bluuebunny/crossref_metadata_2025 huggingface dataset:
Coherent perfect absorption and transmission of a generalized three-mode cavity optico-mechanical system
Authors: Zhang Yong-Tang  ,   Department of Computer Science and Technology, Guangdong Neusoft Institute, Foshan 528225, China
Published: December 2020

With the rapid development of nano-physics and quantum optics, optico-mechanical coupling system is developing toward the miniaturization and lightweight. The physical characteristics of optical cavity and applications of optic-mechanical devices have received much attention. In this paper, a generalized three-mode cavity optico-mechanical system is presented, the steady-state responses of the system to the characteristics of weak detection of light absorption and dispersion in several different coherent driving modes are studied. Situated in the middle of system is a portable total reflection mechanical oscillator with a reflectance of 100%, and located on each side is a fixed optical cavity mirror with partial transmittance, Three-mode cavity optical mechanical system consists of fixed-mirror, removable-vibrator, fixed-mirror structure. in which the two optical cavities are coupled by coupling a stronger control field and weak probe light with the same mechanical oscillator. Analysis and numerical results show that under the mechanism with different parameters, due to nonlinear effect of pressure, in the three-mode cavity optical mechanical system, there appear some interesting quantum coherent phenomena such as coherent perfect absorption, coherent perfect transmission and coherent perfect synthesis. When coherent perfect absorption occurs, the mutual conversion between input signal power full-field energies and oscillator vibration of internal coherence can be realized, and the law of conservation of energy is satisfied. When relaxation rate due to mechanical oscillator is very small, the coherent perfect transmission is completely transmitted from the system side of the input field to the other side in the case of no loss of energy. And mechanical relaxation rate of the oscillator approaches to zero in the middle, which can ensure that the perfect transmission of the detection field takes place on one side, and the field total reflection and coherent perfect synthesis happen on the other side of. In addition, we alsofind that the adjustment of coupling between cavity and cavity can change the intensity of the probe field of quantum coherent control thereby realizing that the output of the detection field is transformed between coherent perfect absorption and coherence transmission; through simple phase modulation the output direction and input direction of detection field for left cavity-right cavity can swap mutually. So, these dynamic controls in quantum information networks can be used to construct some optical devices with special functions, such as photon switch, photo router, photon exchange machine, etc.
First-principle study of structure stability and electronic structures of graphyne derivatives
Authors: Chen Xian  , Cheng Mei-Juan  , Wu Shun-Qing  , Zhu Zi-Zhong  ,   Department of Physics, Semiconductor Optoelectronic Material and High Efficiency Conversion Device Collaborative Innovation Center, Xiamen University, Xiamen 361005, China
Published: December 2020

A new carbon allotropegraphyne has attracted a lot of attention in the field of material sciences and condensed-matter physics due to its unique structure and excellent electronic, optical and mechanical properties. First-principles calculations based on the density functional theory (DFT) are performed to investigate the structures, energetic stabilities and electronic structures of -graphyne derivatives ( -N). The studied -graphyne derivative consists of hexagon carbon rings connected by onedimensional carbon chains with various numbers of carbon atoms (N=1-6) on the chain. The calculation results show that the parity of number of carbon atoms on the carbon chains has a great influence on the structural configuration, the structural stability and the electronic property of the system. The -graphyne derivatives with odd-numbered carbon chains possess continuous CC double bonds, energetically less stable than those with even-numbered carbon chains which have alternating single and triple CC bonds. The electronic structure calculations indicate that -graphyne derivatives can be either metallic (when N is odd) or direct band gap semiconducting (when N is even). The existence of direct band gap can promote the efficient conversion of photoelectric energy, which indicates the advantage of -graphyne in the optoelectronic device. The band gaps of -2, 4, 6 are between 0.94 eV and 0.84 eV, the gap decreases with the number of triple CC bonds increasing, and increases with the augment of length of carbon chains in -2, 4, 6. Our first-principles studies show that introducing carbon chains between the hexagon carbon rings of graphene gives us a method to switch between metallic and semiconducting electronic structures by tuning the number of carbon atoms on the chains and provides a theoretical basis for designing and preparing the tunable s-p hybridized two-dimensional materials and nanoelectronic devices based on carbon atoms.
Thermoluminescence and optical stimulated luminescence trap parameters of LiMgPO4: Tm, Tb
Authors: Guo Jing-Yuan  , Tang Qiang  , Tang Hua-Ming  , Zhang Chun-Xiang  , Luo Da-Ling  , Liu Xiao-Wei  ,   School of Physics, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

