受激布里渊散射光脉冲波形的研究

从实验和理论上研究了受激布里渊散射(SBS)光脉冲波形.在Nd∶YAG调Q激光器中实验研究了SBS光脉冲波形随抽运光参数、结构参数和介质参数的变化规律，并利用SBS理论模型进行了数值模拟，实验与数值模拟结果的变化趋势基本一致.结果表明，抽运光能量越小，透镜焦距越短，镜-池间距越长，介质声子寿命越长，SBS光脉冲波形就越不容易出现调制现象.分析和讨论了抽运光参数、结构参数和介质参数对SBS光脉冲波形的影响机理. 关键词： 受激布里渊散射 脉冲波形 抽运光参数 结构参数     

第一性原理研究half-Heusler合金CoVTe和FeVTe半金属性及磁性的稳定性

本文构建了half-Heusler合金CoVTe和FeVTe.运用基于第一性原理的全势能线性缀加平面波方法,计算half-Heusler合金CoVTe和FeVTe的电子结构.电子结构的自旋极化计算结果表明,合金CoVTe和FeVTe具有半金属性,它们的半金属隙分别为0.21 eV和0.20 eV.磁性计算结果显示,合金CoVTe和FeVTe的晶胞总磁矩分别为2.00μ_B和1.00μ_B;合金晶胞中过渡金属V具有较强的原子磁矩,Te的原子磁矩较弱,而且为负值.使合金晶格均匀形变△a/a_0在±7%的范围内变化,分别计算CoVTe和FeVTe的电子结构.计算结果表明,晶格均匀形变△a/a_0分别为-7%—+7%和-4.8%—+7%时,合金CoVTe和FeVTe仍然保持半金属性,并且晶胞总磁矩分别稳定于2.00μ_B和1.00μ_B.     

Placement Scheme of Numerous Laser Beams in the Context of Fiber-Based Laser Fusion

A simple scheme based on the uniform distribution for the placement of numerous laser beams in the context o~ fiber-based laser fusion is proposed. It is theoretically demonstrated that all modes of the geometrical factor can be eliminated if sufflcient laser beams are uniformly distributed on the sphere. In the case of a finite number of laser beams, a quasi-uniform distribution of beams can be achieved based on the equal area subdivision algorithm. Numerical simulations indicate that with the increasing number of laser beams, the order of the dominant geometrical mode increases, and the irradiation nonuniformity decreases accordingly.     

NiFeNb种子层对坡莫合金磁滞回线的影响

以NiFeNb为种子层，制备(Ni₇₉Fe₂₁)_1-xNb_{x(5nm)/(Ni79Fe21) (20nm)/Ta(3nm)系列膜，并对其颗粒大小、 磁滞回线及表面粗糙度等进行测量，探讨种子层中Nb含量x对坡莫合金磁滞回线的影响.结果 表明，以NiFeNb作种子层能更好地改善坡莫合金的微结构. Nb含量为23％时的磁滞回线有最 小的最大磁能积、矫顽力.种子层影响坡莫合金磁滞回线的一个重要原因是脱附激活能等因 素造成种子层具有不同的表面粗糙度，进而使坡莫合金具有不同的微结构和磁性能. 关键词： NiFeNb种子层 坡莫合金 磁滞回线 粗糙度}     

Structure and optical properties of sol–gel derived Gd2O3 waveguide films

Pure and rare earth doped gadolinium oxide (Gd₂O₃) waveguide films were prepared by a simple sol–gel process and dip-coating method. Gd₂O₃ was successfully synthesized by hydrolysis of gadolinium acetate. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structure of Gd₂O₃ films annealed at different temperature ranging from 400 to 750 °C were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Gd₂O₃ starts crystallizing at about 400 °C and the crystallite size increases with annealing temperature. Oriented growth of (4 0 0) face of Gd₂O₃ has been observed when the films were deposited on (1 0 0) Si substrate and annealed at 750 °C. The laser beam (λ=632.8 nm) was coupled into the film by a prism coupler and propagation loss of the film measured by scattering-detection method is about 2 dB/cm. Luminescence properties of europium ions doped films were measured and are discussed.     

Theoretical analysis of all-optical 2R regeneration in a SOA-based Mach–Zehnder interferometer

All-optical 2R regeneration in a semiconductor optical amplifier-based Mach–Zehnder interferometer is theoretically analyzed. It is shown that the chirp of the regenerated signal is positive, while the input signal has no chirp. The peak extinction ratio (ER) of the regenerated signal is associated with the input wavelength and there exists an input wavelength corresponding to the largest ER of the output signal. The output peak ER is also found influenced by the input power, with lower input power getting higher peak ER.