基于悬臂梁的光纤光栅线性调谐器研究

分析了基于悬臂梁的光纤光栅线性调谐的基本原理及调谐公式,指出了调谐范围、调谐灵敏度和反射波谱展宽与悬臂梁结构的关系,并提出了优化方案.实验中选用适当尺寸的悬臂梁,对粘贴其上的光纤光栅的反射波长实现了线性调谐,并可对调谐范围、灵敏度等指标进行灵活控制.     

Evaluation of the dosimetric characteristics of a radiophotoluminescent glass dosimeter for high-energy photon and electron beams in the field of radiotherapy

We aimed to evaluate the suitability of a glass dosimeter (GD) for high-energy photon and electron beams in experimental and clinical use, especially for radiation therapy. We examined the expanded dosimetric characteristics of GDs including dose linearity up to 500 Gy, uniformity among GD lots and for individual GDs, the angular dependence, and energy dependence of 4 therapeutic x-ray qualities. In addition, we measured the dosimetric features (dose linearity, uniformity, angular dependence, and energy dependence) of the GD for electron beams of 10 different electron energy qualities. All measurements with the exception of dose linearity for photon beam were performed in a water phantom. For high-energy photon beams, dose linearity has a linear relationship for a dose ranging from 1 to 500 Gy with the coefficient of determination; R² of 0.998. The uniformity of each GD of dose measurements was within ±0.5% for four GD lots and within ±1.2% for 80 GDs. In terms of the effects of photon beam angle, lower absorbed doses of within 1.0% were observed between 60° and 105° than at 90°. The GD energy dependence of 4 photon beam energy qualities was within ±2.0%. On the other hand, the result of the dose linearity for high-energy electron beams showed well fitted regression line with the coefficient of determination; R² of 0.999 between 6 and 20 MeV. The uniformity of GDs exposed to the nominal electron energies 6, 9, 12, 16, and 20 MeV was ±1.2%. In terms of the angular dependence to electron beams, absorbed doses were within 2.0% between 60° and 105° than at 90°. In evaluation of the energy dependence of the GD at nominal electron energies between 5 and 20 MeV, we obtained responses between 1.1% and 3.5% lower than that for a cobalt-60 beam. Our results show that GDs can be used as a detector for determining doses when a high-energy photon beam is used, and that it also has considerable potential for dose measurement of high-energy electron beam.     

Investigations on Pd:SnO2/porous silicon structures for sensing LPG and NO2 gas

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO₂/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO₂ gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO₂ gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO₂ gases, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Preparation and electrical characterization of (PVC + KBrO3) polymer electrolytes for solid state battery applications

This paper presents results of studies on dc electrical conductivity and transference number measurements on potassium bromate (KBrO₃) complexed polyvinyl chloride (PVC) films prepared by solution cast technique. Temperature dependence of dc electrical conductivity and transference number data indicated the dominance of ion type charge transport in these specimens. The magnitude of conductivity increased with increase in concentration of the salt and temperature. Using this (PVC + KBrO₃) electrolyte, solid-state electrochemical cells were fabricated, and their discharge profiles were studied under a constant load of 100 kΩ. Several cell profiles such as open circuit voltage, short circuit current, power density, and energy density associated with these cells were evaluated and were reported. The features of complexation of the electrolytes were studied by X-ray diffraction and Fourier transform infrared spectroscopy. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006     

同轴线-矩形波导结散射特性的数值分析

 提出了一种数值分析同轴线-矩形波导结散射特性的模式匹配方法。采用同轴线和矩形波导的本征模函数表示电磁场分量,通过同轴线-矩形波导结截面横向场分量匹配获得波导结的散射参数,引入电场模式匹配矩阵的解析形式提高了计算效率。给出了基于模式匹配法数值仿真的各种同轴线-矩形波导结散射特性及仿真结果分析,并与3维全电磁波分析软件HFSS的仿真结果进行了比较,二者非常吻合。模式匹配法计算效率高,能广泛应用于微波毫米波元器件及系统结构的设计与优化。     