In recent years, the preparation and luminescent properties of LiMgPO4 as a matrix have received much attention, but most of the studies are limited to the trap parameters of thermoluminescence (TL), which do not involve the trap parameters of optical stimulated luminescence (OSL). In this paper, LiMgPO4:Tm, Tb powder samples are synthesized by solid-state reaction at high temperature. All the experiments reported here are measured by Riso TL/OSL-15-B/C reader after being irradiated by beta-rays. The TL glow curves obtained show that the high temperature peak at 300℃ belongs to the first-order kinetic peak because the peak temperature does not change as irradiation dose increases. Based on the first-order kinetics, the TL trap depth E = 1.72 eV and the frequency factor s= 3.97 1014 are determined by the methods of various heating rates.However, LiMgPO4:Tm, Tb is also an OSL material, the analysis of its OSL trap kinetic parameters would help to understand the OSL mechanism and to know the relationship between TL and OSL traps. The pulse annealing method is suitable for OSL trap parameter analysis. For low sensitivity samples, the fluctuation of the pulse annealing method is relatively large. And this method only records the OSL signal of fast decay component, which is suitable for measuring the samples with high sensitivity and fast fading OSL signals. In order to study the OSL signal of slow decay component, the multiple annealing method is proposed based on the pulse annealing method. The multiple annealing procedure is as follows. Firstly, the sample is annealed from room temperature to 500℃ which lasts 30 s. The heating rate is 5℃/s. Secondly, the sample is irradiated with 90Sr beta radiation doses of 1 Gy. Thirdly, the sample is preheated to 150℃ with a heating rate of 0.2 ℃/s. And then OSL measurement lasts 500 s after cooling to room temperature. The above steps are repeated in preheating temperature steps of 10℃. Four repetitive measurements are made for each preheating rate. The preheating rates are 0.2, 0.5, 1, and 2℃/s.Finally, the OSL trap parameters E = 1.69 eV and s = 1.05 1014 are determined by the multiple annealing method. The correlation between TL and OSL trap parameters shows that the TL and OSL signals are likely to come from the same traps. Besides, the trap depth of the main peak of the phosphor shows that the sample has better thermal stability than those of the other phosphors of LiMgPO4 as the matrix.
Effect of Ni doping on optical and magnetic properties of ZnO
Authors: Hou Qing-Yu  , Jia Xiao-Fang  , Xu Zhen-Chao  , Zhao Chun-Wang  ,   College of Science, Inner Mongolia University of Technology, Hohhot 010051, China;,   Key Laboratory of Thin Films and Coatings of Inner Mongolia, Hohhot 010051, China;,   College of Arts and Sciences, Shanghai Maritime University, Shanghai 201306, China
Published: December 2020

Nowadays, the experimental results of absorption spectrum distribution of Ni doped ZnO suffer controversy when the mole fraction of impurity is in a range from 2.78% to 6.25%. However, there is still lack of a reasonable theoretical explanation. To solve this problem, the geometry optimizations and energies of different Ni-doped ZnO systems are calculated at a state of electron spin polarization by adopting plane-wave ultra-soft pseudo potential technique based on the density function theory. Calculation results show that the volume parameter and lattice parameter of the doping system are smaller than those of the pure ZnO, and they decrease with the increase of the concentration of Ni. The formation energy in the O-rich condition is lower than that in the Zn-rich condition for the same doping system, and the system is more stable in the O-rich condition. With the same doping concentration of Ni, the formation energies of the systems with interstitial Ni and Ni replacing Zn cannot be very different. The formation energy of the system with Ni replacing Zn increases with the increase of the concentration of Ni, the doping becomes difficult, the stability of the doping system decreases, the band gap becomes narrow and the absorption spectrum is obviously red shifted. The Mulliken atomic population method is used to calculate the orbital average charges of doping systems. The results show that the sum of the charge transitions between the s state orbital and d state orbital of Ni2+ ions in the doping systems Zn0.9722Ni0.0278O, Zn0.9583Ni0.0417O and Zn0.9375Ni0.0625O supercells are all closed to +2. Thus, it is considered that the valence of Ni doped in ZnO is +2, and the Ni is present as a Ni2+ ion in the doping system. The ionized impurity concentrations of all the doping systems exceed the critical doping concentration for the Mott phase change of semiconductor ZnO, which extremely matches the condition of degeneration, and the doping systems are degenerate semiconductors. Ni-doped ZnO has a conductive hole polarization rate of up to nearly 100%. Then the band gaps are corrected via the LDA (local density approximation)+U method. The calculation results show that the doping system possesses high Curie temperature and can achieve room temperature ferromagnetism. The magnetic moment is derived from the hybrid coupling effect of p-d exchange action. Meanwhile, the magnetic moment of the doping system becomes weak with the increase of the concentration of Ni. In addition, the absorption spectrum of Ni-interstitial ZnO is blue-shifted in the ultraviolet and visible light bands.
Influence of phenyl-C61-butyric acid methyl ester (PCBM) electron transport layer treated by two additives on perovskite solar cell performance
Authors: Liu Yi  , Xu Zheng  , Zhao Su-Ling  , Qiao Bo  , Li Yang  , Qin Zi-Lun  , Zhu You-Qin  ,   Key Laboratory of Luminescence and Optical Information, Ministry of Education, Beijing Jiaotong University, Beijing 100044, China;Institute of Optoelectronics Technology, Beijing Jiaotong University Beijing 100044, China
Published: December 2020

