bluuebunny/crossref_metadata_2025 huggingface dataset:
First-principles study of the electronic structures and absorption spectrum of Fe:Mg:LiNbO3 crystals
Authors: Zhao Bai-Qiang  , Zhang Yun  , Qiu Xiao-Yan  , Wang Xue-Wei  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

In this paper, the electronic structures and absorption spectra of LiNbO3 (LN) and Fe:Mg:LiNbO3 crystals are studied by the first-principles under the generalized gradient approximation. The supercell structures of the LN crystal are established with 60 atoms, including four models: pure LN crystal, Fe:LiNbO3 crystal (Fe:LN), Fe:Mg:LiNbO3 crystal with Mg of 2 mol%-3 mol% (Fe:Mg(L):LN), and Fe:Mg:LiNbO3 crystal with Mg of 5.0 mol% (Fe:Mg(E):LN). The electronic structures show that the extrinsic defect levels (within forbidden band) of Fe:LN are contributed by Fe 3d orbital and O 2p orbital, and the band gap of Fe:LN (about 2.85 eV) is narrower than that of LN. For Fe:Mg:LN crystals, the band gap changes to 2.90 eV and 2.81 eV respectively for the Mg ion concentration less than and equal to the threshold (～5.0 mol%). The two absorption peaks at 2.3 eV and 2.6 eV are attributed to the Fe ions in crystal. Moreover, the intensities of these peaks vary with the concentration of Mg ion. It is revealed that the concentration of Mg ion influences the concentrations and the sites of Fe2+ and Fe3+ ions in crystal. From the absorption spectrum, the values of ratio Fe2+/Fe3+ in Fe:Mg(E):LN and Fe:Mg(L):LN can be obtained, and the ratio of first sample is smaller than that of the second one. With the one-center model, one can distinctly deduce that the photoconductivity of Fe:Mg(E):LN is relatively weak compared with that of Fe:Mg(L):LN, but this is inconsistent with many experimental results. One notices the contribution of O 2p orbital to extrinsic defect level in electronic structure. Therefore, it is reasonable to presume that the one-center model is not suitable enough for this condition. Based on the research work, we find that the formations of photoelectrons are related to orbital electron states of iron ions and oxygen atoms at extrinsic defect levels in Fe:LN and Fe:Mg:LN crystals.
From plasmon to nanoplasmonics-the frontiers of modern photonics and the role of liquid crystals in tuneable nanoplasmonics
Authors: Yang Fu-Zi  ,   Chemistry Department, Tsinghua University, Beijing 100084, China
Published: December 2020

This review is intended to be a fundamental lecture. It focuses on systematically introducing the reader to the physical and optical background to certain basic concepts in nanoplasmonics, before devoting attention to the many new developments at the frontiers of modern photonics, such as tuneable nanoplasmonics. There is a special discussion of the advantages and applications of liquid crystals in this area. First, in optics according to the special requirements of an optical surface wave propagating alone a smooth boundary the concept of surface plasmon polariton (SPP) has been introduced from physics. After discussing the influences from more rough surfaces upon the SPP and the response from larger metallic particles to the optical electro-magnetic waves the results from interaction between the optical waves and metallic particles with dimensions much small than the wavelength of the optical waves-the exist of the local surface plasmon polariton, i.e. the base of nanoplasmonics, has been confirmed. Secondly, this review describes many new and interesting aspects from this important branch at the frontiers of modern photonics-nanoplasmonics, which are supported by metamaterials consisting of metallic particles with various shapes and nano-scale size from modern manufacture technologies and more powerful and functional software. Many device system based upon these aspects have broken through the limitations of classical optics and developed in many special new directions, for example the quantum coincidence of lasers-Spaser (surface plasmon amplification by stimulated emission of radiation) etc. Finally, we address tuneable nanoplasmonics, which is a very important topic that has warranted great attention. by reason of liquid crystals’ many special advantages in optical responses-for example their larger optical birefringence, which can be easily modulated by applying electric and/or magnetic fields etc.-the application of liquid crystals in tuneable nanoplasmonic devices is a more practical research direction. This review introduces recent developments in this area, and also discusses various challenges and possible research topics.
Effect of magnetic field on single-bubble in water
Authors: Mo Run-Yang  , Wu Lin-Yan  , Zhan Si-Nan  , Zhang Yin-Hong  ,   Shaanxi Key Laboratory of Ultrasonic, College of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, China
Published: December 2020

