广角任意反射面速度干涉仪的光学性质研究

研究了广角任意反射面速度干涉仪(VISAR)的光学性质。阐述了广角VISAR的原理,指出广角诊断靶中椭球镜的作用是将靶丸内表面成虚像在靶丸中心附近。使用Zemax模拟了成像弯曲对动态干涉条纹形成的影响,提出使用异形光纤面板进行像面矫正。研究了工程误差对干涉仪成像的影响,若要取得良好的成像效果,椭球镜的位置偏差不得多于30 μm,倾角不得超过4°,长轴方向加工误差需小于0.1 μm,短轴方向误差需小于4 μm,镜面反射率应高于70%。讨论了广角VISAR光学研究的进一步发展方向如影响动态条纹的更多可能因素、像面矫正的其他方法、物与像面的光学对应等。     

一种强电磁脉冲辐射场均匀性校准测试装置

目前,辐射场均匀性主要采用单点多次测试的方式来实现,该方式将不可避免地引入因辐照信号自身时变特性带来的测量误差;此外,单点多次测试极大地增加了测试时间、测试效率低下。为解决这些问题,本文设计了一种可实现一次多点测试、测试区域可自动调节的装置,仿真表明：该装置可满足500 mm×500 mm~1500 mm×1500 mm区域辐射场9点均匀性测试;在此基础上,在1000 mm×1000 mm测试区域,针对1.35 GHz和2.88 GHz两个频点开展了实验验证,实验表明：设计的测试装置可满足辐射场均匀性9点自动测试要求,大幅提高了测试效率和自动化程度。     

Dynamical current–current correlation in two-dimensional parabolic Dirac systems

We theoretically investigate the current–current correlation of the two-dimensional (2D) parabolic Dirac system in hexogonal lattice. The analytical expressions of the random phase approximation (RPA) susceptibility, Ruderman–Kittel–Kasuya–Yosida (RKKY) Hamiltonian, and the diamagnetic orbital susceptibility in noninteracting case base on the density–density or current–current correlation function are derived and quantitatively analyzed. In noninteracting case, the dynamical polarization within RPA, and spin transverse susceptibility as well as the RKKY interaction (when close to the half-filling) are related to the current–current response in the 2D parabolic Dirac systems. Both the cases of anisotropic dispersion and isotropic dispersion are discussed.     

水杨醛类希夫碱在LB膜上的光谱性能的研究

合成了两种末端碳锭长度不同的水杨醛类希夫碱N-十二烷基（2-羟基-5-硝基苯甲亚胺）和N-十六烷基（2-羟基-5-硝基苯甲亚胺），研究了它们在气-液界面上的成膜性能，并通过紫外、荧光、红外显微镜等光谱手段对它们在LB膜上的性能进行了表征。实验结果表明两种希夫碱分子在LB膜中都形成了J-聚体，末端碳链较长的希夫碱 成膜性能相对较好，并且在膜上也能光致发光，但希夫碱分子的LB膜存在一定的缺陷。     

镧系离子(Eu3+,Tb3+)氧氟沙星配合物的合成和光谱表征

本文报道了镧系离子Eu3 + ,Tb3 + 同喹诺酮羧酸类衍生物氧氟沙星形成配合物的合成。用元素分析法和ICP确定了配合物的组成为Ln(oflo) 3 Cl3 ·8H2 O。红外光谱表明氧氟沙星配体羧基同中心离子发生螯合 ,并可能与邻位羰基形成六元环稳定结构。荧光光谱表明 ,Eu配合物具有很宽的激发谱带 (2 0 0～ 45 0nm) ,明显区别于其他羧酸类的稀土配合物 ;中心离子Eu3 + 发射谱位于 5 79 0nm(5D0 7F0 ) ,5 92 2nm(5D0 7F1) ,6 12 2nm(5D0 7F2 ) ;而Tb3 + 配合物则同时有配体和中心离子的荧光发射     

