脉冲磁场处理对碳纳米管掺杂MgB2线材临界电流密度的影响

对碳纳米管(CNT)掺杂MgB₂超导体磁场处理后的行为进行了研究. 结果表明，CNT掺杂MgB₂超导体经5T脉冲磁场处理后临界电流密度J_c(H)在低磁场下提高了2—3倍，高场下提高一个数量级以上，扫描电镜结果显示CNT沿着处理磁场方向规则排列并且成为MgB₂基体的形核中心和高效的磁通钉扎中心. 关键词： 2')" href="#">MgB₂ 碳纳米管 脉冲磁场处理     

外腔反馈对半导体激光器振荡特性的影响

通过有效反射系数的引入，根据激光谐振腔的自再现条件和对腔内光子密度、载流子密度方程的求解，分析了外腔反馈对半导体激光器的阈值增益、振荡频率和输出功率等振荡特性的影响，并通过实验进行了验证.外腔反馈后，半导体激光器的阈值电流从420mA降为370mA，输出功率的斜率效率获得了提高，理论计算的输出功率曲线与实验结果符合的很好. 关键词： 半导体激光器 外腔反馈 振荡特性     

AFM study of gold nanowire array electrodeposited within anodic aluminum oxide template

Uniform gold nanowires were synthesized by electrodepositing the gold under a very low ac frequency in the pores of an anodic aluminum oxide (AAO) template. The surface of the Au/AAO composite is very even and appeared purplish red. Atomic force microscopy observation indicates that the template membranes we obtained have hexagonally close-packed nanochannels. The gold nanowire array is very orderly arranged after partially dissolving the aluminum oxide membrane. Gold nanowires were also characterized by transmission electron microscopy and the phase structure of the Au/AAO composite was proved by X-ray diffraction. Received: 19 April 2001 / Accepted: 28 April 2001 / Published online: 27 June 2001     

Structural and optical properties of ZnO film by plasma-assisted MOCVD

High quality ZnO film was deposited by plasma-assisted metal-organic chemical vapor deposition (MOCVD). We observed a dominant peak at 34.6° due to (0 0 2) ZnO, which indicated that the growth of ZnO film was strongly C-oriented. The full-width at half-maximum (FWHM) of the -rocking curve was 0.56° indicating relatively small mosaicity. Photoluminescence (PL) measurement was performed at both room temperature and low temperature. Ultraviolet (UV) emission at 3.30 eV was found with high intensity at room temperature while the deep level transition was weakly observed at 2.513 eV. The ratio of the intensity of UV emission to that of deep level emission was as high as 193, which implied high quality of ZnO film. From PL spectrum at 10 K, we observed A-exciton emission at 3.377 eV and D°X bound exciton transition at 3.370 eV. The donor–acceptor transition and LO phonon replicas were observed at 3.333 and 3.241 eV respectively. Raman scattering was performed in back scattering at room temperature. The E₂, A_1(LO) and A_1(TO) mode was seen at 437.6, 575.8 and 380 cm^–1 respectively. In comparison with Raman spectrum of ZnO powder, we found that ZnO film was nearly free of strain, which indicated high crystal quality.     

Fabrication of bamboo-shaped GaN nanorods

Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated that the nanorods were single-crystal wurtzite GaN. Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001     

脉冲电场屏蔽效能测试系统及测试方法

 自主研制了一套小型脉冲电场屏蔽效能测试系统,该系统由脉冲电场发射设备和脉冲电场测试设备构成。脉冲电场发射设备的天线口面前60 cm处可产生峰值达7.5 kV/m的脉冲电场,测试设备的动态测试范围达97 dB。系统采用光纤测量设备,在测量工作中能有效抑制强电磁场干扰。采用Matlab编写自动测量及数据处理程序,实现了数据采集与处理自动化。实验测量了金属桥架、控制柜、屏蔽帐篷、导电水泥混凝土房的脉冲电场屏蔽效能,其脉冲电场峰值衰减量分别为52,64,66,30 dB。实验表明可用脉冲电场的峰值衰减量来评估屏蔽体的脉冲电场屏蔽效能。     

闪光照相中FXRMC和MCNP4B的散射比较研究

 散射问题是高能辐射成像研究中的一个重要问题,采用蒙特卡罗模拟来确定散射对提取客体信息的影响是一种重要的研究手段。简单介绍了FXRMC和MCNP4B程序的特点及其记录方式;在确保相同输入参数的条件下,针对不同的照相模型进行了对比计算。结果表明两个程序计算的散射照射量相对差别小于5%,说明这两个程序具有较高的符合程度。通过与实验结果的比较发现,这两个程序模拟的散射分布与实验结果基本一致,均可用于高能闪光照相的模拟研究。还给出了在散射检验方面的一些建议。     

大电流两电极气体开关研究

 由于引燃管难以满足现在能源系统对放电开关承受大电流的要求,因此研制了大电荷转移量两电极气体开关。这种新型气体开关电极间距可调,无触发极,采用同轴结构,并将主电极置于金属腔体内,减少了放电对绝缘支撑的污染。主电极为铜钨合金材料,设计为平顶圆柱状,以提高烧蚀均匀度和热传导效率,减少电极材料喷溅,延长其寿命。绝缘支撑采用碗状结构,提高了机械强度,增加了沿面击穿距离。该开关工作电压达25 kV,放电电流超过100 kA（脉冲宽度600 μs）,单次脉冲电荷转移量达50 C。实验结果显示该气体开关触发性能稳定,电极表面烧蚀均匀,多次大电流实验后电极表面保持完好,可应用于强激光能源系统。     

准分子激光等离子体开关控制脉宽研究

 利用准分子激光等离子体技术,在紫外预电离XeCl准分子激光器上获得了最短1.58 ns的短脉冲激光输出。实验中分析了聚焦到薄膜表面的光束能量密度对所产生的等离子体密度的影响,并对不同等离子体密度及维持时间情况下脉冲压缩效果进行了讨论,给出了激光器谐振腔在稳定腔及非稳腔两种工作方式下的实验结果。激光器在稳定腔工作时,脉宽可压缩至2.87 ns;采用非稳腔结构时,在脉冲能量不变情况下减小聚焦光斑面积,提高入射到薄膜表面的能量密度,得到了最短1.58 ns的短脉冲激光输出。该技术适用于任何其它准分子器件。     

微加工薄膜变形镜特性分析

 借助测量微加工薄膜变形镜驱动器的面形影响函数,分析了驱动器的电压-位移函数和驱动器之间的线性叠加性;通过对连续面形变形镜拟合像差的理论分析和实验研究,建立了微加工薄膜变形镜电压解耦模型。分析了对前36阶Zernike模式的拟合残差和拟合能力,指出微加工薄膜变形镜仅可用来拟合低级像差并且有较大的拟合能力和较小的拟合残差,而不能拟合高级像差。