The organic-inorganic metal halide perovskite materials have excellent optical and electrical properties such as high absorption coefficient, high carrier mobility, long carrier lifetime, tunable bandgap, facile fabrication process, etc. Owing to the above excellent properties, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has increased significantly from 3.8% to 22.1% in the last few years. The PSCs have attracted intensive interest in recent years and show great commercial potential. Previous approaches to increasing the PCE of PSCs have focused on the optimization of the morphology of perovskite film. However, there are relatively few studies on the electron transport layer (ETL) in the typical p-i-n sandwiched structure. In this work, the PCE of PSCs with device structure of ITO/PEDTO: PSS/CH3NH3PbI3/PCBM/Al is improved from 10.8% to 12.5% by using polystyrene (PS) and 1,8-diiodooctane (DIO) as binary additives during the deposition of phenyl-C61-butyric acid methyl ester (PCBM) layer. With the addition of PS, a highly smooth and uniform PCBM ETL is formed due to the increase of viscosity. The morphologies of the PCBM films prepared with and without PS are analyzed using an atomic force microscope in the tapping mode. The root-mean-square surface roughness decreases from 1.270 to 0.975 nm with the addition of PS increasing, which is more effective in preventing electron and hole from recombining at the interface between the perovskite layer and the top electrode. Addition of DIO improves the morphology of PCBM, which plays an important role in charge dissociation, charge transportation, and charge collection. From the time-resolved photoluminescence decay curves of ITO/CH3NH3PbI3/PCBM (with different additives), it is clear to conclude that the exciton dissociation between the perovskite layer and PCBM layer is faster and faster. Electrons and holes can be quickly separated, indicating that charge transport performances of electron transport layer with the addition DIO turn better. The addition of two additives is a simple and low-cost approach to improving the morphology of the electron transport layer, which provides a path-to the further improvement of the performance of p-i-n PSCs.
Modeling of radio wave propagations under sporadic-E influence at low and middle latitudes
Authors: Hao Shu-Ji  , Zhang Wen-Chao  , Zhang Ya-Bin  , Yang Ju-Tao  , Ma Guang-Lin  ,   National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave Propagation, Qingdao 266107, China
Published: December 2020

The sporadic-E (Es) layer is a thin layer of several kilometers existing at an altitude around 100 km and features extremely dense ionized irregularities, which can reflect or scatter high frequency (HF) and very high frequency (VHF) radio waves. The most popular theoretical explanation for mid-latitude Es formation is the wind shear theory. Measurements by rocket souding have shown that Es has high electron density and relatively sharp density gradient in the vertical direction. The one-hop propagation of VHF signal in Es can even reach as far as 2000 km. In this paper, we consider incident radio waves influenced by Es via both reflecting and scattering processes at low and middle latitudes, the coefficients of which are related to and vary with the critical frequency of Es (foEs). Firstly, with a supposed parabolic density distribution and the autocorrelation function of the electron density given by Booker, HF and VHF radio wave propagations in Es are analyzed according to the reflection and scattering theory. Secondly, a numerical model for the combined reflecting and scattering processes is developed in the form of piecewise function, the contribution of which can be distinguished by the portion factor of reflection (kr). According to the model, there are two threshold ratios of the critical frequency to the wave frequencies fr and fs respectively. The incident radio waves are totally reflected by Es when foEs/f is higher than fr and mostly scattered when foEs/f is lower than fs. A transition zone exists between two critical points, with the combined processes working together. Thirdly, HF/VHF radio wave propagations in low and middle latitudes of Es are are in the north-southern direction and east-western direction separately. The experiment link in the north-southern direction is from Kunming to Xi'an at distance of 1065 km, and the ionosonde used for Es observation is located at Chongqing. Two east-west links are arranged, one of which is from Dehong to Huaihua and the other is from Dehong to Chenzhou, with the ionosonde located at Kunming and the ground distance as far as 1240 km and 1590 km respectively. The measurement data are treated and parameters of the above mentioned model for wave propagation in Es are experimentally determined. Finally, our model is verified by comparing with ITU-R model. Our results are consistent with the results from the ITU-R model when the foEs/f is high (i.e., the reflecting process plays a main role). When the scattering process dominates, the attenuation value of VHF signal is far less than that predicted by the ITU-R model, which is closer to actual measurements. It is concluded that our model is more preferable for HF and VHF radio wave propagations in Es at low and middle latitudes.
High-efficiency intrusion recognition by using synthesized features in optical fiber perimeter security system
Authors: Huang Xiang-Dong  , Zhang Hao-Jie  , Liu Kun  , Ma Chun-Yu  , Liu Tie-Gen  ,   School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China;,   College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

