控制光和信号光频差对太赫兹光非对称解复用器性能的影响

讨论了半导体光放大器中的带间效应，及载流子热效应、谱烧孔效应、双光子吸收以及超快非线性折射等带内效应对半导体光放大器的动态特性的影响，讨论了两种情况：1)保持控制光波长不变而改变信号光频率，2)保持控制光和信号光频率相同而同时改变它们的频率下半导体光放大器的增益、相位动态特性以及太赫兹光非对称解复用器的开关窗口特性。数值结果表明，为了得到较为平坦而窄的开关窗口，控制光波长应与信号光波长相同，且其与半导体光放大器增益谱中心波长的差值应该大一些。     

Silicon nanowires grown from Au-coated Si substrate

Amorphous Si nanowires were grown on an Au-coated Si substrate by heat treatment at 1000 °C under an H₂ atmosphere. The nanowires have a length of several tens of a micron and a diameter of 10–20 nm. The growth mechanism of the nanowires was investigated and explained with a solid–liquid–solid model. Received: 11 July 2002 / Accepted: 7 July 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +86/10-62751615, E-mail: yudp@pku.edu.cn     

一种低频大功率调频声波束扫描发射系统

本文介绍一种中心工作频率在４．５ｋＨｚ发射电功率８ｋＷ的１６基元线列阵发射系统，并介绍了使用ＤＳＰ５６００１数字信号处理产生线性调频扫描波束发射信号及接收信号的频域处理和和一些测试结果。     

Exact Boundary Synchronization by Groups for a Kind of System of Wave Equations Coupled with Velocities*

This paper deals with the exact boundary controllability and the exact boundary synchronization for a 1-D system of wave equations coupled with velocities. These problems can not be solved directly by the usual HUM method for wave equations, however, by transforming the system into a first order hyperbolic system, the HUM method for 1-D first order hyperbolic systems, established by Li-Lu(2022) and Lu-Li(2022), can be applied to get the corresponding results.     

Local hydrated structure of an Fe2+/Fe3+ aqueous solution: an investigation using a combination of molecular dynamics and X-ray absorption fine structure methods

The hydrated shell of both Fe2+ and Fe3+ aqueous solutions are investigated by using the molecular dynamics (MD) and X-ray absorption structure (XAS) methods. The MD simulations show that the first hydrated shells of both Fe2+ and Fe3+ are characterized by a regular octahedron with an Fe-O distance of 2.08 for Fe2+ and 1.96 for Fe3+, and rule out the occurrence of a Jahn-Teller distortion in the hydrated shell of an Fe2+ aqueous solution. The corresponding X-ray absorption near edge fine structure (XANES) calculation successfully reproduces all features in the XANES spectra in Fe2+ and Fe3+ aqueous solution. A feature that is located at energy 1 eV higher than the white line (WL) in an Fe3+ aqueous solution may be assigned to the contribution of the charge transfer.     

原位成形光学微透镜的聚光性能研究

为解决荧光谱微检测系统中光学微透镜制作的困难,提出一种原位成形微透镜的制作方法,研究该微透镜的聚光性能,利用传统几何光学原理,分别推导出激发微透镜与检测微透镜的光线追迹方程,用该方程计算了2种微透镜的照射点分布几率,画出相应的分布曲线图,讨论了不同形状参数的微透镜对聚光性能的影响。研究结果表明,通过在光学胶中适当掺杂及打磨基底玻璃,可减小接触角,加大微透镜的形状参数,既能坚固透镜与基底间的粘接强度,又能提高微透镜的聚光本领。制作了使用原位成形光学微透镜的荧光谱微检测器,对生物荧光试剂进行了测试。实验结果表明,使用原位成形光学微透镜进行聚光,可使生物荧光谱强度提高4倍以上,通过在光学胶中掺杂以及打磨玻璃的办法,可以提高透镜的聚光本领约1.2倍。     

2.45 GHz ECR离子源的微波阻抗匹配

ECR离子源的等离子体阻抗对其微波传输与阻抗匹配设计至关重要。在中国科学院近代物理研究所现有的2.45 GHz ECR 质子源上,对等离子体阻抗进行了测量。首先用水吸收负载代替等离子体负载测量得到了所用微波窗阻抗,然后根据质子源测量数据,推算得到了等离子体阻抗。实验结果表明,脊波导输出端阻抗与后续负载不完全匹配,等离子体阻抗随微波功率变化呈非线性。这些结果为ECR离子源过渡匹配和微波窗的设计提供了参考依据。Plasma impedance of an ECR ion source is important for microwave transmission and impedance matching design. Plasma impedance was measured indirectly with the 2.45 GHz ECR proton source at the Institute of Modern Physics, Chinese Academy of Sciences. In the test, we got microwave window mpedance by using water absorption load instead of plasma load, and the source plasma impedance was derived from the test data with the 2.45 GHz ECR proton source and microwave window impedance. The experimental results show that ridge waveguide output impedance and the subsequent load does not exactly match, plasma impedance variation is nonlinear with microwave power. The achievedresult is useful in the design of ridged waveguide and microwave window.     

Electrical characteristics of AlInN/GaN HEMTs under cryogenic operation

Electrical properties of an AlInN/GaN high-electron mobility transistor (HEMT) on a sapphire substrate are investi-gated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AlInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density.     

360 GHz辐射计探测地面目标试验

为验证亚毫米波辐射计在弹药末制导中的应用可行性,计算了不同天气条件下天空亮温和视在温度,利用360 GHz辐射计对地面金属目标和涂层隐身目标进行了模拟探测试验。计算和试验表明,在寒冷干燥的季节,辐射计可以探测到地面金属目标,随着温度和湿度的升高,辐射计很难再探测到目标;对于高温涂层隐身目标,辐射计可以探测到,而不受天气的限制。     

4H-SiC肖特基二极管的电荷收集特性

针对极端环境下耐辐照半导体核探测器的研制需求,采用耐高温、耐辐照的4H碳化硅(4H-SiC)宽禁带材料制成肖特基二极管,研究了该探测器对241Am源粒子的电荷收集效率。从电容-电压曲线得出该二极管外延层净掺杂数密度为1.991015/cm3。从正向电流-电压曲线获得该二极管肖特基势垒高度为1.66 eV,理想因子为1.07,表明该探测器具备良好的热电子发射特性。在反向偏压高达700 V时,该二极管未击穿,其漏电流仅为21 nA,具有较高的击穿电压。在反向偏压为0~350 V范围内研究了该探测器对3.5 MeV 粒子电荷收集效率,在0 V时为48.7%,在150 V时为99.4%,表明该探测器具有良好的电荷收集特性。