Phase and direction dependence of photorefraction in a low-frequency strong circular-polarized plane wave

Contrary to the superposition principle, it is well known that photorefraction exists in the vacuum with the presence of a strong static field, a laser field, or a rotational magnetic field. Different from the classical optical crystals, the refractive index also depends on the phase of the strong electromagnetic field. We obtain the phase and direction dependence of the refractive index of a probe wave incident in the strong field of a circular-polarized plane wave by solving the Maxwell equations corrected by the effective Lagrangian. It may provide a valuable theoretical basis to calculate the polarization evolution of waves in the strong electromagnetic circumstances of pulsar or neutron stars.

Different angle-resolved polarization configurations of Raman spectroscopy: A case on the basal and edge plane of two-dimensional materials

Angle-resolved polarized Raman（ARPR） spectroscopy can be utilized to assign the Raman modes based on crystal symmetry and Raman selection rules and also to characterize the crystallographic orientation of anisotropic materials.However, polarized Raman measurements can be implemented by several different configurations and thus lead to different results. In this work, we systematically analyze three typical polarization configurations： 1） to change the polarization of the incident laser, 2） to rotate the sample, and 3） to set a half-wave plate in the common optical path of incident laser and scattered Raman signal to simultaneously vary their polarization directions. We provide a general approach of polarization analysis on the Raman intensity under the three polarization configurations and demonstrate that the latter two cases are equivalent to each other. Because the basal plane of highly ordered pyrolytic graphite（HOPG） exhibits isotropic feature and its edge plane is highly anisotropic, HOPG can be treated as a modelling system to study ARPR spectroscopy of twodimensional materials on their basal and edge planes. Therefore, we verify the ARPR behaviors of HOPG on its basal and edge planes at three different polarization configurations. The orientation direction of HOPG edge plane can be accurately determined by the angle-resolved polarization-dependent G mode intensity without rotating sample, which shows potential application for orientation determination of other anisotropic and vertically standing two-dimensional materials and other materials.

Precision integration of grating-based polarizers onto focal plane arrays of near-infrared photovoltaic detectors for enhanced contrast polarimetric imaging

Polarimetric imaging enhances the ability to distinguish objects from a bright background by detecting their particular polarization status,which offers another degree of freedom in infrared remote sensing.However,to scale up by monolithically integrating grating-based polarizers onto a focal plane array(FPA)of infrared detectors,fundamental technical obstacles must be overcome,including reductions of the extinction ratio by the misalignment between the polarizer and the detector,grating line width fluctuations,the line edge roughness,etc.This paper reports the authors’latest achievements in overcoming those problems by solving key technical issues regarding the integration of large-scale polarizers onto the chips of FPAs with individual indium gallium arsenide/indium phosphide(In Ga As/In P)sensors as the basic building blocks.Polarimetric and photovoltaic chips with divisions of the focal plane of 540×4 pixels and 320×256 superpixels have been successfully manufactured.Polarimetric imaging with enhanced contrast has been demonstrated.The progress made in this work has opened up a broad avenue toward industrialization of high quality polarimetric imaging in infrared wavelengths.

Electron acceleration by tightly focused radially polarized few-cycle laser pulses

Within the framework of plane-wave angular spectrum analysis of the electromagnetic field structure, a solution valid for tightly focused radially polarized few-cycle laser pulses propagating in vacuum is presented. The resulting field distribution is significantly different from that based on the paraxial approximation for pulses with either small or large beam diameters. We compare the electron accelerations obtained with the two solutions and find that the energy gain obtained with our new solution is usually much larger than that with the paraxial approximation solution.

Strain effects on the polarized optical properties of InGaN with different In compositions

Strain effects on the polarized optical properties of c-plane and m-plane InxGa1-xN were discussed for different In compositions （x = 0, 0.05, 0.10, 0.15） by analyzing the relative oscillator strength （ROS） and energy level splitting of the three transitions related to the top three valence bands （VBs）. The ROS was calculated by applying the effective-mass Hamiltonian based on k .p perturbation theory. For c-plane InxGa1-xN, it was found that the ROS of 〈X〉 and 〈Y〉-like states were superposed with each other. Especially, under compressive strain, they dominated in the top VB whose energy level also went up with strain, while the ROS of the ｜Z〉-like state decreased in the second band. For m-plane InxGa1-xN under compressive strain, the top three VBs were dominated by 〈X〉, 〈Z〉, and 〈Y〉-like states, respectively, which led to nearly linearly-polarized light emissions. For the top VB, ROS difference between [X） and [Z）-like states became larger with compressive strain. It was also found that such tendencies were more evident in layers with higher In compositions. As a result, there would be more TE modes in total emissions from both c-plane and m-plane InGaN with compressive strain and In content, leading to a larger polarization degree. Experimental results of luminescence from InGaN/GaN quantum wells （QWs） showed good coincidence with our calculations.

