激光激发水中产生超声波的实验研究

采用压电陶瓷水听器研究了Nd：YAG脉冲激光激发水中产生瞬态超声波的特性,给出了声压信号随距离的变化关系。研究结果表明：用激光产生水下声波是完全可行的。当观测点与光击穿区的距离r远大于柱体长度时,垂直于光传播方向的激光瞬态超声波幅值与r成反比;当观测点与光击穿区的距离r很小时,垂直于光传播方向的声压幅值与产成反比。此外,当激光入射角度发生变化,超声脉冲的幅值也随之发生变化,其幅值在激光束垂直入射的时候最大。     

High-voltage SOI lateral MOSFET with a dual vertical field plate

A new silicon-on-insulator(SOI)power lateral MOSFET with a dual vertical field plate(VFP)in the oxide trench is proposed.The dual VFP modulates the distribution of the electric field in the drift region,which enhances the internal field of the drift region and increases the drift doping concentration of the drift region,resulting in remarkable improvements in breakdown voltage(BV)and specific on-resistance(Ron,sp).The mechanism of the VFP is analyzed and the characteristics of BV and Ron,spare discussed.It is shown that the BV of the proposed device increases from 389 V of the conventional device to 589 V,and the Ron,sp decreases from 366 m·cm2to 110 m·cm2.     

受激布里渊散射新介质——全氟胺的研究

本文从介质化学结构与受激布里渊散射(SBS)特性的关系入手,寻找出了SBS特性良好的全氟胺系列新介质——FC-131,FC-3283,FC-40,FC-43,FC-70等,并测定或计算出了新介质的SBS参数. 结果表明,新介质的吸收系数均小于10^-3 cm^-1,光学击穿阈值均高于100 GW/cm². 全氟胺系列新介质不仅具有良好的SBS特性,而且还具有无毒、低挥发性和高稳定性等一系列独特的物理化学性质. 新介质的发现不仅增加SBS介质的种类,而且能够有效提高SBS系统的性能,对于SBS相位共轭镜在高功率激光系统中的应用打下了良好的基础. 关键词： 受激布里渊散射(SBS) 全氟胺 吸收系数 光学击穿阈值     

Laser-induced quadrupoleben quadrupole collisional energy transfer in Xe-Kr

By considering the relative velocity distribution function and multipole expansion interaction Hamiltonian, a three-state model for calculating the cross section of laser-induced quadrupole-quadrupole collisional energy transfer is presented. Calculated results in Xe-Kr system show that in the present system, the laser-induced collision process occurs for ~4 ps, which is much shorter than the dipole-dipole laser-induced collisional energy transfer (LICET) process. The spectrum of laser-induced quadrupole-quadrupole collisional energy transfer in Xe-Kr system has wider tunable range in an order of magnitude than the dipole-dipole LICET spectra. The peak cross section decreases and moves to the quasi-static wing with increasing temperature and the full width at half peak of the profile becomes larger as the system temperature increases.     

Ultra-low on-resistance high voltage (>600 V) SOI MOSFET with a reduced cell pitch

A low specific on-resistance (R S,on) silicon-on-insulator (SOI) trench MOSFET (metal-oxide-semiconductor-field-effect-transistor) with a reduced cell pitch is proposed.The lateral MOSFET features multiple trenches:two oxide trenches in the drift region and a trench gate extended to the buried oxide (BOX) (SOI MT MOSFET).Firstly,the oxide trenches increase the average electric field strength along the x direction due to lower permittivity of oxide compared with that of Si;secondly,the oxide trenches cause multiple-directional depletion,which improves the electric field distribution and enhances the reduced surface field (RESURF) effect in the SOI layer.Both of them result in a high breakdown voltage (BV).Thirdly,the oxide trenches cause the drift region to be folded in the vertical direction,leading to a shortened cell pitch and a reduced R S,on.Fourthly,the trench gate extended to the BOX further reduces R S,on,owing to the electron accumulation layer.The BV of the MT MOSFET increases from 309 V for a conventional SOI lateral double diffused metal-oxide semiconductor (LDMOS) to 632 V at the same half cell pitch of 21.5 μm,and R S,on decreases from 419 m · cm 2 to 36.6 m · cm 2.The proposed structure can also help to dramatically reduce the cell pitch at the same breakdown voltage.     

