High-power,low-noise,Yb-doped,cladding-pumped,three-level fiber sources at 980 nm

We present results on a high-power, cladding-pumped, Yb-doped fiber emitting at 977 nm in laser and ampllified-spontaneous-emission source configurations. We obtained up to 1.4 W of fiber-coupled, single-mode output power and slope efficiency as high as 68%. To our knowledge these are the highest powers efficiencies achieved from a single-mode fiber laser at approximately 980 nm and the first demonstrated results on a high-power amplified-spontaneous-emission source in this wavelength range. High power and high slope efficiency are achieved by using a high numerical aperture (> 0.7), a jacketed air-clad fiber, and a high-brightness pump source. Both types of sources exhibit relative intensity noise below -130 dB/Hz and are thus suitable for a wide range of applications.     

高温压电材料、器件与应用

作为重要的功能材料,压电材料已经在国民经济的多个领域里有着重要应用.随着现代工业的快速发展,特别是新能源、交通和国防工业的高速发展,功能材料的应用已经从常规使用转向极端环境下的服役.本文综述了具有高居里点的压电材料,包括钙钛矿型压电陶瓷、铋层状结构氧化物压电陶瓷、钨青铜结构压电陶瓷以及非铁电压电单晶等;介绍了其晶体结构特征和高温压电性能、最新研究进展,并列举了一系列的高温压电器件和应用,包括高温压电探测器、传感器、换能器和驱动器等.另外,本文总结了高温压电材料的热点研究问题,并展望了今后的发展方向.     

电感耦合等离子体-原子发射光谱法测定苹果浓缩果汁中钾、钠、钙、镁、磷、铁、锌、铜和铅

研究了ICP-AES测定苹果浓缩果汁中K、Na、Ca、Mg、P、Fe、Zn、Cu和Pb的各种条件.样品处理方法简便,避免了待测元素的污染和损失,结果准确.检出限、精密度和准确度均符合质量管理的要求.     

高分辨高灵敏度 CCD图像传感器驱动时序设计许涛1,张振海1, *,石志国2,张东红3,侯帅1,张亮1,王健1,

在分析面阵CCD图像传感器结构和驱动时序基础上,针对高分辨率高灵敏度ICX694ALG大面阵CCD图像传感器 ,研究其驱动时序发生器。以现场可编程门阵列 ( FPGA) 作为硬件平台 ,通过Verilog HDL硬件描述语言对该驱动时序发生器进行了硬件描述,采用ISE软件进行功能仿真,并针对XILINX公司的可编程逻辑器件XC3S1000进行了硬件适配。仿真测试表明,FPGA驱动时序发生器能够满足高分辨高灵敏ICX694ALG大面阵CCD图像传感器驱动要求,达到了设计要求。     

Exploring the effect of dopant (Si,P, S,Ge, Se,and Sb) in arsenene: A DFT study

The structural, electronic and magnetic properties of arsenene were investigated using DFT (density functional theory). The charge transfer, large biding energies, and short bond lengths indicate that the doped structures are robust. Si, S, Ge and Se doping induce magnetic state in arsenene. The principal contribution to the magnetic moment is originated in the p-orbital of dopants and adjacent As atoms, as is suggested by the results of the application of PDOS (Projected Density of States). More importantly, the low effective mass of electrons in arsenene doped by Si, P and Sb implies high carrier mobility, which indicates the three types of structures are high efficiency n-type semiconductors.     

Cell sorting in three dimensions: topology, fluctuations, and fluidlike instabilities

Previous 2D and 3D models concluded that cell sorting requires cytoskeletal fluctuations and is stalled by high tension at heterotypic interfaces. New deterministic and stochastic models show that this is not true in 3D. Sorting in 3D involves both topological untangling and domain coalescence. Coalescence requires fluctuations and low tension, but untangling does not. It occurs by a Plateau-Rayleigh instability of cell threads-deterministically driven by high tension. At high minority-cell fractions, untangling dominates and significant partial sorting can occur without fluctuations.     

Stripes, electron fractionalization, and ARPES

Although structurally the high temperature superconductors are quasi-two-dimensional, there is both theoretical and experimental evidence of a substantial range of temperatures in which ‘stripe’ correlations make the electronic structure locally quasi-one-dimensional. We consider an array of Josephson coupled, spin gapped one dimensional electron gases as a model of the high temperature superconductors. For temperatures above T_c, this system exhibits electron fractionalization, yielding a single particle spectral response which is sharp as a function of momentum, but broad as a function of energy. For temperatures below the spin gap but above T_c, there are enhanced one-dimensional superconducting fluctuations and pseudogap phenomena. Pair tunneling induces a crossover to three-dimensional physics as T_c is approached. Below T_c, solitons are confined in multiplets with quantum numbers which are simply related to the electron, and a coherent piece of the single particle spectral function appears. The weight of this coherent piece vanishes in the neighborhood of T_c in proportion to a positive power of the interchain superfluid density. This behavior is highly reminiscent of recent ARPES measurements on the high temperature superconductors.     