Field-induced ionization and Coulomb explosion of nitrogen

Femtosecond-laser field-induced ionization and Coulomb explosion of diatomic nitrogen were systematically investigated using time-of-flight mass and photoelectron spectrometry. Both linearly and circularly polarized femtosecond laser pulses were used at intensities varying from 5×10¹³ to 2×10¹⁵ W/cm². Strong N₂ ⁺, N₂ ²⁺, N⁺, N²⁺ and N³⁺ ion signals were observed for horizontally polarized pulses. Moreover, signals from the atomic ions exhibited a double-peak structure. Suppression of ionization was observed for circularly polarized pulses, while for vertically polarized pulses, only N₂ ⁺ and N₂ ²⁺ ions were observed. The angular distributions of the ions were measured under zero-field conditions in the ionization zone. The atomic ions N⁺, N²⁺ and N³⁺ exhibited highly anisotropic distributions, with maxima along the laser polarization vector and zeroes normal to the laser polarization vector. In contrast to the atomic ions, N₂ ⁺ exhibited a strong isotropic angular distribution. These observations indicate that dynamic alignment is responsible for the observed anisotropic angular distribution of the atomic ions. The kinetic energy spectrum of the photoelectrons is featureless and broad, extending above the ponderomotive potential of the laser pulse. The angular distribution is markedly anisotropic, with a maximum along the laser polarization vector. These observations further support the notion that the field-ionization mechanism is dominant under our experimental conditions. Received: 29 January 2002 / Revised version: 15 March 2002 / Published online: 12 July 2002     

Active dielectric metasurface based on phase‐change medium

We propose all‐dielectric metasurfaces that can be actively re‐configured using the phase‐change material Ge₂Sb₂Te₅ (GST) alloy. With selectively controlled phase transitions on the composing GST elements, metasurfaces can be tailored to exhibit varied functionalities. Using phase‐change GST rod as the basic building block, we have modelled metamolecules with tunable optical response when phase change occurs on select constituent GST rods. Tunable gradient metasurfaces can be realized with variable supercell period consisting of different patterns of the GST rods in their amorphous and crystalline states. Simulation results indicate a range of functions can be delivered, including multilevel signal modulating, near‐field coupling of GST rods, and anomalous reflection angle controlling. This work opens up a new space in exploring active meta‐devices with broader applications that cannot be achieved in their passive counterparts with permanent properties once fabricated.

     

Defect structure of Cu2+ center in K2SO4‒Na2SO4‒ZnSO4 glasses

The spin Hamiltonian parameters (g factors g _//, g _⊥ and hyperfine structure constants A _//, A _⊥) of Cu²⁺ in K₂SO₄?Na₂SO₄?ZnSO₄ glasses are calculated from the high-order perturbation formulas of 3d⁹ ion in tetragonal octahedral sites. The calculated results are in agreement with the observed values. Since the EPR parameters are sensitive to the local structure of a paramagnetic impurity center, the defect structure of Cu²⁺ center in K₂SO₄?Na₂SO₄?ZnSO₄ glasses is estimated. The validity of results is discussed.     

Structural transition of secondary phase oxide nanorods in epitaxial YBa2Cu3O7−δ films on vicinal substrates

A theoretical study of a structural transition of secondary phase oxide nanorods in epitaxial YBa₂Cu₃O_7?δ films on vicinal SrTiO₃ substrates is presented. Two possible types of film/substrate interface are considered, with one assuming complete coherence, while the other is defective as manifested by the presence of antiphase grain boundaries. Only in the former case does the increase of the vicinal angle of the substrate lead to a substantial change of the strain field in the film, resulting in a transition of the nanorod orientation from the normal to the in-plane direction of the film. The calculated threshold vicinal angle for the onset of the transition and lattice deformation of the YBa₂Cu₃O_7?δ film due to the inclusion of the nanorods is in very good agreement with experimental observations. This result sheds lights on the understanding of the role of the film/substrate lattice mismatch in controlling self-assembly of dopant nanostructures in matrix films.     

Multi-pass,multi-bunch beam breakup for 9-cellTesla cavities in the ERL

Generally, the Energy Recovery Linac (ERL) needs specially designed high current superconducting RF cavities. In this paper, the threshold current of beam breakup for compact ERL facilities with 9-cell Tesla type cavities are investigated. The results show that it is feasible to adopt the 9-cell Tesla cavity for compact ERL test facilities with just a few cavities and beam current around 10 mA.