铷原子饱和吸收光谱与偏振光谱对780nm半导体激光器稳频的比较

将激光频率锁定于合适的参考频率,可以有效地抑制激光器的频率起伏。本文采用铷原子D2线超精细跃迁线的饱和吸收光谱和偏振光谱分别获得鉴频曲线,通过电子伺服系统将频率校正信号负反馈到780 nm光栅外腔反馈半导体激光器外腔的压电陶瓷上的方法对激光器进行稳频。介绍了两种方法的基本原理和实验方案。与激光器自由运转300s时激光器典型的频率起伏约6.6 MHz相比,采用饱和吸收光谱和偏振光谱进行稳频,运转300 s时激光器典型的残余频率起伏分别约为1.5 MHz和0.6 MHz。分析表明,饱和吸收光谱稳频采用了相敏检波技术,需要对激光器进行频率调制,带来了额外的频率噪声,而偏振光谱稳频则是一种完全无频率调制的稳频方案。     

分数阶系统有限时间稳定性理论及分数阶超混沌Lorenz系统有限时间同步

研究了分数阶系统有限时间稳定性理论及分数阶混沌系统的同步问题.根据分数阶微分性质及分数阶系统稳定性理论,建立了分数阶系统有限时间稳定性理论并进行了证明.根据该理论设计控制器实现了分数阶超混沌Lorenz系统有限时间同步并运用数值仿真进行了验证. 关键词： 分数阶 超混沌Lorenz系统 稳定 有限时间同步     

一种基于OTF稳定性的波前编码相位板优化方法

提出了一种简单的可用于光学系统中子午弧矢方向白光OTF稳定性评价的波前编码相位板参量优化方法.该方法仅以标准偏差来评价OTF在目标景深范围内的稳定性,并且结合自适应模拟退火算法在参量空间内优化得到相位板的最佳参量.使用该方法优化得到的相位板参量,可以大幅度提高光学系统的景深,并且可以获得更为清晰、稳定的成像.对应用波前编码技术前后光学系统的成像性能作了比较,并且考察了优化参量的容差性.     

超声探头的响应特性及暂态回波模型

建立检测系统的数学模型,可以更好地理解超声检测的物理本质。分析了超声波从产生、介质中传播、缺陷耦合以及接收的全过程,将缺陷回波表示为探头响应函数与缺陷响应的时域卷积。利用空间脉冲响应和基尔霍夫近似建立了超声波与平面型缺陷的耦合模型,用大平面试块底面回波和大平面响应进行反卷积求得了探头的响应函数,并详细分析了探头在不同偏置位置时不同大小缺陷响应的特点,发现缺陷回波由直达回波和边缘回波组成,直达回波和边缘回波极性相反,且直达回波的幅值远远大于边缘回波。     

短波红外成像系统对激光光斑探测能力分析

通过短波红外探测器灵敏度、目标和环境探测输出信噪比、对比度等分析,计算给出不同大气能见度、环境照度条件下,短波红外热像对外界景物和激光光斑的探测距离,并对理论分析进行试验验证。结果表明,在大气能见度1 km~3 km、环境照度1 lx~1 000 lx、阈值信噪比2.25~10、阈值对比度0.01~0.02的条件下,短波红外热像对激光光斑探测距离为0 km~3.5 km。     

铀在Nd_2Zr_2O_7烧绿石中的固溶量及重离子辐照效应

Nd_2Zr_2O_7烧绿石因其稳定的物理化学性质和辐照稳定性可以作为高放废物中锕系核素的固化基材.通过溶胶凝胶—喷雾热解—高温烧结方法制备了含铀的Nd_2Zr_2O_7烧绿石固化体;开展了Nd_2Zr_2O_7和Nd_(1.9)U_(0.1)Zr_2O_7固化体的重离子辐照实验,辐照剂量为1 dpa和3 dpa;利用X射线衍射和Raman光谱对固化体结构进行了分析.研究发现铀在Nd_2Zr_2O_7烧绿石体系的固溶量仅为10 at%,高价态铀掺杂导致固化体结构向无序化转变.重离子辐照实验表明, Nd_2Zr_2O_7烧绿石基材具有较高的抗辐照稳定性;而Nd_(1.9)U_(0.1)Zr_2O_7在较低辐照剂量下,固化体烧绿石体系结构破坏,重离子辐照诱导固化体结构转变为更加无序化的萤石结构.低固溶量和抗辐照能力减弱主要是由于锕系核素烧绿石固化体的结构无序化所致.     

声波水平折射引起水平位移椭圆极化和声能流水平偏转

针对矢量水听器测向的应用要求,研究了三维水声传播问题中水平折射对声矢量场特性的影响。理论分析表明,水平折射可使质点水平位移从线性极化转变为椭圆极化,同时引起声能流方向的水平偏转。声能流方向的水平偏转导致波达方向偏离目标水平方位,对目标水平方位估计造成误差。采用虚源法仿真了倾角为2.86°的楔形波导中的三维声矢量场,并给出了空间各点处由水平折射引起的单矢量水听器目标方位估计误差。结果显示,部分区域中由水平折射引起的目标方位估计误差可达10°以上。     

Orbital Angular Momentum Generation Using Circular Ring Resonators in Radio Frequency

Electromagnetic field generators based on circular ring resonators,whose perimeters are integer times of equivalent wavelength,are well known to have attractive potential for producing radio vortexes carrying orbital angular momentum(OAM).We study the radiation characteristics of the generators based on radiation vector and antenna array theory.The behaviors of radiation patterns,field intensity and phase distribution are investigated in detail,and show classical features of OAM beams.The evolution of the generators performance versus the OAM state is also analyzed.The proposed generators can be realized by all kinds of microwave transmission lines,verified by two different prototypes.The discussions and conclusions drawn in this study are useful and meaningful for the radio OAM generator design.     

Effect of Mg-Preflow for p-AlGaN Electron Blocking Layer on the Electroluminescence of Green LEDs with V-Shaped Pits

In GaN-based green light-emitting diodes(LEDs) with and without Mg-preflow before the growth of p-Al GaN electron blocking layer(EBL) are investigated experimentally.A higher Mg doping concentration is achieved in the EBL after Mg-preflow treatment,effectively alleviating the commonly observed efficiency collapse and electrons overflowing at cryogenic temperatures.However,unexpected decline in quantum efficiency is observed after Mg-preflow treatment at room temperature.Our conclusions are drawn such that the efficiency decline is probably the result of different emission positions.Higher Mg doping concentration in the EBL after Mg-preflow treatment will make it easier for a hole to be injected into multiple quantum wells with emission closer to pGaN side through the(8-plane rather than the V-shape pits,which is not favorable to luminous efficiency due to the preferred occurrence of accumulated strain relaxation and structural defects in upper QWs closer to p-GaN.Within this framework,apparently disparate experimental observations regarding electroluminescence properties,in this work,are well reconciled.     

Metastable Electron Traps in Modified Silicon-on-Insulator Wafer

We perform the total ionizing radiation and electrical stress experiments to investigate the electrical characteristics of the modified silicon-on-insulator(SOI) wafers under different Si ion implantation conditions. It is confirmed that Si implantation into the buried oxide can create deep electron traps with large capture cross section to effectively improve the antiradiation capability of the SOI device. It is first proposed that the metastable electron traps accompanied with Si implantation can be avoided by adjusting the peak location of the Si implantation reasonably.