bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of phase error of optical elements on optical path design of laser facilities
Authors: Xu Lin-Bo  , Lu Xing-Qiang  , Lei Ze-Min  ,   Key Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Optical path design of high power laser facilities should consider several optimization measures such as those that are related to image transmission, ghost avoidance, and stray light management. According to the diffraction optical propagation theory, we study the the influences of wavefront characteristics of large aperture optical components on optimizing the design parameters of optical path in view of increasing the output load. The results show that the arrangement interval of the last stage optical drive can be very useful in improving the output load of the laser facilities if it is controlled to be over 6 m long. In general, a large aperture optical element with a phase error peak value of 0.34 can reduce the near field beam quality of a high-power laser by about 10% and give rise to a maximum decrease of about 21% when the phase error reaches 1.36. Superposition of multiple optical elements with different phase error distribution characteristics can reduce the negative effect of the mid frequency phase error. However, the nonlinear effect of large aperture optical components can aggravate the influence of the intermediate frequency phase error on the damage resistance capacity of the device. Under the premise that the damage threshold of the large caliber optical element is limited to 20 J/cm2, the using of a laser facility with a compact optical path, with an input laser energy density controlled to be below 16.8 J/cm2, will avoid damaging the optical components efficiently. A relatively flexible optical layout can further increase the average energy density of the final output laser and is very beneficial to the enhancing of the output load capacity of the laser facility.
Normal-mode splitting induced by homogeneous electromagnetic fields in cavities filled with effective zero-index metamaterials
Authors: Xu Xiao-Hu  , Chen Yong-Qiang  , Guo Zhi-Wei  , Sun Yong  , Miao Xiang-Yang  ,   College of Physics and Information Engineering, Shanxi Normal University, Linfen 041004, China;,   Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application, School of Physics and Technology, Soochow University, Suzhou 215009, China;,   Key Laboratory of Advanced Microstructure Materials, Ministry of Education, Department of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

In cavity quantum electrodynamics (cQED), how an atom behaves in a cavity is what people care about. The coupling strength (g) between cavity field and atoms plays a fundamental role in various QED effects including Rabi splitting. In the solid-state case, when an atomic-like two-level system such as a single quantum dot (QD) is placed into a cavity, Rabi splitting would occur if g is strong enough. In the classical limit, when a QD in a cavity changes into a classical oscillator, the normal-mode splitting would also take place. It is known that g relies on the local fields at the places of the QDs or classical oscillators inside the cavity. However, for both cases, the traditional cavity modes involved are all in the form of standing waves and the localized fields are position-dependent. To ensure strong coupling between QDs or classical oscillators and photons, they should be placed right at the place where the cavity field is maximum, which is very challenging. How is the positional uncertainty overcome?
Recently, the peculiar behaviors of electromagnetic (EM) fields inside zero-index metamaterial (ZIM) in which permittivity and/or permeability are zero have aroused considerable interest. In ZIMs the propagating phase everywhere is the same and the effective wavelength is infinite, which strongly changes the scattering and mode properties of the EM waves. In addition to the above characteristics, the fields in ZIM could be homogeneous as required by Maxwell equations. While the special properties of ZIMs are investigated, the fabrication of ZIMs is widely studied. It is found that a two dimensional (2D) photonic crystal consisting of a square lattice of dielectric rods with accidental degeneracy can behave as a loss-free ZIM at Dirac point.
To overcome the positional uncertainty, in this paper we propose a cavity filled with effective zero-index metamaterial (ZIM). When the ZIM is embedded in a cavity, the enhanced homogeneous fields can occur under the resonance condition. Finally, experimental verification in microwave regime is conducted. In the experiments, we utilize a composite right/left-handed transmission line with deep subwavelength unit cell to mimic a ZIM and use a metallic split ring resonator (SRR) as a magnetic resonator whose resonance frequency is determined by structural parameters. The experimental results that in general agree well with the simulations demonstrate nearly position-independent normal-mode splitting.
