bluuebunny/crossref_metadata_2025 huggingface dataset:
Visible light emission from surface of nickel bombarded by slow Xeq+ (4 q 20) ion
Authors: Xu Qiu-Mei  , Yang Zhi-Hu  , Guo Yi-Pan  , Liu Hui-Ping  , Chen Yan-Hong  , Zhao Hong-Yun  ,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   College of Astronautics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

Bombarded by slow highly charged ion (SHCI), particles including ions and atoms of metal are excited and ejected from the sample. Optical emission can be observed for the radiative de-excitation of some excited atomic particles. The important information about particle ejection and incident ion neutralization, as well as the nature, the kinetic energy, and the number of the sputtered excited particles can be obtained by studying the optical emission process. The optical emission from the the collisions between slow (V~0.38 VBohr) highly charged Xeq+ (4 q 20) ions and high purity Ni (99.995%) surface is studied. The experiment is carried out at the 320 kV for multi-discipline research with HCIs in the Institute of Modern Physics, Chinese Academy of Sciences. The spectral lines are analyzed by using an Sp-2558 spectrometer equipped with a pattern of 1200 groves/mm blazed at 500 nm and an R955 photomultiplier tube at the exit slit. The target beam current corresponding to the dwell time is recorded, which can be translated into the incident ion current. Based on the formula of Y=N/(t/Ceq), the spectral line intensity is normalized. The normalized spectrum can be obtained from the interaction of 0.38VBohr Xe20+ ions with Ni surface in a wavelength range of 400-510 nm. The species at excited state can be identified by comparing the wavelengths of spectral lines with those in the standard spectroscopic table. Most of the observed spectral lines are identified as being from the electron transitions of Ni I 3d9(2D)4p-3d9(2D5/2)4d, Ni I 3d8(3F)4s4p(3P)-3d84s(4F)5s and Ni Ⅱ 3p63d9-3p63d8(3P)4s, as well as Xe I 5p5(2P3/2)6s-5p5(2P3/2)8p, Xe Ⅱ 5p4(3P2)6p-5p4(3P2)6d and Xe Ⅲ 5s25p3(2D)6s-5s25p3(2D)6p. Compared with the single charged ion, some neutralized incident ions yield Xe I, Xe Ⅱ, Xe Ⅲ spectral lines. The photon yields of spectral lines, such as Xe Ⅱ 410.419, Xe Ⅲ 430.444, Xe Ⅱ 434.200, Xe Ⅱ 486.254, Ni I 498.245, Ni I 501.697, Ni I 503.502, Ni I 505.061 and Ni I 508.293 nm, are presented each as a function of charge state of incident ion. The results show that the photon yield increases with the increase of the charge state, which is consistent with the potential energy of the incident ion. The potential energy is the driving force for photon emission of excited Ni atom. The neutralization of Xeq+ is in good agreement with that indicated by the classical over-the-barrier model.
Establishment of ionospheric model containing sporadic E and its applications in target height measurement
Authors: Luo Huan  , Xiao Hui  ,   519 Air Force Army of PLA, Zunyi 563000, China;,   Aerospace Early Warning Equipment Department, Air Force Early Warning Academy, Wuhan 430019, China
Published: December 2020