POLARIZED SHEARING HOLOGRAPHIC-MOIR INTERFEROMETRY

A new holographic-moirè method is presented to obtain the in-plane strain fringe patterns. During the recording,double object beams and dual reference beams of orthogonally polarized state are used to illuminate the object and the holographic plate,respectively.Two carriers modulated by deformation are obtained through double-exposure or in real time.Pure in-plane displacement derivative patterns are then obtained through twice filtering.

有限大接地板对圆极化微带贴片天线等化波束宽度影响的研究

基于数值仿真和实验测量,研究了接地板尺寸对微带贴片天线圆极化等幅条件的影响规律。结果表明:当接地板尺寸变化时,铅垂极化分量幅度(|E_(θ)|)和水平极化分量幅度(|E_(φ)|)受到地板尺寸变化的敏感度和规律不同,从而影响了圆极化天线主波束范围内保持其幅值相等的条件。最终推得接地板尺寸在0.6~1.0波长范围内,铅垂、水平极化分量保持等幅条件(按幅度差不大于3dB计)的“等化波束宽度”经验公式,为可穿戴圆极化贴片天线的波束宽度调控及选择提供理论依据。

基于分焦平面偏振成像的冬青卫矛含水率快速无损检测

针对目前在植物含水率检测中存在的使用场景受限、含水率检测不及时等问题,该研究搭建了一套基于分焦平面偏振相机的偏振成像系统,通过对偏振成像信息的解析建立了线偏振度这一物理量与含水率的依赖关系,揭示了偏振光与植物内水分间的相互作用机理,实现了对冬青叶片含水率的快速、无损检测。结果表明:1)针对于不同月份、晴雨天气条件以及不同部位这3种不同影响因素下的冬青卫矛叶片,都可以通过线偏振度来反映其含水率情况,其统一表现为随着含水率的梯度降低,线偏振度逐渐增大;2)该研究通过采集大量的植物叶片建立预测模型,含水率与线偏振度存在较强的负相关关系,决定系数达到0.85,均方误差仅为0.45%;3)另取叶片对含水率检测模型进行验证,结果表明该模型在含水率检测的验证中均方根误差为4.53%,即可以通过线偏振度表征叶片的真实含水率。该研究成果在推动光学手段在植物健康状态检测的进程中具有应用价值。

Calculation of Valence Subband Structures for Strained Quantum-Wells by Plane Wave Expansion Method Within 6×6 Luttinger-Kohn Model

The valence subband energies and wave functions of a tensile strained quantum well are calculated by the plane wave expansion method within the 6×6 Luttinger Kohn model.The effect of the number and period of plane waves used for expansion on the stability of energy eigenvalues is examined.For practical calculation,it should choose the period large sufficiently to ensure the envelope functions vanish at the boundary and the number of plane waves large enough to ensure the energy eigenvalues keep unchanged within a prescribed range.

均匀平面电磁波在不同介质中传播过程的仿真分析

为了使初学者更能直观理解电磁波在不同介质中的传播过程,该研究通过运用MATLAB图形化编程,对电磁波进入不同的导电介质中的传播过程进行可视化仿真。以5G Wi-Fi信号采用的电磁波为研究对象,仿真其在距波源足够远的地方进入干燥的混凝土墙体、海水以及不锈钢墙体中的传播过程。此外对更一般的情况的椭圆极化波在一般导体中的传播过程进行了仿真。仿真结果形象反映了不同介质对电磁波传播的影响以及椭圆极化波的本质特征。

Experimental study of polarity dependence in repetitive nanosecond-pulse breakdown

