bluuebunny/crossref_metadata_2025 huggingface dataset:
GGA+U study on the effects of Ag doping on the electronic structures and absorption spectra of ZnO
Authors: Xu Zhen-Chao  , Hou Qing-Yu  ,   College of Science, Inner Mongolia University of Technology, Hohhot 010051, China
Published: December 2020

Nowadays, the studies on absorption spectra of Ag-doped ZnO have given two distinctly different experimental results, that is, the red shift or blue shift when the mole fraction of the impurity increases in a range from 0.0278 to 0.0417. To solve this contradiction, according to the first-principles plane-wave pseudopotential of the spin-polarized density functional theory (DFT), we set up three models for Zn1-xAgxO (x=0, 0.0278, 0.0417) to calculate the geometric structure and energy via the method of generalized gradient approximation (GGA+U). Calculated results indicate that compared with the Zn-O bond in pure ZnO system, the value of population decreases, and the bond length of Ag-O in Ag-doped ZnO system increases, this means covalent bond weakens and ionic bond strengthens. With the mole fraction of impurity increases in a range from 0.0278 to 0.0417, the orbital charges of O-2p, Zn-4s and Zn-3d keep unchanged, while the orbital charge of Ag-5s increases, and that of Ag-4d is reduced; the volume and total energy of the doped system increases, causing the system more unstable. Moreover, the formation energy of the doped system becomes lower, thereby making the doping difficult. Meanwhile, the band gap in the system narrows, and its absorption spectra exhibits a redshift. The calculated results are consistent with the experimental data, and can explain the phenomena reasonably. These results may be used in future design and preparation of new type photocatalyst from Ag-doped ZnO as a theoretical basis.
Effects of spin polarization on absorption saturation and recombination dynamics of carriers in (001) GaAs quantum wells
Authors: Fang Shao-Yin  , Lu Hai-Ming  , Lai Tian-Shu  ,   State Key laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
Published: December 2020

In this paper, the ultrafast dynamics of spin relaxation and recombination of photoexcited carriers has been studied in (001) GaAs quantum wells using a time-resolved pump-probe absorption spectroscopy under a nearly resonant excitation of heavy-hole excitons. It is found that the spin polarization of carriers influences both absorption saturation of linear polarized light and recombination dynamics of carriers. Pump fluence dependence of the ultrafast dynamics of spin relaxation and recombination of carriers is further studied, which shows that the effect of spin polarization on linearly polarized absorption saturation is reduced with lowering pump fluence. Spin-polarization-dependent absorption saturation effect can be ignored only as the pump fluence is weak. However, spin-polarization dependence of recombination dynamics is presented in turn at low pump fluence. Our analysis shows that such dependence originates from the spin-polarization dependence of the density of excitons formed in the excited carriers because recombination time constants of excitons and free carriers are very different so that the ratio of exciton density to free carrier density can influence the recombination dynamics. The spin-polarization dependence of ultrafast recombination dynamics of photoexcited carriers implies that the recombination time constant in the calculation of spin relaxation time from spin relaxation dynamics should be the recombination time of spin-polarized carriers, rather than the recombination lifetime of non-spin-polarized carriers as done currently. Exciton density is estimated based on 2D mass action law, which agrees very well with our experimental results. The good agreement between theoretical calculation and experimental results reveals that the effect of Coulomb screening on the formation of excitons may be ignored for a lower excited carrier density.
Effects of electron incident angle on the secondary electron yield for polyimide
Authors: Weng Ming  , Hu Tian-Cun  , Cao Meng  , Xu Wei-Jun  ,   Key laboratory for Physical Electronics and Devices of the Ministry of Education, Department of Electronic Science and Technology, Xi’an Jiaotong University, Xi’an 710049, China;,   Science and Technology on Space Microwave Laboratory, China Academy of Space Technology, Xi’an 710100, China.
Published: December 2020

Relationship between secondary electron yield (SEY) and electron incident angle has been measured for a polyimide sample. SEY as a function of incident angle at different incident electron energy is measured by use of a system with a single pulsed electron beam and a special surface charge neutralization technology based on the negatively biased collector. Measured results show that the SEY may deviate from the traditional law of monotonic increase with the incident angle when the angle is higher than a certain critical value. This deviation is even more obvious at lower incident electron energy. The critical incident angle decreases with decreasing incident energy. A theoretical analysis on the deviation is given in a simplified electron elastic scattering process. The distribution of the scattering region has an important effect on the relation of SEY versus incident angles. A sector region is introduced to describe the electron scattering region. Due to the limit of sample surface, the electron scattering region will decrease if the angle between the incident direction and the sample surface is smaller than half of the central angle of the sector. Corresponding SEY might no longer increase. Based on the Rutherford’s elastic scattering formula, a formula for the critical incident angle is derived as a function of incident electron energy, which is also confirmed by our measurement results. Finally, a revised SEY computation formula is developed which can give more accurate results at high incident electron angle.
A coding metasurfaces used for wideband radar cross section reduction in terahertz frequencies
Authors: Yan Xin  , Liang Lan-Ju  , Zhang Ya-Ting  , Ding Xin  , Yao Jian-Quan  ,   College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China;,   School of Opto-Electronic Engineering, Zaozhuang University, Zaozhuang 277160, China
Published: December 2020

