 1.5 mm by observing the expansion of the atoms from the MOT. The populations of cold atoms finally trapped in the MOT are 1.6×106 of 88Sr and 1.5×105 of 87Sr. The 1S0 → 1P1 transition used for the blue MOT is not perfectly closed due to the decay channel of the 5p1P1 → 4d1D2, and a part of atoms are stored in the 3P2 and 3P0 states. To prevent the atoms from losing, 707 and 679 nm repumping lasers are employed to recycle these atoms in the 3P1 state, and then the atoms decay to the ground state 1S0. Now the typical number of loaded atoms dramatically increases by 5 times compared with before. The slowing efficiency of Zeeman slower is also optimized for the operation with deceleration related to the parameter of magnet length, which uses more effectively available magnetic field distribution, in contrast to the usual constant deceleration mode. Our future work will focus on constructing a Zeeman slower combined with permanent magnets or an electric magnet for better tuning of the magnetic field.
Development of high-pressure multi-wire proportional chamber neutron detector for the China Spallation Neutron Source multipurpose reflectometer
Authors: Wen Zhi-Wen  , Qi Hui-Rong  , Zhang Yu-Lian  , Wang Hai-Yun  , Liu Ling  , Wang Yan-Feng  , Zhang Jian  , Li Yu-Hong  , Sun Zhi-Jia  ,   School of Nuclear Science and Technology, University of Lanzhou, Lanzhou 730000 China;,   State Key Laboratory of Particle Detection and Electronics, Beijing 100049, China;,   Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

As a multipurpose reflectometer device, the two-dimensional (2D) position resolution neutron detector with a 200 mm×200 mm effective area is developed for China Spallation Neutron Source (CSNS) in Dongguang, China. Due to the requirements for the specific parameters of the multipurpose reflectometer, it should be designed to have a more than 50% (@2 Å) detection efficiency, better than 2 mm position resolution and 3 times n/γ resolution ability during the whole operation period of 10 years. The high pressure multi-wire proportional chamber (MWPC) neutron detector filling 3He gas is used as a key detector. Some simulation results and the experimental results show that the optimized thickness of the neutron entrance window should be 9 mm with using the 7075 aluminum alloy, the high pressure chamber should be sealed by the aluminous ring and a gas mixture should be filled with 6 bar 3He+2.5 bar C3H8. The assembled detector can achieve a more than 54% (@2 Å) detection efficiency in the normal operation.With the 100 μm wide collimator slit, the position resolution for X-rays is about 0.235 mm. Therefore, the position resolution for neutron is about 1.4 mm when 2.5 bar propane is used as the stopping gas for proton and triton. In the chamber, the water vapor, the oxygen and the organic impurity gases will reduce the gas gain, cause the detector electrodes to break down and the detector to speed up aging. To solve the outgassing effect of the detector components and keep the stable operation, the recycled device is designed to have the purification function for the working gases. It could purify the working gas at a flow rate of 2 L/min to remove the oxygen, the water vapor and the organic impurity gases. The detector gain increases about 27% with the purification function. Finally, the n/γ resolution and 2D imaging ability of the detector are tested with the 252Cf neutron source in Institute of High Energy Physics, Chinese Academy of Sciences, the peak ratio of neutron to gamma is obtained to be above 5 from the energy spectra and the detecor has good 2D imaging ability. The performance of the high-pressure MWPC neutron detector could meet the requirements for the multipurpose reflectometer, and the detector will be mounted in the CSNS in this year.
