Experimental observations of a left-handed material that obeys Snell's law

We measure two-dimensional profiles of collimated microwave beams transmitted through composite wire and split-ring resonator prisms. Prior experiments suggest these structures have a negative index of refraction, though these claims have been questioned. Our 2D measurements demonstrate that transmission obeys Snell's law with a negative index, confirming the refractive nature of this signal and refuting alternatives posed in the criticisms. In addition, we present preliminary evidence that a flat rectangular slab of this material can focus power from a point source.     

Mid-IR dual-wavelength difference frequency generation in uniform grating PPLN using index dispersion control

A novel widely tunable dual-wavelength mid-IR difference frequency generation （DFG） scheme with uniform grating periodically poled lithium niobate （PPLN） is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching （QPM） peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 ℃, respectively, based on the fiber laser fundamental lights.     

激光诱导击穿光谱技术的研究与应用新进展

激光诱导击穿光谱技术(LIBS)是一种近年来随着激光技术和光谱检测技术的发展而兴起的对元素定性和定量分析的光谱技术。详细介绍了LIBS技术最新的研究发展情况,以及在冶金、环境污染检测、生物医学、植物学、空间探索等领域的最新应用进展。     

塞曼效应与边缘离子温度的光谱测量

通过理论推导得到了谱线实际宽度和塞曼展宽之间的关系。在磁感应强度分别为1、2、2．5和3T的情况下，用数值方法进行了求解，用得到的结果拟合出了校正因子随离子温度变化的经验公式和拟合曲线，结果表明：离子温度较低时，塞曼效应对谱线宽度的影响很大，温度较高时，塞曼效应对谱线宽度的影响可以忽略。     

基于区域分解和逐级光线分裂的杂散光分析

针对蒙特卡罗法运算量大的问题,通过引入区域分解和逐级光线分裂技术,减少杂散光线与表面交点求解时所涉及的表面数及跟踪光线数,降低计算量.区域分解时,考虑子区域与表面数的匹配关系;并基于杂散光传播过程的模拟信息,逐级确定光线分裂倍数.以大衰减比抑制结构和多传感器系统为例,进行杂散光分析.结果表明,对复杂系统杂散光传播的蒙特卡罗法模拟,应用区域分解和逐级光线分裂技术,可以在保持计算精度的前提下,有效地提高计算效率.     

Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature

Hydrogen-free silicon nitride （SiNx） films were deposited at room temperature by microwave electron cyclotron resonance （MW-ECR） plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the N2 flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9 GPa, could be obtained at lower N2 flow rate of 4 sccm.     

Experimental realization of an order-finding algorithm with an NMR quantum computer

We report the realization of a nuclear magnetic resonance quantum computer which combines the quantum Fourier transform with exponentiated permutations, demonstrating a quantum algorithm for order finding. This algorithm has the same structure as Shor's algorithm and its speed-up over classical algorithms scales exponentially. The implementation uses a particularly well-suited five quantum bit molecule and was made possible by a new state initialization procedure and several quantum control techniques.     

一种基于新型查表方法的统一计算设备架构并行计算全息算法

为解决点源法计算全息速度较慢的问题,提出了一种新的查表算法,命名为三角函数查表法(T-LUT算法)。该算法是基于点源法基本的数学公式,通过一系列数学近似与恒等变换,生成了一种纯相位查找表,该查找表具有三维特性,并具有生成速度快、精度高、占用内存少等特点,克服了点源法重复计算相位的缺点。同时采用统一计算设备架构(CUDA)并行计算在图形处理器(GPU)上加以实现,并进行了三次并行优化。在算法的验证与对比实验中,采用单显卡(GPU显卡)实现T-LUT算法,在不牺牲全息图再现像质量的前提下,成功地将点源法计算全息的速度大幅度提升。实验发现在不同的物空间采样点数量的情况下,速度相对于点源法GPU运算提升30倍至近千倍不等。     

Elastic heterogeneity in metallic glasses

When a stress is applied on a metallic glass it deforms following Hook's law. Therefore it may appear obvious that a metallic glass deforms elastically. Using x-ray diffraction and anisotropic pair-density function analysis we show that only about 3/4 in volume fraction of metallic glasses deforms elastically, whereas the rest of the volume is anelastic and in the experimental time scale deform without resistance. We suggest that this anelastic portion represents residual liquidity in the glassy state. Many theories, such as the free-volume theory, assume the density of defects in the glassy state to be of the order of 1%, but this result shows that it is as much as a quarter.