In this paper, we propose a flexible, non-directional lowering scattering 1 bit coding metasurface which can significantly reduce the radar cross section (RCS) within an ultra wide terahertz (THz) frequency band. The total thickness of the coding metasurface is only 40.4 μm. The 1 bit coding metasurface is composed of “0” and “1” elements. And the “0” and “1” elements of metasurface are realized separately by a substrate without any metallic covering and that with a square metallic ring covering, the reflection phase difference of the two elements is about 180 degree in a wide THz frequency range. The theoretical, analytical, and simulation results show that the coding metasurfaces simply manipulate electromagnetic waves by coding the “0” and “1” elements in different sequences. Specific coding sequences result in the far-field scattering patterns varying from single beam to two, three, and numerous beams in THz frequencies. The metasurface with the numerous scattering waves can disperse the reflection into a variety of directions for non-periodic coding sequence way, and in each direction the energy is small based on the energy conservation principle. Full-wave simulation results show that the reflectivity less than -10 dB for coding metasurface can be achieved in a wide frequency range from 1-1.4 THz at normal incidence, and the RCS reduction as compared with a bare metallic plate with the same size is essentially more than 10 dB, in agreement with the bandwidth of reflectivity being less than -10 dB; the maximum reduction can be up to 19 dB. The wideband RCS reduction results are consistent with the bandwidth of 180 degrees phase difference between the two elements “0” and “1”. This wideband characteristic of RCS reduction can be kept up as the coding metasurface is wrapped around a metallic cylinder with a diameter of 4 mm. The presented method opens a new way to control THz waves by coding metasurface, so it is of great application values in stealth, imaging, and broadband communications of THz frequencies.
Operator-ordering identities for mutual transformation of power of coordinate-momentum operators obtained by a new concise method
Authors: Fan Hong-Yi  , Lou Sen-Yue  , Zhang Peng-Fei  ,   Department of Physics, Ningbo University, Ningbo 315211, China;,   Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Since the foundation of quantum mechanics, operator-ordering identities for mutual transformation of power of coordinate-momentum operators have been a fundamental and tough topic. To the best of our knowledge, this topic has not been tackled smoothly because there is no elegant and direct way to investigate it. In this paper we report a very concise and novel method to handle this topic, i.e., we employ the generating function of two-variable Hermite polynomial and the characteristics of ordered operators to derive a series of operator-ordering identities for mutual transformation of power of coordinate-momentum operators: they surly possess potential applications. The essence of our method lies in the fact that coordinate-momentum operators can be permutable within ordered product of operators, just as the scenarios in P-Q ordering, Q-P ordering and Weyl ordering. We also derive the integration transformation formula about two-variable Hermite polynomial in phase space. The correspondence relation between operator ordering and quantization recipe is established. The beauty of theoretical physics is embodied extensively in the paper.
Hyper-parallel photonic quantum computation and manipulation on hyperentangled states
Authors: Ren Bao-Cang  , Deng Fu-Guo  ,   Department of Physics, Beijing Normal University, Beijing 100875, China
Published: December 2020

Photon system is a promising candidate for quantum information processing, and it can be used to achieve some important tasks with the interaction between a photon and an atom (or a artificial atom), such as the transmission of secret information, the storage of quantum states, and parallel quantum computing. Several degrees of freedom (DOFs) of a photon system can be used to carry information in the realization of quantum information processing, such as the polarization, spatial-mode, orbit-angular-momentum, time-bin, and frequency DOFs. A hyperparallel quantum computer can implement the quantum operations on several DOFs of a quantum system simultaneously, which reduces the operation time and the resources consumed in quantum information processing. The hyperparallel quantum operations are more robust against the photonic dissipation noise than the quantum computing in one DOF of a photon system. Hyperentanglement, defined as the entanglement in several DOFs of a quantum system, can improve the channel capacity and the security of long-distance quantum communication, and it can also be conductive to completing some important tasks in quantum communication. Hyperentangled Bell-state analysis is used to completely distinguish the 16 hyperentangled Bell states, which is very useful in high-capacity quantum communication protocols and quantum repeaters. In order to depress the effect of noises in quantum channel, hyperentanglement concentration and hyperentanglement purification are required to improve the entanglement of the quantum systems in long-distance quantum communication, which is also very useful in high-capacity quantum repeaters. Hyperentanglement concentration is used to distill several nonlocal photon systems in a maximally hyperentangled state from those in a partially hyperentangled pure state, and hyperentanglement purification is used to distill several nonlocal photon systems in a high-fidelity hyperentangled state from those in a mixed hyperentangled state with less entanglement. In this reviewing article, we review some new applications of photon systems with multiple DOFs in quantum information processing, including hyperparallel photonic quantum computation, hyperentangled-Bell-state analysis, hyperentanglement concentration, and hyperentanglement purification.
Chaotic signal denoising in a compressed sensing perspective
Authors: Li Guang-Ming  , Lü Shan-Xiang  ,   School of Computer Science, Dongguan University of Technology, Dongguan 523808, China;,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China
Published: December 2020