Coverage measurement of graphene film on metallic substrate using scanning electron microscopy
Authors: Chen Cai-Yun  , Liu Jin-Xing  , Zhang Xiao-Min  , Li Jin-Long  , Ren Ling-Ling  , Dong Guo-Cai  ,   Jiangnan Graphene Research Institute, Changzhou 213149, China;,   National Institute of Metrology, Beijing 100013, China;,   Changzhou Guocheng New Material Technology Co., Ltd, Changzhou 213149, China
Published: December 2020

Graphene films grown on metallic substrates by chemical vapor deposition have wide potential applications, such as serving as transparent electrodes, transistors, sensors, etc. The coverage of graphene on metal surface can influence many performance parameters, such as square resistance and transparence, after it has been transferred to other substrates. As most of the performance parameters cannot be measured while graphene is still on the metal, it is very useful to evaluate the coverage of graphene before further actions. In this paper, we present a method to measure the coverage of graphene on metal by using scanning electron microscopy and image processing software. We also calculate and measure the uncertainty of the measured coverage. There are two main factors, namely the determination of the boundary between the covered areas and the uncovered areas, and the number of the graphene islands or vacancy islands in view, which can bring uncertainty to the coverage. The former factor raises the uncertainty of the coverage while the number of graphene (vacancy) islands in view is higher, because the more the islands in view, the smaller the islands are, therefore the total boundaries become more. The latter factor reduces uncertainty with the number of islands increasing, because of the quantum fluctuation. The uncertainty of the latter factor is proportional to 1/√N, where N is the number of islands in view. As we can see, the number of islands in view is the key parameter to balance the two factors. We measure the graphene coverage with different graphene islands in view, and also measure the uncertainty by using the statistics knowledge. Meanwhile, we also build a model to calculate the uncertainty under different numbers of islands in view. The experiments and the calculations accord with each other reasonably well. By these carefully modeling and experimentations, we optimize and balance the two faces and suggest the number of islands in view to reduce the uncertainty of the measured coverage to a lowest value. The use of these measured data can ensure the accuracy of the graphene coverage measurement with minimal time cost.
Molecular dynamics simulations of surface effects on Couette gas flows in nanochannels
Authors: Zhang Ran  , Xie Wen-Jia  , Chang Qing  , Li Hua  ,   College of Aeronautics and Astronautics, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Molecular dynamics method is used to investigate gas flows in nanoscale channels. A set of Couette gas flows with the same Knudsen number but different channel heights and densities is simulated to study the dimensional effects on dynamically similar flow conditions. Results show that the gas flow in the channels is divided into two regions:near wall region affected by a wall force field and bulk flow region affected by no wall force field. The flow characteristics in the bulk flow region are in good accordance with the kinetic theory predictions, which are characterized by constant density, normal stress, shear stress and linear velocity distribution while within the near wall region, the velocity, density, normal stress and shear stress distributions exhibit deviations from the kinetic theory predictions. The density and velocity sharply increase, accompanied with a single peak appearing. The normal stress which is dominated by the surface virial is anisotropic and changes drastically. Shear stress value is constant in bulk flow region and part of the near wall region, while the surface virial induces variation at a place about one atom diameter far from the wall. In the near wall region, the normalized density, velocity and stress tensor are constant under different channel heights and densities, which indicates that the gas flow characteristics in this area are determined by the wall force field. Besides, the tangential momentum accommodation coefficient (TMAC) values for different cases can be obtained through the relationship between TAMC and shear stress. It is found that under the same Knudsen number, the TMAC remains constant no matter what the height and density are. Furthermore, another set of Couette gas flows with different gas-surface potential strength ratios but the same channel height and density is simulated to study the gas-surface interaction effects on nanoscale gas flow. The results show that the gas density and velocity in the near wall region increase with increasing potential strength ratio between wall atoms and gas molecules. Large potential strength ratio cases (C 3.0) result in velocity sticking on the surface, which is induced by the gas molecule accumulation and surface adsorption. Using the same approach, the TMAC values for various potential strength ratios are calculated, varying from 0.63 to 0.96 for different cases (C=0.5-4.0), which indicates that the stronger the potential energy acting on the gas molecules, the more easily the gas molecules generate the diffuse reflection on the walls
Evolutions of different crystalline textures in Sm-Fe film fabricated under high magnetic field and subsequent tuning magnetic properties