In an optical fiber perimeter security system, due to the fact that a large quantity of samples are collected in the process of data acquisition, this heavy data burden inevitably degrades the efficiency and accuracy of intrusion recognition. Hence, it is urgent to remove the redundancy of the collected data records, which essentially requires to describe event features in a concise and proper way. In this paper, we propose a synthesized feature based intrusion recognition method, which is especially suitable to describing the fiber intrusion vibration signals with both wide bandwidth and high nonstationarity. Firstly, the all-phase filter bank characterized by large sidelobe attenuation and high flexibility of coefficient configuration, is employed to parallelly divide the input signal into multiple frequency channels, from which the power values can be accurately calculated. Secondly, the crossing rate of the input signal is combined with these power values to construct a synthetical feature vector, in which both the time-domain information and frequency-domain information are incorporated together. Finally, these synthetical feature vectors are fed into a radial-basis-function network based classifier to recognize 4 common intrusions (climbing, knocking, waggling and cutting). Essentially, the high efficiency of our proposed scheme lies in the parallel pipeline mode of the configurable filter bank and simple calculation of features, which facilitates speeding up the intrusion recognition. The high accuracy of our proposed scheme lies in two aspects: 1) the all-phase filter bank possesses small inter-channel interference, which helps to reduce the inter-coupling between output power values; 2) the synthesis of both frequency-domain information and time-domain information ensures the completeness of feature description. Experiments show that the sensing range of the proposed scheme can reach 2.25 km. Moreover, compared with the empirical mode decomposition based method, the proposed method not only improves the precision, but also significantly speeds up the recognition.
Calibrations of ground based airglow imaging interferometer for the upper atmospheric wind field measurement
Authors: Tang Yuan-He  , Cui Jin  , Gao Hai-Yang  , Qu Ou-Yang  , Duan Xiao-Dong  , Li Cun-Xia  , Liu Li-Na  ,   School of Science, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Ground based airglow imaging interferometer (GBAⅡ) prototype made by our group is used to successfully detect the atmospheric wind velocity and temperature at the altituded of 90-100 km. In order to improve GBAⅡ's velocity accuracy, its calibrations are studied in this paper where covered are the calibration of imaging interference fringe center position, CCD dark noise and flat field, the decay coefficient of GBAⅡ's optical system, the phase step length, GBAⅡ's optical path difference with the angle of incidence, GBAⅡ instrument response and the zero wind speed phase calibration, etc. The theoretical and experimental researches of calibration show the following conclusions. The fringe center coordinates by shooting 30 imaging interference fringes are confirmed on the pixel of CCD (123.3, 121.1) by using the least squares method; by 632.8 nm laser for the CCD flat field calibration, the parameters of CCD's flat field coefficients, dark intensity, dead pixels and the imaging interference fringes before and after flat field are all obtained, respectively; the comparison between GBAⅡ's one edge fringe bright whose incidence angle of 10.24 and the center fringe bright whose incidence angle of 0 shows that the edge fringe phase is stepped by 0.356 fringes relative to the center fringe. After taking the sample of 200 imaging interference fringes, from the sine fit curve of the phase step interval at an incident angle of 10.24, the fitted root mean square (RMS) deviation is obtained to be 90.34% and the step interval of 4.06 nm for one interference fringes is corresponding to the stepped phase of 0.0094up; According to the forward formula, GBAⅡ's system decay coefficient calibration is performed after taking imaging interference fringes by IDL programming, the RMS deviation of fitted curve is 99.98%; GBAⅡ's response is 4.9710-3 counts (Rayleigh)-1 from the 632.8 nm laser experiment; GBAⅡ's zero wind speed calibration phases are obtained to be -9.2442 and -68.6353 for the 532.0 nm and 632.8 nm lasers for the outdoor experiment, respectively. This paper provides a series of calibration methods for GBAⅡ and these methods are all verifies experimentally. These calibration methods can support the upper atmospheric wind field passive measurement.
Middle-wave infrared and broadband polarization conversion based on metamaterial
Authors: Jin Ke  , Liu Yong-Qiang  , Han Jun  , Yang Chong-Min  , Wang Ying-Hui  , Wang Hui-Na  ,   Xi'an Institute of Applied Optics, Xi'an 710065, China
Published: December 2020