Ionosperic sporadic-E layer (Es layer) is the irregular structure in ionosphere which often occurs in summer of China, but the current model of height estimation with high frequency rays does not consider the Es layer, which often makes a large error in the estimation of the target height. In this paper, the parameters of the actual ionosphere are analyzed by using the measured data of the ionospheric vertical measurement station and the information about the variation of the ionosphere in southeastern China which was obtained in recent years. The measured data indicate that the probability of occurrence of Es in China is relatively high, especially in summer. When Es appears in summer, the probability of its cut-off frequency greater than 4.5 MHz reaches up to 83.6%, therefore, it is necessary to study the target height measurement model and algorithm when the ionosphere contains Es. Firstly, on the basis of the quasi-parabolic segments ionosphere model and real ionosphere parameters, the ionosphere model containing the Es layer is established. In this model, Es layer and its connection layer with the E layer are represented by parabola and reverse parabola respectively. Then, the high frequency transmission characteristics of the target micro multipath are analyzed based on Es model. The simulation shows that 4 multipath echoes can be simulated by the characteristics of different slant ranges and Doppler frequencies in the multiple echoes of the target. By matching the simulated 4 multipath echoes with the actual high frequency echo of the target, when the matching degree reaches a maximum value, the estimated height value can be obtained. Finally, based on the micro multipath difference between high frequency rays and the ionospheric model with Es layer, a height estimation method using matched-field processing and hill climbing search algorithm is proposed. This method can greatly reduce the search time for obtaining the real height value. Through theoretical analysis and experimental verification, the relationships between the ionospheric plasma frequency and height, between the transmission path of high frequency rays and the elevation angle/transmitting frequency, and between the micro path characteristics of high frequency rays and the height of target are obtained. Ionospheric model with the Es layer and the new target height measurement method based on the matched-field processing can accurately estimate the height of the target and have a faster calculation speed.
Study on uniform irradiance of micro curved-light-emitting diode array
Authors: Ban Zhang  , Liang Jing-Qiu  , Lü Jin-Guang  , Liang Zhong-Zhu  , Feng Si-Yue  ,   State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The curved light-emitting diode (LED) array has so many advantages over conventional planar micro LED array such as wider viewing angles, and convenience in its actual applications:curved mobile phone screen, curved smart watch screen, and wide-angle communication illumination light source, etc. Irradiance uniformity is considered to be one of the momentous parameters for evaluating the degree of display or communication lighting devices. In order to improve the untilization of micro-curved LED array in display illumination, we focus on uniform irradiance of cylindrical and spherical micro-LED array by the method of ray-tracing. The calculation results show that the curved radius R and LED radiation parameter m are main factors affecting the uniform irradiance of the cylindrical array. We can improve the energy utilization efficiency by arranging the array pixel positions rationally. The simulation of 1010 cylindrical array with bending radius R=5 cm shows that the uniformity of maximum irradiance can reach 90.5% when detection distance z=300 cm and the detection area is defined as {(x, y)|-100 x 100, -100 y 100}. Furthermore, the irradiance distribution of spherical array is calculated and the results show that the irradiance uniformity of the single spherical array is unrelated to the number of pixels when it surpasses three. The main factors that affect the irradiance distribution of the multi-ring LED array are the ring distribution coefficient K, the normal angle 0, and the luminous flux ratio of each ring . Also the two-ring LED array model is calculated when the pixel number of the first ring is set to be 6 and the second ring is assumed to be 12. And the simulation results show that the maximum irradiance uniformity of the two-ring LED array can reach 94.8% in which the value of 0 is set to be 20, the ring distribution coefficient K=0.5 and the two ring pixel unit luminous flux ratio =20. Experimentally, we adopt the approach of the two micro LEDs to confirm the accuracy of the theory. And the results show that the irradiance distributions of two LEDs with the values of angle =13, 15 and 17 are consistent with the theoretical calculations. Thus, the theoretical and the experimental results in the paper can offer references for curved-LED display and multi-mode intelligent illumination.
Design and analysis of medium wave infrared miniature static Fourier transform spectrometer
Authors: Wang Hong-Liang  , Lü Jin-Guang  , Liang Jing-Qiu  , Liang Zhong-Zhu  , Wang Wei-Biao  ,   State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

This paper presents a spatial modulation Fourier transform micro-spectrometer based on micro-optical elements. The infrared microstructure diffractive optical elements, multi-step micro-mirrors and microlens array are introduced to realize the miniaturization of the instrument. In addition, the structure and basic principle of Fourier transform infrared micro-spectrometer are introduced. The design theory of micro-collimation system is analyzed based on the negative dispersion, the abberation correction and the arbitrary phase modulation characteristics of diffractive optical element. Combined with the characteristics of micro-static interference system, the micro-focusing coupled optical system is analyzed and designed. Based on the wave aberration theory and the Sellmeier dispersion formula, the influence of residual aberration on spectral recovery and the diffraction efficiency of diffraction surface in single-chip hybrid diffractive-refractive collimating lens are studied. The effects of diffraction of multi-stage micro-mirrors and the aperture diffraction of microlens array on spectral recovery are studied by using the scalar diffraction theory. Furthermore, the influence of axial assembly error of relay system on the whole system performance is studied. The results show that the diffraction efficiency of the diffraction surface, the diffraction of the multistage micro-mirror and the microlens array have no effect on the recovery spectrum when the working band of the system is 3.7-4.8 μm. Finally, in order to verify the accuracy of the system design results, an optical simulation software is used to simulate the infrared micro-Fourier transform spectrum. The accuracy of the system model is verified by the simulation that the reconstructed spectrum is in agreement with the ideal spectral curve and the actual spectral recovery error is 2.89%. The medium-wave infrared micro-static Fourier transform spectrometer has no movable parts and adopts micro-optics element to replace the traditional infrared lens. Therefore, it has the advantages of not only good stability, but also small size and light weight so that it is helpful in on-line monitoring applications and provides a new design idea about the micro-Fourier transform spectrometer.
Coherent rainbows come from liquids
Authors: Sun Tian-Jiao  , Shang Ya-Xuan  , Qian Xuan  , Ji Yang  ,   State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China;,   College of Materials Science and Opto-Electronic Technology, School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

