金纳米环双体尺寸和耦合效应对表面等离子体共振特性的影响

采用离散偶极子近似方法系统地研究了金纳米环双体的消光光谱及其电场分布. 计算结果表明, 金纳米环双体在耦合作用下的共振消光峰对应着不同振动模式, 改变金纳米环双体的排列方式、 间距和尺寸大小, 其表面等离子体共振消光峰发生红移或蓝移. 因此可以通过对金纳米环双体结构参数和排列方式的设定, 调节其表面等离子体共振消光峰的位置. 电场分布表明, 水平排列的金纳米环双体较单个金纳米环产生更强的局部表面增强电场. 适当的小间距, 较大的内外半径的金纳米环水平阵列更适合做表面增强拉曼散射的衬底, 在生物分子检测等领域具有潜在的应用.     

垂直入射条件下金属环的谐振特性

本文研究垂直入射条件下水平极化和垂直极化时金属开口谐振环(split ring resonator, SRR)的电磁响应行为. 通过分析这两种情况下的透射系数、介电常数和磁导率, 发现垂直极化时, SRR可以产生电谐振实现负介电常数, 其频段远高于磁谐振频段; 水平极化时, SRR只能产生磁谐振实现负磁导率, 其频段与水平入射时的SRR的磁谐振频段相对应. 通过仿真对此进行了证明, 并对产生电谐振和磁谐振的原因进行了分析.     

涡旋光束在反射中的正交偏振特性研究

本文从角谱理论出发建立了涡旋光束在空气-玻璃界面反射时的傍轴传输模型, 并研究了反射过程中诱导产生的正交偏振效应. 当一水平偏振涡旋光束以不同角度入射时, 反射光束的正交偏振分量呈现出类似于一阶厄米-高斯模式的双峰强度分布, 而水平偏振分量强度分布呈现与入射光束相似的分布, 且只在布儒斯特角附近入射时才现出与正交偏振分量垂直的双峰分布. 对于任意线偏振入射光, 其正交偏振分量的偏振方向不再垂直于入射时的偏振方向, 而是与反射光束的中心波矢垂直, 此时正交偏振分量出现有趣的旋转特性, 其物理原因归结于任意线偏振光入射时所对应的水平与垂直偏振分量的反射系数不同. 最后进行了相关实验验证, 发现实验结果与理论分析符合得较好. 关键词： 正交偏振 涡旋光束 任意线偏振     

Spatial coherence measurements from two L-shape arrays in Shallow Water

In the Shallow Water’ 06 experiment, two L-shape arrays (ARRAY52 and ARRAY32) were deployed. The vertical line array (VLA) components of both ARRAY52 and ARRAY32 were exactly perpendicular to the direction of sound propagation. The horizontal line array (HLA) component of ARRAY52 was exactly perpendicular to the direction of sound propagation. The HLA component of ARRAY32 was exactly parallel to the direction of sound propagation. This configuration offered an opportunity to simultaneously analyze the three dimensional (3-D) spatial coherences: vertical, transverse horizontal and longitudinal horizontal. When the source and the receivers were below the thermocline, both the vertical and longitudinal horizontal coherence lengths in units of wavelength increased with increasing range and frequency. When the source was within the thermocline, the transverse horizontal coherence length in units of wavelength decreased with frequency and exhibited weak range dependence. The text was submitted by the authors in English.     

“Hot spots” induced near-field enhancements in Au nanoshell and?Au nanoshell dimer

The influence of “hot spots” on the near-field properties of Au nanoshell and Au nanoshell dimers have been investigated by means of the finite element method. It is found with increasing the pinhole radius R that the maximal enhancement of near-field for Au nanoshell with pinhole parallel to the polarization increases from 17.906 at R=0 nm to 36.979 at R=0.8 nm, and then almost shows a negligible radius dependence. Large electric fields also can be observed inside the pinhole perpendicular to the polarization, which increases with increasing the pinhole radius. The near-field of Au nanoshell dimer depends strongly on the polarization and propagation directions of the incident light. Exponential decay behavior is found for the maximal enhancement of the electric field in the dimer junction as a function of the dimer separation. Furthermore, a very strong electric field is found in the junction between two Au nanoshells when the pinholes are located near the gap between the nanoshells.     

Experimental Demonstration of an Easy Method to Realize Weak Measurement for the Arrival Time of a Single Photon

We present a realization of weak measurement for the arrival time of a single photon. Our experimental setup is based on a Hong-Ou-Mandel interferometer, and a birefringent crystal is used to perform weak measurement between a preselected and a postselected measurement by two polarizers, for the crystal can separate the two components of horizontal polarization and vertical polarization by a small distance compared to the coherence length of photon pairs. In addition, we found that a quartz plate with nonideal length may decrease weak values in some degree.     

