Effects of spot size on the operation mode of Ga As photoconductive semiconductor switch employing extrinsic photoconductivity

To guide the illuminating design to improve the on-state performances of gallium arsenide(GaAs)photoconductive semiconductor switch(PCSS),the effect of spot size on the operation mode of GaAsPCSS based on a semi-insulating wafer with a thickness of 1 mm,triggered by a 1064-nm extrinsic laser beam with the rectangular spot,has been investigated experimentally.It is found that the variation of the spot size in length and width can act on the different parts of the output waveform integrating the characteristics of the linear and nonlinear modes,and then significantly boosts the PCSS toward different operation modes.On this basis,a two-channel model containing the active and passive parts is introduced to interpret the relevant influencing mechanisms.Results indicate that the increased spot length can peak the amplitude of static domains in the active part to enhance the development of the nonlinear switching,while the extended spot width can change the distribution of photogenerated carriers on both parts to facilitate the linear switching and weaken the nonlinear switching,which have been proved by comparing the domain evolutions under different spot sizes.

Strongly Gain Coupled DFB Laser Monolithically Integrated with a Self Alignment Spot Size Converter

A new type strongly gain coupled (GC) DFB laser and a new type self alignment spot size converter (SA SSC) are proposed and successfully fabricated.The strongly GC DFB laser is monolithically integrated with the SA SSC with three step epitaxies.A high single mode yield and large side mode suppression ratio is obtained from the strongly GC DFB laser.A near circle far field pattern is obtained by using the SA SSC.

Design of Tapered Rib Spot-Size Converter with Double-Cladding Structure

A novel structure of spot size converter is designed to allow low loss and large alignment tolerance between single mode rib waveguide devices and fiber arrays theoretically.The spot size converter consists of a tapered rib core region and a double cladding region.Through optimizing parameters,an expanded mode field can be tightly confined in the inner cladding and thus radiation loss be reduced largely at the tapered region.The influence of refractive index and thickness of the inner cladding on coupling loss is analyzed in particular.A novel,easy method of fabricating tapered rib spot size converter based on silicon on insulator material is proposed.

1.55μm Laser Diode Monolithically Integrated with Spot-Size Converter Using Conventional Process

A novel 1 55μm laser diode with spot size converter is designed and fabricated using conventional photolithography and chemical wet etching process.For the laser diode,a ridge double core structure is employed.For the spot size converter,a buried ridge double core structure is incorporated.The laterally tapered active core is designed and optically combined with the thin and wide passive core to control the size of mode.The laser diode threshold current is measured to be 40mA together with high slop efficiency of 0 35W/A.The beam divergence angles in the horizontal and vertical directions are as small as 14 89°×18 18°,respectively,resulting in low coupling losses with a cleaved optical fiber (3dB loss).

聚合物波导折射率渐变型Spot-size converter设计

围绕光致折射率变化聚甲基苯基硅烷高分子光波导,设计了新型的折射率渐变型 Spot-size converter,可有效改善光纤与光波导的端面耦合效率．BPM 仿真计算显示,耦合效率由78%提高到 91%,为器件制备提供了理论依据．

An Artificial Neural Network for Estimating Sizes of Spot Welding Nuggets

Sizes of nuggets are often used to evaluate spot weld quality in production. This paper presents a neural estimator used to carry out non-destructive on-line analysis of spot weld quality in which trained ANN functions to map dynamic resistance characteristics into sizes of spot weld nuggets and results confirm the validity of neural network for this type of application.

Influence of transverse mode on retinal spot size and retinal injury effect:A theoreticalan alysis on 532-nm laser

The fundamental transverse mode(TEM00)is preferable for experimental and theoretical study on the laser-induced retinal injury effect,for it can produce the minimal retinal image andestablish the most strict laser safety standards.But actually lasers with higher order mode werefrequently used in both earlier and recent studies.Generally higher order mode leads to largerretinal spot size and so higher damage threshold,but there are few quantitative analyses on thisproblem.In this paper,a four-surface schematic eye model is established for human and macaque.The propagation of 532-nm laser in schematic eye is analyzed by the ABCD law of Gaussianoptics.It is shown that retinal spot size increases with laser transverse mode order.For relativelower mode order,the retinal spot diameter will not exceed the minimum laser-induced retinallesion(25~30μm in diameter),and so has little effect on retinal damage threshold.While forhigher order mode,the larger'retinal spot requires more energy to induce injury and so the damage threshold increases.When beam divergence is lowered,the retinal spot size decreasescorrespondingly,so the efect of mode order can be compensated.The retinal spot size of macaqueis slightly smaller than that of human and the ratio bet ween them is independent of mode order.We conclude that the laser mode order has significant influence on retinal spot size but limitedinfluence on the retinal injury ffect.