Pulsed breakdown of dry air at ambient pressure has been investigated in the point-plane geometry, using repetitive nanosecond pulses with 10 ns risetime, 20-30 ns duration, and up to 100 kV amplitude. A major concern in this paper is to study the dependence of breakdown strength on the point-electrode polarity. Applied voltage, breakdown current and repetitive stressing time are measured under the experimental conditions of some variables including pulse voltage peak, gap spacing and repetition rate. The results show that increasing the E-field strength can decrease breakdown time lag, repetitive stressing time and the number of applied pulses as expected. However, compared with the traditional polarity dependence it is weakened and not significant in the repetitive nanosecond-pulse breakdown. The ambiguous polarity dependence in the experimental study is involved with an accumulation effect of residual charges and metastable states. Moreover, it is suggested that the reactions associated with the detachment of negative ions and impact deactivation of metastable species could provide a source of primary initiating electrons for breakdown.

The Growth of Semi-Polar ZnO (1011) on Si (111) Substrates Using a Methanol Oxidant by Metalorganic Chemical Vapor Deposition

Semi-polar ZnO (1011) epitaxial films are demonstrated using a methanol oxidant by metalorganic chemical vapor deposition on Si (111) substrates at 500℃.X-ray (O) scanning indicates that there are six kinds of in-plane domain growths,with the ZnO [1012] parallel to the Si (11(2)〉 direction families.The crystallographic orientation of ZnO is supposed to be caused by surface passivation.The methanol,as a polar molecule,may be adsorbed on the Si (111) surface to form a passivation layer,which inhibits the (0001) ZnO plane deposition on the substrate surface,and as a result the ZnO (1011) plane becomes preferred.The optical properties,examined by a roomtemperature photoluminescence spectrum,exhibit a strong near-band-edge emission peak at 379nm,indicating that the (1011) ZnO film has good crystal quality.These results are significant for research into and for the applications of semi-polar ZnO films.

On the Kinematics for the Closed Planar Homothetic Inverse Motions in Complex Plane

In this paper, the Steiner area formula and the polar moment of inertia were expressed during one-parameter closed planar homothetic inverse motions in complex plane. The Steiner point was defined when the rotation number was different zero and it was called the Steiner normal when the rotation number was equal to zero. The fixed pole point was given with its components and its relation between Steiner point or Steiner normal was explained. The sagittal motion of a telescopic crane was considered as an example. This motion was described by a double hinge consisting of the fixed control panel of the telescopic crane and the moving arm of the telescopic crane. The theoretical concepts and results were applied for this motion.

Effects of V/III ratio on the growth of a-plane GaN films

The non-polar a-plane GaN is grown on an r-plane sapphire substrate directly without a buffer layer by metal- organic chemical vapour deposition and the effects of V/III ratio growth conditions are investigated. Atomic force microscopy results show that triangular pits are formed at a relatively high V/III ratio, while a relatively low V/III ratio can enhance the lateral growth rate along the c-axis direction. The higher V/III ratio leads to a high density of pits in comparison with the lower V/III ratio. The surface morphology is improved greatly by using a low V/III ratio of 500 and the roughness mean square of the surface is only 3.9 nm. The high resolution X-ray diffraction characterized crystal structural results show that the rocking curve full width at half maximum along the m axis decreases from 0.757° to 0.720°, while along the c axis increases from 0.220° to 0.251° with the V/III increasing from 500 μmol/min to 2000 μmol/min, which indicates that a relatively low V/III ratio is conducible to the c-axis growth of a-plane GaN.

Effect of the thickness of InGaN interlayer on a-plane GaN epilayer

In this paper,we use the a-plane InGaN interlayer to improve the property of a-plane GaN.Based on the a-InGaN interlayer,a template exhibits that a regular,porous structure,which acts as a compliant effect,can be obtained to release the strain caused by the lattice and thermal mismatch between a-GaN and r-sapphire.We find that the thickness of InGaN has a great influence on the growth of a-GaN.The surface morphology and crystalline quality both are first improved and then deteriorated with increasing the thickness of the InGaN interlayer.When the InGaN thickness exceeds a critical point,the a-GaN epilayer peels off in the process of cooling down to room temperature.This is an attractive way of lifting off a-GaN films from the sapphire substrate.

