金属表面镀高分子膜对真空击穿阈值的影响

探索提高金属表面真空击穿阈值的方法,对脉冲功率技术的发展和应用具有重要意义。在金属表面电子发射理论分析的基础上,采用有限元法计算阴极杆表面电场随二极管电压的变化规律,设计了实验系统,并开展了实验研究。实验对比了在脉宽约30 ns、阴极杆与阳极筒间隙12 mm时,钛合金TC4阴极杆在不同种类高分子膜（膜厚30～60 μm）下真空击穿阈值的变化情况。在表面粗糙度R_z（轮廓最大高度）为0.8 μm的TC4阴极杆表面分别镀环氧树脂膜和丙烯酸膜,实验结果表明,镀丙烯酸膜阴极杆的击穿阈值约505 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约20.6%;在表面粗糙度R_z为0.2 μm的TC4阴极杆表面分别镀聚酰亚胺膜和聚醚醚酮膜,实验结果表明,镀聚酰亚胺膜阴极杆的击穿阈值为584 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约28.1%。因此,在金属表面镀丙烯酸膜、聚酰亚胺膜可以有效提高金属表面的真空击穿阈值。     

三能级钾原子气体三维傅里叶变换频谱的解析解

利用投影切片定理、傅里叶位移定理和误差函数给出三能级钾原子气体三维傅里叶变换频谱在T=0界面的解析解.固定均匀线宽,非均匀展宽和对角线相关系数可以定量地识别,通过在适当方向上拟合三维傅里叶变换频谱谱峰的切片来确定.结果表明,非均匀展宽增大,频谱图沿着对角线方向延伸,对角线相关系数增大,频谱图逐渐变圆,振幅也逐渐变小.     

Terahertz wave emission from water lines

To make further understanding of terahertz(THz)wave generation from liquid water,we study THz wave emission from water lines of different diameters.The water line with a smaller diameter generates a stronger THz electric field for the diameters from 0.2 mm to 0.5 mm.The THz electric field strength and polarity change with the relative position between the incident laser and water line.Moreover,the THz energy has an optimal radiation angle of about 60°.A two-dimensional dipole array model is introduced to illustrate the phenomenon.Our observations contribute to optimizing the scheme of the liquid THz source.     

Overview of finite elements simulation of temperature profile to estimate properties of materials 3D-printed by laser powder-bed fusion

Laser powder bed fusion(LPBF),like many other additive manufacturing techniques,offers flexibility in design expected to become a disruption to the manufacturing industry.The current cost of LPBF process does not favor a try-anderror way of research,which makes modelling and simulation a field of superior importance in that area of engineering.In this work,various methods used to overcome challenges in modeling at different levels of approximation of LPBF process are reviewed.Recent efforts made towards a reliable and computationally effective model to simulate LPBF process using finite element(FE)codes are presented.A combination of ray-tracing technique,the solution of the radiation transfer equation and absorption measurements has been used to establish an analytical equation,which gives a more accurate approximation of laser energy deposition in powder-substrate configuration.When this new analytical energy deposition model is used in in FE simulation,with other physics carefully set,it enables us to get reliable cooling curves and melt track morphology that agree well with experimental observations.The use of more computationally effective approximation,without explicit topological changes,allows to simulate wider geometries and longer scanning time leading to many applications in real engineering world.Different applications are herein presented including:prediction of printing quality through the simulated overlapping of consecutive melt tracks,simulation of LPBF of a mixture of materials and estimation of martensite inclusion in printed steel.     

埋层界面和空气表面和频光谱信号贡献的调控

本文研究表明通过膜厚控制和表面等离激元增强方法可有效区分隐藏界面和空气表面的和频振动光谱信号. 以氟化钙基底支撑的PMMA薄膜为模型,观察到隐藏界面和空气表面对和频信号贡献的变化. 通过监控羰基和甲基伸缩振动基团,发现薄PMMA膜的和频信号来自PMMA/空气表面的化学基团-CH₂、-CH₃、-OCH₃和C=O,而厚PMMA膜的和频信号则来自基底/PMMA埋层界面的-OCH₃和C=O基团. 随制膜浓度增大,埋层界面C=O基团的取向角从65°下降到43°,且浓度大于或等于0.5 wt%时,取向角等于45°±2°. 相比之下,空气表面C=O的取向角落在21°∽38°之间. 在金纳米棒存在条件下,表面等离激元可以极大地增强和频信号,尤其是来自埋层界面信号.     