Nonlinear time series denoising is the premise for extracting useful information from an observable, for the applications in analyzing natural chaotic signals or achieving chaotic signal synchronizations. A good chaotic signal denoising algorithm processes not only a high signal-to-noise ratio (SNR), but also a good unpredictability of a signal. Starting from the compressed sensing perspective, in this work we provide a novel filtering algorithm for chaotic flows. The first step is to estimate the strength of the noise variance, which is not explicitly provided by any blind algorithm. Then the second step is to construct a deterministic projection matrix, whose columns are polynomials of different orders, which are sampled from the Maclaurin series. Since the noise variance is provided from the first step, then a sparsity level with regard to this signal can be fully constructed, and this sparsity value in conjunction with the orthogonal matching pursuit algorithm is used to recover the original signal. Our method can be regarded as an extension to the local curve fitting algorithm, where the extension lies in allowing the algorithm to choose a wider range of polynomial orders, not just those of low orders. In the analysis of our algorithm, the correlation coefficient of the proposed projection matrix is given, and the reason for shrinking the sparsity when the noise variance increases is also presented, which emphasizes that there is a larger probability of error column selection with larger noise variance. In the simulation, we compare the denoising performance of our algorithm with those of the wavelet shrinking algorithm and the local curve fitting algorithm. In terms of SNR improvement for the Lorenz signal, the proposed algorithm outperforms the local curve fitting method in an input SNR range from 0 dB to 20 dB. And this superiority also exists if the input SNR is larger than 9 dB when compared with the wavelet methods. A similar performance also exists concerning the Rössler chaotic system. The last simulation shows that the chaotic properties of the originals are largely recovered by using our algorithm, where the quantity for "chaotic degree" is described by using the proliferation exponent.
Two-photon radio frequency spectroscopy of 49S Rydberg state
Authors: Li Jing-Kui  , Yang Wen-Guang  , Song Zhen-Fei  , Zhang Hao  , Zhang Lin-Jie  , Zhao Jian-Ming  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China;,   National Institute of Metrology, Beijing 100029, China
Published: December 2020

Rydberg atoms, with large principal quantum number, exhibit certain properties, such as long lifetimes and strong interactions with fields and other atoms, which have been extensively investigated recently. One of the properties is the electromagnetically induced transparency (EIT) of Rydberg ladder system, which can be used to measure the radio frequency (RF) field with high sensitivity. In this paper, we investigate the quantum coherent effect of cesium Rydberg atom in a three-level ladder system involving the ground state (6S1/2), the excited state (6P3/2) and 49S1/2 Rydberg state in room temperature vapor cell. The probe laser (852 nm) drives the transition of 6S1/2(F=4)→6P3/2(F'=5), while the coupling laser (510 nm) couples the Rydberg transition of 6P3/2 (F'=5)→nS1/2. A typical electromagnetically induced transparency spectrum is obtained when the weak probe laser is scanned through the transition of 6S1/2(F=4)→6P3/2(F'=5) and the coupling laser tuning to Rydberg transition. The two-photon RF spectra are observed when the RF field with a frequency of ～16.9 GHz couples the Rydberg transition of 49S1/2→47D3/2, where the EIT signal is split into two EIT peaks due to the interaction between the RF field and Rydberg atoms. The dependences of EIT splitting on the power of RF field are investigated. The results show that the EIT splitting increases with the power of RF field, which can inversely be used to measure the RF field with a higher spatial resolution in the future.
Quantum calculations for photodetachment cross sections of H- in an equilateral triangle cavity
Authors: Liu Zhi-Gang  , Liu Wei-Long  , Zhao Hai-Jun  ,   Center for Molecules Research, School of Physics and Information Science, Shanxi Normal University, Linfen 041000, China
Published: December 2020

