电流变液中的双折射现象观察

本文研究了电流变液(ER流体)可调节的双折射现象,激光束垂直于电场方向,利用He-Ne激光器对SiO₂、季戊四醇和硅油组成的ER流体进行测量.发现当一对偏振片互相正交,不加电场时,没有光线射出;当施加电场时,就有光线射出,透射光强度随电场增大.对于相同材料的ER流体,低浓度的ER流体双折射现象更加明显,电流变液双折射现象起因于颗粒在电场作用下排列成链状或柱状结构.     

电流变液的旋光与椭偏光行为

本文研究了电流变液(ER流体)的旋光行为及椭偏光行为.激光束垂直于电场方向,利用HeNe激光器对SiO₂、Si₃N₄和硅油组成的ER流体进行测量.发现电流变液样品存在旋光现象,且对于同一种浓度的ER流体,随着电场强度的增大,旋光角度增大.在同一电场强度下,旋光角度随着浓度的增大而增大.当浓度大于某一值c₀时,旋光角度开始减小,在不同电场强度下,透过电流变液的椭圆偏振光性质不发生改变,且随着电场强度的增大,透射光强度随之增大.电流变液的旋光行为及椭偏光行为起因于在电场作用下ER流体由各向同性的液体转变为各向异性的液体.     

奇特的电流变液

 电流变液(ＥｌｅｃｔｒｏｒｈｅｏｌｏｇｉｃａｌＦｌｕｉｄ)是由高介电常数的固体颗粒悬浮于某种低介电常数、低黏性的不导电液体中所形成的,未加电场时,电流变液内的颗粒无序分布,施加电场后,颗粒迅速聚集成跨越电极的链或柱,当施加的电场足够大时,电流变液转变为类似固态,撤去外电场时,又恢复为液态,这一液固两态相变的响应时间为毫秒量级,这一奇特属性,再加上电流变液的电导率低,产生电流变效应所需的电功输入少,电流变液的电热效应低,使得电流变液在工业技术中有着极大的潜在应用。     

外电场与微波交互作用下BaTiO3电流变液的透射特征

分别考虑了微波传播方向与电流变液颗粒链相垂直和平行的情况,对BaTiO3电流变液微波透射行为进行了实验研究。发现BaTiO3电流变液微波透射率可由外电场调控。在垂直的情形,当流体浓度较低时,透射率随电场强度增加而减小,并且随浓度增加电场调节微波透射率的变化幅度增加。浓度超过一定值时,透射率随电场出现由减小向增加的改变,存在透射率的极小点。在平行的情形,发现透射率随电场强度增加而减小。另外透射率随电场强度变化具有延时性,对于给定浓度的情形,电场强度增加延时性明显减小。     

电流变液在平行平板剪切下的动态响应

建立了用于测试电流变液在两平行平板间剪切时对外加高压阶跃电场的剪切应力响应的实验测试系统。此系统对剪切应力变化的时间分辨率可以达到10μs量级。利用此系统对基于沸石和硅油的电流变液的极化和退极化过程,电流变液在不同外加电场强度和不同剪切速率条件下的剪切应力上升和撤去电场时剪切应力的下降过程进行了研究。研究发现电流变液的剪切速率越高,其响应时间越短,随着外加电场的升高,响应时间略有增加。此实验结果与其他现有相关研究结果比较吻合。     

电流变液微波反射可调控性

研究了纳米二氧化钛包覆高岭土和钇掺杂钛酸钡两种电流变液的微波反射行为.实验发现，在垂直于微波传播方向电场作用下，两种电流变液微波反射系数均随电场强度的增大而增大；钇掺杂钛酸钡电流变液微波反射系数变化幅度比二氧化钛包覆高岭土电流变液宽，并且电场调节的能力随浓度的增加有减弱的趋势.对钇掺杂钛酸钡电流变液存在一个临界浓度，低于这个浓度，电场的调控能力随电场强度的增加而增大，高于这个浓度，电场的调控能力随电场的增加先增大后减小.另外，二氧化钛包覆高岭土电流变液反射回波相位随电场强度的增大出现最大值后逐渐减小趋于平 关键词： 电流变液 微波反射 相位     