Newton trajectories for the tilted Frenkel–Kontorova model

ABSTRACT

Newton trajectories are used for the Frenkel–Kontorova model of a finite chain with free-end boundary conditions. We optimise stationary structures, as well as barrier breakdown points for a critical tilting force were depinning of the chain happens. These special points can be obtained straight forwardly by the tool of Newton trajectories. We explain the theory and add examples for a finite-length chain of a fixed number of 2,?3,?4,?5 and 23 particles.     

介质材料二次电子发射特性对微波击穿的影响

以介质填充的平行板放电结构为例,本文主要研究了介质填充后微波低气压放电和微放电的物理过程.为了探究介质材料特性对微波低气压放电和微放电阈值的影响,本文采用自主研发的二次电子发射特性测量装置,测量了7种常见介质材料的二次电子发射系数和二次电子能谱.依据二次电子发射过程中介质表面正带电的稳定条件,计算了介质材料稳态表面电位与二次电子发射系数以及能谱参数的关系.在放电结构中引入与表面电位相应的等效直流电场后,依据电子扩散模型和微放电中电子谐振条件,分别探讨了介质表面稳态表面电位的大小对微波低气压放电和微放电阈值的影响.结果表明,介质材料的二次电子发射系数以及能谱参数越大,介质材料的稳态表面电位也越大,对应的微波低气压放电和微放电阈值也越大.所得结论对于填充介质的选择有一定的理论指导价值.     

一种用于冶金炉前快速分析的新仪器——激光诱导击穿光谱仪

冶金炼钢要求快速分析冶金炉前样品来及时掌握冶炼过程。文章介绍了自主研制的一种新型的光谱仪——激光诱导击穿光谱仪,该仪器采用ns级脉宽的Nd∶YAG激光器作为样品离子化光源,激光聚焦样品表面激发产生的等离子体光谱依次经帕邢-龙格光学系统进行分光、光电倍增管探测、门控积分器积分、模拟数字转换器转换后获得的最终结果输入计算机进行数据处理。和目前冶金炉前样品分析常用的光谱仪相比,该仪器无需样品预处理,分析速度快(1 min或更少),准确灵敏度高,非常适用于冶金炉前样品的快速分析。近年来随着光纤技术的迅速发展,使用该仪器进行钢液实时在线分析和动态控制冶金工艺必将成为现实。     

脉冲激光在液体中激发的声波特性研究

理论上分析了脉冲激光在液体中产生的声波波阵面随光声源形状的变化,以及不同激发机制下光声脉冲波形的差别,并从实验中得出了脉冲CO2激光光声脉冲频谱特性.结果表明光声波波阵面为球面或柱面,热弹机制激发双极性的光声脉冲,汽化机制激发单极性的光声脉冲,CO2脉冲激光在水中激发的声波频谱峰值主要在100 kHz以下.通过选择光声源的形状和激发机制可以获得所需的光声信号.     

体结构GaAs光导开关实验研究

为解决光导开关耐受场强的提高问题,研制了2种体结构光导开关,并进行了实验研究。两种开关均由半绝缘GaAs材料制成,一种尺寸为10.0 mm×10.0 mm×0.6 mm,电极位于10.0 mm×10.0 mm面上相对位置,电极直径6 mm;另一种尺寸为15.0 mm×15.0 mm×3.0 mm,8 mm直径电极位于15.0 mm×15.0 mm面上相对位置。测试了第1种开关在不同半高宽脉冲加载电压下的击穿电压,结果表明其最大耐受电压达7.6 kV,击穿电场127 kV/cm。对第2种结构测试了开关在直流加载条件下的暗态伏安特性并进行了触发实验,结果表明在15 kV工作电压下,其放电最大电流超过3.5 kA。