When the highly-intensive and highly-directional white light from pulsed fiber laser is focused into water, many directional and colorful rings, coherent rainbows, are observed. The laser generates bubbles with similar sizes in the water, which serve as scatters. The intensive light leads to spatial self-phase modulation and thus generates the coherent rainbows. Such a phenomenon has been observed in many kinds of liquids.
Review on high power microwave device with locked frequency and phase
Authors: Huang Hua  , Wu Yang  , Liu Zhen-Bang  , Yuan Huan  , He Hu  , Li Le-Le  , Li Zheng-Hong  , Jin Xiao  , Ma Hong-Ge  ,   Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

There are many kinds of high power microwave devices.According to the phase and frequency characteristics of the output microwave,they can be divided into the phase and frequency locking high power microwave (HPM) devices and HPM oscillator.Among them,the frequency and phase of HPM devices with locked frequency and phase can be adjusted by the injecting microwave,which has achieved great progress of the HPM research.In this paper,the latest progress of HPM devices with locked frequency and phase which have been developed by the Institute of Applied Electronics,China Academy of Engineering Physics in recent years are reviewed,covering relativistic klystron amplifier (RKA) and relativistic backward-wave oscillator (RBWO) with injection-locked.Aiming at the problems encountered in the research of high power and long pulse RKA,in this paper we briefly introduce the key technologies in design and experiment,including the beam-wave interaction merits,the suppression of multi-frequency oscillation,pulse shortening, high frequency and high power operation,high gain,etc.The performances of RKA,such as power,phase stability and gain,have been improved remarkably.High-power output with stable frequency and phase has been realized by single-annular beam RKA in S-band,whose output power reaches more than 1 GW with a pulse width of 165 ns and phase fluctuation of 18 at a repetitive pulse of 25 Hz/1 s.The high gain RKA also achieves a similar output power and phase stability under the condition of injected microwave power of several kW.In X-band RKA,a structure of coaxial multi-beam has been used to break through the limitations of high frequency and high power capacity,which generates more than 1 GW output power with an input power of 30 kW,the beam-wave conversion efficiency is 34% and the phase fluctuation is 15 with a pulse width of 140 ns.On the basis of an in-depth understanding of RBWO technology, and using the advantages of high efficiency and compact structure,the RBWO research of injection modulated electron beam is proposed and carried out.More than 1 GW output microwave with locked phase is realized by 100 kW seed microwave.These results not only extend scientific and technological research of a large family of HPM devices,but also make it possible for HPM devices to be used in power synthesis,particle acceleration,high-performance radar,etc.
Experimental investigation of angular anisoplanatism for sodium beacon
Authors: Luo Xi  , Li Xin-Yang  , Hu Shi-Jie  , Huang Kui  , Wang Xiao-Yun  ,   Laboratory on Adaptive Optics, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China;,   Key Laboratory on Adaptive Optics, Chinese Academy of Sciences, Chengdu 610209, China
Published: December 2020