In this paper, we extend the Rayleigh-Plesset model by considering the effect of a magnetic field on the nonlinear response of an oscillating spherical air bubble in water. Water molecules in motion, derived by a time varying ultrasound pressure field, suffer a torque from the magnetic field by Lorentz force. The rotational energy and the translational energy together constitute the kinetic energy of the water molecule. The work done by the pressure during the contraction and expansion of bubble is equal to the total kinetic energy of the water molecule in liquid. According to energy conservation, we establish a modified control equation of the bubble motion under the action of an applied external magnetic field. The integration of the nonlinear differential equation governing the bubble motion is performed analytically by using a regular expansion, and is solved numerically by using a fourth-order Runge-Kutta method. It is shown that the variation of ambient pressure changes the bubble dynamics when the magnetic field is off. The ambient pressure is increased due to the effect of external magnetic field. The pressure induced by magnetic field increases linearly with the increase of magnetic field intensity and the coefficient is about 103 times. The bubble expansion rate, maximum radius, and the velocity of the collapsing bubble decrease as the magnetic field increases. It is predicted that the applying of a magnetic field can widen the pressure range and modify bubble dynamics.
Dynamical behaviors of cavitation bubble under acoustic standing wave field
Authors: Shen Zhuang-Zhi  ,   Shaanxi Key Laboratory of Ultrasonics, Institude of Applied Acoustics, Shaanxi Normal University, Xi’an 710119, China
Published: December 2020

Considering the compressibility of liquid, we investigate the dynamical behaviors of a cavitation bubble in an acoustic standing wave field by regarding water as a work medium. The motion state of the cavitation bubble at each position is simulated in the standing wave field, the influences of the primary Bjerknes force on the motion direction of the cavitation bubble at each position are also simulated with different relevant parameters. The results show that in the standing wave field, the motion state of the cavitation bubble is divided into three aspects: the cavitation bubble is of steady-state cavitation near the pressure antinode; the cavitation bubble is of transient cavitation at the position deviating from the pressure antinode; in the vicinity of the acoustic pressure node, the cavitation bubble has been moving to the acoustic pressure node due to the primary Bjerknes force, so the phenomenon of cavitation does not occur. In the standing wave field, when the acoustic pressure amplitude exceeds its upper limit, the primary Bjerknes force makes the cavitation bubble move to pressure node, it is not conducive to the occurrence of cavitation. When the acoustic frequency is smaller than the bubble resonant frequency, the primary Bjerknes force will make more cavitation bubbles move to acoustic pressure node with the increase of the acoustic pressure, so this is not conducive to the occurrence of cavitation. Especially, the height of the liquid level should not be a quarter of acoustic wavelength. For a given acoustic frequency, the larger the initial radius of cavitation bubble, the more favorable the occurrence of cavitation is. But when the initial radius of cavitation bubble exceeds the resonant radius of acoustic frequency, the bubble will be pushed to pressure node. That is to say, the acoustic pressure amplitude, the acoustic frequency, and the initial radius of cavitation bubble each have a corresponding limit. Moreover, the lower limit is conducive to the occurrence of the phenomenon of cavitation.
Variations of implosion performance with compression ratio in plastic DD filled capsule implosion experiment
Authors: Yan Ji  , Zhang Xing  , Zheng Jian-Hua  , Yuan Yong-Teng  , Kang Dong-Guo  , Ge Feng-Jun  , Chen Li  , Song Zi-Feng  , Yuan Zheng  , Jiang Wei  , Yu Bo  , Chen Bo-Lun  , Pu Yu-Dong  , Huang Tian-Xuan  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

The plastic DD filled capsule implosion experiment is performed on Shenguang III prototype laser facility. One-dimensional hydrodynamic numerical simulations show that the implosion compression ratio can be controlled by changing the capsule ablator thickness. In experiments, two types of capsules are studied and most of important implosion parameters are collected, such as neutron yield, X-ray bang-time, trajectory, and shape of hot core. The comparison between post-simulations and experimental results is performed. In our experiments, the neutron yield is 6.8×107 and YOC1D reaches 34% for low compression ratio implosion; the neutron yield is 6.3×106 and YOC1D is only 2.3% for middle compression ratio implosion. Meantime, the shape of hot core obtains an extra higher Legendre partial (P2 is 18% and P4 is 5%). On another side, the trajectory and bang-time are compared with simulations well.
Effect of interface nucleation time of the GaN nucleation layer on the crystal quality of GaN film
Authors: Guo Rui-Hua  , Lu Tai-Ping  , Jia Zhi-Gang  , Shang Lin  , Zhang Hua  , Wang Rong  , Zhai Guang-Mei  , Xu Bing-She  ,   Key Laboratory of Interface Science and Engineering in Advanced Materials Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, China;,   Research Center of Advanced Materials Science and Technology, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

