ECR源的新工作模式

叙述了兰州重离子加速器ECR2源所使用的新工作模式的条件、特点及高电荷态离子束的输出性能,给出了对该模式特点的初步分析.     

1.3μm GaAs基量子点垂直腔面发射激光器结构设计与分析

结合垂直腔面发射激光器（VCSEL）原理以及量子点增益特点，计算了不同结构VCSEL的腔内损耗和量子点的模式增益.分析了激光器阈值特性以及氧化限制层对光损耗的影响.设计了含 氧化限制层的13μm量子点VCSEL结构. 关键词： 量子点 垂直腔面发射激光器 增益     

增益波导垂直腔面发射激光器中的模式分析及实验研究

本文研究了增益波导垂直腔面发射激光器的横向及纵向模式特性。采用二维延伸抛物型复折射率波导结构从理论上分析了增益波导垂直腔面发射激光器中模式的横向电场分布、模式间隔、模式增益对远场分布图和光束发射角、耦合效率等.实验中在阈值电流之上既观测到稳定的基模工作,也观测到高阶非简并模工作等不同的光谱结构及远场分布,理论和实验基本吻合.     

注入电流引起质子轰击VCSEL中的模式竞争

为了分析质子轰击垂直腔面发射激光器(VCSEL)中注入电流引起的激光模式竞争过程,在三维空间中对VCSEL激射后光电热进行了研究。给出仿真光电热的方程之后,在室温连续工作条件下,对电流孔半径r为4μm、阈值电流Ith为4.5 m A的VCSEL进行自洽求解。当注入电流Iin分别为5.0,5.5,6.0 m A时,得到了对应的外加电压和输出光功率,并绘制了VCSEL的电势、注入电流、载流子、光场和热场的空间分布,给出了连续工作下输出光功率随注入电流变化的曲线。仿真结果表明:随着注入VCSEL中的电流增加,电流密度增大,激光的横向基模和横向一阶模式同时增强。横向一阶模式增加的强度及扩展的范围大于横向基模,激光输出能量逐渐向横向一阶模式过渡,横向模式竞争的同时产生载流子空间烧孔,因此在电流孔半径r≥4μm的VCSEL中,连续工作激光模式不稳定。     

胡椒孔法在强流脉冲离子束中的发射度测量

真空弧离子源的引出束流具有低能、强流等特点,当离子源工作在单脉冲模式时,被广泛采用的缝-杯式和Alison式发射度测量方法不再适用。采用基于成像板的胡椒孔法测量了真空弧离子源的发射度。初步研制了胡椒孔法发射度测量装置,利用该装置测量了引出电压为64 kV时脉冲束流的发射度和发射相图。在x方向和y方向,测得归一化均方根发射度分别为6.41,4.61 mmmrad。测量结果表明该真空弧离子源在64 kV时的归一化发射度远大于其他类型的离子源的发射度。     

外包壳对具有氧化孔径层的圆柱形VCSEL阈值增益的影响

采用矢量场模型，对具有诱人应用前景的圆柱形垂直腔面发射半导体激光器（VCSEL）的模式阈值增益进行了数值模拟；为减弱金属圆柱的反射以使理论计算更接近实际，采用两种方案，将外加金属包壳视为非理想导体，或在此基础上，将金属包壳与激光器主体结构隔开. 从模式的阈值增益与顶Bragg反射镜层周期数的关系方面，与理想金属外包壳情况进行了比较. 结果表明，高阶贝塞耳函数模式的阈值增益变化规律基本相同，而0阶贝塞耳函数模式的阈值增益变化规律相差较大.     

表面等离子体调制单模面发射激光器的研究

对单模面发射半导体激光器的研究随着其应用的不断扩展而引起了人们的广泛的重视,应用多种方法可以提高其输出功率并改善其模式抑制比.利用金属表面等离子体纳米结构调制的方法可以获得单模面发射激光器输出功率的提高,理论计算表明这种方法增强效应可达近50%. 关键词： 表面等离子体 单模面发射激光器 模式选择     

Pt/Au/n-InGaN肖特基接触的电流输运机理

基于热电子发射和热电子场发射模式,利用I-V方法研究了Pt/Au/n-InGaN肖特基接触的势垒特性和电流输运机理,结果表明,在不同背景载流子浓度下,Pt/Au/n-InGaN肖特基势垒特性差异明显.研究发现,较低生长温度制备的InGaN中存在的高密度施主态氮空位（V_N）缺陷导致背景载流子浓度增高,同时通过热电子发射模式拟合得到高背景载流子浓度的InGaN肖特基势垒高度和理想因子与热电子场发射模式下的结果差别很大,表明V_N缺陷诱发了隧穿机理并降低了肖特基势垒高度,相应的隧穿电流显著增大了肖特基势垒总的输运电流,证实热电子发射和缺陷辅助的隧穿机理共同构成了肖特基势垒的电流输运机理.低背景载流子浓度的InGaN肖特基势垒在热电子发射和热电子场发射模式下拟合的结果接近一致,表明热电子发射是其主导的电流输运机理.     