存储器用铁电薄膜及电极材料的研究

铁电体独特的自发电极化双稳性质和非线性光学性质使其在光电子器件中得到广泛应用．为了实现器件的小型化和与微电子、光电子工艺兼容，铁电薄膜已成为一个研究热点．自发电极化的大小和取向以及外电场、缺陷和铁电薄膜／电极界面与自发电极化的交互作用决定了铁电薄膜的性质和服役行为．文章以铁电存储器和光电子器件应用为背景，选择了具有重大应用前景的Bi4-xLaxTi3O12（BLT）、SrBi2Ta2O9（SBT）、PbZrxTi1-xO3（PET）和LiNbO3（LN）铁电薄膜以及相关的La（Sr，Co）O3（LSCO）和LaNiO3（LNO）等电极材料为研究对象，研究了缺陷电荷和电畴的交互作用和它们在交变外电场中的动力学行为，探明了铁电薄膜疲劳现象的物理本质；从晶格结构与缺陷的观察研究入手，探索了材料铁电性质的起源和优化材料铁电性质的途径；从铁电薄膜／电极界面结构与性质的研究入手，寻找更有效、更稳定的电极材料与结构，从而为器件应用打下了基础；在研究外电场对铁电薄膜生长机制影响的基础上，找到了利用外电场调控铁电薄膜结构的新途径，发展了新的、与半导体器件和光电子器件工艺兼容的制膜方法．     

不同高光谱特征参数区分马铃薯品种的优劣势分析

对马铃薯关键生育期的高光谱遥感图像进行特征提取和分析,提出了一种快速区分不同马铃薯品种的方法。以两个早熟和中熟马铃薯品种为研究对象,采集其块茎形成期、块茎膨大期和淀粉积累期的冠层反射光谱曲线,对实测反射光谱曲线进行Savitzky-Golay滤波平滑和一阶微分处理,以高光谱位置参数、振幅参数、面积参数、宽度参数和反射率参数为研究指标,根据21个高光谱特征参数的贡献率大小,评价了其区分不同马铃薯品种的优劣。结果表明：(1)同一类高光谱特征参数在不同生育期区分马铃薯品种的能力不同: 高光谱位置参数、宽度参数和反射率参数在块茎膨大期区分不同马铃薯品种的能力最强,淀粉积累期次之;高光谱振幅参数和面积参数在淀粉积累期的区分能力最强,块茎膨大期次之,五类高光谱特征参数在块茎形成期的区分能力均最差。(2)同一生育期5类高光谱特征参数区分马铃薯品种的能力也存在差异。在块茎形成期,五类高光谱特征参数的区分能力从强到弱依次为：反射率参数>振幅参数>面积参数>宽度参数>位置参数;在块茎膨大期和淀粉积累期,从强到弱依次为：面积参数>振幅参数>反射率参数>宽度参数>位置参数。综合能力从强到弱依次为：面积参数>振幅参数>反射率参数>宽度参数>位置参数。     

从诺贝尔物理学奖看光学的发展

从一个新的角度分析、讨论了光学的发展过程.并对光学今后的发展做了展望.     

激光相干合成中单元的相位和振幅波动对合成光束远场分布的影响

运用傅里叶光学分析法推导出系统抖动造成单个光源的相位和振幅发生波动时的远场光强表达式,以1维阵列为例分析了系统抖动对远场的影响.研究表明:随着参与合束的发光单元数目的增加,尖峰变锐,能量更集中;系统抖动引起了远场峰值光强的减少.出现了本底现象,破坏了远场的对称性和光束质量;激光阵列单个光源的相位随机抖动应该控制在3 π/8范围内;相干合束发光单元数目越多,系统抖动对远场的影响越小.     

Cr4+:YAG被动调Q激光器输出特性

采用理论与实验相结合的方法研究了激光二极管阵列泵浦的Cr4+:YAG被动调Q Nd:YAG激光器的输出特性.重点分析了调Q晶体小信号透过率和反射镜的反射率对激光器的输出能量、脉冲宽度的影响.对数值模拟结果进行了实验验证,数值计算与实验结果基本一致.研究结果表明,在特定的激光晶体参数下,Cr4+:YAG被动调Q激光器的输出能量与脉冲宽度由调Q晶体的小信号透过率和输出镜的反射率决定:输出能量随着小信号透过率增加而减小,对应于一个调Q晶体透过率,有一个最佳反射率使输出能量最大;脉冲宽度随着初始透过率与反射率的增大而增大.