In this paper, the influences of the growth time of low-temperature (LT) GaN nucleation layer on the crystal quality and optical properties of GaN film are investigated. It is found that the optimal LT nucleation layer growth time can effectively reduce the crystal defects and is favorable to forming the annihilation of dislocations. GaN films are grown on c-plane sapphire substrates by metal-organic chemical vapor deposition. Crystal quality and optical properties are characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution X-ray diffraction (HRXRD), and photoluminescence spectra, respectively. In the AFM images, the island density decreases as growth time increases, while the size of island becomes larger and the uniformity of island size deteriorates as growth time increases, leading to the phenomenon that the number of interfaces formed during the nucleation island coalescence, first decrease and then increase as detected by SEM, which also induces the screw dislocation density and edge dislocation density to first decrease and then increase as measured by HRXRD. This first-decrease-and-then-increase variation trend is consistent with the first-increase-and-then-decrease variation trend of the ratio of the band edge emission peak intensity to the yellow luminescence peak intensity tested by photoluminescence, which is confirmed by HRXRD. It is shown that GaN islands with different sizes and densities could lead to different mechanisms of dislocation evolution, thereby forming GaN epitaxial layers with different dislocation densities and optical properties. Through controlling the nucleation time, GaN films with the smallest dislocation density could be obtained.
Research on the coherence of partially coherent radially polarized beam during propagation
Authors: Chen Shun-Yi  , Ding Pan-Feng  , Pu Ji-Xiong  ,   College of Information Science and Engineering, Fujian Provincial Key Laboratory of Light Propagation and Transform, Huaqiao University, Xiamen 361021, China
Published: December 2020

Based on the generalized Huygens theory and the unified theory of coherence and polarization, study is made on the module value of complex degree of coherence of partially coherent radially polarized beam (PCRPB) which changes with transmission distance at different reference point. Results show that the module value distribution of the complex degree changing with the transmission distance is different for different reference point while PCRPB propagates in a free space. When the reference point is at the origin, with the increase of the transmission distance, μxx and μxy hold a symmetric distribution, and the distribution range increases. When the reference point is confined on the x-axis, μxx changes from single peak to three peaks, and the two valleys lie symmetrically; and μxy changes from two peaks to four peaks, and the four valleys lie symmetrically. The transmission distance of the evolution is related to the distance between the reference point and the origin: the closer the distance between the reference point and the origin, the shorter the transmission distance is needed to achieve the evolution process. When the reference point lies on the y-axis, μxx holds a symmetric distribution, its distribution range increases, and μxy changes from two peak values to four peaks and four valleys which are in symmetric form. The transmission distance is related to the spacing between the reference point and the origin, the closer the distance between the reference point and the origin: the shorter the transmission is needed to achieve the evolution process. In addition, when the reference point lies at other positions on the observation plane, the module value distribution of μxx and μxy is obtained by combining the distribution rules of reference point at x-axis and y-axis: i.e., when the reference point lies at other positions of the observation plane, the module values μxx and μxy can be composed of three peaks and four peaks with the increase of transmission distance, respectively.
Study on the relationship between coherent population beating signal and the coherence of ground-state hyperfine sublevels
Authors: Zhao Xiao-Na  , Zhuang Yu-Xin  , Wang Zhong  ,   School of Electronics Engineering & Computer Science, Peking University, Beijing 100871, China
Published: December 2020

Coherent population beating (CPB) phenomenon occurs in a typical three-level system. When the frequency difference between two coherent pumping laser fields has a certain detuning from the ground-state hyperfine splitting, the excited state population will experience a transient oscillation before reaching equilibrium, and the oscillation frequency is equal to the detuning. The CPB phenomenon enables us to directly obtain the beat frequency between the measured radio frequency (RF) signal and the atomic transition frequency. Then we can get the standard frequency by compensating the beat frequency to the RF. We propose a scheme to implement atomic clock based on the CPB phenomenon in 2009, and the scheme has been implemented. When this effect is used to achieve an atomic clock, the frequency stability is directly related to the amplitude and SNR (signal to noise ratio) of the CPB signal. Influence of the ground-state hyperfine sublevels' coherence on CPB signal is theoretically simulated and experimentally investigated in this paper. A formula of the CPB signal is derived by using the semi-classical model of the interaction of atoms with light, and the theoretical simulation is done using the formula obtained. In the experiment two coherent pumping laser fields are used to interact with 87Rb atoms. A CPB process includes the coherence build-up and the CPB stimulation. The coherence of the ground-state hyperfine sublevels is achieved by controlling the pumping time of the coherent laser fields that are resonant to the ground-state hyperfine sublevels. With this method, the relationship between CPB signal and coherence of the ground-state hyperfine sublevels can be observed. Result shows that the amplitude of CPB signal is proportional to the ground-state hyperfine sublevels' coherence. The hign quality CPB signal can be achieved when the CPB stimulation is started with a pure coherent population trapping (CPT) state. In the CPB process, the coherence build-up rate is approximately equal to the coherence decay rate. So a 50% duty cycle square wave can be used to modulate the RF, and the period of the square wave had better be twice of the decay time of the ground-state hyperfine sublevels' coherence. To improve the SNR of CPB signal and the stability of atomic frequency standard, the ground-state hyperfine sublevels' coherence must be built up, improved, and maintained before the CPB stimulation. The feasibility of applying CPB phenomenon to the weak magnetic field measurement and other applications is also discussed in this paper.
Study on atomic localization of Λ-type quasi-four level atoms based on absorption with quantum coherent control
Authors: Zhang Lei  , Ge Yan  , Zhang Xiang-Yang  ,   School of Science, Jiangnan University, Wuxi 214122, China
Published: December 2020