介质阻挡放电丝模式和均匀模式转化的特性

利用水电极介质阻挡放电装置,采用电学方法和发射光谱,研究了空气中介质阻挡放电从微放电丝模式向均匀放电模式转化的过程. 结果表明,大气压下增大外加电压或者电压一定减小气压,放电都能够从微放电丝模式过渡到均匀模式. 高气压下放电为流光击穿而低气压下为辉光放电. 利用放电发射光谱,研究了高能电子比例随实验参数的变化. 结果表明气压减小时高能电子比例增大,电压增加时高能电子减少. 利用壁电荷理论对以上实验结果进行了定性分析. 结果对介质阻挡均匀放电的深入研究具有重要价值. 关键词： 介质阻挡放电 光学发射谱 微放电丝 均匀放电模式     

腔体系统电磁脉冲模拟中的电子发射面

对电子发射面设置问题进行了研究,给出了底入射腔体系统电磁脉冲模拟中电子发射面的实现方法,分析了侧入射腔体系统电磁脉冲模拟中电子发射面的特点,并利用虚拟发射面的方法实现了侧入射腔体系统电磁脉冲模拟中电子发射面的设置。结果显示,利用该方法可以较简洁地实现腔体系统电磁脉冲模拟中平面和曲面电子发射面的设置,发射面电子发射参数和时序符合物理规律。     

Distinction between pre-formed cluster emission and heavy ion decay by fission

For studying cluster radioactivity in the actinide region as well as trans-tin region two types of models are used: the pre-cluster formation model and the unified fission model. In the case of the actinide region, the cluster-like shapes are preferred for very high asymmetry while fissioning shapes are more suitable for less asymmetry and symmetry (the line of demarcation being around A _c =31). In this work this line of demarcation is studied in the case of the trans-tin region. The results of this study show that the transition from cluster mode to fission mode takes place at A _c =16.     

Secondary ion mass spectrometry for quantitative surface and in-depth analysis of materials

Secondary ion mass spectrometry (SIMS) is a technique based on the sputtering of material surfaces under primary ion bombardment. A fraction of the sputtered ions which largely originate from the top one or two atomic layers of the solid is extracted and passed into a mass spectrometer where they are separated according to their mass-to-charge ratios and subsequently detected. Because the sputter-yields of the individual species, coupled with their ionization probabilities, can be quite high and the mass spectrometers can be built with high efficiencies, the SIMS technique can provide an extremely high degree of surface sensitivity. Using a particular mode like static SIMS where a primary ion current is as low as 10^?11 amp, the erosion rate of the surface can be kept as low as 1 Å per hour and one can obtain the chemical information of the uppermost atomic layer of the target. The other mode like dynamic SIMS where the primary ion current is much higher can be employed for depth profiling of any chemical species within the target matrix, providing a very sensitive tool (～ 1 ppm down to ppb) for quantitative characterization of surfaces, thin films, superlattices, etc. The presence of molecular ions amongst the sputtered species makes this method particularly valuable in the study of molecular surfaces and molecular adsorbates. The range of peak-intensities in a typical SIMS spectrum spans about seven to eight orders of magnitude, showing its enormously high dynamic range; an advantage in addition to high sensitivity and high depth-resolution. Furthermore, the high sensitivity of SIMS to a very small amount of material implies that this technique is adaptable to microscopy, offering its imaging possibilities. By using this possibility in static SIMS or dynamic SIMS mode of analysis, one can obtain a two-dimensional (2D) surface mapping or a three-dimensional (3D) reconstruction of the elemental distribution, respectively within the target matrix. Secondary ion yields for elements can differ from matrix to matrix. These sensitivity variations pose serious limitations in quantifying SIMS data. Various methods like calibration curve approach, implantation standard method, use of relative sensitivity factor, etc. are presently employed for making quantitative SIMS analysis. The formation of secondary ions by ion bombardment of solids is relatively a complex process and theoretical research in this direction continues in understanding this process in general. The present paper briefly reviews the perspective of this subject in the field of materials analysis.     