激光剥蚀电感耦合等离子体质谱法微区原位定量分析锂铍矿物化学成分

锂、铍是当前全球战略性关键金属,采用激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)建立分析方法可以实现微区原位定量分析天然矿物样品中的锂、铍元素含量,为锂铍资源高效利用以及赋存状态的研究提供分析技术支撑。锂辉石和绿柱石等矿物是提取锂、铍元素的主要原料,微区分析常用的电子探针方法对于能量较低的轻元素难以准确定量,而LA-ICP-MS方法亟待改进降低非基体匹配校准带来的基体效应提高分析的准确度和精密度。本文探讨了仪器工作条件(同位素选择及计数模式、载气He气流速、样品气Ar气流速、束斑直径、能量密度大小)和数据处理方法(外部标准物质、内标元素)对定量结果精密度和准确度的影响。实验结果表明:He和Ar气体流速不仅会影响锂、铍信号强度,而且适当降低载气He流速(0.6L/min)可以减小相对误差。增加束斑直径虽可以将数据精密度提高10%以上,但是对于准确度影响不大;对于绿柱石这类硬度高的透明矿物应提高能量密度(相对强度>75%,通量>2.7J/cm^(2))以保证产生稳定剥蚀信号。测定7Li时选择现有标准物质中含量较高的GSE-1G校准、9Be选择NIST610校准,以Al作为内标补偿元素,计算结果相对误差较小。LA-ICP-MS方法通过调整仪器工作条件和数据处理方法,可以降低基体差异,提高数据准确度,解决微区原位准确定量分析锂、铍轻元素的难题,为锂、铍资源的勘探开发和高效利用提供有力的技术支撑。但是也亟待开发高锂、铍含量的微区标准物质,解决因现有标准物质与样品中含量差异造成的基体效应来进一步提高数据质量。

狭缝法测量X射线管焦点尺寸的研究

目前EN 12543标准中的狭缝法广泛应用于工业用X射线管焦点尺寸的测量和标注。然而所需的测试设备——狭缝相机,由于其复杂和精密的设计要求,导致生产加工难度大、成本高且不利于推广使用。本文采用双钨合金圆柱代替狭缝相机,基于圆柱法中距离和位置参数校准方法,改进了狭缝法中焦点尺寸测量的计算公式,研究了不同狭缝大小对X射线管焦点尺寸测量的影响和变化规律。实验结果表明,使用间距与焦点尺寸相当的双钨合金圆柱测量COMET公司的MXR-225HP/11工业X射线管,也可以获得较为精确的测量结果,同时实验发现当狭缝宽度较大时,可以直接用来计算焦点测量装置的几何放大倍数,并且计算结果与圆柱法中使用距离和位置参数校准方法所测量的结果相一致。

High-Efficiency Dynamic Scanning Strategy for Powder Bed Fusion by Controlling Temperature Field of the Heat-Affected Zone

Improvement of fabrication efficiency and part performance was the main challenge for the large-scale powder bed fusion(PBF)process.In this study,a dynamic monitoring and feedback system of powder bed temperature field using an infrared thermal imager has been established and integrated into a four-laser PBF equipment with a working area of 2000 mm×2000 mm.The heat-affected zone(HAZ)temperature field has been controlled by adjusting the scanning speed dynamically.Simultaneously,the relationship among spot size,HAZ temperature,and part performance has been established.The fluctuation of the HAZ temperature in four-laser scanning areas was decreased from 30.85℃to 17.41℃.Thus,the consistency of the sintering performance of the produced large component has been improved.Based on the controllable temperature field,a dynamically adjusting strategy for laser spot size was proposed,by which the fabrication efficiency was improved up to 65.38%.The current research results were of great significance to the further industrial applications of large-scale PBF equipment.