A scheme of two-dimensional atomic localization of the Λ-type quasi-four-level atoms based on quantum-coherent-controlled absorption is proposed. Using the perturbation theory of the density matrix, the filter function is derived for the position probability distribution of atoms, which is determined by the imaginary part of the optical susceptibility. Because of the space-dependent interaction between atoms and fields, the position information is contained in the filter function, which provides an approach to explore the spacial position probability distribution of a single atom. Effect of the initial state of the atom under coherent control on the atomic localization is analyzed. It is found that the atomic localization is related to the initial atom distribution and the dipole moment between two lower levels under the coherent field control. When probing field and coupling field are under the configuration of the electromagnetically induced transparency, the position of atoms can be localized in the domain of sub wavelength; when the electromagnetically induced transparency is not satisfied, an atom can be measured in a sub wave region with the probability of 100% by changing the traveling wave amplitude in the controlling field and the detuning in the probing field.
Research on the oscillation effect of near-surface metal defect based on laser-generated acoustic surface wave
Authors: Zeng Wei  , Wang Hai-Tao  , Tian Gui-Yun  , Hu Guo-Xing  , Wang Wen  ,   College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;,   Faculty of Electrical and Computer Engineering, Technology University Dresden, Dresden 01069 Germany;,   School of Electrical and Electronic Engineering, Newcastle University, Newcastle NE1 7RU, UK
Published: December 2020

According to the thermoelastic equations and heat conduction equations of laser-generated acoustic surface wave (SAW), the SAW propagation images are obtained by taking finite element solutions to the equations. When the SAW propagates through the aluminum plate with the near-surface defects at different depths, producing an oscillating effect between the surface acoustic wave and the near-surface defects, and then there is a gradual decrease after the gradual decrease of the oscillation waves as getting through the near-surface defect. When the SAW propagates through the aluminum plate with the near-surface defect at different depth, there is a certain variation of the center frequency of the oscillation waves. Simulation results show that, when the depth of near-surface defect changes from 0.1 to 0.5 mm, the center frequency of the oscillation signal generated by the oscillation effect changes from 0.4 to 0.76 MHz, and the center frequency of the oscillation signal is seriously attenuated with increasing width of the near-surface defect, thus providing a theoretical basis for quantitative detection of the near-surface defects.
Conformal invariance and conserved quantity of Mei symmetry for Appell equation in a holonomic system in relative motion
Authors: Zhang Fang  , Zhang Yao-Yu  , Xue Xi-Chang  , Jia Li-Qun  ,   College of Electric and Information Engineering, Pingdingshan University, Pingdingshan 467002, China;,   School of Science, Jiangnan University, Wuxi 214122, China
Published: December 2020

For a holonomic system in relative motion, the conformal invariance and the conserved quantity of Mei symmetry with Appell equations are investigated. First, by using the infinitesimal one-parameter transformation group and the infinitesimal generator vector, the definitions of Mei symmetry and the conformal invariance with Appell equations in a holonomic system in relative motion are given, and the determining equations of the conformal invariance of Mei symmetry for the system are derived. Relationship between the conformal invariance and Mei symmetry for the system is mainly studied. Then, by means of the structural equation which the gauge function satisfies, the expression of Mei conserved quantity deduced from Mei symmetry for the system is obtained. Finally, an example is given to illustrate the application of the result.
CT imaging method with varying energy based on logarithm demodulation
Authors: Chen Ping  , Han Yan  , Pan Jin-Xiao  ,   National Key Laboratory for Electronic Measurement Technology, Key Laboratory of Instrumentation Science & Dynamic Measurement, Shanxi Key Laboratory of signal capturing & Processing, North University of China, Taiyuan 030051, China
Published: December 2020