Finite element simulation and analytical analysis for nano field emission sources that terminate with a single atom: A new perspective on nanotips

Nanotips are highly demanded for various applications in nanotechnology. For instance, nanotips with a single atom end can be used as a source of self collimated electron or ion beams. Such tips are usually characterized in the field ion microscope (FIM) or the field emission microscope (FEM), where only a top view can be captured and analyzed. We have noticed that single atom tips fabricated by different methods produce electrons in FEM mode, or ions in FIM mode, at a wide range of applied voltages for the respective mode. In this work we present numerical and analytical analyses to the distribution of the electric field in the vicinity of the nanotip apex that holds the topmost single atom. We demonstrate that although the electric field is relatively enhanced by the nano protrusion it is still significantly dominated by the tip base. The analyses explicitly show that nanotips with broad bases produce even less field than some modest tips, at the same applied voltage. This pronounced effect of the tip base accounts for the relatively high voltages needed at the imaging threshold field. The results reveal that single atom tips are not necessarily sharp at a mesoscopic scale and the tip sharpness has to be determined from the combination of the nanotip apex (FIM or FEM) image and the applied voltage.     

Preparation of nonclassical states and measurement of the Wigner function for the collective motion of N trapped ions

We propose a scheme for generating nonclassical states for the centre-of-mass vibrational mode of N trapped ions,including superpositions of several coherent states on a circle and Fock states. In the scheme N trapped ions are driven by a laser beam tuned to the carrier. The scheme also provides a new prospect for laser cooling. The scheme can be used to measure the Wigner function of the collective vibrational mode.     

极坐标系统下进行直角坐标扫描的离子束抛光

在离子束抛光设备研制过程中,离子源扫描运动方式的选择是很关键的,一般分为直角坐标方式扫描和极坐标方式扫描两种。根据两种扫描方式的特点,在极坐标系统下进行直角坐标扫描方式加工。该种方法采用直角坐标扫描方式下的驻留时间计算,算法相对简单。该种方法在极坐标系统下进行加工,同等情况下可加工圆形镜面的口径比直角坐标系统下更大些;而且离子源的可移动区域是一条直线,其余地方可以摆放其他设备,空间利用率较高。对这种新思路进行仿真分析,证实了其具有可行性。     

二能级系统自发辐射的动力学抑制

研究了在二能级原子系统中有环境诱导的退相干的控制问题.通过对量子位系统施加适当的扰动可以减少由自发辐射引起的退相干.本文提出了一种新的基于频率位移技术和宇称反演技术的机制.这种机制可由两束均匀经典大失谐光场作用于原子来实现.通过应用这种机制,在存在自发辐射的情况下,可以有效地抑制退相干.     

两等同双能级原子与三模腔场六光子共振相互作用辐射谱研究

研究了两个偶极－偶极力关联的等同双能级原子与三模腔场六光子共振相互作用的辐射谱，对三模分别处于不同数态时辐射谱的结构特征和物理特性进行了详细分析，从而揭示了一系列重要的新特点。     

Angular Distribution Analysis of Nitrogen Ions in a Low Energy Dense Plasma Focus Device

Angular distribution of nitrogen ions from a 4 kJ plasma focus device (PFD), as obtained by two detection methods was studied. The results obtained with two methods including consisting of (i) polycarbonate (PC) detectors (1 mm thick with about 15 cm diameter large etchable area) using electrochemical etching (ECE) at 50 Hz and 48 kV cm^–1 field strenth and (ii) an array of five Faraday cups (FC) are analyzed, compared and discussed in this paper. The results obtained by the two detectors are quite different. A new concept is proposed in this paper for the ring‐shaped angular distribution of ions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

计算半导体平板微腔自发发射的近似方法

引入新变量,并利用高阶泰勒展开完成半导体平板微腔自发发射的空间积分,由此得到半导体平板微腔TE模式自发发射的近似表达式.在腔长为半个中心波长和高反射率腔面的半导体平板微腔中,结合电子和空穴的费米分布函数,用近似方法计算垂直方向小角度内自发发射谱和总的自发发射谱,分别与数值空间积分基本相同,可以用于计算量子阱平板微腔自发发射谱.     

Discharge characteristics of the DUHOCAMIS with a high magnetic bottle-shaped field

For the purpose of producing high intensity, multiply charged metal ion beams, the dual hollow cathode ion source for metal ions (DUHOCAMIS) was derived from the hot cathode Penning ion source combined with the hollow cathode sputtering experiments in 2007. To investigate the behavior of this discharge geometry in a stronger magnetic bottle-shaped field, a new test bench for DUHOCAMIS with a high magnetic bottle-shaped field up to 0.6 T has been set up at the Peking University. The experiments with magnetic fields from 0.13 T to 0.52 T have indicated that the discharge behavior is very sensitive to the magnetic flux densities. The slope of discharge curves in a very wide range can be controlled by changing the magnetic field as well as regulated by adjusting the cathode heating power; the production of metallic ions would be much greater than gas ions with the increased magnetic flux density; and the magnetic field has a much higher influence on the DHCD mode than on the PIG mode.