Authors: Li Guo-Jian  , Chang Ling  , Liu Shi-Ying  , Li Meng-Meng  , Cui Wei-Bin  , Wang Qiang  ,   Key Laboratory of Electromagnetic Processing of Materials(Ministry of Education), Northeastern University, Shenyang 110819, China;,   School of Metallurgy, Northeastern University, Shenyang 110819, China;,   School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
Published: December 2020

In order to tune the crystalline texture evolution and magnetic properties of the Sm-Fe film, molecular beam vapor deposition method is used to fabricate the Sm-Fe films. Sm content, thickness, and high magnetic field are used to affect the crystalline texture and magnetic properties. X-ray diffraction is used to analyze the texture evolution. Atomic force microscope is used to observe the surface morphology and roughness. Energy-dispersive X-ray spectroscopy is used to measure the compositions of the film. Vibrating sample magnetometer is used to test the magnetic properties. The results show that the crystalline textures are tuned through the Sm content. The crystalline texture evolution and high magnetic field have significant effect on the magnetic properties of the Sm-Fe film. The Sm-Fe film with 5.8% atomic content is of bcc crystal structure and is of amorphous structure with 33.0% Sm. Neither the thickness nor the high magnetic field has an influence on the crystalline texture. The surface roughness and particle size on the surface of the amorphous film are smaller than those of the crystal film. A 6 T high magnetic field increases the surface particle size and reduces the surface roughness. Saturation magnetization Ms of the amorphous film is 47.6% lower than that of the crystal film (1466 emu/cm3, 1 emu/cm3=410-10 T). The 6 T high magnetic field reduces the Ms of crystal and amorphous film by about 50%. The coercivity Hc values of the Sm-Fe films are in a range of 6-130 Oe (1 Oe=103/(4) A/m). The Hc of the amorphous film is higher than that of the crystal film. The 6 T high magnetic field increases the Hc of the crystal film and reduces the Hc of the amorphous film. The highest reduction is 95%. The anisotropy of the crystal film transforms to isotropy of the amorphous film. High magnetic field increases the anisotropy of the crystal film. The squareness of the crystal film is much higher than that of the amorphous film. High magnetic field has a significant effect on the measured magnetic field to obtain saturation magnetization in the film. This measured saturation magnetic field increases in the amorphous film and decreases in the crystal film after the high magnetic field has been exerted during the film growth. These results indicate that the Sm content and high magnetic field can be used to tune the crystal textures and magnetic properties of the Sm-Fe films.
Magnetism and electronic properties of LiFeAs superconducting thin filma under two-dimensional strains effect
Authors: Wang Xin , Li Hua , Dong Zheng-Chao , Zhong Chong-Gui ,   School of Sciences, Nantong University, Nantong 226019, China,   School of Physical Science and Technology, Soochow University, Suzhou 215006, China
Published: December 2020

The magnetism, band properties and electronic density of states of LiFeAs superconducting thin film with two-dimensional strain are investigated by using the first principles calculations based on density functional theory, and the influences of different strains on the characteristics of superconducting films are analyzed in detail. The results show that the magnetic ground configuration is the striped antiferromagnetic state of nostrained LiFeAs thin film, and the ground structure of this system is unchanged in the range of applied 1%−6% compressive and tensile strain. The density of states near the Fermi level is mainly from the contribution of Fe-3d orbital and a few As-4p electrons. The electron spin exchange coupling between Fe ions is realized by As ions. Furthermore, unlike the case of the nostrain and the tensile strain, with increasing the compressive strain, the localized antiparallel electron spin magnetic moments of Fe ion decrease, the density of states at the Fermi surface improves, and the itinerant electron magnetism of Fe ions increases, which all greatly suppress the antiferromagnetic properties of thin film and enhance the superconducting phase transition temperature. The superconductivity of LiFeAs thin film originates from the Cooper pairs of electrons between the hole-type and electronic-type bands near the Fermi surface through the antiferromagnetic superexchange coupling effect. Instead, the LiFeAs thin film with the tensile strain presents completely opposite properties, that is to say, the decrease of the electronic density of states in the Fermi level brings about the weakening of the metal properties and the increasing of the antiferromagnetic exchange coupling. Particularly, the band structure of hole-type near the Fermi surface disappears, and the occurrence of Cooper pairs of electrons becomes significantly reduced, resulting in the suppressed superconducting phase transition when the LiFeAs thin film is subjected to tensile strain. In addition, the change of antiferromagnetic exchange coupling and magnetic moments of Fe ions are also explained according to the variation of electronic density of states of the Fe-3d energy levels during the distortion of FeAs tetrahedrons due to compressive strain. In brief, our researches provide an effective way to improve the superconducting properties of LiFeAs thin film and may promote the relevant practical applications of iron-based superconductors in the future.