To understand the characteristics of the anisoplanatic error resulting from different return-light experiences between the sodium beacon with a greater angular offset and the science object through atmospheric turbulence, the angular anisoplanatism for sodium beacon is investigated experimentally based on the technique of synchronized range gating. The return-light spot arrays through turbulent atmosphere from the natural star and the sodium beacon with 50 rad angular offsets are synchronously collected by using a single Hartmann wavefront sensor, consequently the synchronous turbulence-induced wavefront distortion sequences are recovered for the on-axis natural star and the off-axis sodium beacon. According to the experimental data, the temporal correlations of the wavefront distributions and decomposed Zernike modes between the on-axis natural star and the off-axis sodium beacon are discussed. By comparing the off-axis sodium beacon with the on-axis natural star, we analyse the statistics of the acquired angular anisoplanatism error and its associated Zernike-modal variances for the off-axis sodium beacon, and derive the Zernike-modal relative anisoplanatic errors as well. Furthermore, the influence of the acquired angular anisoplanatism error on the quality of imaging point spread function (PSF) is studied. The experimental results show that the existence of 50 rad angular deviation between the sodium beacon and the natural star causes that there are a certain correlation between just low-order Zernike modes of these two types of wavefronts (e.g. from the 3rd order to the 9th order), but the correlations between other high-order Zernike modes of these two types of wavefronts are severely degenerated and even these modes are de-correlated, resulting from the improper turbulence probing with off-axis sodium beacon off the ray path from the natural star to the telescope aperture. The angular anisoplanatism error has a great influence on the quality of imaging PSF, which leads to a degradation of Strehl ratio of 0.31-0.22 and beam quality factor of 2.70-3.35. Therefore, the influence may not to be ignored. At the end of this paper, according to the derived experimental turbulence coherence length and the generalized Hufnagel-Valley model, we calculate the theoretical anisoplanatic phase variance for the sodium beacon with 50 rad angular offsets, which is in good accordance with the measured anisoplanatic phase variance. This investigation is useful in promoting our knowledge of sodium beacon angular anisoplanatism effect on turbulence probing.
Detection of nitrous oxide by resonant photoacoustic spectroscopy based on mid infrared quantum cascade laser
Authors: Zhou Yu  , Cao Yuan  , Zhu Gong-Dong  , Liu Kun  , Tan Tu  , Wang Li-Jun  , Gao Xiao-Ming  ,   Anhui Institute of Optics and Fine Mechanics, Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China;,   University of Science and Technology of China, Hefei 230026, China;,   Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Atmospheric greenhouse gases have great influence on the climate forcing, which is important to human being and also for natural systems. Nitrous oxide (N2O), such as carbon dioxide and methane, is an important greenhouse gas. It plays an important role in the atmospheric environment. Therefore, sensitive measurement of N2O concentration is of significance for studying the atmospheric environment. In this paper, a photoacoustic spectroscopy (PAS) system based on 7.6 m mid infrared quantum cascade laser combined with resonant PAS technique is established for the sensitive detection of N2O concentration. The PAS has been regarded as a highly sensitive and selective technique to measure trace gases. Compared with laser absorption spectroscopy, the PAS offers several intrinsic attractive features including ultra-compact size and no cross-response of light scattering. In addition, the signal of PAS is recorded with low-cost wavelength-independent acoustic transducer. The performance of the developed system is optimized and improved based on the traditional photoacoustic spectroscopic detection. Dual beam enhancement method is used to increase the effective optical power which effectively improves the detection sensitivity of the system. The N2O absorption line at 1307.66 cm-1 is chosen as the target line, and an operation pressure of 50 kPa is selected for reducing cross-talking from H2O absorption line. By detecting the photoacoustic signals of a certain concentration of N2O at different modulation frequencies and modulation amplitudes, the optimal modulation frequency and modulation amplitude of the system are determined to be 800 Hz and 90 mV, respectively. Different concentrations of N2O gas are detected under the optimized parameters, and calibration curve of the system, that is, the curve of photoacoustic signal versus concentration of N2O is obtained, which shows good linearity. The experimental results show that the minimum detection limit of the system is 150 ppb at a pressure of 50 kPa with an integration time of 30 ms. The system noise can be further reduced by increasing the averaging time. A minimum detection limit of 37 ppb is achieved by averaging signals 100 times, and the signal of N2O in the atmosphere is obtained.
General method of constructing entanglement witness
Authors: Yang Ying  , Cao Huai-Xin  ,   School of Mathematics and Information Science, Shaanxi Normal University, Xi'an 710119, China;,   School of Mathematics and Information Technology, Yuncheng College, Yuncheng 044000, China
Published: December 2020

