掺铥氟磷玻璃的结构、热学性质和光谱性质

制备了不同Al(PO3)3含量的掺铥系列氟磷玻璃,研究了其结构、热稳定性和光谱性质。随着Al(PO3)3含量的增加,该系列玻璃的密度降低,折射率增加,差热分析表明,转变温度、析晶起始温度、析晶峰温度和熔化温度增加。Al(PO3)3摩尔浓度在7%~9%时析晶稳定性最佳。采用归一化的拉曼光谱分析了材料的结构和声子状况,对于该系列氟磷玻璃,Al(PO3)3含量的增加不会影响声子能量,但使声子密度增大。测试了样品的吸收光谱,Tm3 的3H6→3F4在第三通信窗口的L波段有明显吸收。与在其它玻璃基质中相比,Tm3 的3F4能级对应能量偏高,3H4能级对应能量偏低,使得3H4→3F4跃迁波长较大,接近于增益迁移光纤放大器的放大波长。扎得奥菲而特(Judd-Ofelt)理论分析表明随着Al(PO3)3含量增加,离子强度参量Ω2增大,Ω6保持相对稳定,Tm3 的能级寿命降低。     

Fabrication of three-dimensional crystalline microstructures by selective ion implantation and chemical etching

We present a new fabrication technique to produce three-dimensional (3D) microstructures on crystalline substrate using selective ion implantation and chemical etching. Localized lattice-damage layers at the specified depth beneath the substrate surface are formed by selective ion implantation. After etching out the partial surface regions and the buried lattice-damage layers by chemical etching, the 3D crystalline microstructures are produced. This technique is demonstrated on LiNbO₃ crystal to produce undercutting and free-standing microstructures, including microwire, microring, and microdisk. The measurement results of micro-Raman spectra show that the used fabrication process does not affect the original crystalline structure. The features of this technique include smooth structure surface, large undercutting range, and auto-etching stop. By using multiple implantations or repeating the proposed process several times, versatile 3D crystalline microstructures can be produced.     

耦合微盘及带输出波导的单微盘腔的耦合模式特性

光学微腔具有很高的品质因子和很小的模式体积,在光电子器件研究方面具有重要的应用价值.运用时域有限差分(FDTD)法和Padé近似频谱分析法模拟研究了耦合微盘及带输出波导的单微盘微腔由于空间对称性破坏导致的模式耦合现象;特别计算了耦合模式的场分布和品质因子,并由场分布得出不同角量子数模式的能量比例.对耦合微盘,模式耦合引...     

铬和镍的添加对Fe3Al合金力学性能影响的DFT研究

利用第一原理研究了过渡金属元素 Cr 或 Ni 在 Fe₃Al合金中的优先占位行为及其合金化效应. 计算结果表明: Cr 或 Ni 的取代有助于Fe₃Al 合金体系更稳定, Cr 优先占据 Fe_I 位, Ni 优先占据 Fe_II位. Fe₂NiAl-II 具有最小的剪切模量G, 杨氏模量E和G/B值, 因此Fe₂NiAl-II合金的韧性、延展性最佳. 态密度和电荷密度图表明, 过渡金属元素的取代提高了它们与近邻基体原子之间的相互作用, 削弱了Al和Fe的相互作用.     

Transport through artificial single-molecule magnets: Spin-pair state sequential tunneling and Kondo effects

The transport properties of an artificial single-molecule magnet based on a CdTe quantum dot doped with a single Mn+2 ion(S=5/2) are investigated by the non-equilibrium Green function method.We consider a minimal model where the Mn-hole exchange coupling is strongly anisotropic so that spin-flip is suppressed and the impurity spin S and a hole spin s entering the quantum dot are coupled into spin pair states with(2S+1) sublevels.In the sequential tunneling regime,the differential conductance exhibits(2S+1) possible peaks,corresponding to resonance tunneling via(2S+1) sublevels.At low temperature,Kondo physics dominates transport and(2S+1) Kondo peaks occur in the local density of states and conductance.These peaks originate from the spin-singlet state formed by the holes in the leads and on the dot via higher-order processes and are related to the parallel and antiparallel spin pair states.     

染料掺杂光子晶体荧光带隙边缘的激射研究

利用激光全息光刻技术, 在重铬酸盐明胶 感光材料中制备了掺杂有机染料的层状光子晶体. 在532 nm纳秒脉冲激光激励下, 样品的荧光光谱表现出良好的带隙特征; 随着抽运能量的增加, 在荧光带隙带边位置获得了激射光, 并进一步研究了光子晶体的带边位置与染料荧光峰的匹配对激射的影响.带边位置越靠近染料的荧光峰, 激射阈值越低, 反之则不易产生激射.该研究为超低阈值光子晶体激光器的发展提供了思路和方法. 关键词： 全息光刻 光子晶体 荧光带隙 低阈值激射     

First-principles studies of the vibrational properties of amorphous carbon nitrides

Raman spectra of amorphous carbon nitride films (a-C:N) resemble those of typical amorphous carbon (a-C), and no specific features in the spectra are shown due to N doping. The present work provides a correlation between the microstructure and vibrational properties of a-C:N films from first principles. The six periodic model structures of 64 atoms with various mass densities and nitrogen contents are generated by the liquid-quench method using Car-Parinello molecular dynamics. By using Raman coupling tensors calculated with the finite electric field method, Raman spectra are obtained. The calculated results show that the vibrations of C=N could directly contribute to the Raman spectrum. The similarity of the Raman line shapes of N-doped and N-free amorphous carbons is due to the overlapping of C=N and C=C vibration bands. In addition, the origin of characteristic Raman peaks is also given.     

超衍射成像中 双螺旋点扩展函数的三维定位精度

开关效应和单分子定位的结合可以实现样品的超衍射分辨成像, 双螺旋点扩展函数将单分子定位纳米分辨从二维扩展到了三维.本文对双螺旋点扩展函数的三维定位精度展开了探讨.首先, 基于费希尔信息量, 计算了双螺旋点扩展函数的无偏估计, 得出其理论定位精度, 并分析了光子数、背景噪声以及有效像元尺寸大小对其定位精度的影响; 其次, 基于单分子定位实验过程中对于数据分析通常采用的高斯拟合质心定位算法, 通过误差传递函数定律求得双螺旋点扩展函数的轴向定位精度.计算机模拟结果表明, 在光子数大于1000的条件下, 高斯拟合质心定位精度和费希尔信息量理论定位精度符合较好. 本文的讨论不仅为双螺旋点扩展函数的三维定位精度提供了理论依据, 同时也可为实验提供理论指导. 关键词： 双螺旋点扩展函数 费希尔信息量 定位精度 高斯拟合     

群论在对称结构电磁散射问题中的应用

用T矩阵方法计算电磁散射问题时, 如果散射体的几何结构满足点群对称性, 即在群变换作用下保持不变, 可以利用群论找出散射体的几何对称性和T矩阵元的对称性之间的关系, 通过预知部分矩阵元的精确值以及 它们之间的关系来达到数值求解过程 中节约运行时间的目的. 关键词： 群论 对称结构 电磁散射 对称算子     

A Quantum Watermarking Protocol Based on Bell Dual Basis

This paper presents a Bell-dual-basis-based quantum watermarking protocol composed of three major algorithms: watermark embedding and extracting and the intercepting test. The first two are completed by using the entanglement swapping property of Bell dual basis and the test is accomplished through IBF protocol to guarantee its bottom security. The watermarking protocol is mainly designed for the protection of digital copyright in the existence of classical information. This design finds that the quality of digital contents is not damaged with its zero-watermark attributes when embedding watermarks.