1.6kW全光纤掺镱激光器

高功率全光纤连续激光器以其转换效率高、光束质量好、热控管理方便和结构紧凑灵活等优点,成为国际激光技术领域的研究热点之一。最近,清华大学光子与电子技术研究中心成功实现了全光纤连续激光器1.63kW激光输出。高功率全光纤激光器采用种子源加两级级联放大器方案,结构原理如图1所示。光纤种子源模块由LD抽运耦合器、双     

超热电子的产生与输运背向辐射的实验研究

报道了在100TW fs激光器上采用电子磁谱仪和光学CCD积分成像相机分别对激光-固体靶相互作用在靶背方向产生的超热电子能谱及其光学渡越辐射进行的测量。能谱测量结果显示：超热电子能谱呈单温类-麦克斯韦分布,拟合的温度为107keV;光学渡越辐射(OTR)测量结果显示：OTR是由于超热电子输运穿越固体靶所致,而辐射区域呈圆盘状、有发散角、有光强分布;如果考虑超热电子的产生和加热机制,则占主导地位的加热机制是共振吸收对电子的加热。     

超热电子的产生与输运背向辐射的实验研究

报道了在100TW fs激光器上采用电子磁谱仪和光学CCD积分成像相机分别对激光-固体靶相互作用在靶背方向产生的超热电子能谱及其光学渡越辐射进行的测量.能谱测量结果显示:超热电子能谱呈单温类-麦克斯韦分布,拟合的温度为107 keV;光学渡越辐射(OTR)测量结果显示:OTR是由于超热电子输运穿越固体靶所致,而辐射区域呈圆盘状、有发散角、有光强分布;如果考虑超热电子的产生和加热机制,则占主导地位的加热机制是共振吸收对电子的加热.     

6-疏基嘌呤,硫唑嘌呤,8-氮杂鸟嘌呤的滤纸基质室温燐光法研究

建立了 6 巯基嘌呤、硫唑嘌呤和 8 氮杂鸟嘌呤 3种抗癌嘌呤化合物的滤纸基质室温光分析新方法。详细探讨了影响其室温光发射的各种因素。该方法的线性范围、检出限、精密度分别为 6 巯基嘌呤2 0～ 4 .0× 10 2 μmol/L ,1.3μmol/L ,4 .1% ;硫唑嘌呤 2 .0～ 6 .0× 10 2 μmol/L、1.2 μmol/L、3.8% ;8 氮杂鸟嘌呤1.1～ 2 .2× 10 2 μmol/L、7.4× 10 -2 μmol/L、1.3%。用该方法进行尿液中嘌呤化合物的回收测定 ,回收率为 96 .2 %～ 10 1.7% ;进行 6 MP在药片中的回收测定 ,回收率为 96 .2 %～ 10 2 .1%。     

用于帧头识别的全光比较器的最新研究进展

就全光比较器的功能模型及性能指标提出见解.综述了用于帧头识别的光比较器最新研究进展,阐述了不同结构的光比较器的原理、优缺点,以及进一步改进的可能性.     

Ⅰ-Ⅱ复合型裂纹等ε_θ线体积应变能断裂准则

利用裂纹尖端附近能量的变化去建立Ⅰ-Ⅱ型裂纹断裂准则是有效的方法之一。本文利用Ⅰ-Ⅱ型裂纹尖端周向应变ε_θ所围成的区域内体积应变能的变化,建立了基于等ε_θ线内体积应变能Ⅰ-Ⅱ复合型裂纹断裂准则;讨论了Ⅰ-Ⅱ复合型裂纹断裂中的两种应力状态下的临界荷载比值;并将准则的预测值与最大正应力理论和应变能密度因子准则预测值以及已有部分材料的实验结果进行了对比分析。结果表明,本文的理论预测值与铬锰钢、混凝土材料以及PMMA材料的实验值相比基本吻合。说明该准则对于工程材料的复合型断裂问题分析具有一定的理论意义和参考价值。     

冲击高压下硝基甲烷的拉曼光谱及其结构稳定性

在单次冲击压缩实验中,借助新建的瞬态拉曼光谱技术实现了对液态硝基甲烷冲击拉曼光谱的原位观测,来探究该样品分子在冲击波作用下的结构稳定性。实验发现,在10.6GPa的冲击加载下硝基甲烷的拉曼特征峰仅发生了蓝移和展宽,而在观测波段未发现化学变化产生的迹象。这一结果否定了文献所报道的硝基甲烷在6GPa~8.5GPa的单次冲击压力区间内发生了化学反应的推论,同时也证实了在10.6GPa的冲击压力下硝基甲烷分子在约为516ns的压缩时间内能够保持其结构的稳定。     

借助探究活动实现深度学习的措施研究

随着“双减”政策的落实,提高课堂教学效率成了初中教育工作者热衷的话题.探究活动的应用,不仅能培养学生的直观想象素养,还能让深度学习真实发生.本文中从“情境创设,引发探究性思考;实验探究,引发认知冲突;设计问题串,发散数学思维”三方面具体展开阐述.     

Electrical Resistivity of Silane Multiply Shock-Compressed to 106 GPa

Since Wigner et al. proposed that hydrogen would become metallic under sufficient pressure compres- sions in 1935,scientists have paid their attention on making metallic hydrogen at high pressures, and con- siderable progresses were made in theoretical and ex- perimental researches. Nellis et al. observed that the electrical resistivity of fluid hydrogen declined by several orders of magnitude when liquid hydrogen was multiply shocked to 140 GPa, and concluded that fluid hydrogen underwent metallization phase tran- sition from semiconductor to metal in their experi- ments. Although further researches should be carried out to distinguish the highly conductive state and the metallic state of fluid hydrogen, researchers have made great efforts to find new technical approaches to de- crease the threshold pressure for hydrogen metalliza- tion. For this purpose, hydrogen-rich compounds at- tract much attention. Some researchers believed that non-hydrogen elements in those compounds may re- duce, to some extent, the activation energy of met- allization by the effect of chemical pre-compression. Silane, a typical hydrogen-rich compound of group IV hydrides, has been the subject of most of the theoretical and experimental research so far, and it was also expected to be a potential candidate for a high-To superconductor at high pressure research.[61 Compared to hydrocarbons,[71 the chemical bonds in the silane molecule are theoretically more sensitive to pressure and temperature. At sufficiently high pres- sure and temperature, the fluid silane possibly be- comes some metallic alloy consisting of hydrogen and silicon elements. Theoretical calculations showed thatthe metallic transition for the silane system may oc- cur even below 100 GPa, while there are also some other later articles that claimed that silane would re- main an insulator up to around 200 GPa and became metallic and supconducting at 220 GPa with a theo- retical Tc of 16 K. Recently, Eremets et al. have re- ported that silane can transform to metal at 50 GPa,