The polarization state is one of the most important basic properties of the electromagnetic wave. Researchers have made great efforts to manipulate it. Control of the polarization state of an electromagnetic wave is a promising promotion for figuring out many practical engineering problems in infrared remote sensing, optical communication and infrared target recognition. In this paper, we propose a wide-band and high-efficient linear-polarization converter on the basis of the metamaterial, which is comprised of silicon nanorod array and subwavelength metal grating that can realize a 90 polarization converter of linearly polarized light and is composed of silicon nanorod array cascade subwavelength metal grating:on one side of design located is the cuboid silicon nanorod array, on the other side of the design the subwavelength metallic grating on the silicon substrate, and the angle between silicon nanorod array and subwavelength metal grating is 45. Because of the deference in geometrical dimension between the long axis and the short axis of the nanorod, results of the equivalent refractive index of the long axis direction and the short axis direction are different, and the anisotropic birefrigent effect is formed. Based on the Jones matrix, the feasibility of polarization converter is described. The polarization converter efficiency and polarization state of the structure are simulated and analyzed by the finite-difference time-domain method. And the variation characteristics of polarization converter transmittance are simulated under several nanorod with different heights and widths. In order to improve the contrast ratio and the transmission, the effective medium theory is used to design the metal grating for improving the transmission. According to the theory of optical thin film, we design the subwavelength metal grating with suitable duty cycle as the anti-reflection coating. The simulation results show that the structure can realize 90 rotation of linearly polarized light, the polarization converter efficiency is greater than 60% in a spectral range of 3.4-4.5 m and the contrast ratio is greater than 104 in a spectral range of 3-5 m. This structure can effectively realize the 90 polarization conversion in the spectral range of medium wave infrared and has the advantages of high conversion efficiency and high contrast ratio. In addition, the range of spectral of polarization conversion can be changed by adjusting the height and width of the nanorod. It can be applied to optical transmission control of optical network and optical information system, because of its excellent optical performance with the advantages of high polarization conversion efficiency and wide band in the mid-infrared waveband and low preparation difficulty.
Dual-wavelength mode-locked Er-doped fiber laser based on optimizing gain fiber length
Authors: Shi Jun-Kai  , Ji Rong-Yi  , Li Yao  , Liu Ya  , Zhou Wei-Hu  ,   Laboratory of Laser Measurement Technology, Academy of Opto-Electronics, Chinese Academy of Sciences, Beijing 100094, China;,   University of Chinese Academy of Sciences, Beijing 101407, China
Published: December 2020

Recently,multi-wavelength pulsed lasers have become a research hotspot due to their versatile applications,such as precision spectroscopy,microwave/terahertz photonics,optical signal processing,and wavelength division multiplexed optical fiber communication systems.As a promising candidate,passively mode-locked fiber laser has the advantages of ultrashort pulse,ultrahigh peak power,compact structure and low-cost.In the existing multi-wavelength passively mode-locked fiber lasers,multi-wavelength mode-locked operation is achieved by adjusting the intracavity modulators to a proper state after laser has worked.It is inconvenient for practical use,so,its application scope is restricted.In this paper,a new method to achieve dual-wavelength mode-locked operation in an erbium-doped fiber laser is proposed. For an erbium-doped fiber,the peaks of both absorption and emission spectra overlap in the 1530 nm-region.So the emission light in the 1530 nm-region will be re-absorbed by the erbium-doped fiber with low pump power or long gain fiber.Utilizing the emission re-absorption effect,the gain spectrum can be modified by different lengths of gain fiber. In the experiment,an all-fiber ring cavity is adopted and a transmission-type semiconductor saturable absorber is used as a modelocker.The cavity consists of ～3.2-m-long single mode fiber and an erbium-doped fiber.Gain fibers with different lengths are used in the cavity to reveal the dependence of emission re-absorption on both gain spectrum and mode-locked output spectrum.According to the experimental results,there are two humps in the amplified spontaneous emission spectrum located in the 1530 nm-region and 1560 nm-region,respectively.With the gain fiber length increasing, gain spectrum in the 1530 nm-region is suppressed,and gain intensity in the 1560 nm-region gradually surpasses that in the 1530 nm-region.Based on the experimental results,self-starting dual-wavelength mode-locked operation is achieved with a 31-cm-long gain fiber.The two spectral peaks with close intensity are located at 1532.4 nm and 1552.3 nm, respectively.The maximum output power is 4.8 mW at a repetition rate of 58.01 MHz and a signal-to-noise ratio of 58.2 dB.This self-starting dual-wavelength mode-locked erbium-doped fiber laser is convenient for practical use and can meet the requirements for many potential applications.
Electromagnetic scattering characteristics analysis of freak waves and characteristics identification
Authors: Wu Geng-Kun  , Song Jin-Bao  , Fan Wei  ,   Ocean College, Zhejiang University, Zhoushan 316000, China
Published: December 2020