Research progress of molecular structure and dynamics of biological water
Authors: Ye Shu-Ji  , Li Chuan-Zhao  , Zhang Jia-Hui  , Tan Jun-Jun  , Luo Yi  ,   Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The specific water molecules that are confined within the solvation shell adjacent to the surface of biological macromolecules (including protein, enzyme, DNA, RNA, cell membrane, etc.) are called biological water molecules. Such water around the biomolecule surface plays a very important role in the structure, stability, dynamics, and function of biological macromolecules. A molecular-level understanding of the structure and dynamics of biological water, as well as the nature of its influence on biological structure and function is the key to revealing the mechanism of the biological functions. However, the researches in this field are still in the initial stage. Here in this paper, we review the relevant researches and recent progress of hydration water from three aspects. The first aspect is about the influence of hydration water on biological structure and function. It is evident that water actively participates in many biological processes such as protein folding, proton donation and migration, ligand binding and drug design, and allosteric effects. For example, water mediates the collapse of the chain and the search for the native topology through a funneled energy landscape. The second aspect is about the structure of water molecules around the biomolecules investigated by nuclear magnetic resonance (NMR), dielectric relaxation, neutron scattering, X-ray diffraction and ultrafast optical spectroscopy. The third aspect is about the dynamic behaviors of biological water, including the relaxation time scale, dynamic property, dynamic coupling between biomolecules and water molecules, and sub-diffusive motion of the water molecules along the protein surfaces. Different techniques measure different timescales for the motion of proteins and their hydration environment. While NMR and dielectric relaxation methods reveal the motion of biological water on a time scale from several tens of picoseconds to nanoseconds, ultrafast optical spectroscopy such as fluorescence and vibrational spectroscopy probes the hydrogen-bonding fluctuations of water on a time scale from the femtosecond to picosecond. It is therefore highly necessary to acquire a real and complete picture of the structure and dynamics of biological water by combining several different techniques. Finally, some unsolved scientific problems are also summarized in this review.
Two-dimensional silicon annular photonic crystals for realizing polarization-independent unidirectional transmission
Authors: Liu Dan , Hu Sen ,   Department of Physics and Mechanical and Electrical Engineering, Hubei University of Education, Wuhan 430205, China,   College of Physical Science and Technology, Central China Normal University, Wuhan 430079, China
Published: December 2020

Optical diode is a device that can realize unidirectional transmission of light. Its function is similar to that of an electronic diode. It has important applications in the field of optoelectronic integration and all-optical communications. Unidirectional wave transmission requires either time-reversal or spatial inversion symmetry breaking. The magneto-optical effect and optical nonlinearity are usually utilized to break the time-reversal symmetry and obtain the unidirectional transmission. However, these schemes all need high light intensity or magnetic field strength to be realized, and limit the usage. Therefore, spatial inversion symmetry breaking is highly desirable because of totally linear materials under low intensities. Quit a lot of researchers have designed optical diodes based on the photonic crystals and achieved unidirectional transmission for TE-like or TM-like light. The early design realized light unidirectional transmission by PC structures for only one polarization state (TE-like or TM-like incident light). It limits the application for the high integration and reconfigurable optical interconnection. The structure which can achieve unidirectional transmission for both TE and TM polarizations needs to be designed. The annular PCs have been verified to realize polarization-independent phenomena, such as beam splitting, self collimation and waveguide. In this paper, an annular PC is proposed. The plane wave expansion method is used to calculate band structures. The results show that it exhibits a significant directional band gap for both TE and TM mode. Then, the triangular annular PC is constructed, and its transmission spectra and field distributions are calculated by the finite-different time-domain method. It is found that the structure can realize the polarization-independent unidirectional transmission, but the forward transmissivity is too low (about 20%). Moreover, another smaller size annular PC is further introduced to form annular PC heterojunction, which effectively improves the polarization-independent unidirectional transmission performance and the forward transmissivity has doubled. Through the adjustment of the interface structure, the forward transmissivity is further increased. The optimized annular PC heterostructure can realize polarization-independent unidirectional transmission, and the forward transmissivity reaches 44%. The heterostructure can be used to fabricate polarization-independent optical diode, and may have potential applications in complex all-optical integrated circuits.
