超短强激光脉冲在大气传播中的自聚焦行为

通过建立涉及克尔效应和多光子电离效应的非线性数学模型,利用数值方法研究了超短激光脉冲在大气传播中的聚焦行为。结果表明由自聚焦导致的成丝现象具有间断,而不是一种稳态的模式。每次轴上的成丝都会由于光场损耗减弱,但同时由于克尔效应会使离轴区域的能量间断地补充到光轴上。     

含有注入信号的双向环形激光场中的驱动效应

用含有背散射和饱和效应的双模激光场的理论模型讨论了背散射和外加注入信号对环形激光场的统计性质的影响。结果表明,背散射可以抑制系统的涨落。对于均匀展宽的双向环形激光场,注入信号可以将其中的弱模光场由非相干光驱动成为相干光,而对于非均匀展宽的环形激光场则没有这种驱动效应。进一步研究发现,这种驱动效应与注入信号的强弱及两模式光场的抽运参量差异△α有关。     

State selective detection of sputtered Al neutrals by resonant laser ionization SNMS

It is important to optimize the resonance ionization efficiency of the sputtered particle by evaluating the internal energy of it. And also the dependence of the change of the internal energy of it on primary ion species and accelerating voltages was investigated. For this study, we developed proto-type resonance laser ionization SNMS instrument, which is a quadrupole SIMS apparatus combined with a wavelength tunable laser. The internal energy of the sputtered aluminum atoms, which has lowly lying excited state (112 cm⁻¹) on the ground state, was monitored. As the results, the internal energy of the sputtered aluminum atoms was not influenced by the change of the surface work function and primary ion beam energy at all. On the contrary, the density on lowly lying excited state drastically increased due to the existence of the oxygen on aluminum surface.     

Magnetocaloric effect in high-energy ball-milled Gd5Si2Ge2 and Gd5Si2Ge2/Fe nanopowders

Evolution of structure and magnetocaloric properties in ball-milled Gd₅Si₂Ge₂ and Gd₅Si₂Ge₂/0.1 wt% Fe nanostructured powders were investigated. The high-energy ball-milled powders were composed of very fine grains (70–80 nm). Magnetization decreased with milling time due to decrease in the grain size and randomization of the magnetic moments at the surface. The magnetic entropy change (ΔS_M) was calculated from the isothermal magnetization curves and a maximum value of 0.45 J/kg K was obtained for 32 h milled Gd₅Si₂Ge₂ alloy powder for a magnetic field change of 2 T while it was still low in Fe-contained alloy powders. The thermo-magnetic measurements revealed that the milled powders display distribution of magnetic transitions, which is desirable for practical magnetic refrigerant to cover a wide temperature span.     

Solution calorimetry of organic nonelectrolytes as a tool for investigation of intermolecular interactions

The paper is mainly the review and generalization of the previous publications of the authors. It demonstrates that solution calorimetry method gives the opportunities of more detailed understanding of various aspects of intermolecular interactions in solution. We are assured that prerequisite to such an understanding is the successive analysis of various solute–solvent systems from the simplest ones which include alkanes as a solute or as a solvent to the most complex systems with solvent self‐association via hydrogen bonding. Particular findings discussed in this paper are (i) an inconspicuous contribution of electrostatic solute–solvent interaction to the solvation enthalpy and, accordingly, the dominating contribution of dispersion interactions for nonspecifically solvated solutes; (ii) new, very general method for the extraction of specific interaction enthalpy from the enthalpy of solvation; (iii) new method of determination of self‐association enthalpies for the solvents associated via hydrogen bonding; (iv) new method for determination of cooperative hydrogen bonding enthalpies of proton acceptors with associated species of alcohols; (v) the unique method of experimental determination of the hydrophobic effect enthalpy. Copyright © 2007 John Wiley & Sons, Ltd.     

Large roomtemperature magnetocaloric effect with negligible magnetic hysteresis losses in Mn1−xVxCoGe alloys

The magnetic and magnetocaloric properties have been investigated in a series of Mn_1−xV_xCoGe (x=0.01, 0.02, 0.03, and 0.05) alloys. The substitution of V for Mn reduces the structural transformation temperature of MnCoGe alloy effectively and results in a second-order magnetic transition in Mn_0.95V_0.05CoGe alloys. Large room temperature magnetocaloric effect and almost zero magnetic hysteresis losses are simultaneously achieved in the alloys with x=0.01, 0.02, and 0.03. The reasons for the negligible magnetic hysteresis losses and the potential application for the roomtemperature magnetic refrigeration are discussed.     

Structural, optical and electrical properties of Zn1−xCdxO thin films prepared by PLD

Ternary polycrystalline Zn_1−xCd_xO semiconductor films with cadmium content x ranging from 0 to 0.23 were obtained on quartz substrate by pulse laser deposited (PLD) technique. X-ray diffraction measurement revealed that all the films were single phase of wurtzite structure grown on c-axis orientation with its c-axis lattice constant increasing as the Cd content x increasing. Atomic force microscopy observation revealed that the grain size of Zn_1−xCd_xO films decreases continuously as the Cd content x increases. Both photoluminescence and optical measurements showed that the band gap decreases from 3.27 to 2.78 eV with increasing the Cd content x. The increase in Cd content x also leads to the broadening of the emission peak. The resistivity of Zn_1−xCd_xO films decreases evidently for higher values of Cd content x. The shift of PL emission to visible light as well as the decrease of resistivity makes the Zn_1−xCd_xO films potential candidate for optoelectronic device.     

强激光条件下5CB液晶中的激光诱导衍射环现象

强激光经5CB液晶传播时会产生非线性自相位调制现象,利用532 nm和1 064 nmCW激光研究了强激光条件下5CB液晶中的激光诱导衍射环现象,并对强激光在5CB液晶中产生自相位调制的现象和机理进行了讨论.当532 nm激光和1 064 nm激光功率密度分别大于10 kW/cm2和300W/cm2时,接收白屏上有较明...     

超声波多普勒实验仪

基于多普勒效应原理,分别测得波源的频率和发生相对运动时观测到的频率即可分析出物体相对运动的速度.实验仪以单片机为测控系统核心实现超声波多普勒效应演示实验及速度测量并提供了具体的设计方案与实验结果.同时单片机赋予了仪器以软件为核心的技术特点,具有重塑性与可扩展性.     

碳纤维复合材料在航天领域的应用

综述了碳纤维复合材料的应用现状和发展前景。首先,概述了碳纤维的分类和力学性能以及碳纤维复合材料的特性;重点介绍了碳纤维复合材料在国内外航天领域,特别是在卫星结构、运载火箭、精密支撑构件以及空间镜体等方面的应用情况。指出了目前碳纤维复合材料的主要问题是湿热效应。最后,结合我国国情,对碳纤维复合材料需要解决的问题提出了一些建设性的措施。