For complicated structural components with wider X-ray attenuation ranges, the projection information is short of single-energy computed tomography (CT) imaging because the attenuation thickness of the components along the orientation of X-ray penetration exceeds the limit of the dynamic range of the CT imaging system. Then under this circumstance, in the conventional imaging mode of fixed ray energy the phenomenon of overexposure and underexposure easily occurs. The whole structure information cannot be obtained, and the projection information is seriously lacking, hence it will affect the quality of CT reconstruction. This paper proposes a CT imaging method with varying energy based on logarithm demodulation.#br#For the incomplete projection due to the limited dynamic range, we collect images at various rotation angles, as in standard CT; also, at each angle we collect a series of images at different energies and fuse them into a single high dynamic range (HDR) image. Based on this HDR image, the conventional CT reconstruction methods can get the full construction information. However, the CT quality is poor, because of noise amplification in the fusion process of X-ray image sequences which are gathered during varying the X-ray energy. To solve this problem, this paper proposes to use logarithm transformation to reduce the dynamic range for the varying energy image sequences. This can change the weight coefficients' access in the projection sequences to suppress the noise. Also in the transformation sequences, we can also use the fusion method, which is based on image gray consistency, to compute the weighting coefficient, to obtain the HDR projection, because the logarithm transformation does not change the image structure, and the overlap area between image sequences is definite. Finally we use the conventional CT reconstruction algorithm to make the CT imaging with the complicated structural components.#br#An accompanying experiment with a complicated instrument demonstrates that the new method can extend the dynamic range of X-ray imaging system and provide a complete representation of the internal structure of the complicated structural components as compared with the conventional CT imaging method. So, it will be of important significance and may be applied to the potential system, so as to improve the detecting sensitivity of the system, and make the high-quality reconstruction about complex products.
Analysis of induced-transparency in an original three-order resonator system
Authors: Jiao Xin-Quan  , Chen Jia-Bin  , Wang Xiao-Li  , Xue Chen-Yang  , Ren Yong-Feng  ,   Beijing Institute of Technology, Beijing 100081, China;,   Science and Technology on Electronic Test and Measurement Laboratory, Taiyuan 030051, China;,   Key Laboratory of Instrumentation Science and Dynamic Measurement of Ministry of Education, North University of China, Taiyuan 030051, China
Published: December 2020

For the application requirements of resonant micro-cavity, an original three-ring resonant micro-cavity structure is proposed in this paper. Like electromagnetically induced transparency in an atomic system, the coupled resonator-induced transparency (CRIT) phenomenon in a new optical micro-cavity system is proven experimentally. Up to now, most of the resonators based on CRIT are just in the theoretical exploration stage, and the analysis of the double-ring structure has been relatively common. The CRIT effect of a resonator has a significant relationship with the coupler insertion loss, the ring circumference, and the multiples of the rings, which need high requirements in the structural design and preparation process. In order to reduce the difficulty in design and preparation, we propose a new three-ring cascade resonator structure with the same cavity size on silicon. According to the transfer matrix method and coupled mode theory, we find a CRIT effect after theoretical analysis. Our devices are fabricated on an SOI wafer. By using the micro-cavity measurement platform to repeat and analyze the tests of single ring and three-ring cascade resonator structure, we obtain a grating coupler efficiency of 30%. By applying the antireflection coating, the coupling efficiency of the grating coupler is up to 34%. During the test, the mutual interference between annular cavities of the three-ring resonators produces two transmission peaks, the output spectrum of the resonator with a narrow transparency peak at a low group velocity, which is verified in CRIT phenomenon. Compared with the traditional single-ring structure, the resonator has a quality factor increasing four times, reaching a value of up to 0.65×105, the through and drop transmission spectra of the resonator are reconciled well with each other. At the same time, in order to obtain the sensitivity of the resonator to temperature, we conduct tuning tests of the resonator temperature characteristics, the resonant peak is moved to the large wavelength direction with temperature increasing, and detuning wavelength of the resonance can be controlled by changing temperature, which is called red-shift. Therefore, the original three-ring cascaded resonators have significant applications in the rotation sensing, optical filters, optical storage and temperature sensing elements.
Sound field simulation of ultrasonic processing to fabricate carbon nanotubes reinforced AZ91D composites
Authors: Zhao Fu-Ze  , Zhu Shao-Zhen  , Feng Xiao-Hui  , Yang Yuan-Sheng  ,   Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China;,   College of Materials and Metallurgy, Northeastern University, Shenyang 110819, China
Published: December 2020

The sound field in the melt processed by 20 kHz ultrasonic to fabricate CNT-AZ91D is investigated by numerical simulation. Firstly, the distribution of sound pressure in the AZ91D melt is calculated by the finite element method after the model of the sound filed of the ultrasonic processing has been built. The simulation results show that a radial sound field forms under the ultrasonic probe, which means that the sound pressure decreases with increasing distance from the sound source. After the sound field is revealed, we study the ultrasonic cavitation in the AZ91D melt with a single-bubbly-change model and examine the bubble change rule under different sound pressures by solving the Rayleigh-Plesset equation. The relationship between sound pressure amplitude and the ultrasonic cavitation in the melt is also discovered. The higher the sound pressure amplitude, the smaller the threshold radius for the bubble collapse is, and thus the ultrasonic cavitation in AZ91 melt happens more easily. Secondly, the sound fields of the melt with different immersed depths of the ultrasonic probe are calculated. The results show the optimal immersed depth is about 30 mm for the same crucible size used in the present study. Furthermore, the corresponding optimal immersed depth can be calculated for different crucible sizes or different melts by the present numerical method, which is important for the practical ultrasonic processing. After analyzing the calculated results for sound field and the cavitation rule of in the AZ91D synthetically, we find that the volume of the effective cavitation zone rapidly increases with the smaller ultrasonic power and then rises almost linearly with the ultrasonic power larger than 500 W. Finally, to verify the simulation method of the sound field, the contrast study between the simulation and experiment of ultrasonic processing using glycerol-water solution is performed. The simulation result of the sound field in glycerol-water solution is similar to that in AZ91D melt. The highest sound pressure occurs near the end face of ultrasonic probe, while the experimental observation shows that the strongest cavitation also happens near the end face of ultrasonic probe, which indicates that the highest sound pressure occurs in the zone.
First-principles study of electronic and optical properties of BiTiO3
Authors: Luo Zui-Fen  , Cen Wei-Fu  , Fan Meng-Hui  , Tang Jia-Jun  , Zhao Yu-Jun  ,   Guizhou Minzu University, Polytechnic College, Guiyang 550025, China;,   Department of Physics, South China University of Technology, Guangzhou 510640, China;,   Guizhou University, College of Big Data and Information Engineering, Guiyang 550025, China
Published: December 2020