Phase delay error analysis of wave plate of division-of-amplitude full Stokes simultaneous polarization imaging system
Authors: Yin Yu-Long , Sun Xiao-Bing , Song Mao-Xin , Chen Wei , Chen Fei-Nan ,   Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China,   University of Science and Technology of China, Hefei 230026, China,   Key Laboratory of Optical Calibration and Characterization, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

The division-of-amplitude full Stokes simultaneous polarization imaging system has prominent merits, such as real time, high spatial resolution, high precision, etc. The development of the division-of-amplitude full Stokes simultaneous polarization imaging system has a high application value. The division-of-amplitude full Stokes simultaneous polarization imaging system uses polarization beam splitters, a half wave plate (HWP) and a quarter wave plate (QWP) to modulate the incident Stokes vector into four intensity images. Using the four intensity images, the incident Stokes vector can be analyzed. In the system, the phase delay errors of the HWP and the QWP have a direct influence on the measurement accuracy of the incident Stokes vector. A Stokes vector measurement error equation containing the phase delay errors of the HWP and the QWP is established. When there are the phase delay errors of the HWP and the QWP in the system, the Stokes vector measurement errors of the unpolarized light, 0° liner polarized light, 90° liner polarized light, 45° liner polarized light, 135° liner polarized light, right circularly polarized light and left circularly polarized light are analyzed. A method of solving the Stokes vector measurement error of incident light with any polarization state is given. When the Stokes vectors with different degrees of polarization (DOPs) are used as the incident light, the simulation results show that both the Stokes vector measurement error and the DOP measurement error increase with the DOP of incident light increasing. Therefore, we select the polarization measurement accuracy to evaluate the system when the DOP of incident light equals 1. To ensure that the polarization measurement accuracy of the system is within 2%, the phase delay error of the HWP should be within ±1.6° and the phase delay error of the QWP should be within ±0.5°. The analysis results of the phase delay errors of the HWP and the QWP are of great significance for improving the polarization measurement accuracy of the division-of-amplitude full Stokes simultaneous polarization imaging system, and also provide important theoretical guidance in designing and developing the system.
Three-dimensional numerical simulation of electromagnetic diffusion problem and magnetization effects
Authors: Li Zhi-Xuan , Yue Ming-Xin , Zhou Guan-Qun ,   School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China,   Anhui Huizhou Geology Security Institute Co., Ltd, Hefei 231202, China
Published: December 2020

We present a newly developed algorithm for three-dimensional (3D) magnetotelluric model based on the vector finite element method. In this paper, unstructured grids which are composed of irregular tetrahedrons are used in our finite element model, which can be refined locally and adaptively according to the complex geometry of computational domain or subsurface structure. For obtaining more accurate solutions, secondary field rather than total field is numerically computed, which makes the errors limited to relatively small secondary field. Traditional node-based finite element method does not satisfy the condition that the normal electrical field is discontinuous at the interface of electric separatrix and the electrical current density is divergence-free throughout the regions without source, which obviously violates Maxwell equations. In order to overcome these drawbacks of node-based finite element, vector finite element method is employed to solve the secondary field-based partial differential equation. Moreover, in this study, the heterogeneous permeability is taken into consideration in our algorithm, as a consequence, which can deal with heterogeneous permeability model. The accuracy of our approach is verified by comparing with previously published numerical simulations of a COMMEMI-3D model. The advantages of our approach are also illustrated by the numerical simulations of model with arbitrary topography and complicated anomalous body. In addition, the simulation results of the irregular anomaly and the complex model of arbitrary terrain are both ideal results. It proves that the effect of 3D terrain is more serious and complex than that of two-dimensional (2D) terrain, and dealing with 3D models or data with 2D algorithm may bring in large errors. In the area where the magnetic permeability is abnormal, the magnetic permeability has an important influence on the numerical simulation results, and the magnetic permeability must be treated as an independent parameter in the magnetotellurics survey.