Quantum entanglement, as an indispensable resource in quantum communication and quantum computation, is widely used in the field of quantum information. However, people's understanding on entanglement is quite limited both theoretically and experimentally. How to determine whether a given quantum state is entangled is still an important task. The entanglement witness is a kind of special self-adjoint operator, it can be used to determine whether a quantum state is an entangled state. This provides a new direction for the determination of entangled states. Entanglement witness has its own unique characteristics in various kinds of entanglement criterion. It is the most effective tool for detecting multipartite entanglement, and the most useful method to detect entanglement in experiments. In the background of quantum theory, we use theory of operators to make a thorough and systematic study of the construction of entanglement witness in this paper. First, from the definition of an entanglement witness, a general method is given to construct an entanglement witness. It is proved that when the maximal expectation CA of an observable A in the separable pure states is strictly less than its biggest eigenvalue max(A), the operator WC=CI-A is an entanglement witness provided that CA C max(A). Although the entanglement witness WCA can detect more entangled states than WC, but it is difficult to calculate the exact value of CA, and the estimate of the upper bound of CA is easier. Therefore, it is more convenient to construct entanglement witness WC than WCA.
In quantum computation, a graph state is a special kind of multi-qubit state that can be represented by a graph. Each qubit is represented by a vertex of the graph, and there is an edge between every interacting pair of qubits. Graph states play a crucial role in many applications of quantum information theory, such as quantum error correcting codes, measurement-based quantum computation, and quantum simulation. Consequently, a significant effort is devoted to the creation and investigation of graph states. In the last part of this paper, as applications of our method, a series of methods for constructing an entanglement witness is obtained in the stabilizer formalism. It is also proved that how entanglement witnesses can be derived for a given graph state, provided some stabilizing operators of the graph state are known. Especially, when A is made up of some stabilizing operators of a graph state, entanglement witness WCA becomes one in literature.
Optical frequency comb active filtering and amplification for second cooling laser of strontium optical clock
Authors: Xu Qin-Fang  , Yin Mo-Juan  , Kong De-Huan  , Wang Ye-Bing  , Lu Ben-Quan  , Guo Yang  , Chang Hong  ,   Key Laboratory of Time and Frequency Primary Standards of Chinese Academy of Sciences, National Time Service Center, Chinese Academy of Sciences, Xi'an 710600, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In this paper, we propose an optical frequency comb active filtering and amplification method combined with injection-locking technique to select and amplify a single mode from a femtosecond mode-locked laser. The key concept is to optically inject an optical frequency comb into a single mode grating external cavity semiconductor laser. The optical frequency comb based on a femtosecond mode-locked laser with a narrow mode spacing of 250 MHz is used as a master laser. The center wavelength of the optical frequency comb is 689 nm with a 10 nm spectral width. A single mode grating external cavity semiconductor laser with a grating of 1800 lines/mm is used as a slave laser, and the external-cavity length from the diode surface to the grating is approximately 50 mm. The master laser is injected into the slave laser, and in order to select a single comb mode, we adjust the power of the master laser to control the locking range of the slave laser whose linewidth is smaller than the optical frequency comb repetition rate (250 MHz). While the operating current of the slave laser is set to be 55 mA and a seeding power is adopted to be 240 W, a single longitudinal mode is selected and amplified from 2.5104 longitudinal modes of the femtosecond optical comb despite the low power of the single mode. By tuning the optical frequency comb repetition frequency, the single longitudinal mode follows the teeth of the femtosecond optical comb, indicating the success in the optical frequency comb active filtering and amplification. The locking range is measured to be about 20 MHz. Meanwhile, the repetition frequency of the optical frequency comb is locked to a narrow linewidth 698 nm laser system (Hz level), thus the slave laser inherits the spectral characteristics of the 698 nm laser system. The linewidth is measured to be 280 Hz which is limited by the test beating laser. Then a continuous-wave narrow linewidth 689 nm laser source with a power of 12 mW and a side-mode suppression ratio of 100 is achieved. This narrow linewidth laser is used as a second-stage cooling laser source in the 88Sr optical clock, the cold atoms with a temperature of 3 K and a number of 5106 are obtained. This method can also be used to obtain other laser sources for atomic optical clock, and thus enabling the integrating and miniaturizing of a clock system.
Julia fractal based multi-scroll memristive chaotic system
Authors: Xiao Li-Quan  , Duan Shu-Kai  , Wang Li-Dan  ,   School of Electronic and Information Engineering, Southwest University, Chongqing 400715, China;,   Chongqing Key Laboratory of Nonlinear Circuits and Intelligent Information Processing, Chongqing 400715, China
Published: December 2020

A memristor can be used in chaotic system as a nonlinear term, and thus enhancing the complexity of the chaotic system. Fractal theory is a leading and important branch of nonlinear science, and has been widely studied in many fields in the past few decades. The fractal and chaos are bound tightly and their relevant researches are well-established, but few of them focus on the research of the possibility of combining the fractal and the chaotic system. In order to obtain a multi scroll chaotic attractor, the fractal process is novelty introduced into the memristive chaotic system. In this paper, at first, a new memristive chaotic system is proposed. Then, the dynamic characteristics of the system are discussed from the aspects of symmetry, dissipation, stabilization of equilibrium points, power spectrum, Lyapunov exponent and fractional dimension. A mapping relationship based on classical Julia fractal is established. Through this mapping relationship, a multi-scroll memristive chaotic system based on the Julia fractal is obtained. Moreover, several deformed Julia fractal processes are applied to the memristive chaotic system, and abundant chaotic attractors are obtained. For example, the square term of the Julia fractal expression is multiplied by a coefficient, and according to the difference in coefficient, the resulting chaotic attractors have the same shape but different sizes. The exponent of the square term in the Julia fractal is changed into a variable, and the chaotic attractor of different scroll numbers is obtained according to the difference in power exponent. In addition, a rich multi-scroll chaotic attractor is obtained by using the fractal expression in the form of weighted sum polynomial. Finally, the influence of a complex constant in the fractal process on the system is discussed. The simulation results show that the combination of fractal process and chaotic system can obtain rich chaotic attractors, such as multi-scroll chaotic attractors. In general, compared with the single-scroll chaotic attractor, the multi-scroll chaotic attractor has a higher complexity and more adjustability. In addition, compared with other multi-scroll chaotic system, the proposed multi-scroll chaotic system is easy to adjust the number of the scrolls. To summarize, this work not only provides a new method of generating multi-scroll chaotic attractors, but also makes up for the lack of smoothness of the chaotic system caused by using functional methods.
Calculation of CsI photocathode spectral response in 10-100 keV X-ray energy region
Authors: Li Yu-Kun  , Chen Tao  , Li Jin  , Yang Zhi-Wen  , Hu Xin  , Deng Ke-Li  , Cao Zhu-Rong  ,   Laser Fusion Research Center, China Academy of Sciences, Mianyang 621900, China
Published: December 2020