高温高压下碳化钨晶体的结构、力学、电子、光学以及热力学性能的第一性原理计算

本文利用密度泛函理论中的广义梯度近似对碳化钨晶体的三种结构(碳化钨相、闪锌矿相以及纤锌矿相)进行了优化,得到能量最低的稳定构型,并在此基础上计算了它的力学、电子、光学和高温高压下的热力学性质.研究表明:在0～300 GPa压力范围内,碳化钨相具有最高的稳定性.同时,高压下碳化钨相的弹性常数满足Born-Huang准则,且0 GPa和300 GPa下的声子色散没有虚频,证明了高压下碳化钨相的静力学稳定性和动力学稳定性.电子性质表明了碳化钨的金属性.光学性质表明碳化钨在高能区很难吸收光.热力学性质的研究表明:体积比V/V_0对压强的变化更敏感;高温时C_V曲线近似一条直线;给定压强下热膨胀系数α在600 K温度以上增长非常缓慢;压强对德拜温度Θ_D的影响较大;在低压下格林艾森系数γ的变化较大.     

Temporal resolution in radio, seismic, and acoustic detection

We consider the possibility of using a monochromatic sounding signal modulated in amplitude by a slowly varying function for detection purposes. It is shown that when conventional processing techniques are used, such a sounding signal should be considered as a narrow-band signal not providing high temporal resolution, whereas with another well-known technique this sounding signal allows one to obtain a higher temporal resolution corresponding to the total width of the signal spectrum. In the latter case, the signal-to-noise ratio is determined by the maximum of the sounding signal, while the resolution is determined by the spectrum width measured at the level of the spectrum minimum. We discuss the spectral and cepstral methods for obtaining high temporal resolution. The considered methods for obtaining high temporal resolution in detection are compared with the methods of image formation by monochromatic wave fields. Talk delivered at the scientific seminar of the Radiophysics Department of the Nizhny Novgorod University on November 4, 1999. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 5, pp. 406–412, May, 2000.     

Conductively-cooled,high-energy,single-frequency diode pumped slab laser for space applications

A laser-diode-pumped high efficiency, high pulse energy and single-frequency oscillator and amplifier for potential space environment applications have been developed and demonstrated using conductively-cooled heat removal. A diode-pumped injection seeded single-frequency oscillator was achieved by using the resonance-detection technique in Q-Switching operation, and Nd: YAG zigzag slabs based on “pump on bounce” are used in power amplifier stage for high-efficiency pulse energy extraction. Output pulse energy of 800 mJ with 11 ns pulse duration is obtained at a repetition rate of 100 Hz, with a near 3× diffraction-limit beam and an optical-to-optical efficiency of 18%. The experimental result shows that the laser has compact structure, high efficiency, reliability, conductive cooling and can be used for space environments.     

Island, pit, and groove formation in strained heteroepitaxy

We study the morphological evolution of strained heteroepitaxial films using a kinetic Monte Carlo method in three dimensions. The elastic part of the problem uses a Green's function method. Isolated islands are observed under deposition conditions for deposition rates slow compared with intrinsic surface roughening rates. They are hemispherical and truncated conical for high and low temperature cases, respectively. Annealing of films at high temperature leads to the formation of closely packed islands as in instability theory. At low temperature, pits form via a multistep layer-by-layer nucleation mechanism in contrast to the conventional single-step nucleation process. They subsequently develop into grooves, which are energetically more favorable.     

Spectrally resolved thermoluminescence of highly irradiated LiF:Mg,Cu,P detectors

Well known, widely applied high sensitive thermoluminescence (TL) detector LiF:Mg,Cu,P (MCP-N) was investigated. This paper analyses changes of the TL emission spectrum of MCP-N after irradiation with ultra high doses (up to 500 kGy). Spectral dependence of TL on dose is very complex especially in the region of very high doses (>1 kGy). As a general trend we found that the number of peaks increases with dose in the long-wavelength region indicating new types of recombination centres (RCs). Wavelength peak positions for increasing doses are quite stable. Only some of them show slight red-shift.     

Pressure-induced structural phase transition in transition metal carbides TMC (TM = Ru,Rh, Pd,Os, Ir,Pt): a DFT study

First-principles calculations based on density functional theory was performed to analyse the structural stability of transition metal carbides TMC (TM = Ru, Rh, Pd, Os, Ir, Pt). It is observed that zinc-blende phase is the most stable one for these carbides. Pressure-induced structural phase transition from zinc blende to NiAs phase is predicted at the pressures of 248.5 GPa, 127 GPa and 142 GPa for OsC, IrC and PtC, respectively. The electronic structure reveals that RuC exhibits a semiconducting behaviour with an energy gap of 0.7056 eV. The high bulk modulus values of these carbides indicate that these metal carbides are super hard materials. The high B/G value predicts that the carbides are ductile in their most stable phase.     