Fiber evanescent wave quartz-enhanced photoacoustic spectroscopy
Authors: He Ying  , Ma Yu-Fei  , Tong Yao  , Peng Zhen-Fang  , Yu Xin  ,   National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

In a conventional system of quartz-enhanced photoacoustic spectroscopy (QEPAS), the size of block-like optical collimation focusing lens group is difficult to reduce, and the structural stability is poor, which makes it hard to adapt itself to some special conditions, such as narrow space and vibrating circumstance. Based on this situation, in this research the fiber evanescent wave technique is combined with QEPAS. Therefore, trace gas detection for acetylene (C2H2) based on an all-fiber structural QEPAS system is developed. To obtain the characteristics of fiber evanescent wave, the optical distribution of micro structural fiber is simulated and the evanescent wave power ratio is calculated based on the COMSOL Multiphysics software. In order to increase the QEPAS 2f signal amplitude, the optical path between fiber taper and quartz tuning fork (QTF) and the laser wavelength modulation depth are optimized. In addition, two kinds of QTFs with different resonant frequencies are optimized. Finally, a QTF with a lower resonant frequency of 30.720 kHz is adopted as the acoustic wave transducer, and a minimum detection limit (MDL) of 6.2510-4 (volume fraction) is obtained with a laser wavelength modulation depth of 0.24 cm-1. To investigate the evanescent wave power of micro structural fiber, the fiber taper diameter is measured by a scanning electron microscope. Subsequently, by combining the diameter of fiber taper with the theoretical calculation results, we determine an evanescent wave power of 455.9 W, and the normalization of noise equivalent absorption (NNEA) which indicates the sensor sensitivity is 4.1810-7 cm-1WHz-1/2.
One-dimensional magneto-hydrodynamic simulation of the magnetic drive isentropic compression experiments on primary test stand
Authors: Zhang Yang  , Xue Chuang  , Ding Ning  , Liu Hai-Feng  , Song Hai-Feng  , Zhang Zhao-Hui  , Wang Gui-Lin  , Sun Shun-Kai  , Ning Cheng  , Dai Zi-Huan  , Shu Xiao-Jian  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The 10 MA primary test stand (PTS), the most powerful pulse power generator in China, is used to obtain isentropic compression of Al samples under a pressure of about 100 GPa. The high performance of laser-triggered gas switches enables the precise synchronization of the 24 modules according to the required timing sequence. This advantage makes the PTS a very good platform for dynamic material compression with fundamental capability of pulse shaping. Tens of isentropic compression experiments have been conducted on the PTS, among which two distinct loading profiles were designed and used to obtain distinct compression processes. The first current, which is used to obtain a shockless compression, has a relatively smooth rise, and the rise-rate keeps almost constant during the 400 ns-long compression. The second current shape has a mild rise but a sharp ends, which is designed to make an artificial turn-point in the velocity history, which is helpful for the numerical code verification. The current profile, as well as the sample thickness, is optimized by a one-dimensional magneto-hydrodynamic (1D MHD) code MADE1D coupled with a full circuit model for the PTS. The equation of state and conductivity model used here have a wide coverage in the density, temperature and pressure range. The strength of material and its constitution model are also taken into consideration to simulate the elastic and plastic flow of metal at relatively low pressure and temperature. Compared with the experimental results, the simulated velocity at the sample/window interface is found to agree well with the measurement for most of the cases. This suggests that the MHD simulations with the circuit model are able to reflect the main process of the loading history, and help to analyze and elucidate the phenomena contributing to the compression. It shows that the current waveform is one of the most important factors that affect the loading process. For the PTS and strip-line electrodes it uses, a current rise ratio less than 15 kA/ns helps to obtain a smooth off-Hugoniot pressure rise. The temperature rise due to the pdV work is very small, and most of the sample material, except those in the skin layer where current passes through, keeps solid during the compression. However, for a current rises at 40 kA/ns or more, the ramp loading wave could be sharpened into a shock within the sample thicker than 1.2 mm. Based on the PTS flexibility of pulse shaping, a wide range of desired load processes can be gained by designing and controlling the load current and sample thickness precisely.
Singular spectrum analysis for precision improvement in dual-comb laser ranging
Authors: Cao Hui  , Song You-Jian  , Yu Jia-He  , Shi Hao-Sen  , Hu Ming-Lie  , Wang Qing-Yue  ,   Key Laboratory of Opto-electronic Information Technology, Ministry of Education(Tianjin University), School of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Optical methods in distance measurement, which are categorized by interferometry and time-of-flight (TOF) detection, have received widespread attention in recent years. However, interferometry cannot provide absolute distance and traditional TOF measurement cannot obtain a high precision measurement result either. The TOF ranging by femtosecond lasers, a novel precise measurement approach, enabling a sub-micrometer precision for long distance absolute ranging, can solve the problems above and has a wide application prospect in aerospace, remote sensing and surface profilometry. Particularly, a dual-comb ranging approach has attracted great attention due to high update rate (~kHz) and a simple system structure (i.e., working with free running mode-locked laser system). However, the quantum limited timing jitter of mode-locked lasers will inevitably introduce uncertainty into TOF estimation due to the equivalent sampling nature of a dual-comb scheme. As a result, the distance measurement precision is significantly degraded. Even though a simple multiple averaging can be used to alleviate this problem, the measurement speed is limited to a very low level, which is unacceptable to many applications. Moreover, multiple averaging fails in the presence of more complex noise sources. Singular spectrum analysis (SSA), known as a non-parametric spectral estimation technique, has been widely used in dynamic systems to distinguish complex patterns in signals without a priori knowledge of the dynamical model. In this paper, for the first time, we apply SSA to extract distance information from a noisy time series generated by a high update rate dual-comb ranging system. Numerical simulation shows that the SSA is a powerful tool for separating distance series into signal and random noise regardless its color. Specifically, we extract a one-dimensional step profile with high precision in the presence of violet noise (density proportional to f2). In experiment, a dual-comb ranging system is built based on two home-built polarization maintaining mode-locked fiber lasers by using carbon nanotube as saturable absorber. Their repetition rates are both about 74 MHz, their difference being about 2 kHz. We measure the distance of a moving target placed at ~0.5 m away from the range finder and use the SSA for signal extraction. The direct measurement precision is 1.9968 m rms at 200 Hz update rate. The SSA successfully separates the quantum noise from the ranging time series, resulting in 0.1522 m rms ranging precision, corresponding to about 13 times ranging precision improvement. This method can be further extended to high dimension, enabling high precision and high speed profilometry for complex surfaces based on femtosecond laser ranging.