Based on the Longuet-Higgins wave model theory, a modified phase modulation method of simulating freak waves is improved in this paper. The method can generate freak waves at assigned time and place, and their waveforms can not only maintain the frequency spectrum structure of the target spectrum and also satisfy the wave series statistics to a great extent. Then, the electromagnetic backscattering model of freak and background wave is established by the finite difference time domain method and the two-scale method. After averaging relative deviation and analyzing the error of the root mean square deviation within the measurement uncertainties, considering the computational efficiency, we use the two-scale model method to calculate the electromagnetic scattering coefficient of freak wave. Numerical results show that the normalized radar cross section (NRCS) of freak wave is much smaller than that of background wave. On the other hand, we analyze the electromagnetic scattering properties of freak waves under the different polarization modes, incident angles and incident frequencies. We find that in the condition of grazing incidence, the backscatter coefficient of freak wave increases with the increase of the incident frequency, but the increase amplitude is reduced, which meets the rough surface scattering theory. When the incident frequency is fixed and the incident〉is small, the backscatter coefficient calculation results of freak wave are similar under the condition of different polarizations VV's and HH's, but the backscatter coefficient of freak wave decreases obviously with the increase of incident angle, which is caused by the radar electromagnetic wave that is parallel to the sea surface and contacts it gradually. In addition, we find that the backscatter coefficient calculation result of freak waves under the VV polarization is much higher than under HH polarization from the two groups of experimental figures. According to the result of datum analysis, a conclusion is drawn that we can determine where the freak wave is when the NRCS difference of synthetic aperture radar (SAR) image is smaller than -11.8 dB. In the practical engineering application, the characteristic parameters are difficult to observe, while the difference in electromagnetic scattering coefficient between freak wave and background wave can be calculated from the SAR image of sea surface. This conclusion provides a reference standard for predicting the freak waves in engineering application, through which we can calculate the characteristic parameters of freak wave, determine its position, and study the electromagnetic scattering characteristics under the different polarization modes, incident angles and incident frequencies in future researches.
Effects of surface polarization on the bandgap and the absorption-peak wavelength of quantum dot at room temperature
Authors: Cheng Cheng  , Wang Guo-Dong  , Cheng Xiao-Yu  ,   Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023, China;,   Department of Chemistry, Temple University, Philadelphia PA 19122, United States
Published: December 2020

The surface polarization energy that arises from the difference in dielectric coefficient between the quantum dot (QD) and the background medium is investigated by the equivalent image charge method. A general expression for the bandgap of QD depending on the dielectric coefficient of background medium is presented by solving the exciton Schrödinger equation with the perturbation method. As examples, the sizedependent bandgaps, bandgap shifts, absorption-peak wavelengths and absorption-peakwavelength shifts of PbSe, PbS and CdSe QDs doped in different background media are determined in detail. There is evidence to show that the effects of surface polarization on the bandgap and the first absorption-peak wavelength of QD are considerable. The bandgap decreases with the increase of dielectric coefficient of background medium, which causes the absorption-peak wavelength to be red shifted. The effect of surface polarization on the bandgap depends substantially on the sign and value of image charge. When the dielectric coefficient of QD is greater than that of background medium, the absorption-peak wavelength comes to blue shift due to surface polarization of QD. On the contrary, the absorption-peak wavelength comes to redshift. The absorption-peak wavelength shifts of QDs doped in different background media will reach a maximum in a certain diameter depending on the kind of QD.
Interplanetary coronal mass ejection induced forbush decrease event:a simulation study with one-dimensional stochastic differential method
Authors: Ni Su-Lan  , Gu Bin  , Han Zhi-Yi  ,   Department of Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Institute of Space Weather, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

Forbush decrease (FD) event is one of the most important short-term modulations of galactic cosmic rays (GCRs) caused by intense solar activities such as interplanetary coronal mass ejection (ICME). The modulation mechanisms of GCRs by the disturbed interplanetary magnetic fields (IMF) of ICME and the accompanying forward interplanetary shock (IP) are not clear yet.
In this work, we present a one-dimensional dynamic model of the GCR barrier driven by ICME. In our model, the time dependent radial diffusion coefficient rr of GCRs is depressed to be (r)rr (0 (r) 1) as they run into the disturbed IMF. The scale factor (r) is inversely proportional to the local solar wind speed away from the Sun. Within the disturbed area at any time, (r) increases exponentially from the local minimum (rsh)) at the IP front to 1 at the end of the ICME tail. In addition, (rsh)) switches gradually from its global minimum m at the bursting of the CME to 1 as the shock moving toward the outer boundary of the heliosphere. The geometrical and dynamic parameters of the ICME and IP are derived from the observations of GOES and ACE satellites.
Based on the stochastic transport theory, the one-dimensional backward stochastic differential equation (SDE) method is adopted to simulate the transport of GCRs modulated by single halo ICME. The evolution of the neutron flux at the ground is calculated according to the recently reported proton-neutron yield function. As an example, the FD event on 15 May 2005, caused by the CME event bursting on 13 May 2005, is studied and simulated. The results show that the calculated neutron flux evolution, including not only the main and recovery phases, but also the pre-enhancement before the arriving of the CME at the Earth, is consistent with the observation of Oulu neutron monitor.
According to the trajectories of GCRs, it can be found that, the per-enhancement of the neutron flux is a result of the scattering by the forward IP passing 1 AU. Before the IP reaches the switch cutoff Rc, GCRs are evidently confined in the sheath between the IP and CME. After that, the GCRs will stay for longer time in the magnetic cloud of the ICME as a result of the damping of IP strength.
The parameterzed one-dimensional GCRs modulation model and the SDE method, as have been confirmed by the neutron monitor observation on the Earth, can be used further to calculate and predict the GCRs fluxes of other places, such as the Mars, in the heliosphere.
Research progress of plasmonic cathodoluminesecence characterization
Authors: Jiang Mei-Ling  , Zheng Li-Heng  , Chi Cheng  , Zhu Xing  , Fang Zhe-Yu  ,   School of Physics, State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, Peking University, Beijing 100871, China
Published: December 2020