In this paper, the photodetachment cross section of negative hydrogen ion inside a tube cavity with an equilateral triangle cross section is investigated by the traditional quantum approach. Then the analytic formulas each as a function of photon energy having been derived, some interesting oscillations in the photodetachment cross section are shown from the numerical illustrations. The formulas indicate that the oscillations are related to the positions of the ion and the photon polarization. The polarization of photons being perpendicular to the normal direction of the triangle, the cross sections apparently display large amplitude sawtooth-shaped oscillations, while being parallel to the normal direction of the triangle, oscillations are still present and observable from the quantum calculations, although the amplitudes of the oscillations are rather small. The subtle effect is also observed in the quantum theory for photodetachment in an electric field. The formulas also reveal threshold behaviors in the photodetachment cross sections. The threshold is expressed as Eth=(8π2/9l2)(m2+n2-mn), where l is the length of the triangle side, n and m are for all integers with m≥2n. When the polarization of photons is perpendicular to the normal direction of the triangle and the energy of the detached electron is above each threshold, the threshold behavior is Δσ∝(E-Eth)-1/2. When the polarization of photons is parallel to the normal direction of the triangle and the energy of the detached electron is above each threshold, the threshold behavior is Δσ∝(E-Eth)1/2. Furtherly, if the negative hydrogen ion is placed near one corner of the equilateral triangle, the quantum results show agreement with those from the closed-orbit theory when the negative hydrogen ion is in a wedge with an opening angle of 60 degrees. If that occurs, the five sinusoidal oscillations, each of which will correspond to one closed orbit, can be extracted from the photodetachment cross sections. These five closed orbits are definitely the orbits when the negative hydrogen ion is in a wedge with an opening angle of 60 degrees.
Dynamic behavior of hydrogen clusters under intense femtosecond laser
Authors: Zhang Chun-Yan  , Liu Xian-Ming  ,   School of Science, Hubei Minzu University, Enshi 445000, China
Published: December 2020

The molecular dynamics model is adopted to investigate the dynamical behavior of hydrogen cluster irradiated by an intense femtosecond laser. Being contrary to the predictions from the Coulomb explosion model, this paper points out that the explosion of hydrogen cluster is anisotropic. The component of proton energy along the laser polarization direction is much larger than the component perpendicular to the polarization direction. This paper discusses the mechanism responsible for the anisotropy explosion. In the process of the interaction of femtosecond laser with cluster, the electrons undergo the inner ionization and then oscillate along the direction of laser polarization. During the oscillation of electrons, part of them will escape from cluster. The escaping of the electrons would lead to two correlation effects. First, the anisotropic distribution of the electric field caused by the oscillation of electrons would not be neutralized. For one thing, during the oscillating of electrons, they will be pulled to one pole of cluster so the electric field of the opposite pole would be larger, the electrons in this region will experience larger Coulomb repulsive force and gain lager acceleration. For another thing, the electron number contained in the cluster will decline during each laser cycle. So the proton in this region will gain a pure acceleration. Second, during the oscillation of electrons, part of electrons will escape from cluster. During their escaping they will pull the protons at the pole and the protons move toward the direction of electron escaping direction. These two correlation effects cause the anisotropic explosion of hydrogen cluster. This paper also discusses the influences of cluster and laser parameters on the degree of anisotropy.
A broad stopband common-mode suppression defected ground structure filter with complementary structure
Authors: Zeng Zhi-Bin  , Yao Yin-Di  , Zhuang Yi-Qi  ,   School of Microelectronics, Xidian University, Xi'an 710071, China;,   School of Communication and Information, Xi'an University of Posts and Telecommunications, Xi'an 710121, China
Published: December 2020

A low-cost defected ground structure (DGS) wideband stopband filter adopting complementary structure is proposed, which is designed for common-mode noise suppression in high-speed differential signals. The filter is etched below the low cost FR4 printed circuit board. To avoid stimulating the common-mode noise, the DGS cells on ground planes are kept symmetrical to the central line of the two differential signal lines. Both sides of the filter adopt a symmetric cup-shape DGS structure and the middle of the filter adopts a symmetric umbrella-type structure. All of the DGS structures are complementary, which makes the filter compact and miniaturized. What is more, because the spaces among the three DGS are closer, there exist the mutual inductances among them, which are utilized to achieve a wide stopband filter. The simulated result demonstrates the proposed filter has a wideband bandwidth of 6.8 GHz over 20 dB. In order to analyze the effect of compact structure of the filter, a filter having the same DGS patterns but large spaces among them is compared with it. The simulated result demonstrates that the stopband bandwidth of the compared filter has a wideband bandwidth of 4.4 GHz over 20 dB, of which the bandwidth is about 2.4 GHz less than that of the proposed filter. It is obvious that there exists a mutual inductance in the compact DGS structure common-mode filter, which plays an important role in broadening the bandwidth of the proposed filter. In order to facilitate analysis, an equivalent model of LC circuit is also given. The equivalent parameters of LC can be deduced from the definition of 3 dB cut-off frequency and resonant frequency, of which the values can be obtained by the HFSS simulation. The simulated and measured results show that the differential signal under the DGS filter is nearly intact, and the common-mode noise can be reduced over 20 dB from 4.6 GHz to 11.4 GHz and over 15 dB from 4.3 GHz to 12 GHz, while the area of the filter is only 10 mm by 10 mm. Compared with the periodic DGS at the same suppression depth of common-mode noise over 20 dB, the method has the advantages that surface area is reduced to no more than 30%, and the stopband width is increased by over 50%.
Design and radar cross section reduction experimental verification of phase gradient meta-surface based on cruciform structure
Authors: Wu Chen-Jun  , Cheng Yong-Zhi  , Wang Wen-Ying  , He Bo  , Gong Rong-Zhou  ,   School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