Design and experimental study on high quality beam and high stability power of laser
Authors: An Ran  , Fan Xiao-Zhen  , Lu Jian-Xin  , Wen Qiao  ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

High-performance lasers with high-quality beam laser and high-stability power are widely used for laser machining, laser precision measuring, etc. Reflection curved mirrors are widely used in lasers to provide several small intracavity focal spots and reduce the dispersion and volume of the laser. The primary disadvantage of using reflection curved mirrors in folded resonators is that relatively large angles of incidence deform the circular transverse pattern of the output beam and limit laser performance. In addition, in high power lasers or ultra short pulse lasers, the gain medium thermal lens focal length fluctuation is the primary cause of the instability of laser output power. This paper focuses on beam quality and power stability of laser, and an effective method of solving the two problems, i.e., astigmatism and instability power of laser, is presented. The laser resonator with high-quality laser beam and high-stability power is very easy and intuitive to design by this method, in which the resonator transform circle graphic theory is used and the thermal lens and astigmatism compensation is taken into account. The theoretical investigation shows that the astigmatism in two terminal arms of the folded laser resonator can be successfully eliminated by using this method, and the experimental measurements of the pattern of the laser output beam show that the deformations of spot intensity profiles in the two terminal arms can be simultaneously compensated for completely in the cavity, which is in good agreement with the analytical prediction. When the focal length of the laser crystal thermal lens varies, the variations of radii of spots not only at some key position, but also at all locations of the laser resonance designed by this method, are overtly smaller than the variation of the normal resonant cavity. The stability of the output laser power of the laser is better than that of a universal laser resonator under the same external conditions.
Simulations of return flux of polychromatic laser guide stars based on Bloch equations
Authors: Wang Gong-Chang  , Wei Kai  , Li Yan  ,   Department of Precision Instrument, Tsinghua University, Beijing 100084, China;,   Key Laboratory on Adaptive Optics, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
Published: December 2020

Sodium laser guide star (LGS) becomes an essential part in modern astronomical adaptive optics system, especially for the next generation extremely large ground based telescope. The LGS technology has experienced the developmental stages as natural guide star, Rayleigh LGS, sodium LGS and constellation of LGS. The sky coverage is still limited in that the LGS cannot not be used to detect the tip/tilt aberrations. While the polychromatic laser guide star (PLGS) is one of the most effective ways to enlarge the sky coverage to 100%. Previous simulation models are insufficient for the accurate calculation of the return flux, especially for the simulation model of PLGS which is generated by one-photon excitation of mesospheric sodium atoms. The simulation model based on Bloch equations proposed in this paper can be used to compute the return flux of one-photon excited PLGS precisely. Doppler broadening, beam atom exchanging, collisions and recoil are taken into account in the model. The return flux is validated by the return efficiency. The simulation results indicate that with one-photon excitation of sodium atoms, a return efficiency of 330 nm is minimum compared with those of other wavelengths; the saturation power density will decrease with recoil increasing and increase with collision rate increasing; an optimal line-width exists up to maximum the photon return efficiency. In the best case, when the power density is 10 W/m2 at the sodium layer, the maximum return efficiency at 330 nm is 0.907 photons/s/sr/atom/(W/m2) with an optimal laser line-width of 18 MHz.