Surface plasmons as the collective electrons oscillation at the interface of metal and dielectric materials, have induced tremendous applications for the nanoscale light focusing, waveguiding, coupling, and photodetection. As the development of the modern technology, cathodoluminescence (CL) has been successfully applied to describe the plasmon resonance within the nanoscale. Usually, the CL detection system is combined with a high resolution scanning electron microscope (SEM). The fabricated plasmonic nanostructure is directly excited by the electron beam, and detected by an ultra-sensitive spectrometer and photodetector. Under the high energy electron stimulation, all of the plasmon resonances of the metallic nanostructure can be excited. Because of the high spatial resolution of the SEM, the detected CL can be used to analyze the details of plasmon resonance modes.
In this review, we first briefly introduced the physical mechanism for the CL generation, and then discussed the CL emission of single plasmonic nanostructures such as different nanowires, nanoantennas, nanodisks and nanocavities, where the CL only describes the individual plasmon resonance modes. Second, the plasmon coupling behavior for the ensemble measurement was compared and analyzed for the CL detection. Finally, the CL detection with other advanced technologies were concluded. We believe with the development of the nanophotonics community, CL detection as a unique technique with ultra-high energy and spatial resolution has potential applications for the future plasmonic structure design and characterization.
Valley Hall effect induced by pseudomagnetic field in distorted photonic graphene
Authors: Deng Fu-Sheng  , Sun Yong  , Liu Yan-Hong  , Dong Li-Juan  , Shi Yun-Long  ,   Institute of Solid State Physics, Shanxi Datong University, Datong 037009, China;,   Shanxi Provincial Key Laboratory of Microstructure Electromagnetic Functional Materials, Shanxi Datong University, Datong 037009, China;,   Key Laboratory of New Microstructure Function Materials in Shanxi Province, Shanxi Datong University, Datong 037009, China;,   Key Laboratory of Advanced Microstructure Materials, Ministry of Education, Tongji University, Shanghai 200092, China
Published: December 2020

Like the spin in spintronics, the valley index in graphene can be viewed as a new carrier of information, which is useful for designing modern electronic devices. Recently, we have applied the concept of valleytronics to photonic graphene, revealed valley-dependent beam splitting effect and realized pseudomagnetic field. The pseudomagnetic field enables a novel manipulation of photons. In this paper, the photonic analogy of valley Hall effect in uniaxially distorted photonic graphene is investigated. It is found that photons in two valleys are subjected to pseudomagnetic fields that are equal in strength but opposite in sign. With the increasing of distortion, the valley Hall effect becomes stronger. In addition, it is found that the photonic valley Hall effect can still be maintained under the influence of loss, although the beam intensity decreases. The photonic analogy of valley Hall effect induced by pseudomagnetic field in uniaxially distorted photonic graphene may be very useful for controlling the flow of light in future valley-polarized devices.
Optical super-oscillation and super-oscillatory optical devices
Authors: Chen Gang  , Wen Zhong-Quan  , Wu Zhi-Xiang  ,   Key Laboratory of Optoelectronic Technology and Systems, College of Optoelectronic Engineering, Chongqing University, Chongqing 400044, China
Published: December 2020

The diffraction limit of traditional optical device greatly restricts the further development of optical super-resolution systems. It is a great challenge to overcome the diffraction limit at a device level, and achieve label-free far-field super-resolution imaging. Optical super-oscillation provides a new way to realize super-resolution since it allows the generation of arbitrary small structures in optical fields in the absence of evanescent waves. The researches of optical super-oscillation and super-oscillatory optical devices have grown rapidly in recent decades. Optical super-oscillation and super-oscillatory optical devices have been demonstrated theoretically and experimentally to show great potential applications in label-free far-field optical microscopy, far-field imaging and high-density data storage. In this paper, we gives a broad review of recent development in optical super-oscillation and super-oscillatory optical devices, including basic concepts, design tools and methods, testing techniques for super-oscillatory optical field, and their applications.
Structural, mechanical and thermodynamic properties of Ti2AlX (X= C, N) at high pressure
Authors: Deng Shi-Jie  , Zhao Yu-Hong  , Hou Hua  , Wen Zhi-Qin  , Han Pei-De  ,   School of Materials Science and Engineering, North University of China, Taiyuan 030051, China;,   School of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