Palladium atoms and its dimers adsorbed on graphene: First-principles study

In this work we have studied the stabilty, electronic and magnetic properties of Pd adatoms and dimers adsorbed on graphene system using first-principles calculations. The adsorption energies for Pd adatom and its dimer have been found to range from −0.986 to −1.135 eV and −0.165 to −1.101 eV, respectively, which signify stable configuration and future utilization of this system in catalysis. A shift but no separation of π and π^? bands at the Dirac point has been observed in case of Pd dimer adsorption in perpendicular configuration, which can be accounted for the breaking of symmetry of the graphene structure due to adsorption. 64-68% spin polarization P(E_F) and 1.944-1.990 μ_B magnetic moment have been observed for Pd dimers adsorbed on graphene in perpendicular configuration for different sites. The unequal values of partial density of states for 4d and 5s orbitals of Pd dimers at Fermi level have been found to be responsible for the generation of high spin polarization.     

基于表面等离激元的偏振态控制光开关

利用四个Au纳米棒组成的类矩形纳米棒四聚体结构设计了一种基于偏振态控制的光开关,并采用有限元法研究了该结构对入射光偏振态的响应特性.研究发现,该结构的透射光谱对入射光的偏振方向具有很强的依赖性,当入射光的偏振角度变化π/2时,其特征峰的开关比分别能达到27.81dB和21.65dB.分析表明,该结构的开关效应主要由不同偏振态下所导致的水平双纳米棒和竖直双纳米棒之间的近场耦合强度不同而实现,该结构透射系数与偏振角度的关系服从Malus law.此外,通过改变类矩形纳米棒阵列结构参数,研究了结构参数对其光开关响应特性的影响.在此基础上,通过改变阵列的周期参数,研究了入射光水平偏振和垂直偏振下周期参数对单元结构透射光谱的影响.该研究结果能够为可调谐双波长偏振光开关的设计提供理论依据.     

Polarization control of an X‐ray free‐electron laser with a diamond phase retarder

A diamond phase retarder was applied to control the polarization states of a hard X‐ray free‐electron laser (XFEL) in the photon energy range 5–20 keV. The horizontal polarization of the XFEL beam generated from the planar undulators of the SPring‐8 Angstrom Compact Free‐Electron Laser (SACLA) was converted into vertical or circular polarization of either helicity by adjusting the angular offset of the diamond crystal from the exact Bragg condition. Using a 1.5 mm‐thick crystal, a high degree of circular polarization, 97%, was obtained for 11.56 keV monochromatic X‐rays, whereas the degree of vertical polarization was 67%, both of which agreed with the estimations including the energy bandwidth of the Si 111 beamline monochromator.     

用极化晶体谱仪探测X射线极化度

为了研究等离子体各向异性及确定高温等离子体中电子束的存在,研制了X射线极化晶体谱仪,探讨了极化光谱学的理论,推演了X射线极化度的计算方法.谱仪能够在两个相互垂直的方向分别对X射线进行探测,垂直方向晶体分析器使用云母球面晶体,水平方向为PET平面晶体,摄谱元件采用成像板.在激光聚变研究中心2×10 J激光装置上进行了摄谱实验.实验结果表明,PET晶体分光效果理想,获得了铝的类He共振线(w)、磁四级M2跃迁x线、互组合跃迁y线以及禁戒谱线z线,适合于研究X射线极化光谱学;云母晶体得到铝的类He共振线,其伴线光谱不明显.分析了谱仪垂直方向信号微弱的原因,提出了改进极化晶体谱仪的方案.     

Polarization of the high harmonics of radiation in a laser plasma

The polarization of the high harmonics generated in plasmas by the bremsstrahlung of electrons oscillating under the influence of high-power plasma-heating electromagnetic radiation is described on the basis of a simple model of a cold plasma. It is shown that when the polarization of the heating radiation differs from plane polarization by a small but finite amount, the high harmonics are generated with almost perpendicular polarization, and the degree of circular polarization of the harmonics increases with the number of the harmonic. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 313–316 (10 March 1998)     

Demonstration of a single-layer meanderline phase retarder at infrared

Meanderline wave plates are in common use at radio frequencies as polarization retarders. We present initial results of a gold meanderline structure on a silicon substrate that functions at a wavelength of 10.6 microm in the IR. The measured results show a distinct change in the polarization state of the incident beam after passing through the device, inducing a 74 degrees phase retardance between horizontal and vertical components. A high degree of polarization (88%) is maintained in the transmitted beam with an overall power transmittance of 38% and a beam profile that remains essentially unchanged.     

矩形结构垂直腔顶发射激光器的偏振特性

为了获得高功率的偏振激光,对矩形结构的980 nm大口径顶发射垂直腔面发射激光器(VCSEL)进行了研究.实验结果显示,对于400 μm×80μm出光口径的矩形VCSEL器件,在工作电流内,水平偏振光和竖直偏振光共同存在,并且水平偏振光一直占据主导地位;而且水平偏振光的光谱相对于竖直偏振光有蓝移.这些现象和理论模型的分...     

Nonmonotonic effects of perpendicular magnetic anisotropy on current-driven vortex wall motions in magnetic nanostripes

In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy(PMA) on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations.The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.     