Characterization of high-transconductance long-channel hydrogen-terminated polycrystal diamond field effect transistor
Authors: Zhang Jin-Feng  , Yang Peng-Zhi  , Ren Ze-Yang  , Zhang Jin-Cheng  , Xu Sheng-Rui  , Zhang Chun-Fu  , Xu Lei  , Hao Yue  ,   State Key Discipline Laboratory of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

Diamond has a great potential to be used in high-power, high-voltage and high-frequency semiconductor devices due to its wide band gap (5.5 eV), high breakdown field (> 10 MV/cm), high thermal conductivity (22 W/(cm·K)), and good carrier transport property. High-quality polycrystal diamond with large size wafers (up to several inches) is more easily obtained than the expensive monocrystal diamond plate with the size of only several mm2, and the good performance of electronic device on polycrystal diamond has been reported. So we fabricate a normally-on hydrogen-terminated polycrystal diamond field effect transistor with a 4-μm aluminum gate by using a gold mask process. The saturation drain current is 160 mA/mm, and the on-resistance is as low as 37.85 Ω ·mm. The maximum transconductance reaches 32 mS/mm, and the gate voltage range with the transconductance higher than 90% of its maximum value reaches 3 V (-2 V ≤ VGS ≤ -5 V). An Ohmic contact resistance of 5.52 Ω ·mm and a quite low square resistance of 5.71 kΩ/sq for the hydrogen-terminated diamond are extracted from the analysis of transmission line model measurement. On the basis of the analyses of the obtained results, the on-resistance of device dependent on gate voltage, and the capacitance-voltage data measured at the gate-source diode, we find that the hole sheet density under the gate reaches 1.56×1013 cm-2 at a gate voltage of -5 V, and the extracted effective mobility of the holes stays at about 170 cm2/(V·s) in the afore-mentioned gate voltage range with high transconductance. In summary, the high and broad transconductance peak and the low on-resistance are attributed to the relatively low gate-source and gate-drain series resistance, the high-density carriers in the channel, and the high-level mobility achieved over a large gate voltage range. The relevant research of finding proper dielectrics for the gate insulator and the passivation layer is under way to further improve the device performance.
Mode properties analysis of graphene-coated asymmetric parallel dielectric nanowire waveguides
Authors: Peng Yan-Ling  , Xue Wen-Rui  , Wei Zhuang-Zhi  , Li Chang-Yong  ,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China;,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
Published: December 2020

In this paper, the mode properties of graphene-coated asymmetric parallel dielectric nanowire waveguides are analyzed by the multipole expansion method. First, the surface plasmon modes supported by the waveguides are classified. Then, the influences of frequency, geometry parameters and graphene Fermi energy on the effective refractive index and propagation length of the seven low order modes are studied in detail. The seven low order modes can be divided into two categories: cos mode and sin mode. The cos mode includes modes 0, 2, 4 and 6, while sin mode includes modes 1, 3 and 5. The results show that the characteristics of the modes can be adjusted in a wide range by changing the frequency, geometrical parameters and the Fermi energy of graphene. When the frequency increases from 10 THz to 50 THz, the number of graphene surface plasmon modes increases and the effective refractive index of each mode increases monotonically. Moreover, with the increase of frequency, the propagation length of cos mode decreases monotonically, and the propagation length of sin mode shows the trend of first increasing and then decreasing. As the distance between the two dielectric nanowires increases, the mode properties of modes 0 and 1 change drastically, while the effective refractive indexes and propagation lengths of other modes vary very little. As the radius of one of the dielectric nanowires increases, the number of modes increases in the calculated range, while the effective refractive index and propagation length of each mode are less affected. In the process of increasing the Fermi energy of graphene from 0.3 eV to 0.7 eV, the effective refractive index and propagation length of each mode vary greatly. Moreover, the effective refractive index of each mode decreases monotonically, while the propagation length increases. It is also found that the compositions of the low order modes vary with the size of the two nanowires for this asymmetric structure. The comparison with the finite element method shows that the semi-analytical results based on multipole method are in good agreement with the numerical results from the finite element method. The present work may provide a theoretical basis for designing and fabricating the asymmetric parallel dielectric nanowires coated with graphene.