Characteristics and Applications of Common-Track Constellation in One Orbit Plane

Common-track constellation is a special kind of constellation, all ground tracks of satellites are in one track. With recursive orbit or quasi-recursive orbit, the ground track of the constellation is a closed loop with a repeating track. In particular, if the constellation is in one orbit plane, the constellation can meet the requirement for a multi-satellite launch mission and fast satellite-satellite link establishment. The characteristics and coverage properties of a common-track constellation in one orbit plane are studied in this paper. The simulation results show that a common-track constellation in one orbit plane can provide favorable coverage to a target station in the polar areas.

大尺寸Split型垂直极化有界波EMP模拟器场的特性分析

采用并行时域有限差分(finite-difference time-domain, FDTD)方法对大尺寸分裂型垂直极化有界波电磁脉冲模拟器(简称“Split型模拟器”)的电场进行模拟,研究分析了该类型模拟器天线的尺寸参数对模拟器内对称剖面上监测点电场垂直分量时域特性的影响,给出了该剖面上电场的瞬态分布特性,并与常规模拟器进行了比较。模拟结果表明:模拟器架高越高,监测点处的电场垂直分量的半高宽出现异常的起始高度越高,且同一监测点电场垂直分量的峰值随模拟器最大高度的增大而减小;距离源越近且距离下极板越近的监测点,电场垂直分量的峰值随整个上极板投影长度的增加有明显的减小;同一监测点电场垂直分量的上升沿会随着模拟器梯形金属板投影长度的增加而减小,峰值随该投影长度的增加而增加;监测点电场垂直分量的半高宽随上极板最大空隙宽度的增加而减小,峰值随上极板最大空隙宽度的增加而减小;当Split型模拟器选择合适的尺寸参数及工作空间高度时,电场垂直分量的上升沿和半高宽均满足IEC61000-4-25标准,且电场垂直分量的峰值与常规模拟器差别不大。

分焦平面偏振图像传感器信噪比标定

为了标定分焦平面偏振图像传感器的信噪比,设计了分焦平面偏振图像传感器各通道信噪比标定实验。对分焦平面偏振图像传感器信噪比参数对偏振角度测量结果的影响程度、信噪比标定原理、标定实验流程等进行了研究。根据分焦平面偏振传感器的结构和数字图像传感器的数学模型得到信噪比的标定原理。在不同信噪比、不同入射角度线偏振光情况下,对偏振角度测量结果进行了仿真。然后,根据标定原理设计标定实验的装置结构和实验流程。最后,进行实际标定并对实验数据进行了分析。信噪比-偏振角度测量精度仿真结果表明:分焦平面偏振图像传感器的信噪比越大,偏振角度测量精度越高,且入射偏振光角度也会影响测量精度。分焦平面偏振图像传感器各通道信噪比参数的实际测试结果表明:标定值与指标值相差不超过0.55 dB。实验结果证明,该方法是准确有效的,能够较好地完成分焦平面偏振图像传感器各通道信噪比的标定任务。

In-plane dipolar nano-antenna steers polariton waves at nanoscale

Hyperbolic polaritons can be launched and guided into mirror-symmetric-broken trajectories using an in-plane dipolar nano-antenna,and this asymmetry can be configured by adjusting the polarization direction of the in-plane dipole moment.

Observation of room‐temperature out‐of‐plane switchable electric polarization in supported 3R‐MoS_(2) monolayers

Two‐dimensional(2D)ferroelectrics have attracted considerable attention due to their potential in the development of devices of miniaturization and multifunction.Although several van der Waals(vdW)‐layered materials show ferroelectricity,the experimental demonstrations of ferroelectric behavior in monolayers are very limited.Here we report the observation of room‐temperature out‐of‐plane switchable electric polarization in supported MoS_(2) monolayers exfoliated from 3R‐stacked bulk crystals under ambient conditions.Using in situ piezoelectric force microscopy and Kelvin probe force microscopy in a glovebox,we reveal that trapped water/ice molecules are responsible for this switchable electric polarization and this conclusion is strongly supported by theoretical simulations.It is worth noting that the water/ice trapping in the monolayers exfoliated from 2H‐stacked MoS_(2) crystals is not as much as that in 3R monolayers and,consequently,the out‐of‐plane electric polarization is missing there.Our findings indicate that monolayers with a trapped single layer of polar molecules might be emerging alternatives to 2D ferroelectrics.Furthermore,the stacking sequences may bring new properties and applications to 2D vdW materials not only when we stack them up but also when we thin them down.