Electronic,mechanical, phase transition,and thermo-physical properties of TMC (TM = V,Nb, and Ta): high pressure ab initio study

The structural, electronic, mechanical, phase transition, and thermo-physical properties of refractory carbides, viz. VC, NbC, and TaC have been computed in stable B1 and high pressure B2 phases by means of two different ab initio calculations using pseudo- and full-potential schemes. These materials have mixed covalent-, metallic-, and ionic-type bonding. The calculations of elastic constants show the mechanical stability of these materials in B1 phase only. The brittle nature and anisotropy is observed in these materials in B1 phase. Non-central forces are present in both the phases. Elastic wave velocities and Debye temperature have also been calculated. The present results on structural, phase transition, elastic, and other properties are in reasonably good agreement with the available experimental and theoretical data. The calculations in high pressure phase need experimental verification.     

硼烯和碱土金属硼化物二维纳米材料的制备、结构、物性及应用研究

随着石墨烯研究的兴起,二维纳米材料得以迅速发展.在众多的二维纳米材料中,硼烯和碱土金属硼化物二维材料由于具有高费米速度、高杨氏模量、高透光性、高延展性、高度的各向异性、大的泊松比和高的化学稳定性等独特的性质,成为研究人员关注的焦点.本文侧重介绍目前硼烯和碱土金属硼化物二维纳米材料的制备工艺、结构、物性和应用情况.首先总结了目前硼烯的主要结构构型和制备及掺杂工艺;其次介绍了碱土金属硼化物二维纳米材料的理论结构构型和可能的制备路线;最后对硼烯和二维碱土金属硼化物纳米材料的物理特性进行归纳总结,同时预测它们未来最可能实现应用的领域.     

The response of polymethyl methacrylate (PMMA) subjected to large strains,high strain rates,high pressures,a range in temperatures,and variations in the intermediate principal stress

This article presents the response of polymethyl methacrylate (PMMA) subjected to large strains, high strain rates, high pressures, a range in temperatures, and variations in the intermediate principal stress. Laboratory data from the literature, and new test data provided here, are used in the evaluation. The new data include uniaxial stress compression tests (at various strain rates and temperatures) and uniaxial stress tension tests (at low strain rates and ambient temperatures). The compression tests include experiments at ?ε= 13,000 s^?1, significantly extending the range of known strain rate data. The observed behavior of PMMA includes the following: it is brittle in compression at high rates, and brittle in tension at all rates; strength is dependent on the pressure, strain, strain rate, temperature, and the intermediate principal stress; the shear modulus increases as the pressure increases; and it is highly compressible. Also presented are novel, high velocity impact tests (using high-speed imaging) that provide insight into the initiation and evolution of damage. Lastly, computational constitutive models for pressure, strength, and failure are presented that provide responses that are in good agreement with the laboratory data. The models are used to compute several ballistic impact events for which experimental data are available.     

Dopability, intrinsic conductivity, and nonstoichiometry of transparent conducting oxides

Existing defect models for In(2)O(3) and ZnO are inconclusive about the origin of conductivity, nonstoichiometry, and coloration. We apply systematic corrections to first-principles calculated formation energies Delta H, and validate our theoretical defect model against measured defect and carrier densities. We find that (i) intrinsic acceptors ("electron killers") have a high Delta H explaining high n-dopability, (ii) intrinsic donors ("electron producers") have either a high Delta H or deep levels, and do not cause equilibrium-stable conductivity, (iii) the O vacancy V(O) has a low Delta H leading to O deficiency, and (iv) V(O) has a metastable shallow state, explaining the paradoxical coexistence of coloration and conductivity.     

ICP-AES快速测定珍珠岩矿中Al、Fe、Ca、Mg、K、Na、Ti和Mn

建立了电感耦合等离子体-原子发射光谱法(ICP-AES)同时测定珍珠岩中的Al、Fe、Ca、Mg、K、Na、Ti和Mn的方法,对测试仪器条件及元素谱线等相关参数进行实验和优化,克服了常规化学法测定中步骤繁琐、耗时长、工作量大的不足。精密度(RSD,n=10)为0.22%-0.87%,加标回收率在96.2%-103.8%之间。具有快速、简便及线性范围宽等优点,可用于珍珠岩及其制品的分析,结果满意。     

Formation and evolution of intense, post-filamentation, ionization-free low divergence beams

The mechanisms related to the formation and propagation of post-filamentation intense light channels were rigorously investigated experimentally and numerically. It was found that they originate from a hot spot formed by diffraction of the pulse energy reservoir onto the plasma. Once the hot spot was formed, a channel with intensity estimated at 0.5 TW/cm² could maintain its diameter over several tens of meters such that air was not ionized, but the self-focusing produced was sufficiently high to balance linear diffraction. This propagation regime is of high interest to propagate high intensity laser pulses with limited losses.