Effect of proton irradiation on microstructure evolution of permanent magnet
Authors: Li Zhe-Fu  , Jia Yan-Yan  , Liu Ren-Duo  , Xu Yu-Hai  , Wang Guang-Hong  , Xia Xiao-Bin  , Shen Wei-Zu  ,   Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
Published: December 2020

Nd2Fe14B rare earth and Sm2Co17 type permanent magnets have been widely used in the third generation of synchronous radiation light source and free electron laser facility in undulators and other components of particle accelerators. In addition, the permanent magnets are used in the radiation treatment system for cancer as a beam line component. Compared with Sm2Co17 type permanent magnet, Nd2Fe14B rare earth permanent magnet has the characteristics of large magnet energy product, rich starting materials and low price. Although its Curie point and coercive force are lower than those of Sm2Co17 type of permanent magnet, Nd2Fe14B rare earth permanent magnet is still widely used. As an important part of the accelerator, the magnetic loss phenomenon appears when permanent magnet is used in long-term irradiation environments, which affects the stability and quality of the beam. Therefore, it is important to investigate the magnet demagnetization induced by photon irradiation. Recently, there have appeared many researches of the phenomena of demagnetization for the permanent magnets under the irradiation of various kinds of particles. By using different research methods and experimental conditions, single particle irradiation is performed and then the effect of irradiation on magnetic loss is investigated by comparing the macro magnetic properties (such as magnetic flux loss rate, saturation magnetization, etc.). However, there are not any available reports on the microstructure investigations of permanent magnets after irradiation. Microstructure affects macroscopic magnetic properties. In order to discuss the microscopic demagnetization mechanism, the transmission electron microscope is used to characterize and analyze the microstructure evolutions of Sm2Co17 type permanent magnet and Nd2Fe14B rare earth permanent magnet before and after proton irradiation. The evolution of the number density of nanocrystal and its size distribution induced by proton irradiation are calculated. Moreover, the effect of microstructure evolution on macroscopic magnetic loss is discussed. The results indicate that the microstructure of permanent magnet transforms from single crystal structure to polycrystalline structure with the increase of the proton irradiation damage level. Nanocrystal and the matrix of permanent magnet have the same crystal structure. With the irradiation damage level increasing, the nanocrystal density of Nd2Fe14B first increases and then decreases, while the particle size distribution first increases and then keeps constant; the number density of nanocrystal of Sm2Co17 type permanent magnet gradually decreases, while particle size gradually increases, and comparing with Sm2Co17 type permanent magnet, the crystal structure of Nd2Fe14B permanent magnet shows an obvious tendency to be amorphous in 2 dpa irradiation damage level.
Technical realization and system simulation of ultraviolet multi-mode high-spectral-resolution lidar for measuring atmospheric aerosols
Authors: Gao Fei  , Nan Heng-Shuai  , Huang Bo  , Wang Li  , Li Shi-Chun  , Wang Yu-Feng  , Liu Jing-Jing  , Yan Qing  , Song Yue-Hui  , Hua Deng-Xin  ,   School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Multi-mode high-spectral-resolution lidar is a new concept of high-spectral-resolution lidar, which uses the multiple-longitudinal-mode pulsed laser rather than the single frequency laser. In this paper, we analyze the multiple longitudinal mode and its spectral distribution of a typical Nd:YAG laser, and calculate its corresponding Mie scattering and Rayleigh scattering spectra, which are a convolution between the spectral distribution of multiple-longitudinal-mode laser pulse and that of the Mie and Rayleigh scattering excited by a single frequency laser pulse. According to the spectral analyses of the elastic lidar returns, we design an ultraviolet multi-mode high-spectral-resolution lidar, in which a high-power non-seeded Nd:YAG pulsed laser at the third harmonic 355 nm wavelength is used as a transmitter, and a Cassegrain telescope serves as a receiver. In the polychromator, a narrow band interfering filter is selected to block the solar background, and a tunable Mach-Zehnder interferometer (MZI) is designed to separate the aerosol Mie scattering signals from the molecular Rayleigh scattering signals excited by the multi-mode pulsed laser. The MZI is composed of a roof mirror mounted on a piezoelectric ceramic and two beam splitters. The optical path difference of the MZI can be adjusted by the piezoelectric ceramic, while its optimum value should make the correspondence between the free spectral range of MZI and the interval between longitudinal modes of Nd:YAG pulsed laser. The photomultiplier tube is selected as a detector, whose output is the convolution between the transmission function of MZI and the Mie and Rayleigh signals excited by the multi-longitudinal mode laser pulse. In the practical experiment, the optimal optical path difference of MZI can be determined by using envelope analysis. For the transmitter laser, when one channel has a maximum output signal and the other has a minimum output, the center wavelength of each longitudinal mode of laser is locked in the optimal optical path difference. The channel of MZI with the maximum output is to pass the Mie scattering signal, while the channel with the minimum output is to block the Mie scattering signal. The aerosol optical characteristics are retrievable by using the complementary properties of the two output channels of MZI. In order to verify the feasibility of the multi-mode high spectral resolution lidar, the system simulation is carried out by using the real atmospheric model and the designed lidar system parameters. The simulation results show that the designed ultraviolet multi-mode high-spectral-resolution lidar can realize the accurate measurement of aerosol within a height of 10 km.
