Splitting of an edge dislocation by an optical vortex

In a linear medium an optical vortex induces the splitting of an edge dislocation into vortices of both topological charges. Their positions and number depend on which of the phase dislocations is shifted from the center of the host beam. Violations of the charge conservation law are discussed.     

克尔介质中超连续谱的产生与自聚焦的抑制

 从（3+1）维非线性薛定谔方程出发,理论上分析了超短脉冲频谱展宽与自聚焦的影响因素。分析得出：通过改变泵浦光的功率和光束口径,可以实现光谱的极大展宽并避免自聚焦成丝。数值模拟了小口径强泵浦光束在BK7玻璃中的传输过程并进行了实验验证。模拟结果显示在超连续谱产生的同时小尺度调制被完全抑制。实验结果表明：降低泵浦光功率,使光束不会因为全光束自聚焦而发生塌陷,同时还能控制除自聚焦外的其它非线性效应,进而改善近场光束质量。由于自相位调制是超短超强脉冲产生超连续谱的重要机制之一,需要维持传输过程中的泵浦光功率,由此最佳的入射光功率应选在全光束自聚焦功率阈值附近。     

GaN氢化物气相外延生长系统的设计与制作

根据GaN氢化物气相外延生长(HVPE)的原理,设计制作了双温区卧式HVPE系统．根据实际生长中出现的问题和CaN样品的测试情况,对系统进行了逐步的调试和改进．     

缓冲层Ta对FePt薄膜L10有序相转变及矫顽力的影响

制备了Ta/FePt/C系列多层膜，研究了样品在不同温度退火后的磁特性和微结构.实验结果表明，不同厚度的Ta缓冲层具有不同的微结构特征，显著影响FePt层的L1₀有序相的形成及相应的矫顽力.当Ta缓冲层较薄，Ta层为非晶态，且较为粗糙，由此使FePt在界面处产生较多的缺陷并导致较高密度的晶界，在退火过程中，受束缚相对较弱的非晶态的Ta原子比较容易沿FePt的缺陷和晶界处向FePt层扩散，使FePt在相变过程中产生的应力比较容易释放，同时，Ta在扩散过程中产生的缺陷，降低了FePt有序 关键词： FePt薄膜 0相')" href="#">L1₀相 原子扩散     

六方相InGaN外延膜的显微Raman散射

用X射线衍射(XRD)技术和显微Raman散射方法对金属有机化学气相沉积(MOCVD)法生长的六方相In_xGa_1-xN薄膜样品进行了研究，观察到了相分离现象和LO声子-等离子耦合模(LPP⁺)，讨论了In_xGa_1-xN的A₁(LO)模被屏蔽的主要物理机制.同时，对Raman谱中E₂和A₁(TO)声子模进行了分析和讨论.在In_xGa_1-xN样品的低温Raman谱中还观察到单电子跃迁产生的Raman散射信号. 关键词： Raman散射 X射线衍射 相分离 应力 LO声子-等离子耦合     

Variable Wavelengths Fiber Bragg Gratings Written with A Phase Mask and Four Prisms

Using only one diffractive element, the Talbot interferometer provides a robust and inherently stable method for reproducing fiber Bragg gratings with variable wavelengths, and reduces the complexity of the fiber grating fabrication system. However, the usable length of the grating is limited by the practical length of the mirrors. This paper presents a phase mask with two fixed prisms and two rotational prisms to inscribe fiber Bragg gratings with variable Bragg wavelengths. In this system, the fiber Bragg grating is inscribed by UV interference stripes of 193 nm derived from two rotational prisms and two fixed prisms, where phase mask is used as a beam splitter of ±1 order diffraction light. It is noteworthy that the tunable phase mask interferometer decreases the demand of the length of prism evidently.     

Self-marking phase-stepping electronic speckle pattern interfometry (ESPI) for 3D displacement measurement on cathode ray tube (CRT)-panels

This study demonstrates the feasibility of applying phase-shifting electronic speckle pattern interfometry to measure the deformation field of the front panel of a cathode ray tube, to support analysis to enhance the implosion-resistance capacity under violent collapse. Two effects, the air exhaustion and shrink band constraint effects, are comprehensively investigated. The angle of an adjustable mirror is switched, to provide three sensitivity vectors that are required in 3D-displacement measurement. A Fourier filtration is employed to remove speckle noise and establish a noise-free phase map. Inconsistent points are identified and masked to prevent any possible divergence during phase unwrapping. The results show that the accuracy of this method is satisfactory.     

Quantum computation with ions in microscopic traps

We discuss a possible experimental realization of fast quantum gates with high fidelity with ions confined in microscopic traps. The original proposal of this physical system for quantum computation comes from Cirac and Zoller (Nature 404, 579 (2000)). In this paper we analyse a sensitivity of the ion-trap quantum gate on various experimental parameters which was omitted in the original proposal. We address imprecision of laser pulses, impact of photon scattering, nonzero temperature effects and influence of laser intensity fluctuations on the total fidelity of the two-qubit phase gate.     

Strong,large distance impurity dipole interaction in KNbO3 single crystals

It is found that the unrelaxed impurity dipoles can arrange themselves linearly in the structure joining each other end-to-end in pseudocubic [110] direction at the tetragonal to the orthorhombic phase transition. It is shown that this alignment precedes the domain formation at the phase transition, which implies quick movements of the dipoles in the structure, and a strong dipolar interaction. The experiments with the application of dc fields to the crystals showed that the dipolar interaction becomes stronger with the field. The dipoles can see each other across the existing domain walls implying the large distance nature of the interaction. The observation of impurity clusters arranged in pseudocubic [110] direction confirmed the large distance nature of the interaction. It is concluded that this strong, large distance interaction is very interesting in as much as such an interaction of dipoles forms the basis of ferroelectricity.     

Two-spin-majority cellular automaton as a model of 2D cluster and interface growth

A new probabilistic cellular automaton model is introduced to simulate cluster and interface growth in two dimensions. The dynamics of this model is an extension to higher dimensions of the compact directed percolation studied by Essam. Numerical results indicate that the two-dimensional cluster coarsening and growth can be described only approximately by the conventional cluster size scaling due to a crossover in the growth mode. The spreading of the initially flat interface follows a purely diffusional,t ^1/2, law.