蜂巢光子晶格中光波的无衍射和反常折射

空间频率模式的光子带隙反映了光波在周期性结构中的线性传输特性.以这种线性传输特性为基础,研究了蜂巢光子晶格中光波的无衍射和反常折射.通过详细分析带隙结构第一通带上的衍射与折射特性,得出了光波发生反常衍射和折射的入射条件.匹配不同的入射条件,数值模拟了光波的无衍射传输和反常折射现象.结果表明:将入射光束的波矢设置在蜂巢晶格布里渊区中正常、反常衍射区的交界处,可使高斯光束沿x轴、y轴方向的衍射得到有效抑制;以多光束干涉场作为入射光场,可对蜂巢晶格进行模式匹配,激发第二布里渊区的传输模式;进一步将模式匹配后入射光场的波矢设置在反常折射区,可实现光波的反常折射.     

Anomalous temperature dependence of photoluminescence spectra from InAs/GaAs quantum dots grown by formation–dissolution–regrowth method

Two kinds of InAs/GaAs quantum dot(QD) structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the Ga As barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs.     

Magnetic anisotropy axis reorientation at ultrathin FePt films

Ultrathin FePt films (thickness between 1 nm and 5 nm) were studied for non‐volatile memories applications. The films were magnetron sputtered on monocrystalline MgO?001? substrates at 500 °C. The films are polycrystalline, except the 1 nm thick film which is not continuous. It is shown that films with thickness higher than 2.7 nm have L1₀ structure and perpendicular magnetic anisotropy, while a transition to in‐plane anisotropy occurs for thinner films. The out‐of‐plane coercivity drops from 16 kOe at the thicker film to 0.5 kOe at the thinner one.

Hysteresis cycles of FePt films as a function of film thickness.     

Gradient Chiral Metamirrors for Spin‐Selective Anomalous Reflection

Metasurfaces, the phase‐engineered quasi‐2D interfaces, have attracted intensive interest due to their great capabilities in manipulating the reflection, refraction and transmission of electromagnetic waves. Here, we demonstrate the design and realization of a gradient chiral metamirror tailored for spin‐selective anomalous reflection based on the theory of Pancharatnam‐Berry phase. Asymmetric split ring resonators are employed as the basic meta‐atoms for strong circular dichroism. Dispersionless phase discontinuities are achieved by adjusting the orientation of the meta‐atoms, and spin‐dependent absorption is realized by introducing a chiral resonance. Theoretical results predict both broadband beam deflection and spin‐selective absorption for circularly polarized waves in a designer metamirror. Experimental verification of this bifunctional performance is implemented at microwave frequencies and the measured results agree well with the simulation ones. Such chiral metamirrors could pave an avenue towards spin‐selective modulation of the wavefront and might find promising applications in planar electromagnetic devices.     

Retrieval of aerosol size distribution using improved quantum-behaved particle swarm optimization on spectral extinction measurements

An improved quantum-behaved particle swarm optimization (IQPSO) algorithm is employed to determine aerosol size distribution (ASD). The direct problem is solved using the anomalous diffraction approximation and Lambert–Beer's Law. Compared with the standard particle swarm optimization algorithm, the stochastic particle size optimization algorithm and the original QPSO, our IQPSO has faster convergence speed and higher accuracy within a smaller number of generations. Optimization parameters for the IQPSO were also evaluated; we recommend using four measurement wavelengths and 50 particles. Size distributions of various aerosol types were estimated using the IQPSO under dependent and independent models. Finally, experimental ASDs at different locations in Harbin were recovered using the IQPSO. All our results confirm that the IQPSO algorithm is an effective and reliable technique for estimating ASD.     