A two-dimensional phase gradient meta-surface based on cross structure insensitive to polarization is designed and verified by simulation and experiment. Several periodic metal cross structures are integrated into a superstructure, and an additional component of the wave vector on the meta-surface is formed and the direction of refelction wave can be regulated. Thus the backward radar cross section (RCS) reduction can be realized by the mechanism of anomalous reflection. Experimental results indicate that in a frequency range from 3.2 to 3.4 GHz, the reduction of backward RCS of meta-surface reaches a highest value of 18.19 dB in the normal direction of meta-surface and 8 dB on the average in an angular range between -30° and +30°.
Fast-pulse repetitive frequency emission characteristic of high current carbon nanotubes cathode
Authors: Xiang Fei  , Wu Ping  , Zeng Fan-Guang  , Wang Gan-Ping  , Li Chun-Xia  , Ju Bing-Quan  ,   Key Laboratory on Technology of High Hower Microwave, Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900, China;,   Key Laboratory on Technology of High Power Microwave, Northwest Institute of Nuclear Technology, Xi'an 710024, China;,   Zhengzhou Institute of Aeronautical Industry Management, Zhengzhou 450015, China
Published: December 2020

With the development of high power microwave technology, the demands for electron beam repetition frequency, current density, response time and emission uniformity are higher and higher. Carbon nanotube (CNt) cathode has been widely investigated, because of its special structure and excellent field emission characteristics. CNt cathode is regarded as a thin film high current cathode, and the interface bonding will affect vacuum performance, stability, lifetime and repeat ability. The direct growth of CNt is a simple and effective means for preparing cathode. When electron energy reaches 1 MeV and the pulse upward gradient attains approximately 60 kV/ns, for CNt cathode, its the emission beam intensity reaches 15 kA and the peak bundle density attains about 1 kA/cm2, the response between beam voltage and current is fast. With the increase of repetition frequency, the emission stability decreases gradually. When the emission power is 15 GW and the emission stability repetitive frequency is 50 Hz, the cathode emission is stable. However with the increase of frequency, the stability becomes weak. When the repetition frequency reaches 100 Hz, voltage and current are almost split into two sections, and the delay time is obviously different. The relation between the voltage and the current meet the exponent law, which is different from the field emission characteristic. After a 1000 shot emission, the morphology of CNt cathode is intact, desorption from the interface of CNt does not happen. So the emission mechanism is flashover plasma emission. Through analyzing the experimental data and considering the plasma expansion effect on diode gap, the plasma speed can be estimated to be about to 3.9 cm/μs.
Focusing performance of hard X-ray single Kinoform lens
Authors: Chen Zhi  , Xu Liang  , Chen Rong-Chang  , Du Guo-Hao  , Deng Biao  , Xie Hong-Lan  , Xiao Ti-Qiao  ,   Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Nowadays, X-ray nanoprobe plays an important role in many research fields, ranging from materials science to geophysics and environmental science, to biophysics and protein crystallography. Refractive lenses, mirrors, and Laue lenses, can all focus X-rays into a spot with a size of less than 50 nm. To design a refractive lens at fixed wavelengths, absorption in the lens material can be significantly reduced by removing 2πup phase-shifting regions. This permits short focal length devices to be fabricated with small radii of curvatures at the lens apex. This feature allows one to obtain a high efficiency X-ray focusing. The reduced absorption loss also enables optics with a larger aperture, and hence improving the resolution for focusing. Since the single Kinoform lens can focus hard X-ray into a spot on a nanoscale efficiently, it has very important application prospect in X-ray nano-microscopy and nano-spectroscopy. We present a theoretical analysis of optical properties of the single Kinoform lens. Using Fermat's principle of least time, an exact solution of the single Kinoform lens figure is derived. The X-ray diffraction theory is reviewed. The complex amplitude transmittance function of the X-ray single Kinoform lens is derived. According to Fourier optics and optical diffraction theory, we set up the physical model of X-ray single Kinoform lens focusing. Employing this physical model, we study how the focusing performance of hard X-ray single Kinoform lens is influenced by the material, the photon energy, the number of steps and the vertex radius of curvature. We find that diamond single Kinoform lens can achieve a smaller focusing beam size with higher intensity gain than Al and Si single Kinoform lens. The single Kinoform lens designed at a certain photon energy can also focus other photon energies with different lateral beam sizes, axial beam sizes, intensity gains and focusing distances. The numbers of steps of a single Kinoform lens can be lessened with the thickness of step increasing, while the single Kinoform lens keeps good focusing performance. To improve the focusing performance further, reducing the vertex radius of curvature is proposed. Following these rules, a single Kinoform lens is optimally designed to focus 30 keV hard X-ray down to a lateral size of 14 nm (full-width at half-maximum, FWHM) and an axial size of 62 μm (FWHM) with an intensity gain of four orders of magnitude and transmittance of 30%.
Polarization characteristics of the lattice resonance of metal nanoparticle array
Authors: Yin Cheng  , Xu Tian  , Chen Bing-Yan  , Han Qing-Bang  ,   Jiangsu Key Laboratory of Power Transmission and Distribution Equipment Technology, Hohai University, Changzhou 213022, China;,   Physics Department, Nantong University, Nantong 226007, China
Published: December 2020