电流变液的研究进展及应用前景

电场致流变液体（电流变液）是一些高介电小颗粒和低介电油液的混合体，它在高电场作用下呈现液体与固体间的变换，变换时间为几毫秒，而且变换可逆。阐明了电流变液的原理，综述了电流变液在机制、材料及应用等方面的研究现状，并介绍了电流变液在技术和工业上广泛的应用前景。     

固液双相电流变系统流动过程的相转变特性

考虑电流变液多粒子近程相互作用，利用等效平板电导模型，研究了电流变液流动过程相转变点的特性，并设计实验观察了电流变液中的这种相转变现象.研究结果表明，电流变液在一定压力梯度作用下发生流动，此时为双相流；当外加电场达到某一值时，电流变液中颗粒不流动，由固液双相流转变为液体单相流动，发生场控相转变，理论模拟结果与实验观察结果基本相符.阈值电场随外加压力梯度的增加而加大，随颗粒浓度的增加而减小. 关键词： 电流变液 颗粒流 相转变     

电流变液的微波透射调控行为

依据外电场作用下电流变液结构由各向同性转变为各向异性及介电性能改变的实验事实,建立了微波穿透电流变液样品的理论模型,导出了微波透射率的基本表达形式.理论模拟显示:当电流变液的介电常量小于所处环境的介电常量时,透射率随电场的增加而增加;反之则减小.实验研究表明:电流变液的微波衰减(透射率)的变化可以通过电场来调控.分析认为在外加电场作用下,电流变液结构转变和介电性能的变化是导致微波透射率可调控的主要原因.     

电流变液的微波透射调控行为

依据外电场作用下电流变液结构由各向同性转变为各向异性及介电性能改变的实验事实,建立了微波穿透电流变液样品的理论模型,导出了微波透射率的基本表达形式.理论模拟显示:当电流变液的介电常量小于所处环境的介电常量时,透射率随电场的增加而增加;反之则减小.实验研究表明:电流变液的微波衰减(透射率)的变化可以通过电场来调控.分析认为在外加电场作用下,电流变液结构转变和介电性能的变化是导致微波透射率可调控的主要原因.     

Relic and droplet sizes produced by electrostatic atomisation of ceramic suspensions

Several alumina suspensions were subjected to electrostatic atomisation at a constant applied voltage and constant flow rate. Various spray modes were observed and the sizes of droplets produced from each suspension were measured using laser diffraction. The sizes of relics obtained by depositing these droplets on a silicone release paper substrate were measured using optical microscopy. Using volume equivalence the relic sizes were used to calculate the size of the droplets, thus allowing a comparison with the laser diffraction results. The calculated and measured droplet distributions showed excellent agreement. PACS 81.05.Je; 81.20.Ev; 81.20.Rg; 47.27.Wg; 47.85.Np     

Impact of electric fields on the speed of contact line in vertical deposition of diluted colloids

We report experimental results on the influence of electric fields on the contact line dynamics of the vertical deposition of water-based diluted colloidal suspensions. We measure the speed of macroscopically receding contact line for different initial concentrations and applied voltages. We explain the observed behavior via the electrophoretic effect in the region near the contact line. The electrophoretic effect induces a concentration gradient along the direction of the applied field which influences the morphology of the dried deposit of colloidal particles. Thus the applied field has an effect on the receding contact line through morphological formation and its transition.     