BiTiO3 of C1 C1 structure is found to be the most stable phase according to our first-principles calculations for nine possible structures, with corresponding optimized crystal parameters of a=b=5.606 Å, c=9.954 Å; α=β=105.1°, γ=61.2°. Subsequently, we have investigated the electronic and optical properties of BiTiO3 in C1C1 structure. It is found that BiTiO3 is a semiconductor with an indirect band gap with its energy band near Fermi level being dominated by O-2p and Ti-3d levels. Additionally, the dielectric function, refractive index, and reflectivity of BiTiO3 are also calculated, and it is shown that the optical properties of BiTiO3 are nearly isotropic.
Split modes of composite metal grating and its application for high performance gas sensor
Authors: Sun Xiao-Liang  , Chen Chang-Hong  , Meng De-Jia  , Feng Shi-Gao  , Yu Hong-Hao  ,   Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

To achieve the surface plasmon resonance (SPR) mode splitting in infrared wavelength band, and to improve the figure-of-merit (FOM) of grating based SPR sensor, in this article we present a new composite grating structure, which consists of double metal gratings, and study the gas sensing performance. Split modes of SPR in composite metal grating are observed by using the finite difference time domain method. The original structure symmetry is broken and changed with increasing relative displacement between the double gratings, as a result, the resonant modes move to opposite directions. Calculated electric field distribution of the two separate resonant modes displays two different degrees of coupling effect between the double gratings. When the relative displacement is further increased till the double gratings are connected to form a new symmetrical single grating, the separate resonant modes will merge into another single resonant mode. If the refractive index of analyte (na) is in a range 1.01≤na≤1.05 and the relative displacement of double gratings is zero, the wavelength sensitivity based on composite metal grating gas sensor reaches 1207.5 nm/RIU (per refractive index of unit) and the FOM is obtained to be 1290.7, while the relative displacement of the double gratings is 100 nm, for the double split modes the wavelength sensitivities are 1205.0 nm/RIU and 1210.0 nm/RIU, respectively, and the corresponding FOMs are 1295.4 and 762.3. Therefore, the high FOM of the composite grating based on SPR sensor possesses great potential applications in biochemical sensing.
Intercomparison of one-dimensional detecting methods of unveiling the global ocean striations
Authors: Zhang Yu  , Guan Yu-Ping  , Chen Zhao-Hui  , Liu Hai-Long  , Huang Rui-Xin  ,   Marine Science and Technology College, Zhejiang Ocean University, Zhoushan 316000, China;,   State Key Laboratory of Tropical Oceanography, Chinese Academy of Sciences, Guangzhou 510301, China;,   Key Laboratory of Physical Oceanography, Ocean University of China, Qingdao 266003, China;,   State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China;,   Woods Hole Oceanographic Institution, Woods Hole, MA02543, USA
Published: December 2020

Striation in the ocean is a research frontier in physical oceanography. Interestingly, it has some “sisters and brothers” in Mother Nature, such as the Jovian belts, subtropical jet streams in the atmosphere, and zonal flows in plasma. This meso-scale oceanic phenomenon is, however, concomitant with but covered up by the macro-scale ocean currents or circulations. In order to unveil such zonal jet-like structures, a spatial filtering must be applied to the commonly available time-average data. Previous studies mostly focused on prominent features of striations, such as banded structures, and the generation mechanism; however, the differences revealed by applying different types of filtering methods have not received enough attention. In this paper we present a comprehensive study on the effectiveness of the different detection approaches to unveiling the striations. Three one-dimensional filtering methods: Gaussian smoothing, Hanning and Chebyshev high-pass filtering, are used to analyze SODA data and LICOM model outputs. The first two methods have been used in many previous studies; on the other hand, the Chebyshev filter is a newcomer for this purpose. Our results show that all three methods can reveal ocean banded structures, but the Chebyshev filtering is the best choice. The Gaussian smoothing is not a high pass filter, and it can merely bring regional striations, such as those in the Eastern Pacific, to light. The Hanning high pass filter can introduce a northward shifting of stripes, so it is not as good as the Chebyshev filter. In addition, a cutoff frequency is often needed in applying the high-pass filter, and this frequency depends on the spectrum analysis of the original data. In this paper, we discuss the filtering output and its spatial power spectra of three normalized cutoff-frequencies, 0.1, 0.3 and 0.7. When the cutoff-frequency is too low, the filtering is insufficient; on the other hand, if the cut-off frequency is too high, excessive filtering can happen. Our study shows that for analyzing the global ocean striations, the best normalized cutoff frequency domain is between 0.1 and 0.4. In addition, the bandwidth of striation for using the Chebyshev high pass filter to analyze the SODA data in a depth of 300 m is 150-300 km. In the general case, we propose to use the Chebyshev filter in lieu of Hanning or other methods for investigating ocean striations.
Theoretical study on radiative electron capture and subsequent radiative decay in collision of Xe54+ with Xe
Authors: Liang Teng  , Ma Kun  , Chen Xi  , Xie Lu-You  , Dong Chen-Zhong  , Shao Cao-Jie  , Yu De-Yang  , Cai Xiao-Hong  ,   Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China;,   Institute of Modern Physics, Chinese Academy of Science, Lanzhou 730000, China
Published: December 2020