笔形束质子放疗系统质控中束斑大小测量方法对比研究

目的 研究对比笔形束质子放疗系统质控中束斑大小的测量方法。方法 使用Matrixx One二维平面电离室矩阵、Lynx-PT平面闪烁体探测器及XRV-124锥形闪烁体探测器-三种不同种类、不同形状的探测器对质子放疗系统中不同能量的质子束斑大小进行测量,并将测量结果与加速器验收时束斑大小结果进行对比。结果 Matrixx One的束斑大小测量结果与验收结果相比偏差较大,其中230 MeV时的最大偏差达到41.25%。而Lynx-PT和XRV-124的束斑测量结果与验收结果相比,最大偏差分别为-7.35%和3.69%,Lynx-PT测量结果相较于验收结果系统性偏小。结论 Lynx-PT和XRV-124均适用于质子放疗系统束斑大小的测量,Matrixx One适用于束斑尺寸较大的质子放疗系统,相较于Lynx-PT和Matrixx One, XRV-124在旋转治疗室单能单点束斑尺寸测量中更有优势。

基于灰度共生矩阵的迷彩图像相似度研究

针对迷彩伪装中图案斑点与颜色在相似度效果评估时的权重问题,通过迷彩设计软件生成多种林地和海洋背景四色迷彩,运用灰度共生矩阵计算图像相似度,采用控制变量法研究斑点图案和背景颜色对图像相似度的影响规律。研究结果表明:灰度共生矩阵包含图像的亮度(颜色)信息和分布(纹理)信息,可以综合评价迷彩图像的相似度;在迷彩设计中当图像中的斑点形状尺寸相同时,改变图像的颜色,图像相似度为0.5左右,当颜色相同,改变图像中的斑点形状尺寸,图像相似度达到0.9以上,说明迷彩伪装中颜色权重高于斑点图案权重,可为变形迷彩设计提供依据和指导。

基于热点应力设计弧形焊环栓钉研究

目前随着钢混结构的普遍应用,栓钉作为连接件,其疲劳性能问题也备受关注,尤其是焊趾处的应力集中效应。文中将基于热点应力法对一种新型弧形焊环进行尺寸设计,通过ABAQUS并采用线性外推方式对4种不同直径栓钉的焊环高度、宽度、倒角进行参数分析。研究结果表明,栓钉焊趾处的热点应力随焊环高(宽)度的增加、倒角的减小而减小。说明增加焊环的高(宽)度、减小焊环的倒角能够减小焊趾的应力集中效应。

Understanding the influence of petrographic parameters on strength of differently sized shale specimens using XRD and SEM

Ground failure is a major contributor to fatalities in underground mines in the US.Underground coal mines in the Northern Appalachian have weak roof rock composed of shale,which is prone to failure under high horizontal stress.Understanding the relationship among strength,specimen size and rock petrographic parameters is essential for developing an effective ground control plan.Size effect studies have found that rock strength varies with specimen size.This paper attempts to understand this strength variation using three specimen sizes(254-mm,508-mm,and 762-mm).The specimen strength was measured and the major petrographic parameters affecting the strength,namely grain size,grain shape,quartz content,clay content,etc.were analyzed using X-ray diffraction(XRD)and scanning electron microscopy(SEM).The petrographic parameters were then correlated with the strength of the three differently sized specimens.The results showed that 508-mm specimen had the lowest strength.Quartz content of the 508-mm specimen was lower than that of 254-mm and 762-mm specimens.Clay content and average grain size of the 508-mm specimen were higher than those of 254-mm and 762-mm specimens.These results clearly show that grain size,quartz content and clay content contribute to strength variation observed in differently sized shale specimens.

Small-angle X-ray scattering investigation of aging behavior of Al-Cu-Mg-Ag alloys using synchrotron radiation

The aging behavior of Al-Cu-Mg-Ag alloys with high Cu/Mg was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) using synchrotron radiation. TEM study reveals that the major strengthening phases of the alloy after aging at 160?C for 10 h are Ω and less θ′. SAXS study shows that the scattering patterns are composed of several concentric circles at the beginning of aging process, which is replaced by the butterfly-wings scattering patterns with the increase of aging time. The butterfly-wings scattering patterns are composed of several branches. The angles between the branches are roughly equal to that between the habit planes of precipitates. The evolution of Guinier radius with aging time indicates the good coarsening resistance of the precipitates. The evolution of integrated intensity is consistent with the classical two-step precipitation process.

