小周期波荡器自由电子激光器：数值模拟与实用化设计

采用三维自洽非线性理论计算方法,针对小周期波荡器自由电子激光器进行了数值模拟计算研究.结果表明,在我所现有脉冲线加速器基础上,采用周期为10mm的波荡器,可获得输出功率为20MW,波长为1.7mm的自由电子激光.最后给出实用化总体实验设计方案.     

Characteristic of energy input for laser forming sheet metal

Laser forming is a process in which laser-induced thermal deformation is used to form sheet metal without a hard forming tool or external forces. The energy input of laser beam is the key factor for the temperature and stress distribution of sheet metal. The purpose of this work is to investigate the influence of energy input condition on heat input and deformation angle for two-dimension laser forming. Variations in heat input resulting from material deformation was calculated and discussed in this paper at first. Furthermore, in laser forming under the condition of constant laser energy input, the effects of energy input mode on deformation angle and temperature field were investigated.     

求解双曲守恒律方程的WENO型熵相容格式

通过在单元交界面处进行高阶WENO重构,得到了一种求解双曲型守恒律方程的WENO型熵相容格式。用该格式对一维Burgers方程和Euler方程进行数值模拟,结果表明,该格式具有高精度、基本无振荡性等特点。     

InAs 单量子点中级联辐射光子的关联测量

利用分子束外延生长InAs单量子点样品,温度为5 K时,测量了单量子点中单、双激子自发辐射的荧光(PL)光谱.研究了单、双激子发光强度随激发功率的变化及对应发光峰的偏振特性和精细结构劈裂.基于Hanbury-Brown Twiss(HBT) 实验,测量了单、双激子间发光光谱的关联函数,证实了其发光过程为级联发射过程. 关键词： InAs 单量子点 单、双激子 荧光光谱 级联辐射     

金纳米颗粒调控量子点激子自发辐射速率

将InAs/GaAs量子点样品薄膜置于覆盖有直径为50 nm的金(Au)纳米颗粒的硅衬底上,可以调控量子点激子的自发辐射速率.实验发现,当量子点浸润层距离Au纳米颗粒表面15—35 nm时,激子自发辐射速率受到抑制,且距离为19 nm时抑制作用最大,导致量子点激子的自发辐射速率减小到没有Au纳米颗粒时自发辐射速率的10^-3.基于经典的偶极辐射模型模拟计算的激子自发辐射速率与实验结果一致.     

新型量子点场效应增强型单光子探测器

针对量子点场效应单光子探测器(QDFET)光吸收效率低下的问题, 提出了一种新型量子点场效应增强型单光子探测器(QDFEE-SPD). QDFEE-SPD增加了共振腔的设计, 并采用了GaAs/AlAs多层膜作为下反射镜; 对QDFEE-SPD的光吸收增强效应和光响应度进行了理论分析和模拟, 结果表明, 与没有共振腔时相比, QDFEE-SPD的吸收效率和光相应度都有了大幅度的提升, 同时为了光吸收的最优化, 吸收层厚度一般应在0.1–0.5 μm; 对QDFEE-SPD的材料样品进行了生长和测试实验, 反射谱测试和PL谱测试结果表明, QDFEE-SPD对入射光的吸收具有了明显的增强效应. 文章成果为高效率量子点场效应单光子探测技术的研究提供了新的思路. 关键词： QDFEE-SPD 共振腔 吸收效率 光吸收增强效应     

负二项抽样下需处理数置信区间构造方法的改进

负二项抽样因其在发病率很低的情况下的优良表现而被广泛应用于流行病学及其它学科之中."需处理数"是一种度量药物疗效的重要指标,它常常用来评价那些结果是二值变量的临床试验所研究的药物的疗效.在实际应用中,通常希望得到需处理数的置信区间,但是目前已有的需处理数的置信区间构造方法都存在一个应用上的难题:区间上限过大以至于不可靠.文章旨在解决需处理数区间上限估计过大的问题,为此提出了需处理数的最短区间构造方法并运用蒙特卡洛模拟方法比较其相对传统方法的优劣,还给出了实际应用的例子.模拟结果表明:改进后的方法能够在控制置信系数的情况下极大地减小区间上限,具有重要的实际价值.     

因地制宜巧思解题

解析几何实现了几何方法与代数方法的结合,使形与数统一起来,在解题时,要善于观察、类比、联想、化归,选择恰当的途径,快捷准确地解决问题.一、善于运算,简明快捷解析几何的本质就是解析法,就是用代数方法解几何题,一定量的代数运算是难免的.例如,关于三点共线问题,常常由三点坐标来验证其线性关系.在三点坐标不全明确的情况下往往就先要求出三点坐标,这就需要一     

High quality above 3-μm mid-infrared InGaAsSb/AlGaInAsSb multiple-quantum well grown by molecular beam epitaxy

The GaSb-based laser shows its superiority in the 3–4 μm wavelength range. However, for a quantum well(QW) laser structure of InGaAsSb/AlGaInAsSb multiple-quantum well(MQW) grown on GaSb, uniform content and high compressive strain in InGaAsSb/AlGaInAsSb are not easy to control. In this paper, the influences of the growth temperature and compressive strain on the photoluminescence(PL) property of a 3.0-μm InGaAsSb/AlGaInAsSb MQW sample are analyzed to optimize the growth parameters. Comparisons among the PL spectra of the samples indicate that the In0.485GaAs0.184Sb/Al0.3Ga0.45In0.25As0.22Sb0.78MQW with 1.72% compressive strain grown at 460 C posseses the optimum optical property. Moreover, the wavelength range of the MQW structure is extended to 3.83 μm by optimizing the parameters.     

Spin Relaxation of Electrons in Single InAs Quantum Dots

By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots （QDs） with the configuration of positively charged excitons X＋ （one electron, two holes）. The spin relaxation rate of the hot electrons increases with the increasing energy of exciting photons. For electrons localized in QDs the spin relaxation is induced by hyperfine interaction with the nuclei. A rapid decrease of polarization degree with increasing temperature suggests that the spin relaxation mechanisms are mainly changed from the hyperfine interaction with nuclei into an electron-hole exchange interaction.