A triple function linear fiber laser with passive mode-locking and continuous-wave single-wavelength and multiwavelength lasing

We propose a fiber laser that can operate with passive mode-locking pulse output, continuous single-wavelength emission, and continuous multiwavelength emission. It consists of a nonlinear optical loop mirror (NOLM) in a linear cavity. The NOLM is used to induce different kinds of intensity-dependent feedback, which determine the operation mode of the laser. We have experimentally demonstrated that the fiber laser can easily be switched between the operation modes. The results may find useful applications in optical communication and fiber sensing.     

Tight focusing of a double-ring-shaped, azimuthally polarized beam

We study the focusing properties of a double-ring-shaped azimuthally polarized beam through an annular high NA objective lens. It is shown that a subwavelength focal hole (～0.5λ) with a quite long depth of focus (～26λ) is achieved near the focus. This kind of nondiffracting focal hole is called dark channel, which may have applications in atom optical experiments, such as with atomic lenses, atom traps, and atom switches.     

Effect of nonlinear gradient terms on pulsating,erupting and creeping solitons

The effect of nonlinear gradient terms on the pulsating, erupting and creeping solitons, respectively, of the cubic–quintic complex Ginzburg–Landau equation is investigated. It is found that the nonlinear gradient terms result in dramatic changes in the soliton behavior. They eliminate the periodicity of the pulsating and erupting solitons and transform them into fixed-shape solitons. This is important for potential use, such as to realize experimentally the undistorted transmission of femtosecond pulses in optical fibers. However, the nonlinear gradient terms cause the creeping soliton to breathe periodically at different frequencies on one side and spread rapidly on the other side. PACS 47.20.Ky; 05.70.Ln; 03.40.Gc; 42.65.Tg     

大学物理实验网络教学平台的建构与应用

利用多媒体开发软件及网页制作工具,建构了一个大学物理实验网络教学平台。介绍了此平台的详细设计方案,以及它所具有的功能和特点,探索大学物理实验多媒体网络辅助教学的新应用。     

燃烧法合成Ln2O2 S:RE3+(Ln=Gd,La;RE=Eu,Tb) X射线荧光粉及发光性能

采用燃烧合成法,以稀土硝酸盐和二硫代乙二酰胺为反应物,通过控制两者的摩尔比例,在点燃温度为300—350℃时,制备了掺杂不同浓度稀土激活剂离子的硫氧化物X射线荧光粉。分别以X射线衍射(XRD)、扫描电子显微镜(SEM)、光致发光(PL)光谱及X射线激发的发光(XEL)光谱对样品进行了表征。XRD分析表明,当热处理温度低于500℃时,可得到单一相的硫氧化物X射线荧光粉,这就避免了高温烧结的缺点;而当烧结温度较高时,开始有硫酸氧化物出现。从SEM图像中可以看到荧光粉粉末具有疏松和多孔连续的三维的网络块状结构,但其初级粒子尺寸较小,均小于50nm,这在一定程度上,可以提高成像系统的空间分辨率。PL光谱分析表明,所制备的荧光粉样品分别呈现出Eu^3 ,Tb^3 离子的特征发射。XEL光谱结果表明,尽管它与光致发光的激发原理不一样,但同样呈现出Eu^3 ,TB^3 离子的特征发射;这些样品本身对X射线的吸收系数及掺杂浓度不一样,因此它们的光发射效率也有所差别。     

Spectral studies on erbium doped potassium lithium tantalate niobate single crystal grown by the step-cooling technique

An erbium doped K_0.603Li_0.397Ta_0.428Nb_0.572O₃ single crystal was grown by the step-cooling technique. The crystal has a tetragonal tungsten bronze-type structure at room temperature with a Curie temperature of 303°C. There are Er ions characteristic absorption bands around 449, 485, 521, 550, and 652 nm in the visible absorption spectrum. Upconversion fluorescence spectra and power dependence centered at 527 nm, 548 nm, and 660 nm under 975 nm excitation were measured at room temperature. Decay lifetimes of the 548 nm and 660 nm emission bands are 281 μs and 420 μs, respectively. The lifetime of the 548 nm emission corresponding to the transition of ?⁴ S _3/2→⁴ I _15/2 is ten times the lifetime of the same transition of Er³⁺ in LiNbO₃ crystal and twice in KYb(WO₄)₂ crystal. The crystal might become a promising upconversion laser material. The upconversion mechanism of Er³⁺ in the sample was discussed based on decay curves and pump power dependence analyses in this work.     

轴流式水轮机转轮流固耦合计算

在利用轴流式水轮机全流道三维非定常湍流数值计算和利用弹性力学非稳态有限元法计算轴流式水轮机转轮叶片动态的应力和应变的基础上,利用弱耦合算法完成了轴流式水轮机在有粘有旋条件下的流固耦合计算,得到了叶片的动态应力和动态应变,并对结果进行了讨论.     

Controllable synthesis and shape-dependent photocatalytic activity of ZnO nanorods with a cone and different aspect ratios and of short-and-fat ZnO microrods by varying the reaction temperature and time

ZnO nanorods with a cone and different aspect ratios and short-and-fat ZnO microrods were synthesized via a hydrothermal reaction of Zn with Zn(CH₃COO)₂ and H₂O. The control over these ZnO nanocrystals with a wurtzite structure and different shapes was achieved by adjusting only the reaction temperature and time. A possible kinetic mechanism was proposed to account for the growth of these ZnO nanocrystals with different shapes. Photocatalytic activities of ZnO nanocrystals with distinctive shapes in the degradation of methyl orange were investigated. The results indicate that the photocatalytic ability of the ZnO nanorods with a cone and different aspect ratios is stronger than that of the short-and-fat microrods.     

一种投影式激光方向测量方法

为了在激光告警中实现全方位角度探测,且达到一定的探测精度,提出了一种投影式激光方向测量方法.通过计算激光照射在参量给定的遮光板上形成的投影量.求解在探测器上由不同探测象限产生的不同的探测电流的比值.再根据投影面积的比值与角度一一对应的关系可事先编码的原理.由对应程序判断激光入射方向.在软件Matlab仿真中计箅得到产生最小分辨率的四个极限角度分别为(0°,90°)、(33°,21°)、(33°,69°)、(45°,90°),并由实验得到最小分辨电压为0.05 V.通过仿真计算与实验数据证明该设计可达到最小识别角度1°的探测要求.