OCS经由F 31Π里德堡态生成CO(X1Σ+)+S(1D2)产物的波长相关性光解离

本文利用时间切片离子速度成像技术在134∽140 nm波段研究了OCS分子经由F 3¹Π里德堡态的真空紫外光解离动力学. 在选取的5个分别对应OCS(F 3¹Π, v₁=0∽4)的伸缩振动激发的光解波长,实验测得了来自CO(X¹Σ⁺)+S(¹D₂)产物通道的SS(¹D₂))实验影像,并获得了总平动能谱和CO(X¹Σ⁺, v)共生产物的振动布居及角分布. 结果分析表明OCS分子解离生成CO(X¹Σ⁺)+S(¹D₂)产物的过程经历了上态F 3¹Π 与C_?v和C_s构型的下电子态间非绝热耦合过程. 实验结果显示了很强的波长相关性：OCS (F 3¹Π, v₁)的较低转动激发态(v₁=0∽2)和较高转动激发态(v₁=3, 4)的CO(X¹Σ⁺)产物的振动布居和角分布具有显著差异,表明该解离过程中具有不同的解离机理. 本结果提供了振动耦合可能对真空紫外光解离动力学产生关键作用的相关证据.     

Lyapunov exponent calculation of a two-degree-of-freedom vibro-impact system with symmetrical rigid stops

A two-degree-of-freedom vibro-impact system having symmetrical rigid stops and subjected to periodic excitation is investigated in this paper. By introducing local maps between different stages of motion in the whole impact process, the Poincar'e map of the system is constructed. Using the Poincar'e map and the Gram-Schmidt orthonormalization, a method of calculating the spectrum of Lyapunov exponents of the above vibro-impact system is presented. Then the phase portraits of periodic and chaotic attractors for the system and the corresponding convergence diagrams of the spectrum of Lyapunov exponents are given out through the numerical simulations. To further identify the validity of the aforementioned computation method, the bifurcation diagram of the system with respect to the bifurcation parameter and the corresponding largest Lyapunov exponents are shown.     

单轴分布式光纤传感器管线泄漏探测方法及定位理论分析

利用Sagnac干涉原理的分布式光纤传感器是一种可用于长途油气管线侵入、泄漏探测和定位的新技术.为了克服屏蔽和隔离Sagnac光纤环中未用作传感的那一半光纤所带来的屏蔽困难、成本增加等问题,提出一种单轴分布式光纤传感器的方法.其原理是利用一条光纤代替光纤环,并在光纤尾端设置法拉第旋转镜,构成偏振无关Sagnac干涉仪探测和定位管线泄漏.文中详细分析和讨论了该方法的系统光路和探测定位原理.     

安装偏差对光纤布喇格光栅应变测量的影响

通过理论推导和试验分析研究了安装偏差对光纤应变测量的影响,得到安装误差所带来测量误差的计算公式.发现光纤的轴向与预定安装方向的角偏差越大,测量误差也越大.用光纤光栅进行应变测量时,必须考虑光纤的安装偏差,它直接关系到测量结果的准确性.实际测量中要尽量确保传感器安装方位的准确.     

光谱色散匀滑技术与衍射光学器件联用性能的空间频谱分析

基于空间频谱分析方法,建立了光谱色散匀滑技术(SSD: Smoothing by Spectral Dispersion)与衍射光学器件(DOE: Diffractive Optical Element)联用性能的简化分析模型,为SSD与DOE联用时,SSD参量的优化提供了理论依据.数值模拟了SSD各参量,包括脉冲时间、调制频率、位相调制系数、光栅线色散系数等对束匀滑性能的影响.模拟结果表明,SSD参量经过优化选取,且波前畸变随时间快速变化时,能获得良好的束匀滑性能.