The MAX phase has attracted much attention due to its unique properties combined with the merits of both metal and ceramic, including the low density, high electrical conductivity and good oxidation resistance, which makes it significant for possible applications in various high temperature or other environments. There is a lot of research work on Ti2AlX (X=C, N). However little research about thermodynamic properties at high pressure is carried out. So we study the structural, mechanical and thermodynamic properties of Ti2AlC and Ti2AlN at various pressures and temperatures.
The first-principles calculations based on electronic density-functional theory framework are used to investigate the properties at various pressures. The cut-off energy is 350 eV. Converged results are achieved with 10102 special K-point meshes. The self-consistent convergence of total energy is set to be 5.010-6 eV/atom.
According to the calculated structural parameters at various pressures, we can find that the ratios V/V0 (V0 denotes the system volume at 0 GPa) of Ti2AlX are reduced by 20.59% and 18.93%, respectively, so the compressibility of the system is strong. As the internal pressure increases, the curves of V/V0 become gentle. Then we calculate elastic constants at pressures ranging from 0 to 50 GPa in steps of 10 GPa. It is obvious that the Ti2AlX is mechanically stable because all of the elastic constants satisfy the Born stability criteria. The bulk modulus, shear modulus and Young's modulus linearly increase with internal pressure increasing, implying that the pressure can improve the resistance to volume deformation. The ductility and brittleness can be judged according to Pugh's criterion (ratio of bulk modulus to shear modulus B/G), and the brittle nature turns into ductile nature in a pressure range of 40-50 GPa for the Ti2AlX since the value of B/G exceeds 1.75. Finally, we study the thermodynamic properties at various pressures and temperatures based on the quasi-harmonic Debye approximation theory, including the bulk modulus, heat capacity and thermal expansion coefficient. The bulk modulus decreases with temperature increasing but increases with pressure increasing. The heat capacity at constant volume Cv and the heat capacity at constant pressure Cp have the same variation tendency, while Cv obeys the Dulong-Petit limit. It is easy to see that temperature and pressure have opposite influences on heat capacity and the effect of temperature is more significant than that of pressure. The effects of temperature and pressure on linear expansion coefficient mainly occur at low temperature and the effect of pressure is not so considerable when the pressure exceeds 30 GPa. Above all, the effects of temperature and pressure on thermodynamic properties are inverse.
Meta-antenna: principle, device and application
Authors: Ma Xiao-Liang  , Li Xiong  , Guo Ying-Hui  , Zhao Ze-Yu  , Luo Xian-Gang  ,   State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
Published: December 2020

Since electromagnetic waves were discovered, effectively controlling them has been a goal and radiators with better characteristics have always been chased by researchers. However, limited by the electromagnetic properties of nature materials, traditional radiation technology is reaching its bottleneck. For example, traditional microwave antenna has the disadvantages of large volume, heavy weight, narrow operating frequency band, etc., and cannot satisfy the development requirement of modern communication systems. Therefore, the state-of-art radiation technology meets the challenge of minimizing the size and broadening the bandwidth of radiators, and constructingmulti-functional and reconfigurable antennas. In recent years, metamaterials have aroused great interest due to the extraordinary diffraction manipulation on a subwavelength scale. Fruitful bizarre electromagnetic phenomena, such as negative refraction index, planar optics, perfect lens, etc. have been observed in metamaterials, and the corresponding theories improve the fundamental principle systems of electromagnetics. Based on these novel theories, a series of new radiators has been proposed, which has effectively overcome the difficulties in traditional radiation technology and broken through the limits of natural electromagnetic materials. The relating theory and technology may greatly promote the development of electromagnetics, optics, materials.
In this article, we mainly review the recent progress in the novel electromagnetic radiation technology based on metamaterials, which is named meta-antenna, including the principle of diffraction manipulation of metamaterial to control the amplitude, phase and polarization of the incident electromagnetic waves. Subsequently, a series of radiation devices is introduced, including the new phased array antenna on the concept of phase manipulating metamaterial, and the high directivity antenna based on zero refraction index metamaterial and photonic crystal, and the low RCS antenna simultaneously has the functions of gain enhancement and stealth ability. Besides, the polarization manipulation characteristics of metamaterial are also reviewed. The anisotropic and chiral metamaterials are analyzed, and several polarizers with broadband characteristics and reconfigurable ability are introduced. Furthermore, due to the importance as future radiation sources, nanolasers that work on a subwavelengh scale are demonstrated. Finally, we point out the current problems and future trend of the radiation technology based on metamaterials.
Nonlinear photonic metasurfaces
Authors: Deng Jun-Hong  , Li Gui-Xin  ,   Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
Published: December 2020

In linear optical regime, many novel optical functions have been demonstrated by using ultrathin photonic metasurfaces. The main concept of metasurface is to appropriately assembly the spatially variant meta-atoms on a subwavelength scale, and realize the manipulations of polarization, phase and amplitude of light. Recently, the nonlinear optical properties of photonic metasurfaces have attracted a lot of attention. In this review, we discuss the design, material selection, symmetry consideration of the meta-atoms, as well as the applications such as nonlinear chiral optics, nonlinear geometric Berry phase and nonlinear wavefront engineering. Lastly, we point out the challenges and potentials of nonlinear photonic metasurfaces for manipulating the light-matter interactions.