CsI photocathode is widely applied to high energy X-ray detection. And the spectral response is an important character of CsI photocathode. In this paper, the interaction process of high energy X-ray with CsI is analyzed and the spectral response of CsI photocathode is calculated in a 10-100 keV range. The influences of Compton scattering, X-ray fluorescence radiation and Auger emission on the spectral response are analyzed in accordance with the physical process of high energy X-ray interaction with CsI photocathode. These influences prove to be negligible in comparison with photo-ionization influence. Thus only the photoelectric transition is taken into account in calculation. According to the analyses of the processes of the photoelectron creation, transition and escaping, the formula for CsI spectral response is deduced as a function of secondary electron mean escape depth and photocathode thickness. The formula of secondary electron mean escape depth is then deduced as a function of X-ray energy. These formulae indicate that the mean escape depth of the secondary electrons increases markedly with the rise of X-ray energy and has a remarkable influence on the CsI spectral response. The spectral responses for different CsI thickness values are then calculated in a range of 10-100 keV. The results show that 1000 nm CsI has the best response under 20 keV, while 10000 nm CsI has a higher response over 60 keV. Then the calculation data are compared with experimental data of Hara's and Khan's hard X-ray streak camera measurements. These data agree well with each other and prove that our calculation of CsI spectral response for high energy X-ray is reliable. The spectral responses to CsI thickness for 17.5 keV and 60 keV are also calculated and shown in figures. These calculation data match experimental data of Frumkin and Monte-Carlo simulation data of Gibrekhterman. The measurement error of Frumkin's experiment and the uncertainty of the secondary electron mean escape depth are considered to be the reasons for the deviations of calculation and experimental data. The figures of spectral responses to CsI thickness also reveal the optimal thickness values of CsI for different X-ray photon energies. It is shown that 1 m is the optimal thickness for 17.5 keV X-ray detection, and 10 m is optimal for 60 keV. Finally the spectral response of CsI photocathode in a 10-100 keV range is calculated and the formulae prove to be reliable. According to these formulae and calculations, the optimal thickness of CsI photocathode can thus be given for designing and optimizing the high energy X-ray imaging detectors.
Effects of hydrogen impurities on performances and electrical reliabilities of indium-gallium-zinc oxide thin film transistors
Authors: Shao Yan  , Ding Shi-Jin  ,   State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China
Published: December 2020

The influences of hydrogen impurities on the performances of indium-gallium-zinc oxide (IGZO) thin film transistors (TFT) are summarized in this article. Firstly, the sources of hydrogen impurities in the IGZO channels of the TFTs are proposed, which could originate from the residual gas in the deposition chamber, the molecules absorbed on the sputtering target surface, the neighbor films that contain abundant hydrogen elements, doping during annealing processes, etc. The hydrogen impurities in the IGZO films can exist in the forms of hydroxyl groups and metal hydride bonds, respectively. The former originates from the reaction between H atoms and the O2- ions. This reaction releases free electrons, leading to a rise of the Fermi level of IGZO, and thus enhancing the mobilities of IGZO TFTs. The latter incurs negative charges on H atoms, and thus changing the distribution of the subgap density of states, hence improving the negative bias (or illumination) stabilities of IGZO TFTs. Subsequently, various methods are also proposed to characterize hydrogen elements in IGZO, such as secondary ion mass spectroscopy, thermal desorption spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Finally, the effects of hydrogen impurities on the electrical characteristics of the IGZO TFTs, such as the field effect mobilities, subthreshold swings, threshold voltages, on/off current ratios as well as the positive and negative bias stress stabilities, are discussed. The results indicate that hydrogen element concentration and process temperature are two key factors for the device performances. With the increase of hydrogen element concentration in the IGZO channels, the TFTs exhibit higher electron mobilities, lower subthreshold swings and better reliabilities. However, annealing at too high or low temperatures cannot improve the device performance, and the most effective annealing temperature is 200-300℃. It is anticipated that this review could be helpful to the IGZO TFT researchers in improving the device performances and understanding the underlying mechanism.
Tunable grapheme amplitude based broadband electromagnetically-induced-transparency-like metamaterial
Authors: Wang Yue  , Leng Yan-Bing  , Wang Li  , Dong Lian-He  , Liu Shun-Rui  , Wang Jun  , Sun Yan-Jun  ,   School of Opto-Electronic Engineering, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