Equivalent circuit model for plate-type magnetoelectric laminate composite considering an interface coupling factor
Authors: Lou Guo-Feng  , Yu Xin-Jie  , Lu Shi-Hua  ,   State Key Laboratory of Power System, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

We describe the modeling of magnetoelectric (ME) effect in the plate-type Terfenol-D/PZT laminate composite by introducing a newly proposed interface coupling factor into the equivalent circuit model, aiming at providing a guidance for designing, fabricating and using the ME laminate composite based devices, such as current sensor, magnetic sensor, energy harvester, and wireless energy transfer system. Considering that the strains of the magnetostrictive and piezoelectric layers are not equal in actual operation due to the epoxy resin adhesive bonding condition, the equivalent circuit models of magnetostrictive and piezoelectric layers are created based on the constitutive equation and the equation of motion, respectively. An interface coupling factor kc is introduced which physically reflects the strain transfer condition between the magnetostrictive and piezoelectric phases. Specifically, the respective equivalent circuit models of magnetostrictive and piezoelectric layers are combined with an ideal transformer whose turn-ratio is just the interface coupling factor. Furthermore, the theoretical expressions containing kc for the longitudinal ME voltage coefficient v and the optimum thickness ratio noptim to which the maximum ME voltage coefficient corresponds are derived from the modified equivalent circuit model of ME laminate, where the interface coupling factor acts as an ideal transformer. To explore the influence of mechanical load on the interface coupling factor kc, two sets of weights, i.e., 100 g and 500 g, are placed on the top of the ME laminates, each with the same thickness ratio n in the sample fabrication for comparison. A total of 12 L-T mode plate-type ME laminate samples with different-thickness configurations are fabricated. The interface coupling factors determined from the measured v and the DC bias magnetic field Hbias are 0.15 for 500 g pre-mechanical load and 0.10 for 100 g pre-mechanical load, respectively. Furthermore, the measured optimum thickness ratios are 0.57 for kc=0.15 and 0.50 for kc=0.10, respectively. Both the measured ME voltage coefficient v and optimum thickness ratio containing kc agree well with the corresponding theoretical predictions. The relationship between the optimum thickness ratios under two different mechanical loads remains unchanged, i.e., the measured optimum thickness ratio for kc=0.15 is larger than for kc=0.10. The experimental results verify the reasonability and correctness of the introduction of kc in the modified equivalent circuit model. The possible reasons for different interface coupling factors under different loads are also qualitatively discussed in this paper.
Single-shot incoherent digital holography based on spatial light modulator
Authors: Bai Yun-He  , Zang Rui-Huan  , Wang Pan  , Rong Teng-Da  , Ma Feng-Ying  , Du Yan-Li  , Duan Zhi-Yong  , Gong Qiao-Xia  ,   School of Physical Engineering, Zhengzhou University, Zhengzhou 450001, China
Published: December 2020

Fresnel incoherent correlation holography (FINCH) is a relatively innovative technology, which can achieve incoherent holograms by using the correlation between the object information and a Fresnel zone plate. In this method, the optical wave front scattered from an object propagates and is incident on a spatial light modulator which a phase mask is mounted on, and then the optical beam is split and phase shifted. The biggest advantage of the FINCH is that it can be matched with any standard optical imaging technology, which can realize microscopic imaging, telescopic imaging, spectroscopic imaging, etc. based on incoherent digital holography, and has important application prospect in remote sensing, astronomy, microscopy, and material analysis. In this paper, based on phase modulation characteristic of spatial light modulator, two types of masks are used. The first mask has an optical axis. And the results show that when the distribution intervals of the three phases on the spatial light modulator (SLM) are larger, the reconstruction image is clearer. On this basis, a new method of mode mounting on the SLM is put forward. The second mask has dual-lens array mode with three phases of 0°, 120°, and 240°, and the three phases respectively correspond to their corresponding optical axis, which means that the mask has three optical axes. Both of the two masks can achieve the single-shot of FINCH. By comparing the two mask forms, we find that the field-of-view of the first mask is larger, which can image the entire resolution board; however, because the sub-phase shift holograms are mixed together and cannot be extracted, the quality of the reconstructed image is worse. The second one can extract three sub-holograms, and the reconstructed image has better quality; but because of smaller imaging field of view, it is suitable for the real-time imaging of micro-organisms and objects. Experiments show that a compound digital hologram including three phase-shifting elements is recorded in charge-coupled device in this way. Three sub-holograms with different phase shift angles are extracted from the compound hologram, and there is no overlapping among the three phase shift holograms. Therefore, the three-phase-shifting technique is usually employed. The sample is reconstructed by numerical reconstruction algorithm. The proposed method may be useful in dynamic process real-time measurement and three-dimensional analysis of the object, and thus providing a new way to promote the development of incoherent digital holography.
