915 nm单频Nd∶YAG晶体衍生光纤激光器

报道了一种基于Nd∶YAG晶体衍生光纤(NYDF)的915 nm单频光纤激光器.使用掺杂原子数分数为2.5％的Nd∶ YAG晶体作为纤芯材料,高纯度石英管作为包层材料,利用熔芯法制备Nd∶ YAG晶体衍生光纤,其传输损耗为8 dB/m,在915 nm处其增益系数为1.16 dB/cm.基于Nd∶YAG晶体衍生光纤,实现了一个稳定的915 nm单频光纤激光器,信噪比大于50 dB.实验结果表明Nd∶ YAG晶体衍生光纤有潜力应用于890～920 nm单频激光器.     

单延迟三阶,四阶相关函数确定超短光脉冲形状

本文提出用单延迟三阶、四阶相关函数,经傅里叶交换获得脉冲形状的方法.在实验上用克尔快门测量了YAG被动锁模激光脉冲的三阶和四阶相关函数,并用该方法获得脉冲形状.文中还讨论了脉冲对称性对恢复脉冲的影响.     

5-Fluorouracil derivatives ⅩⅩⅢ. Synthesis and antitumor activities of 1-carbamoyl-5-fluorouracils having aromatic ring

In order to get good antitumor agents especially better than 5-fluorouracil,tegafur and l-hexylcarbamoyl-5-fluorouracil (HCFU),fourty nine 1-carbamoyl-5-fluorouracil having aromatic ring were synthesized from 5-fluorouracil and isocyanates or amines.Antitumor activity was tested in the L-1210 tumor system,and 5 compounds gave better value of therapeutic ratio than 5-fluorouracil,tegafur,HCFU.l-(4-Methoxybenzylcarbamoyl)-5-fluorouracil gave the best result.     

Dislocation formation and twinning from the crack tip in Ni3Al: molecular dynamics simulations

The mechanism of low-temperature deformation in a fracture process of L12 Ni3Al is studied by molecular dynamic simulations.Owing to the unstable stacking energy,the [01ˉ1] superdislocation is dissociated into partial dislocations separated by a stacking fault.The simulation results show that when the crack speed is larger than a critical speed,the Shockley partial dislocations will break forth from both the crack tip and the vicinity of the crack tip;subsequently the super intrinsic stacking faults are formed in adjacent {111} planes,meanwhile the super extrinsic stacking faults and twinning also occur.Our simulation results suggest that at low temperatures the ductile fracture in L12 Ni3Al is accompanied by twinning,which is produced by super-intrinsic stacking faults formed in adjacent {111} planes.     

埋置量子点应力分布的有限元分析

通过衬底材料和外延材料的交替生长方式制备出多层排列的自组装量子点超晶格结构.这些埋置量子点的应力/应变场影响着它们的光电性能、压电性能以及力学稳定性.基于各向异性弹性理论的有限元方法,研究了埋置金字塔形应变自组织Ge/Si半导体量子点的应力/应变分布以及流体静应变和双轴应变分布,并与非埋置量子点的应力/应变分布做了比较,指出了它们之间的异同以及覆盖层对量子点应力/应变分布的影响. 关键词： 量子点 应力分布 应变分布     

晶体光纤及晶体衍生光纤制备与应用综述

晶体光纤是一种新型的高性能光纤材料,具有稀土离子掺杂浓度高、传光性好、耐高温、耐腐蚀等优点.晶体光纤在激光及传感方面具有巨大的应用潜力,然而至今还没有成功制备出真正意义上的同时具有晶体纤芯和晶体包层的小芯径晶体光纤.与传统的玻璃光纤相比,晶体光纤的制备工艺更加复杂,如何对晶体光纤制备工艺进行完善和创新是当前需要解决的重要问题.为了探索提高晶体光纤质量的途径,本文以晶体光纤的四种制备技术为主线,回顾了晶体光纤及其制备方法的发展历程,讨论了每种制备方法的局限性,对晶体光纤目前的应用状况进行了总结,并对其未来发展趋势进行了展望.     

Modelling of passively Q-switched lasers with intracavity Raman conversion

We present a model of passively Q-switched Raman lasers by utilizing the rate equations. The intracavity fun-damental photon density, Raman photon density and the initial population-inversion density of the gain medium are assumed to be of Gaussian spatial distributions. These rate equations are normalized by introducing some synthetic parameters and solved numerically, and a group of general curves are generated. Prom these curves we can understand the dependence of the Raman laser pulse characteristics on the parameters about the pumping, the gain medium, the Raman medium and the resonator. An illustrative calculation for a passively Q-switched Nd^3＋：GdVO4 self-Raman laser is presented to demonstrate the usage of the curves and related formulas.[第一段]     

Finite element analysis of stress and strain distributions in InAs/GaAs quantum dots

In this paper, we perform systematic calculations of the stress and strain distributions in InAs/GaAs truncated pyramidal quantum dots (QDs) with different wetting layer (WL) thickness, using the finite element method (FEM). The stresses and strains are concentrated at the boundaries of the WL and QDs, are reduced gradually from the boundaries to the interior, and tend to a uniform state for the positions away from the boundaries. The maximal strain energy density occurs at the vicinity of the interface between the WL and the substrate. The stresses, strains and released strain energy are reduced gradually with increasing WL thickness. The above results show that a critical WL thickness may exist, and the stress and strain distributions can make the growth of QDs a growth of strained three-dimensional island when the WL thickness is above the critical value, and FEM can be applied to investigate such nanosystems, QDs, and the relevant results are supported by the experiments.     

近垒和垒下重离子熔合裂变碎片各向异性的异常

系统总结了研究近垒和垒下重离子熔合裂变反应碎片各向异性的异常的结果 ,提出一个新的预平衡裂变模型,成功地解释了碎片各向异性的异常现象 .但对异常宽峰结构不能说明 ,有待进一步研究. Systematic summary on the anomalous anisotropies of fission fragments in near and sub barrier fusion fission reactions is presented. A new version of the preequilibrium fission model is put forward to explain the anomalous anisotropies of fission fragments, except the bump of anomaly. Further study is still needed.