A special lattice resonance can be observed when the array period of a metal nanoparticle array matches the resonant wavelength of the localized plasmon resonance of an isolated particle. The lattice resonance is sharper and its linewidth is narrower than the localized plasmonics resonance of a single particle. According to the modified long wavelength approximation approach, we discuss the extinction cross-section of the rectangular array in terms of the array factor and the particle polarizability. In this paper we emphasize the polarization characteristics of the regular array when the laser is incident vertically under different polarizations, and we also discuss in detail the variation of the array factor with the direction of electric dipole, and its influence on extinction cross section of the particle array. The square lattice with big size is polarization independent, while the rectangular lattice is polarization dependent. The coupling between the neighboring particle dipoles along the two lattice vectors of the regular array gives rise to a maximum value of its array factor, which determines a minimum value of the extinction cross section. When the incident light is polarized along one of the lattice vectors, the dipole coupling along that direction can be ignored since the particles are located in the far field of its neighboring particles, and the relevant peak in the array factor disappears.
Multi-transverse-mode and wavelength split characteristics of vertical cavity surface emitting laser
Authors: Guan Bao-Lu  , Liu Xin  , Jiang Xiao-Wei  , Liu Chu  , Xu Chen  ,   Laboratory of Opto-electronics Technology, College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

We study the multi-transverse mode distributions and the wavelength splittings with different designed oxide apertures of the oxide-confined VCSEL. By developing the effective index model and BPM algorithm theory, the characteristics of transverse optical field distribution are calculated with circular aperture and ellipsoid aperture, which are compared with our experimental results of multi-wavelength spectra of high-order transverse modes. The results show that the orthogonality of the different crystal orientation modes will be broken by the oxidation-induced ellipsoid aperture, and the maximum wavelength spltting of the degenerated high-order mode is 0.037 nm, which can be reduced as the diameter of aperture increases. The results in this paper will provide a useful reference for multi-transverse mode locking of oxide-confined VCSELs.
3000 W direct-pumping all-fiber laser based on domestically produced fiber
Authors: Wang Xue-Jiao  , Xiao Qi-Rong  , Yan Ping  , Chen Xiao  , Li Dan  , Du Cheng  , Mo Qi  , Yi Yong-Qing  , Pan Rong  , Gong Ma-Li  ,   Center for Photonics and Electronics, Department of Precision Instruments, Tsinghua University, Beijing 100084, China;,   Wuhan Fiber Home Technologies Group, Wuhan 430074, China;,   No. 46 Research Institute of China Electronics Technology Group Corporation, Tianjin 300220, China
Published: December 2020

In this paper we present an all-fiber directly pumped fiber laser in master oscillator power amplifier configuration based on domestically manufactured fibers. In the amplifier stage of the laser, the gain fibers adopt the 20/400 μm Yb-doped double cladding fibers manufactured separately by Wuhan Fiber Home Technologies Group and China Electronics Technology Group Corporation No. 46 Research Institute in two individual experiments. Via this homemade amplifier stage, the system achieves a 1080 nm fiber laser with output powers of 3050 W and 3092 W respectively with two types of fibers. When the gain fiber of the amplifier adopts the YDF manufactured by Wuhan Fiber Home Technologies Group, the corresponding extraction efficiency and the optical-to-optical efficiency reach 67.3% and 63.0% respectively. No residual pump laser is found in the spectrum of output laser, and the beam quality is measured to be M2<2. Similarly, when the gain fiber of the amplifier adopts the YDF manufactured by China Electronics Technology Group Corporation No. 46 Research Institute, the corresponding extraction efficiency and the optical-to-optical efficiency reach 68.2% and 63.9% respectively. To the best of our knowledge, this is the best result ever reported for directly pumped all-fiber laser. Meanwhile, as we use the domestically manufactured fiber as the gain fiber in the amplifier stage, the result verifies the usage of homemade active fibers in 3-kilowatt level fiber laser. By combining the results of the high power fiber laser, the low efficiency of domestic fiber laser in our experiment might be explained to be due to defects in fiber manufacturing process, the inhomogeneous refractive index of the core, structural flaw of the homemade fiber observed by the microscopic images of the cross section and the splicing fuse of homemade fibers. The main difficulty of these two experiments lies in the heat dissipation of the gain fiber in the amplifier stage. Also, due to the restriction of experimental condition, photodarkening test is unable to run for a longer period of time, which is the focus of our further work. Therefore, measures such as refining fiber manufacturing techniques, increasing pump power and optimizing the length of fiber are suggested to be taken in order to obtain a higher output power from homemade fiber laser.
Two-dimensional observation of atmospheric trace gases based on the differential optical absorption spectroscopy technique
Authors: Liu Jin  , Zou Ying  , Si Fu-Qi  , Zhou Hai-Jin  , Dou Ke  , Wang Yu  , Liu Wen-Qing  ,   Key Laboratory of Environmental Optical and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   Shanghai Academy of Spaceflight Technology, Shanghai 201109, China
Published: December 2020