Based on the multiconfiguration Dirac-Fock method and impulse approximation, the electron capture and following radiation decay of the projectile ion are studied theoretically for Xe atom which is bombarded by Xe54+ ion at 197 MeV/u. The radiative electron capture (REC) cross-sections and the corresponding emitted photon energies have been calculated in detail. Meanwhile, the probabilities of the radiative decay and energies of the REC final states are also calculated; combined with the calculated results in this paper, the X-ray spectra structure of radiative decay from projectile ion is further simulated. It is found that the simulated spectra are in good agreement with the newly measured results at Lanzhou Heavy-Ion Accelerator Device.
Ultrahigh birefringence terahertz porous fibers based on interlacing layered infiltration method
Authors: Li Shan-Shan  , Zhang Hao  , Bai Jin-Jun  , Liu Wei-Wei  , Chang Sheng-Jiang  ,   Office of Informationization Construction and Management, Nankai University, Tianjin 300071, China;,   Institute of Modern Optics, Nankai University, Tianjin 300071, China;,   School of Electronics and Information Engineering, Tianjin Polytechnic University, Tianjin 300387, China
Published: December 2020

In this paper, an interlacing layered infiltration method is proposed, using some liquid material as the common porous fiber with triangular air-hole array in the core region, which can achieve the characteristic of ultrahigh modal birefringence in this circumstance. Förstly, the basic properties of the porous fiber with a porosity of 43.08% are thoroughly analyzed by using a full-vector finite element method, as wellas the dispersion curves of the fiber, modal birefringence, fraction of the fundamental modal power for x and y polarizations, loss characteristics, etc. Secondly, to enhance the asymmetry of the proposed structure, some liquid material with a refractive index of 1.4 is infiltrated into the air holes in the fiber core region, by using interlacing filling method. It is found that the modal birefringence of the fiber dramatically increases. At an operation frequency of 1.1 THz, the peak value of modal birefringence rises from 1.05×10-3 to 1.36×10-2 after the infiltration operation. The fundamental model effective material absorption loss coefficients for x and y polarization modes increase from 0.16 dB/cm to 0.25 dB/cm and 0.28 dB/cm, respectively. And the operation frequency band increases from 1.1 to 1.9 THz. Simulation results indicate that the modal birefringence of the fiber can be remarkably improved by increasing the refractive index of the infiltrated liquid material. With an operation frequency of 2.2 THz and a refractive index of 2, this fiber can realize an ultrahigh modal birefringence of 8.03×10-2. Moreover, to achieve the gradient distribution of the refractive index, an interlacing layered infiltration method to infiltrate the liquid material with different refractive indices in different layers is employed. Results show that the confinement capability to the guided modes has been greatly enhanced. Results also show that the peak value of the modal birefringence for the fundamental modes does not exist in the operation band. It represents a monotonically increasing trend. At an operation frequency of 2.2 THz, the fiber modal birefringence can reach as high as 7.19×10-2. This scheme presents an ultrahigh modal birefringence, and it presents the tunable characteristic as well. This study may be of significance in the practical applications in the field of THz functional devices.
(1+2) dimensional spiraling elliptic spatial optical solitons in the media without anisotropy
Authors: Yu Ya-Dong  , Liang Guo  , Ren Zhan-Mei  , Guo Qi  ,   Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, South China Normal University, Guangzhou 510006, China
Published: December 2020