One-dimensional magneto-hydrodynamics simulation of magnetically driven solid liner implosions on FP-1 facility
Authors: Zhang Yang  , Dai Zi-Huan  , Sun Qi-Zhi  , Zhang Zheng-Wei  , Sun Hai-Quan  , Wang Pei  , Ding Ning  , Xue Chuang  , Wang Guan-Qiong  , Shen Zhi-Jun  , Li Xiao  , Wang Jian-Guo  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China;,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

As an important cylindrical-convergent drive technology, magnetically driven solid liner implosion has been widely used in the high energy density physics (HEDP) experiments for different researches, such as the properties of condensed matter at an extreme pressure, the hydrodynamic behaviors of imploding systems, and the properties and behaviors of dense plasmas. On the 2.2 MA FP-1 facility (with a rise time of 7 s), implosions of aluminum liners and their impact on target liners are studied experimentally for exploring the applications of instability and ejecta mixing. A one-dimensional Lagrangian codeMADE1D is developed to study liner implosions numerically, which is based on magneto-hydrodynamics model with material strength, wide-range equation of state, Lee-More conductivity, and SCG (Steinberg, Cochran and Guinan) constitutive model. The code is based on the finite difference method. The finite difference equations are written in the covariant form for both Cartesian and cylindrical coordinates which enables the accurate simulation of different load geometries. Numerical results, such as the simulated velocity and radius at inner surface of the liner and target, agree well with the measurements. It shows that FP-1 has the ability to accelerate a 0.5 mm thick aluminum liner with an initial radius of 1.5 mm to a speed of more than 1.1 km/s, and the corresponding velocity of inner surface is more than 1.5 km/s due to the cylindrical convergence effect. In our calculation, most of the liner keeps solid throughout the implosion, though its outer surface is melted due to the Ohmic heating. A cylindrical converging shock about 8-10 GPa can be obtained by setting a target with an initial radius of 8-11 mm inside the liner coaxially. The numerical results show that since the imploding liner is fully magnetized when it impacts the target, the shock and the corresponding reflect release wave run faster than in the unmagnetized target. This means that the target will spall near the liner-target interface, though they are impedance-matched acoustically. The movement of the shocked target can be affected by the pre-filled gas inside. Increasing the gas pressure makes the target lose its velocity quickly, and the rebound radius increases as well. By adjusting the load design and gas pressure appropriately, we can obtain the right implosion process to meet the study requirement.
Improved thin layer model of classical Rayleigh-Taylor instability for the deformation of interface
Authors: Zhao Kai-Ge  , Xue Chuang  , Wang Li-Feng  , Ye Wen-Hua  , Wu Jun-Feng  , Ding Yong-Kun  , Zhang Wei-Yan  , He Xian-Tu  ,   Graduate School, China Academy of Engineering Physics, Beijing 100088, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   Center for Applied Physics and Technology, HEDPS, Peking University, Beijing 100871, China
Published: December 2020

The thin shell (layer) configuration is adopted in inertial-confinement fusion (ICF) implosions. The weakly nonlinear deformation of the thin shell significantly influences the performances of implosion acceleration and fusion ignition, which is an important issue for the study of ICF physics. Based on the thin layer model of Ott (Ott E 1972 Phys. Rev. Lett. 29 1429), an improved thin layer model is proposed to describe the deformation and nonlinear evolution of the perturbed interface induced by the Rayleigh-Taylor instability (RTI). Differential equations describing motion are obtained by analyzing the forces of fluid elements (i.e., Newton's second law), which are then solved by numerical method. Then the position of the perturbed interface with an initial perturbation can be obtained. The linear growth rate obtained from our thin layer approximation agrees with that from the classical RTI. For fixed Atwood number (wave number), the total amplitudes of the bubble and spike obtained from the improved thin layer model agree with those from the three-order weakly nonlinear model. In addition, we compare the deformation and evolution of the layer from our model with results of the numerical simulation. In the linear regime, the amplitudes of the bubble and spike obtained from our model agree with those from the numerical simulation. And the evolution of the perturbed interface obtained from the improved thin layer model is consistent with that from the numerical simulation. In the nonlinear regime, the evolution trends of the total amplitude of the bubble and spike for both the improved thin layer model and numerical results are the same. However, the amplitude of the bubble is obviously greater than that of the spike in the later stage of the perturbation. This is because of some shortcomings in the improved thin layer model. The first shortcoming is that ignoring the dynamical pressure in the pressure difference. In fact, the shear velocity of the fluids plays an important role in the nonlinear regime of the perturbation. The second shortcoming is that the surface area of the upper interface equals the lower interface in the whole perturbation process of the present model. Thus, the present model can be used to describe the nonlinear evolution of the perturbed interface before the mushroom structure. Finally, it is worth noting that the improved thin layer model can be used to describe the deformation and nonlinear evolution of a thin layer for arbitrary Atwood number with a perturbation of large initial amplitude and arbitrary distribution. The initial perturbations of the triangular and rectangular waves are also discussed.