Metamaterials, composed of subwavelength resonators, have extraordinary electromagnetic properties which rely on the sizes and shapes of the resonance structures rather than their compositions. Recently, achieving electromagnetically induced transparency (EIT) in metamaterial system, also called electromagnetically-induced-transparency-like (EIT-like) analogue, has attracted intense attention. Many studies of EIT-like metamaterials have been reported at microwave, terahertz, and optical frequencies numerically and experimentally. However, most of the EIT-like metamaterials can only control the transmission window by changing the structure size of the metamaterial which restricts the practical applications of the EIT-like metamaterial. Therefore, a broadband tunable EIT-like metamaterials based on graphene in terahertz band is presented in this paper, which consists of a cut-wire as the bright resonator and two couples of H-shaped resonators in mirror symmetry as the dark resonators. The transmissivity of the metamaterial structure is simulated by the software CST Microwave Studio. And the simulation results show that the transmission window of this structure is in a frequency range from 1.05 THz to 1.46 THz, which is attributed to the interference between the plasmon resonance of wire resonators and the LC resonance of H-shaped resonators. In addition, increasing the number of dark mode resonators leads to an increase in transmission window bandwidth. Furthermore, a broadband tunable property of transmission amplitude is realized by changing the Fermi level of graphene. When the graphene Fermi level gradually increases from 0 eV to 1.5 eV, the transmission amplitude of the transmission window gradually decreases from 87% to 20%, which realizes the broadband tunability of transmission window. At the same time, the distribution of the electric field at a central frequency of 1.26 THz is simulated to analyse the transmission mechanism. Finally, the EIT metamaterial samples are prepared and the transmission curves of the samples are tested by terahertz time-domain spectroscopy. Such an EIT-like metamaterial not only realizes the broadband EIT property but also realizes the characteristic of the tunable amplitude of the transmission window, which has potential applications in designing the active slow-light devices, terahertz active filtering and terahertz modulator.
Optical frequency linked dual-comb absorption spectrum measurement
Authors: Zhang Wei-Peng  , Yang Hong-Lei  , Chen Xin-Yi  , Wei Hao-Yun  , Li Yan  ,   Department of Precision Instruments, Tsinghua University, Beijing 100084, China;,   Science and Technology on Metrology and Calibration Laboratory, Beijing Institute of Radio Metrology and Measurement, Beijing 100854, China
Published: December 2020

Dual-comb spectroscopy is becoming a highlighted topic in broadband spectrum measurement techniques because of two outstanding advantages. One is its highly stable output frequency, which leads to an appealing resolution, and the other is the omitting of moving parts, which helps achieve extreme fast sampling rate. Utilizing the traditional radio frequency linked combs, however, obstructs the dual-comb spectroscopy reaching satisfied performance because the phase noise of the radio frequency standard causes the dual-comb mutual coherence to severely degrade. Specifically, traditional frequency comb stabilizes the carrier envelope offset at a radio frequency by a self-reference system, and the order number of each output comb tooth is over a hundred thousand. Thus, the phase noise of the radio frequency reference is significantly multiplied in output optical frequency by the same order of magnitude as the tooth order number. In this paper, we demonstrate an optical frequency linked dual-comb spectrometer where the two combs are locked to a common narrow linewidth laser. In this configuration, the two combs are synchronized at an identical optical frequency, which means that the carrier envelope offset of the two combs are changed to an optical frequency and the order number of the output comb teeth are reduced by two orders of magnitude. Therefore, not only the complex and costly self-reference system can be removed but also the phase noise of the optical frequency of each comb tooth is effectively reduced, which leads to lower mutual frequency jitters and better mutual coherence. To prove the performance, we measure the 1+3 P branch of 13C2H2 molecular and the results accord well with the reported line positions and reveals a spectral resolution of 0.086 cm-1. The average signal-to-noise ratio exceeds 200:1 (62.5 ms, 100 times on average) and the noise equivalent coefficient is 6.0106 cm-1Hz-1/2. This work provides a solution for pragmatic dual-comb spectroscopy with high resolution and low-cost configuration.
Pump-orientation-probe technique and its applications
Authors: Chen Cong  , Liang Pan  , Hu Rong-Rong  , Jia Tian-Qing  , Sun Zhen-Rong  , Feng Dong-Hai  ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