Signal and pointing accuracy of ultraviolet laser in micro-pattern gaseous detector
Authors: Wang Hai-Yun , Qi Hui-Rong , Liu Ling , Yuan Zhi-Yang , Zhang Yu-Lian , Wen Zhi-Wen , Zhang Jian , Chen Yuan-Bo , Ouyang Qun ,   Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China,   State Key Laboratory of Particle Detection and Electronics, Beijing 100049, China,   University of Chinese Academy of Sciences, Beijing 100049, China,   School of Nuclear Science and Technology, University of Lanzhou, Lanzhou 730000, China
Published: December 2020

In the study of the gas detectors, it is an important calibration method to use the ultraviolet (UV) laser with two-photon ionization mechanism for producing ionized signal. In the last decades, micro pattern gas detector, especially gaseous electron multiplier and micromesh gaseous detector, has been widely used in high energy experiments. These kinds of gaseous detectors have the advantages of higher ion backflow suppression ability, smaller E × B effect and good radiation resistance under the relatively higher count rate environment. To obtain a higher spatial resolution with a UV laser calibration system in gaseous electron multiplier detector, two critical technical issues remain to be resolved: the measurability of the laser signal and the accuracy of the laser beam position. In this paper, the studies in simulation and experiment are conducted to discuss these two critical questions. In the simulation section, the simulation results provide an estimation of signal in the gaseous electron multiplier detector with UV laser of 266 nm wavelength in the mixture working gases of Ar/CO2 (70/30), and give an evaluation of the laser pointing accuracy and the possible relative error of the electron drift velocity. In the experiment section, a UV laser calibration prototype is designed and developed. A pulsed laser of 266 nm wavelength is used as a signal source, which has a Gaussian-like cross section with a frequency of 10 Hz. The experimental results indicate that the signal of the UV laser in a triple gaseous electron multiplier detector reaches 400 mV for a readout strip width of 6 mm, a gain of detector of 5000, and a gain of amplifier of 10 mV/fC. For the calibration laser, the angle accuracy is discussed and tested. The angle uncertainty of the laser can be kept under 5′, and the accuracy of the drift velocity can reach 6.4 × 10−4 with a shift of 0.33 mm in the z direction when the laser beam transmits a distance of 400 mm in the gas chamber. All of these results show that the laser beam specific parameters are the main reference for designing the prototype detector. According to the optimal parameters, a gaseous prototype detector will be tested in the next study.
Characteristics of gain in Ne-like Ar 69.8 nm laser pumped by capillary discharge based on double-pass amplification
Authors: Liu Tao , Zhao Yong-Peng , Cui Huai-Yu , Liu Xiao-Lin ,   College of Electronic Information and Automation, Civil Aviation University of China, Tianjin 300300, China,   National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, Harbin 150080, China
Published: December 2020

In this paper, a double-pass amplification experiment of a Ne-like Ar C line 69.8 nm laser is established. The 45-cmlong capillary is used as the discharge load to obtain a double-pass amplification output of a Ne-like Ar C line 69.8 nm laser. Under the same initial experimental conditions that the initial pressure is 15.4 Pa and the main pulse current amplitude is 13.5 kA, the laser pulse intensity and the full width at half maximum (FWHM) of the laser pulse of the single-pass amplification output and the double-pass amplification output are measured by a vacuum X-ray diode (XRD) behind a vacuum ultraviolet (VUV) monochromator (Acton VSN-515) which is used to disperse the extreme ultraviolet (EUV) emission. And then the laser beam divergence of single-pass amplification output and double-pass amplification output are also measured by a space-resolving flat-field EUV spectrograph combined with an EUV CCD (Andor Newton DO920P-BN). The amplitude of the double-pass amplification laser output is 9 times larger than that of single-pass amplification output, and the FWHM of the double-pass amplification laser pulse is nearly 2.4 ns. While the laser beam divergence angle of the double-pass amplification output is 6.6 times wider than that of single-pass amplification output. By comparing the single-pass amplification and double-pass amplification output experimental results, the gain duration of the gain medium in the double-pass amplification and the radial distribution characteristics of the gain medium are analyzed by using the calculation formula of the double-pass amplification laser intensity. The gain duration is more than 4 ns, during this time the gain coefficient decreases at 1.6 ns. And the gain coefficient is the smallest at 2.8 ns, meanwhile the intensity of the single-pass amplification laser is maximum, and the gain medium is in the gain saturation state. So this result indicates that the minimum gain coefficient at this moment is due to the gain saturation effect. Using a similar calculation method to analyze the spatial distribution of gain coefficients, the gain on the plasma axis is larger than that off the plasma axis. These results lay a foundation for the subsequent establishment of resonant cavity and the multi-pass amplification experiment of capillary discharge Ne-like Ar laser.