DFT+U calculation of Sm3+ and Sr2+ co-doping effect on performance of CeO2-based electrolyte
Authors: Chen Mei-Na  , Zhang Lei  , Gao Hui-Ying  , Xuan Yan  , Ren Jun-Feng  , Lin Zi-Jing  ,   School of Physics and Electronics, Shandong Normal University, Jinan 250358, China;,   Department of Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Solid oxide fuel cells (SOFCs) have been attracting people's attention for their high energy conversion efficiency, good fuel compatibility, no precious metal catalysts, and pollution-free emissions. However, the high operating temperature (800-1200℃) of the traditional SOFC can reduce the long-term stability and cause the difficulties in either the selecting of material or the sealing of SOFC. Therefore, great efforts have been devoted to developing the intermediate temperature SOFC (IT-SOFC), which works at 600-800℃. In the IT-SOFC, the ionic conductivity of doped CeO2-based electrolyte has a significant advantage relative to that of the conventional yttria-stabilized zirconia (YSZ) electrolyte. For example, at 600℃, the ionic conductivity of Sm-doped CeO2 is 0.02 S/cm much higher than that of the traditional YSZ electrolyte (only 0.0032 S/cm). Therefore, the doped CeO2-based electrolyte is a very promising electrolyte for IT-SOFC.Recently, the co-doping of two different elements into CeO2 has become a hot research topic. The ionic conductivity of Sm3+ and Sr2+ co-doped CeO2 has proved to be nearly twice as high as that of Sm3+ doped CeO2 (SDC). However, the mechanism for the co-doping effect on the conductivity of CeO2 is not clear. In this paper, Sm3+ and Sr2+ co-doped CeO2 is systematically studied using the DFT+U method. The microscopic properties of the Sm3+ and Sr2+ co-doped CeO2 including electronic density of states, band structure, oxygen vacancy formation energy and oxygen vacancy migration energy and so on have been calculated and analyzed by comparing with those of the Sm3+ or Sr2+ single doped CeO2. The calculation results indicate that Sm3+ and Sr2+ co-doping has a synergistic effect on the performance improvement of CeO2-based electrolyte, which can not only suppress the electronic conductivity of doped CeO2 system, but also can reduce the oxygen vacancy formation energy on the basis of single doped CeO2. The existence of Sm3+ can help to reduce the trapping effect of Sr2+ on oxygen vacancies, meanwhile the addition of Sr2+ can further reduce the minimum oxygen vacancy migration energy on the basis of SDC. Calculations by the climbing image nudged elastic band (CINEB) method indicate that the oxygen vacancy migration energy of the co-doped system can reach as low as 0.314/0.295 eV, which is lower than the minimum oxygen vacancy migration energy of SDC. Our research reveals the synergistic mechanism for Sm3+ and Sr2+ co-doping effect on the conductivity of CeO2, which is of great instructive significance for the further research and development of other high-performance co-doped electrolyte materials in IT-SOFC.
Secondary electron emission characteristics of gold nanostructures
Authors: Wang Dan  , He Yong-Ning  , Ye Ming  , Cui Wan-Zhao  ,   School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   Science and Technology on Space Microwave Laboratory, China Academy of Space Technology(Xi'an), Xi'an 710100, China
Published: December 2020

Secondary electron emission (SEE), which is a frequent phenomenon in space high power microwave systems, is one of the basic inducement of multipactor in space microwave components. It is already verified that lowering SEE is an effective method to mitigate the undesirable effect. Metal black nanostructures have ever been reported to suppress SEE remarkably, however, the SEE characteristics of the gold nanostructures are rarely investigated. In this work, we use the thermal evaporation to fabricate the gold nanostructures under various evaporation gas pressures, and further analyze their SEE characteristics as well as energy distribution information. Experimental results reveal that the evaporation gas pressure determines the morphology of gold nanostructure, and the morphology dominates the SEE level of the gold nanostructure. To be specific, as the evaporation gas pressure rises, the porosity of the nanostructure increases and the SEE yield decreases. The energy distribution information indicates that the gold nanostructure just suppresses the true secondary electrons (TSEs) effectively. However, the effect of the nanostructure on the back scattered electrons (BSEs) is heavily dependent on the surface morphology. Specifically, the nanostructure fabricated at 70 Pa suppresses the BSEs weakly while the nanostructures fabricated at 40-60 Pa enhance the BSEs to some degree. To theoretically explain the experimental phenomena, we establish an equivalent model, which is made up of the periodical combination of a hemisphere and a composite groove, to imitate the fabricated gold nanostructure and simulate its SEE characteristics based on the SEE phenomenological probability model. Simulation results indicate that the hemisphere induces more TSEs and BSEs while the composite groove suppresses them, besides, the groove suppresses the TSEs much more remarkably than the BSEs. The SEE level of the nanostructure model is determined by the weighted average effect of both the hemisphere and the groove. The simulations qualitatively explain the experimental phenomena. This work in depth reveals the SEE mechanism for the gold nanostructures, and is of considerable significance for developing the low SEE surface on a nanometer scale in a space high power microwave-system.