The pump-orientation-probe technique is a recently-developed novel transient measurement technique, which has unique advantages in probing the ultrafast dynamics of charge separation in colloidal nanostructures. In this technique, the linearly-polarized pump pulse is applied to generating electron-hole pairs, and the circularly-polarized spin-orientation pulse is used to establish the electron spin polarization, whose dynamics is detected by monitoring the polarization change of the linearly-polarized probe pulse. Initially, the wavefunctions of the electron-hole pairs are spatially overlapped, and the lifetime of the electron spin is short because of the strong electron-hole exchange interaction. If the electrons or the holes are trapped by the surfaces of the colloidal nanostructures, the spatial separations between the electrons and the holes weaken the exchange effect, and thus the lifetime of the electron spin is largely lengthened. The evolutions of electrons and holes from their spatial overlap to separation can be revealed by monitoring the change of the electron spin dynamics. Based on the introduction of the conventional two-beam carrier pump-probe and spin pump-probe techniques, the features and optical layout of three-beam pump-orientation-probe technique are described in depth. The application to probing negative or positive photocharging in CdS colloidal quantum dots is taken for example and discussed in depth. Compared with the conventional time-resolved absorption or time-resolved fluorescence spectroscopy, the pump-orientation-probe technique can detect the dynamics of trapping electrons or holes and distinguish the type of charging state easily and directly, which has particular advantages under the high-power excitation condition. Further outlook of the three-beam pump-orientation-probe technique is also presented finally.
Effects of Nd-doping on multiferroic properties of Bi6−xNdxFe1.4Ni0.6Ti3O18 polycrystalline
Authors: Chen Cheng , Lu Jian-An , Du Wei , Wang Wei , Mao Xiang-Yu , Chen Xiao-Bing ,   College of Physics Science and Technology, Yangzhou University, Yangzhou 225002, China,   Guangling College, Yangzhou University, Yangzhou 225127, China
Published: December 2020

Single phase polycrystalline Nd-modified BNFNT-x series samples are obtained from the precursors of the same chemical formula, and prepared by using the citric acid-nitrate method. The X-ray photoelectron spectroscopy measurement indicates that a slight Nd modification does not exert significant influence on the stability of the octahedral FeO6, nor NiO6 nor TiO6. When the molar concentration of Nd exceeds 0.25, the stability of BiO layer is cemented and conducive to the insulating role of BiO layer. It is seen that a small quantity of Nd substitution for bismuth can improve the ferroelectric polarization (2Pr) of ～ 19.7 \begin{document}$ \mu {\rm C/cm }^2$\end{document}. The room-temperature magnetization (2Ms) can reach a maximal value of ～ 4.132 emu/g (1 emu/g = 10−3 A·m2/g)in the BNFNT-0.20 sample. Two anomalies are observed in the temperature-dependent dielectric loss spectrum: one is situated in the temperature range from 200 K to 400 K and the other is located in the vicinity of 900 K. It is considered that the loss anomaly found near 900 K might be associated with the viscous motion of ferroelectric domain walls. In addition, the loss peak shown in a temperature range from 200 K to 400 K shifts toward the higher temperature with measuring frequency increasing, indicating the characteristics of dielectric relaxor behavior. The activation energy is evaluated to be 0.287−0.366 eV, which suggests that the relaxor is associated with the electrons transfer and hop between Fe3+ and Fe2+. The room-temperature magnetization (2Ms) has reached a maximal value of ～ 4.132 emu/g in the BNFNT-0.20 sample. The lattice distortion due to the introduction of Nd changes the angle of such antiferromagnetic coupling bonds as Fe3+—O—Fe3+, Fe3+—O—Ni3+ and Ni3+—O—Ni3+, which leads the AFM spin states to break, and thus increases the magnetic properties. While with further modification of Nd, the drastic lattice distortion reduces the occupation of the B-sites of the magnetic ions, which might be responsible for further deteriorating the magnetic properties.
Water photosplitting: Atomistic mechanism and quantum dynamics
Authors: Shen Yu-Tian  , Meng Sheng  ,   1. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   2. Collaborative Innovation Center of Quantum Matter, Beijing 100190, China
Published: December 2020

Directly splitting water into carbon-free H2 fuel and O2 gases by sunlight is one of the most environmentally-friendly and potentially low cost approaches to solving the grand global energy challenge. Recent progress of electronic structure theory and quantum simulations allow us to directly explore the atomistic mechanism and ultrafast dynamics of water photosplitting on plasmonic nanoparticles. Here in this paper, we briefly introduce the relevant researches in our group. First we propose that the supported gold nanoparticles on oxide thin film/mental should be able to potentially serve as efficient photocatalysts for water splitting. Then, under the light illumination, we identify a strong correlation among light intensity, hot electron transfer rate, and water splitting reaction rate. The rate of water splitting is dependent not only on respective optical absorption strength, but also on the quantum oscillation mode of plasmonic excitation, which can help to design nanoparticles in water photosplitting cells. Finally, we simulate the ultrafast electron-nuclear quantum dynamics of H2 generation with plasmonic gold cluster on a time scale of~100 fs in liquid water. We identify that the water splitting is dominated by field enhancement effect and associated with charge transfer from gold to antibonding orbital of water molecule. Based on all atomistic mechanism and quantum dynamics above, we present a “chain-reaction” H2 production mechanism via high-speed (much higher than their thermal velocity) collision of two hydrogen atoms from different water molecules under light illumination.