托卡马克离子温度梯度湍流输运同位素定标修正中杂质的影响

托卡马克实验发现,在不同参数条件下,等离子体能量约束经验定标律会有或大或小的修正.为解释这种修正现象发生的原因,应用回旋动理学方法,对含重(钨)杂质等离子体离子温度梯度(ITG)(包括杂质模)湍流输运的同位素效应进行了数值研究.结果表明钨杂质效应极大地修改了同位素定标律和有效电荷效应.随着杂质离子电荷数Z和电荷集中度f_z的变化,同位素定标律在较大范围内变化. ITG模最大增长率定标大约为M_i~(-0.48→-0.12),杂质模的定标为M_i~(-0.46→-0.3),其中, M_i表示主离子质量数.在ITG模湍流中,有效电荷数越大,关于M_i的拟合指数偏离-0.5越远,表现为同位素质量依赖减弱.在两种模中,杂质电荷集中度越大,同位素质量依赖越弱.研究了杂质效应使定标关系发生偏离的原因,证实杂质种类、杂质电荷数和杂质浓度的不同,是引起同位素质量依赖发生改变的重要原因.结果证实并解释了不同参数条件下托卡马克同位素定标的差异性.研究成果可以为ITER实验安排及杂质相关输运实验中选择装置材料、工作气体和设置其他参数提供理论参考.     

Intensity‐Enhanced Apodization Effect on an Axially Illuminated Circular‐Column Particle‐Lens

A particle can function as a refractive lens to focus a plane wave, generating a narrow, high intensive, weak‐diverging beam within a sub‐wavelength volume, known as the ‘photonic nanojet’. It is known that apodization method, in the form of an amplitude pupil‐mask centrally situated on a particle‐lens, can further reduce the waist of a photonic nanojet, however, it usually lowers the intensity at the focus due to blocking the incident light. In this paper, the anomalously intensity‐enhanced apodization effect was discovered for the first time via numerical simulation of focusing of the axially illuminated circular‐column particle‐lenses, and a greater than 100% peak intensity increase was realised for the produced photonic nanojets.     

载荷作用方式及范围对简支圆板反直观行为的影响

采用有限元法,研究了周边简支圆板在不同载荷作用方式和作用面积下的反直观动力响应。分析了加载方式和作用面积对反直观行为的影响,得到了不同载荷下反直观行为的特点,发现了反直观行为时程曲线的反弹次数与相应载荷区间之间的关系。研究结果表明:不同载荷下,反直观行为的变化规律基本相同,但各有其特点;首发反直观行为在整个反直观行为中起着重要作用;用首发反直观动力响应的位移历史曲线可以判断继发反直观动力行为所在载荷区间的最少个数。     

基于啁啾相移光纤光栅的滤波器设计及应用

相移光纤光栅作为透射型带通滤波器件降低了使用成本和插入损耗.在光通信和传感领域有着较高的应用价值.啁啾相移光纤光栅的透射峰波长和数量由相移点的位置和数量来确定,透射峰特性受相移量的影响.采用分段切趾的方法获得满足光通信要求的滤波特性,利用传输矩阵法分析了切趾前后透射峰特性的变化,结果表明:切趾改善了滤波器的幅度和相位响应,依据滤波器的设计要求选取不同的切趾函数以及切趾比例;切趾还大大减弱了透射峰波长和深度对相移量的敏感度,适当切趾后相移量的影响可以忽略.并提出一种应用双通道啁啾相移光纤光栅滤波器产生脉冲毫米波副载波信号的方案.     

Hadronic light-by-light scattering contribution to the muon g-2

We review recent developments concerning the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon.We first discuss why fully off-shell hadronic form factors should be used for the evaluation of this contribution to the g-2.We then reevaluate the numerically dominant pion-exchange contribution in the framework of large-NC QCD,using an off-shell pion-photon-photon form factor which fulfills all QCD short-distance constraints,in particular,a new short-distance constraint on the off-shell form factor at the external vertex in g-2,which relates the form factor to the quark condensate magnetic susceptibility in QCD.Combined with available evaluations of the other contributions to hadronic light-by-light scattering this leads to the new result aLμb yL;had=(116±40)×10-11,with a conservative error estimate in view of the many still unsolved problems.Some potential ways for further improvements are briefly discussed as well.For the electron we obtain the new estimate aLe byL;had=(3.9±1.3)×10-14.