Instrument line shape function of laser heterodyne spectrometer
Authors: Lu Xing-Ji , Cao Zhen-Song , Tan Tu , Huang Yin-Bo , Gao Xiao-Ming , Rao Rui-Zhong ,   Key Laboratory of Atmospheric Optics, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China,   Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Laser heterodyne is a kind of technique based on coherent detection with high sensitivity and spectral resolution for spectrum measurements. For these reasons, it has been widely used in many research fields, such as trace gases’ detection of earth’s or terrestrial planets’ atmosphere. However, when the laser heterodyne spectrometer is used for measuring the spectrum, the instrument line shape (ILS) function usually smooth the spectrum, which affects the inversion results of the gas column density. In previous researches, the radio frequency (RF) filter response function was usually used as the ILS, but recent studies indicated that the ILS without consideration of the influence of lock-in amplifier was not precise enough. In order to obtain the ILS function of the laser heterodyne spectrometer, the main factors which influence the ILS are analyzed, including the RF filter bandwidth, integral time and low-pass filter of lock-in amplifier, and the process is based on the principle of laser heterodyne technology and the flow of heterodyne signal processing. The presented ILS is the convolution of RF filter, wavelength variation in the integral time and the low-pass filter. In addition, for testing the effectiveness of the ILS in this paper, the laser heterodyne spectrometer which was built in our laboratory is used for the multiple measurement of the absorption of water vapor and methane in the band of 3.53 \begin{document}${\text{μm}}$\end{document} and the column densities are retrieved with different ILS. The experimental results show that the actual resolutions of the laser heterodyne spectrometer are about 0.005 cm–1 and 0.025 cm–1 when the integral times are set to be 10 ms and 100 ms respectively. Furthermore, the RF filter response function and the ILS function presented in the paper are respectively used in the procedure of water vapor and methane inversion. The results show that when the ILS function used for the retrieval, the sum of squared residual reduces about 16% and the residuals at the peak of methane absorption reduces almost 100% compared with the scenario when using the RF filter function. Above all, the comprehensive analysis of the laser heterodyne spectrometer in this paper indicates that the ILS function is more precise than pioneering studies and this work will be helpful for retrieving the precise profiles of trace gases.
Effects of AlGaN interlayer on scattering mechanisms in InAlN/AlGaN/GaN heterostructures
Authors: Chen Qian  , Li Qun  , Yang Ying  ,   School of Automation and Information Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Recent studies showed that the nominal AlN interlayers in InAlN/AlN/GaN heterostructures had high GaN mole fractions, especially those grown by metalorganic chemical vapor deposition. The Al and Ga mole fraction in the AlGaN interlayer determine the electron wave function and penetration probability, and thus affecting the scattering mechanism related to the InAlN/AlGaN potential layers. In this paper we study the effects of Al mole fraction of the AlGaN interlayer on three scattering mechanisms related to the potential layer, i.e. alloy disorder scattering, subband energy fluctuation scattering and conduction band fluctuation scattering induced by In compositionally inhomogeneous InAlN layer. The wave function and penetration probability in the InAlN/AlGaN/GaN heterostructure are determined by self-consistently calculating the Schrödinger-Poisson equations and then used to calculate the scattering mechanisms. The results show that penetration probabilities in the InAlN and AlGaN both decrease with increasing Al mole fraction. The combination of the contribution of the screening effect and the two-dimensional electron gas (2DEG) density inhomogeneity results in an initial decrease and subsequent increase in the subband energy fluctuation scattering-limited mobility with increasing Al mole fraction, and the heterostructure with a smaller InAlN thickness has a larger mobility increase. The penetration probability and non-periodic arrangement of Al and Ga in the AlGaN predict an Al mole fraction dependence of the alloy disorder scattering-limited mobility similar to the subband energy fluctuation scattering-limited mobility, and the alloy disorder scattering occurs mainly in the AlGaN because the penetration probability in the AlGaN is much higher than in the InAlN. The conduction band fluctuation scattering-limited mobility monotonically increases with increasing Al mole fraction due to the decrease of the penetration probability. The subband energy fluctuation scattering-limited mobility is less sensitive to variation in the Al mole fraction than the other two scattering mechanisms-limited mobilities. In a small Al mole fraction range around 0.1, the alloy disorder scattering is a dominant scattering mechanism, while the subband energy fluctuation scattering dominates the mobility beyond this compositional range. When Al mole fraction is above 0.52, the three scattering mechanisms-limited mobility exceeds that in the InAlN/GaN heterostructure without the AlGaN interlayer, indicating the promotion of the mobility by the AlGaN interlayer. The mobility is raised by more than 50 percent in the InAlN/AlN/GaN heterostructure with an AlN interlayer compared with that in the InAlN/GaN heterostructure without the interlayer.