A two-dimensional observation method of atmospheric trace gases based on differential optical absorption spectroscopy technique is reported in this paper. The conventional multi-axis differential absorption spectrum system is improved to make the telescope point to different directions. Thereby, the trace gas information of different azimuthal angles and consequently the distribution and variation of pollution gases around the measurement point can be obtained simultaneously. Using this method, NO2 concentration and distribution as well as O4 slant column densities are obtained. High degree of similarity is shown between O4 slant column density simulated by radiation transfer model and the measured data. Based on the measured O4 data, light path information can also be extracted. By combining with radiation transfer model, the light path differences caused by different profile modifications are corrected. The corrected NO2 slant column density is further converted into the volume mixing ratio. By comparing the calculated NO2 mixing ratio with the long-path-differential optical absorption spectroscopy data, the results show good consistency with each other.
Optimization design of dichroic plate for the advanced technology in microwave imaging diagnostic
Authors: Yang Hua-Bin  , Tong Li  , Zhu Yi-Lun  ,   Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Taking theories and stimulation as the starting points, this paper gives the optimal design for dichroic plate in the advanced technology of imaging diagnostic. Dichroic plate is firstly analyzed theoretically, whose result shows that it is a wavelength-sensitive device, different from the traditional understanding of dichroic plate. In fact, a dichroic plate is a wavelength selective, and its outward manifestation is a frequency selective plate. There are two ways of putting medium into the dichroic plate. It can be seen that with the increase of the medium's semidiameter, the passband bandwidth increases obviously and the rising slope is sharper. When the medium is fully populated, the passband bandwidth reaches its maximum, the freguency increasing upto 12 GHz, and in the meanwhile the rising slope possessing the top speed. The other is to adopt the method of coating. If a hollow dielectric cylinder is filled to become a waveguide, it can also be seen that with the thickening of the wall of the dielectric cylinder, the passband bandwidth also increases obviously and the rising slope is sharper. When the medium is fully filled in the circular waveguide, the result is the same as that of the first method.
Experimental measurement of liquid deuterium equation of state data
Authors: Jia Guo  , Huang Xiu-Guang  , Xie Zhi-Yong  , Ye Jun-Jian  , Fang Zhi-Heng  , Shu Hua  , Meng Xiang-Fu  , Zhou Hua-Zhen  , Fu Si-Zu  ,   Shanghai Institute of Laser Plasma, Shanghai 201800, China
Published: December 2020

An experimental research platform is built on Shenguang Ⅱ high power laser facility for obtaining the equation of state of liquid deuterium which has ability to control the temperature in a range of 12-300 K with an accuracy of ±0.03 K in 80 min. By optimizing the coating processing and cleaning the target, we solve the problems that the residual reflection is too high and serious frosting takes place on the window of the target at low temperature, then we obtain the experimental image with a good signal-to-noise ratio. By using the impedance matching method and velocity interferometer system for any reflector, experimental Hugoniot data of liquid deuterium are obtained at a pressure of about 60 GPa under the output condition of 3ω, 3 ns, 1200 J on Shenguang Ⅱ high power laser, which agrees well with the other published data in the same pressure regime and provides a good foundation for the next experimental study of liquid deuterium equation in 100 GPa pressure regime.
Influence of powdered state on crystallization during laser solid forming Zr55Cu30Al10Ni5 bulk metallic glasses
Authors: Zhang Yuan-Yuan  , Lin Xin  , Yang Hai-Ou  , Li Jia-Qiang  , Ren Yong-Ming  ,   State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Laser solid forming (LSF) is a viable and promising manufacturing technique for preparing bulk metallic glasses (BMGs) without size limitation. Owing to the structural heredity of alloy melts, the crystallization characteristic of the powder has an important influence on that of the deposit during LSF process. In this work, the as-prepared Zr55Cu30Al10Ni5 (Zr55) alloy powder and the Zr55 alloy powder annealed at 1000 K are used for LSF of Zr55 BMGs. The influence of the crystallization characteristic of Zr55 alloy powder on the crystallization behavior of the remelted zone (RZ) and heat affected zone (HAZ) in the deposit are investigated. It is found that the as-prepared Zr55 powder prepared by plasma rotating electrode process (PREP) is composed of the amorphous phase and Al5Ni3Zr2 phase. When the heat input of laser is low, there exist some Al5Ni3Zr2 residual phases in the amorphous matrix in the RZ, and there appear some Cu10Zr7, CuZr2 and NiZr2 phases besides the Al5Ni3Zr2 phase in the HAZ for the deposit fabricated by as-prepared Zr55 powders. With the increase of the heat input of laser, the RZ remains the amorphous state since the Al5Ni3Zr2 phase is completely remelted, while there are a large quantity of Al5Ni3Zr2 phases and some other crystallization phases precipitated in the HAZ because the heating and cooling rate decrease in the HAZ during LSF. Fabricated by the fully crystallized annealed powder, the deposit is mainly of the amorphous phase, and almost no Al5Ni3Zr2 phase is found even if the incident laser power is low. It is shown that the crystallization of the deposit fabricated by the annealed powder at the low heat input does not change remarkably with the increase of the deposited layers. The Zr55 deposit with five deposited layers could still keep large volume fraction of amorphous phase. This is mainly because the powder experiences the structure relaxation entirely during the annealing treatment, and the volume fraction of the short/medium-range ordered structure associated with the Al5Ni3Zr2 phase in the powder is reduced. Therefore, the volume fraction of the Al5Ni3Zr2 clusters in re-solidified amorphous RZ in the deposited layer decreases during LSF, which is conducible to the increase of the thermal stability of the already-deposited layer. In result, the area of the HAZ in the subsequent deposition decreases and the precipitation of Al5Ni3Zr2 phase is suppressed. In conclusion, increasing the heat input of laser aggravates the crystallization of the deposited layers, and the Al5Ni3Zr2 cluster in the powder has an important influence on the crystallization behavior of the Zr55 deposited layers.
Enhancement and quenching of photoluminescence from Au nanoparticles and CdTe quantum dot composite system
Authors: Zhou Xiao-Dong  , Zhang Shao-Feng  , Zhou Si-Hua  ,   School of Physics and Mechanical & Electrical Engineering, Zhoukou Normal University, Zhoukou 466001, China;,   School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471023, China
Published: December 2020