Investigation of EM scattering from electrically large sea surface with breaking wave at low grazing angles

According to the high-resolution radar data, backscattering scattering from sea surfaces may give rise to super events of strong scattering and large Doppler offsets for horizontal (HH) polarization at low grazing angles (LGA), which are usually considered to be caused by breaking waves. In this paper, the mesoscale breaking wave model is introduced to account for the contribution of breaking waves, which can be responsible for sea spikes and high Doppler shift. The backscattering radar cross-section (RCS) from a single breaking wave is computed and the scattering from sea surfaces is analyzed by a composite surface scattering model, in which the phase factor of every facet is modified by the capillary waves. By using the slope criterion, the spatial distribution of the breaking waves is obtained. At the same time, the RCS of sea surfaces with breaking waves is calculated and the results agree with measured data well at LGA for HH polarization. Considering the Bragg phase velocity, orbital motion of facets and wind drift, the Doppler spectrum of sea surface with breaking wave is simulated, and when compared with the result without breaking wave, there is a good improvement for HH polarization, and for the vertical polarization, the revision is little, which are agreeable with the results of recent researches.     

光束通过在静电场作用下的α-碘酸锂单晶产生的垂直于c向的散射带

激光束通过c向静电场作用下的α-碘酸锂单晶时,观察到与c向正交而且张角很大的散射带,其强度在透射光斑的两侧并不对称。当入射光的电向量垂直于c向时,散射光的电向量则平行于c向;而前者平行于c向时,后者则垂直于c向。如果入射光的电向量既不垂直也不平行于c向,则出现电向量分别平行和垂直于c向的两条散射带,在特定条件下它们相重合。本工作详细研究了散射带的偏振态、强度分布的类准周期结构及其弛豫行为等。我们认为这种散射带很可能是由于晶体中载流子沿c向运动产生的某种效应所引起。同时用显微镜观察了解电场作用下α-腆酸锂单 关键词：     

水平井与直井混合注采井网的流场计算——以五点法注采井网为例

基于保角变换和镜像反映原理,建立五点法水平井与直井混合注采井网流场数学模型,导出其势函数和流函数数学表达式,得到五点法混合注采井网内部等势线和流线分布.研究水平井长度、水平井与直井连线夹角、平面各向异性及水平井不同平面位置等因素对混合注采井网内部流场分布的影响.结果表明：混合注采井网水平井跟端和趾端,流线分布相对密集,两端位置产液能力较强;水平段越长,其流线控制的泄油面积越大;水平井与直井连线成45°角时,水平井与正对的两口直井间的驱替强度相对较大;水平井垂直于主渗透率方向时,流线均匀密集地汇聚到生产井,易形成线性驱替;混合注采井网内部水平井偏离中心位置程度越大,流线分布疏密分化越明显.     

Angular dependence of pp spin correlation and rescattering observables between 1.80 and 2.10 GeV

A polarized proton beam extracted from SATURNE II and the Saclay polarized proton target were used to determine the spin correlation parameter Aoosk and the rescattering observablesK _os″ so; D_os″ok, N_os″sn, andN _onsk at 1.80 and 2.10 GeV. The beam polarization was oriented perpendicular to the beam direction in the horizontal scattering plane and the target polarization was directed either along the vertical axis or longitudinally. Left-right and up-down asymmetries in the second scattering were measured. A check for the beam optimization with the beam and target polarizations oriented vertically provided other observables, of which results forD _onon andK _onno at 1.80, 1.85, 2.04, and 2.10 GeV are listed here. The new data at 2.10 GeV suggest a smooth energy dependence of spin triplet scattering amplitudes at fixed angles in the vicinity of this energy.     

Square-shaped beam generated by phase shifted bounded square zone plate

A novel diffractive element is presented which is made through lateral phase shifted square zone plate bounded along horizontal and vertical axes via two perpendicular rectangle windows, respectively. We demonstrate that under a given condition the element is able to produce a square light beam at the focal plane. We have also elaborated that the produced square beam can be simply manipulated by an appropriate combination of the phase shifting parameter and bounded width. Experimental works verify the simulation results.     

热交联型聚氨酯集成双通道电光调制器的制备及其性质的研究

研究了交联型聚氨酯材料集成衰减全反射型双通道聚合物波导电光调制器的制备和性能。这种电光调制器的制备技术非常简单,只要用两个分立的下电极代替单通道调制器中的下电极即可。通过测量器件的调制特性,在832 nm波长下,获得了最大电光系数为24.2 Pm/V,调制带宽约为500 MHz、插入损耗低于1.5 dB。由于器件上下电极的垂直距离为微米级、而通道之间的水平距离为毫米量级的设计,使各通道之间的场不会引起相互交迭,因而未测到各通道间的串扰。另外,热交联型聚合物材料的采用提高了整个器件的热稳定性,在100℃经过800 h后,电光系数仍然保持初值的88%。