强激光与高密度气体相互作用中电子和离子加速的数值模拟

在现有的一维粒子模拟程序的基础上发展了带光电离和碰撞电离及蒙特卡罗两体碰撞的模拟程序(1D PIC-MCC). 用此程序模拟研究了短脉冲激光与He气靶相互作用时电子和离子的加速过程. 研究表明当强激光与过临界密度的微米厚度的平面靶相互作用时，靶前表面物质将被激光脉冲前沿迅速离化；新生的电子被激光场有质动力加速成为高能电子，这些电子穿入到靶内，通过电子碰撞电离离化靶内物质；一部分高能电子穿透靶后，会在靶的后表面形成强的电荷分离场，该场迅速离化靶后表面物质，同时使得后表面离子得到加速. 部分穿透靶的超热电子将被电荷分离场重新拉回靶内，在靶的前后表面振荡. 一些振荡电子在此过程中得到电荷分离场加速，离开前表面，在前表面也形成电荷分离场，使前表面离子得到加速. 关键词： 激光等离子体 光电离和碰撞电离 电子加速 离子加速     

Controlling the orientation of polar molecules with combined electrostatic and pulsed,nonresonant laser fields

We demonstrate that molecules with a moderate permanent dipole moment can be oriented with combined electrostatic and pulsed, nonresonant laser fields. We use OCS molecules as a sample. The degree of orientation can be increased by increasing the magnitude of electrostatic field and the peak intensity of the laser field or by decreasing the rotational temperature of the molecules.     

单模光纤系统激光偏振传输特性的研究

本文运用激光偏振性矢量传输理论,分析了在单模光纤传输系统中激光偏振性的传输特性.得出了激光偏振状态与单模光纤的双折射、传输系数和拍长的关系.     

Generation of Intense THz Pulsed Lasers Pumped Strongly by CO2 Pulsed Lasers

A theoretical method dealing with two intense laser fields interacting with a three-level molecular system is proposed. A discussion is presented on the properties of the solutions for time-independent and time-dependent absorption coefficients and gain coefficient on resonance for strong laser fields, based on analytic evaluation of the rate equations for a homogeneously broadened, three-level molecular system. The pump intensity range can be estimated according to the analytic expression of pump saturation intensity. The effects of pulse width, gas pressure and path length on the energy absorbed from pump light are studied theoretically. The results can be applied to the analysis of pulsed, optically pumped terahertz lasers.     

Coherent Control of High Harmonic Generation Driven by Metal Nanotip Photoemission

Steering ultrafast electron dynamics with well-controlled laser fields is very important for generation of intense supercontinuum radiation. It can be achieved through coherent control of the symmetry of the interaction between strong-field laser fields and a metal nanotip. We employ a scheme of two-color laser pulses combined with a weak static field to realize the control of a single quantum path to generate high harmonic generation from a single solid-state nanoemitter. Moreover, a smooth and ultrabroad supercontinuum in the extreme ultraviolet region is obtained, which can produce a single attosecond pulse. Our findings are beneficial for efficient generation of isolated sub-100 as XUV pulses from solid-state sources.     

Scintillator and dye lasers in the range 350 to 600 nm pumped by a 200 kW nitrogen laser

A comparative study is presented of the laser output characteristics of ten fluorescent solutes in different solvents, pumped with the 337.1 nm radiation from a 200 kW nitrogen laser. With both 2 mm and 10 mm dye path lengths, peak output powers of several kilowatts were obtained at wavelengths ranging from 350 to 600 nm and with pulse-widths as short as 0.5 nsec FWHM. The dependence of the laser characteristics on such variables as the concentration and the transmission of the solutions and the way of focusing the exciting radiation into the dye cavity were investigated. Three dye cells were made to lase in cascade, one of the stages with an efficiency of 50%.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions. Part Three: Measurements

The theory of transmission fluctuation spectrometry (TFS) was developed for particle size analysis in flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution (PSD) and particle concentration. In the previous parts of this publication high concentration effects on TFS were investigated theoretically and by simulation. This work presents a study on TFS measurements in concentrated suspensions. By introducing an empirical correction to include the high concentration effects from both the monolayer structure and particle overlapping in the inversion algorithm, it is possible to obtain the particle size distribution and particle concentration over broad ranges of particle sizes and concentrations.