Starting from the nonlocal nonlinear Schrödinger equation in Cartesian coordinates, we also obtained nonlocal nonlinear Schrödinger equation in a rotating coordinate system.Assuming that the response function of media is Gaussian, we obtain the stable solutions of the solitons of nonlocal nonlinear Schrödinger equation in rotating coordinate system by means ot the imaginary-time evolution method. The propagation properties of the (1+2) dimensional spiraling elliptic spatial optical solitons in the media is discussed in different degrees of the nonlocality by using the split-step Fourier algorithm.The elliptic soliton profiles of the major and the minor axes are Gaussian shaped in a strongly nonlocal case, but not in a weakly nonlocal case. It is suggested that (1+2) dimensional elliptic solitons be highly dependent on the degree of nonlocality. The angular velocity for the change of the ellipticity is very sensitive when the nonlocality is strong,but in the weakly nonlocal case, the change of the angular velocity is very small.The angular velocity depends strongly on weakly nonlocal case to different degrees of ellipticity. Oppositely, in strongly nonlocal case, the value of the angular velocity is almost unchanged. In another way, the critical power for the solitons decreases as the nonlocality decreases in different degrees of ellipticity.Similarly,the critical power for the solitons decreases as the ellipticity decreases in different degrees of nonlocality.
Effect of coating-induced polarization aberrations on the focusing properties in high numerical aperture optical system
Authors: Li Yang-Hui  , Hao Xiang  , Shi Zhao-Yi  , Shuai Shao-Jie  , Wang Le  ,   College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018, China;,   State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China;,   2 Edwards Street, New Haven 06511, USA
Published: December 2020

The incident angles of the optical systems with high numerical apertures, such as lithography or microscope, are larger than those of normal ones. For these systems, polarized illumination is widely adopted. The coatings on their surfaces will make s and p polarization components of oblique incident light experience diverse amplitudes and phase modulations, and induce extra polarization aberrations. We apply the vectorial diffraction theory to assess the effects of coating-induced polarization aberrations on the focusing properties of these systems. By applying the generalized Debye integral, the relationship between the parameters of coating and electric field vector near the focal spot is established. Considering x linearly polarized light as the incident light field, we evaluate the potential influence of the coatings on the intensity and the full width at half maxium of focal spots. In the further discussion, we compare the results of different coatings when the various optimization goals are set, and certify that the phase difference caused by coating has more effect on focusing property. Based on this, the additional constraint conditions of coating design are proposed to suppress such disturbance, i.e. to properly increase relative weight of phase constraint conditions. With this proposed constraint conditions, we design and optimize an anti-reflection coating with low polarization aberrations. By applying this designing, the central intensity of focal spot can be enhanced by 12.5%, and the light energy utilization will be improved effectively.
Research on the frequency stabilization of pulsed differential absorbing lidar for CO2 detection based on matching algorithm
Authors: Ma Xin  , Gong Wei  , Ma Ying-Ying  , Fu Dong-Wei  , Han Ge  , Xiang Cheng-Zhi  ,   State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan 430079, China;,   Collaborative Innovation Center for Geospatial Technology, Wuhan 430079, China;,   School of Remote Sensing and Information Engineering, Wuhan University, Wuhan 430079, China
Published: December 2020

The differential absorption lidar (DIAL) can help us to obtain the vertical distribution of the atmospheric CO2 concentration, which is important to the study of carbon sources and carbon sinks. We design a seeder injected pulsed laser system, working as the laser source of the CO2 DIAL. Unlike the other CO2 DIALs, our laser source is the result of difference frequency of two lasers at the wavelengths of 1064 nm and 634 nm, respectively. It should be pointed out that the high frequency (wavelength) accuracy and stability of the emission laser, especially the on-line one, are greatly required in the CO2 DIAL system. However, the mechanical properties of the dye laser (634 nm) and the application of laser difference frequency technique make the wavelength drift constantly; besides, the extremely unstable energy of the pulsed laser increases the difficulty in identifying and stabilizing the on-line wavelength. Hence, a fast and efficient frequency (wavelength) stabilization method is needed to achieve a stable emission wavelength. Aiming at the research gap of the high precision requirements of on-line laser for this kind of pulsed DIAL, we propose a frequency stabilization method based on matching algorithm. The basic idea is to utilize the saturable absorption of CO2 molecule, by measuring the differential residual-intensity after the laser passing through dual absorption cells to calculate the optical depth (OD) and obtain the so-called pseudo CO2 absorption spectrum, which can be used to identify the on-line laser accurately. Finally, based on the matching algorithm of one-dimensional image, treating the OD as the gray value in the image, we implement the OD matching as a most important part in the process of frequency stabilization, and determine the exact position of the real-time output laser in the measured pseudo absorption spectrum. Thus, when some errors happen to the monitored ODs, by continuously adjusting the wavelength of the laser, the proposed method can fulfill the wavelength adjustment and accomplish the continuous frequency stabilization for on-line laser. Experimental results show that the frequency stabilization algorithm based on OD matching can satisfy the requirements for pulsed on-line laser frequency stabilization, and the sum of squares of deviation method is the optimal one in this application, with a stabilization accuracy of 0.3 pm. Besides, the proposed method can also be introduced in other laser frequency stabilization.