Small Angle X-ray Scattering Study of Precipitation Kinetics in Al-Zn-Mg-Cu Alloys

The evolution of microstructure parameters （precipitate size and volume fraction） for two types of Al-Zn-Mg-Cu alloys （7075 and 7055） during aging has been studied by synchrotron-radiation small angle X-ray scattering （SAXS）.The results show that the precipitates are only a few nanorneters for both alloys ageing even at higher temperature of 160℃ for 72 h （4.44 and 5.82 nm, respectively）. The maximum of the precipitate volume fraction increases with in creasing Zn content and is about 0.023-0.028 and 0.052-0.054, respectively. The coarsening of precipitate is consistent with LSW （Lifshitz-Slyozov-Wagner） model even at the initial stage where volume fraction is still varying.The activation energy of coarsening regime has been determined to be about 1.22±0.02 eV and 1.25±0.02 eV for alloys 7075 and 7055, respectively.

Stability of the Dividing Distribution Function Method for ParticleSize Distribution Analysis in Small Angle X－Ray Scattering

The Dividing Distribution Function (DDF) method is one of the methods by which the particle size distribution of ultrafine powder can be evaluated from its small angle X-ray scattering data. In this paper, the stability of the solution obtained from DDF method has been investigated through optimizing the coefficient matrix, introducing a damping factor and a least square treatment. All calculations were accomplished with a microcomputer. It was shown that the average deviations of the size distribution obtained are not larger than the assigned random errors to the scattering intensities as long as the corresponding requirements are satisfied.

Prediction and Verification of Resistance Spot Welding Results of Ultra-High Strength Steels through FE Simulations

Resistance spot welding (RSW) is the most common welding method in automotive engineering due to its low cost and high ability of automation. However, physical weldability testing is costly, time consuming and dependent of supplies of material and equipment. Finite Element (FE) simulations have been utilized to understand, verify and optimize manufacturing processes more efficiently. The present work aims to verify the capability of FE models for the RSW process by comparing simulation results to physical experiments for materials used in automotive production, with yield strengths from approximately 280 MPa to more than 1500 MPa. Previous research has mainly focused on lower strength materials. The physical weld results were assessed using destructive testing and an analysis of expulsion limits was also carried out. Extensive new determination of material data was carried out. The material data analysis was based on physical testing of material specimens, material simulation and comparison to data from literature. The study showed good agreement between simulations and physical testing. The mean absolute error of weld nugget size was 0.68 mm and the mean absolute error of expulsion limit was 1.10 kA.

Impact of Different Grinding Aids on Standard Deviation in X-Ray Fluorescence Analysis of Cement Raw Meal

X-ray fluorescence (XRF) analysis utilizes particle size which is resulted from milling of a material. The milling ensures uniform and fine grained powder. The finer and more uniform the particle size is, the better the result and easier it is for material quality control. To ensure uniformity in particle size and finer powder, a comparative analysis was conducted with different grinding aids and pressed pellet method was used in obtaining analysis results. Pressed pellets of cement raw meal sample milled with different grinding aids (graphite, aspirin and lithium borate) were subjected to XRF. Graphite produced better particle size uniformity with a corresponding standard deviation that made quality control of raw meal easier and better than aspirin and lithium borate.

Small Angle Neutron Scattering and X-Ray Diffraction Studies of Nanocrystalline Titanium Dioxide

Nanocrystalline titanium dioxide powder is characterized for phase analysis as well as particle size and its distribution by x-ray diffraction and small angle neutron scattering measurements. Analysis of the SANS data in the momentum transfer range q = 0.1 - 1.8 nm–1 reveals an average particle size of 24.82 nm in good agreement with the particle size determined earlier by transmission electron microscopy. XRD measurement proves co-existence of rutile and anatase phases in this commercial TiO2 nanocrystalline powder.