New composite systems consisting of Au nanoparticles (NPs) and CdTe quantum dots (QDs) are fabricated by spin coating chemically synthesizing CdTe QDs on silica substrates which have already been implanted by Ag ions through using a metal vapor vacuum arc (MEVVA) ion source implanter. By thermally annealing the Au ions implanted silica substrates, the growth and redistribution of Au NPs can be controlled, the influence of localized surface plasmon (LSP) of Au NPs on the photoluminescence (PL) of CdTe QDs is well studied. The optical properties, surface morphologies, microstructures, and light emission properties of the Au-ion implanted samples are investigated by using optical absorption spectroscopy, atomic force microscopy, transmission electron microscopy and PL spectra measurements. PL spectra show that the PL intensities from Au NPs and CdTe QDs composite systems can be enhanced or quenched compared with those of CdTe QDs directly spin coated on bare silica substrate. The underlying interaction processes between Au NPs and CdTe QDs are discussed in depth, and the new mechanisms for the PL enhancement and quenching in the Au-CdTe coupled systems are put forward. These results provide a good reference for the future designing of optoelectronic devices with improved luminescence efficiency by LSP of metal NPs.
Shot noise characteristics of Majorana fermions in transport through double quantum dots
Authors: Zhou Yang  , Guo Jian-Hong  ,   Department of Physics, Capital Normal University, Beijing 100048, China
Published: December 2020

Majorana fermions are their own antiparticles, which play an important role in fault-tolerant topological quantum computation. Recently, the search for Majorana fermions in condensed matter physics, is attracting a great deal of attention as quasiparticles emerge. In this paper we consider a specific model consisting of double quantum dots and a tunnel-coupled semiconductor nanowire on an s-wave superconductor, since the nanowire may support Majorana fermions under appropriate conditions. We study the electron transport through the double quantum dots by using the particle-number resolved master equation. We pay particular attention to the effects of Majorana's dynamics on the current fluctuation (shot noise). It is shown that the current and the shot noise measurement can be used to distinguish Majorana fermions from the usual resonant-tunneling levels. When there exist Majorana fermions coupling to the double quantum dots, a difference between the steady-state source and drain currents depends on the asymmetry of electron tunneling rates. The asymmetric behaviors of the currents can reveal the essential features of the Majorana fermion. Moreover, the dynamics of Majorana coherent oscillations between the semiconductor nanowire and the double quantum dots is revealed in the shot noise, via spectral dips together with a pronounced zero-frequency noise enhancement effect. We find, on the one hand, that the peak of the zero-frequency noise becomes a dip in the case of weak coupling between double quantum dots and the nanowire; on the other hand, for the strong coupling the dip of the zero-frequency noise becomes even further deep with side dips towards high frequency regimes. Furthermore, the dip of the zero-frequency noise disappears and a zero-frequency noise peak gradually develops when the dot-electrode coupling is tuned by gate voltage. As a result, the combination of the current and the shot noise through double quantum dots allows one to probe the presence of Majorana fermions.