Generation of 207-femtosecond pulses from a ytterbium figure-of-eight fibre laser

We report the generation of 207-fs pulses with 1.2mW average power at 1036 nm directly from a passively mode-locked Yb-doped fibre laser with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. These results imply a 4-fold reduction in pulse duration over previously reported figure-of-eight cavity passively mode-locked Yb-doped fibre lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0MHz. On the other hand, this laser offers a cleaner spectrum and greater stability and is completely self-starting.

高电荷态离子~(207)Pb~(36+)与金属Nb表面作用产生的二次离子产额

本文报道了利用兰州重离子加速器国家实验室的ECR离子源引出的高电荷态离子207Pb36+入射到金属Nb表面产生的二次离子的实验测量结果.实验发现,二次离子产额Y随入射初动能Ek的增加有先增加后减小的关系,在初动能为576 keV时二次离子产额达到最大.通过对实验点做高斯拟合发现,曲线峰值对应的入射初动能为602 keV.分析表明,这是势能沉积作用与线性级联碰撞过程协同作用的结果.高电荷态离子本身携带的高势能沉积在靶表面引起势能溅射,促进了二次离子的发射;而主导二次离子溅射的过程是动能溅射,它与靶表面的动量沉积(核能损)过程密切相关.

高电荷态离子~(207)Pb~(q+)(24≤q≤36)与Si(110)固体表面作用的电子发射研究

报道了利用兰州重离子加速器国家实验室ECR源引出的高电荷态离子207Pbq+(24≤q≤36)入射到Si(110)表面产生的电子发射的实验测量结果.结果表明,高电荷态离子与固体表面相互作用产生的电子发射产额Y与入射离子的电荷态q、入射角度ψ和入射能量E都有很强的关联.首次发现,电子发射产额Y与入射角度ψ间有接近1/tanψ的关系.理论分析认为,这些过程与基于经典过垒模型的势能电子发射过程密切相关.

~(207)Rn能级结构的实验研究

利用能量为 85— 95MeV的1 6O束流 ,通过1 96Pt(1 6O ,5n) 2 0 7Rn反应布居了2 0 7Rn的高自旋态 .实验进行了γ射线的激发函数、γ射线的单谱、衰变谱和γ γ t符合测量 .建立了由 1 7条γ射线组成的2 0 7Rn能级纲图 ,并且基于实验测量的DCO系数建议了各能级的自旋值 .用一个f5 2 价中子空穴与2 0 8Rn核芯耦合定性地解释了2 0 7Rn的低位激发态

Electron emission induced by the interaction of highly charged ions Pb-207(q+) (24 <= q <= 36) with solid surface of Si(110)

The electron emission induced by highly charged ions Pb-207(q+) (24 <= q <= 36) interacting with Si(110) surface is reported. The result shows that the electron emission yield Y has a strong dependence on the projectile charge state q, incidence angle psi and impact energy E. In fitting the experimental data we found a nearly 1/tan psi dependence of Y. Theoretical analysis shows that these processes are closely related to the process of potential electron emission based on the classical over-the-barrier model.

藏东及滇东南新生代钾质岩浆作用及其深部制约

The dissertation focuses on the petrology, geochemistry of the volcanic rocks in east Tibet and southeast Yunnan. It lucubrates the Magmatic process, forming mechanism and the possible tectonic settings of the volcanic rocks. The volcanic rocks of Nangqen basin in east Tibet, Qinghai province are mainly Cenozoic intermediate-acid shoshonites. The rocks are LREE enriched and the LREE/HREE = 3～34; (La/Yb)_N = 18.17-53.59, and ΣREE 222～1260μg/g. There are no Eu anomaly, and Nb, Ta, Zr, Hf, Ti are markedly depleted. The isotopic composition is ~(87)Sr/~(86)Sr = 0.70497～0.70614, ~(206)Pb/~(204)Pb = 18.622～18.974, ~(208)Pb/~(204)Pb = 38.431～38.996, ~(207)Pb/~(204)Pb = 15.511～15.613, respectively. K-Ar age of the whole rocks and the single mineral are between 32.0-36.5Ma. Based on the trace elements and isotopic elements, we get the conclusion that the partial melting is one of the dominated forming mechanisms for the volcanic rocks in Naneqen basin. The magma did not experience the crustal contamination en route to the surface; however, the complex mixture took place in the upper mantle before the melt was formed. There are at least two kinds of mixed sources that can be identified. The basalt in southeast Yunnan province is studied. They are distributed in Maguan, Tongguan, and Pingbian County, which is located on the both sides of the Red River belt, and the ultrabasic xenolith are cursory introduced. The volcanic rocks belongs to the alkali series, which can be subdivided into trachybasalt and basanite(Ol normal molecule >5). The volcanic rocks are characteristics by high Ti and low Mg#. According to the magma calculation model, the original rocks of the basalt in southeast Yunnan province are Spinel Lherzolite in Tongguan, Garnet Lherzolite in Pingbian and Maguan, while Togguan undergoes 2-5 percent and percent of partial melting, whereas volcanism in Maguan and Pingbian was so complex to calculate. The fractional crystallization took place during the magma evoltion in southeast Yunnan. The basalt is enriched in LREE with LREE/HREE=9.23-20.19. All of the trace elements display weak Nb, Ta peak, and the depletion of Zr, Hf and Ti in Maguan and pingbian represent the presence of Garnet in the source. The composition of the isotope ratio are ~(87)Sr/~(86)Sr = 0.70333-0.70427, ~(143)Nd/~(144)Nd = 0.512769-0.512940, ~(206)Pb/~(204)Pb = 18.104-18.424, ~(207)Pb/~(204)Pb = 15.483 -15.527; ~(208)Pb/~(204)Pb = 37.938-38.560, respectively, which shows the characteristics of the HIMU type OIB. The volcanic rocks of the southwest Yunnan are derived from the enriched, OIB type mantle sources by synthesizing all the data from trace and isotope elements. It is similar to that of the volcanic rocks in Hawaii, a typical kind of the mixtures of the recycled oceanic crust plume and depleted asthenosphere. To sum up, the volcanic rocks in southeast Yunnan are formed by the intraplate hotpot volcanism.

Surface Tension and Its Temperature Coefficient of Molten Tin Determined with the Sessile Drop Method at Different Oxygen Partial Pressures

The surface tension of molten tin has been determined by the sessile drop method at The surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the oxygen partial pressure (P-O2) range from 2.85 x 10(-19) to 8.56 x 10(-6) MPa, and its dependence on temperature and oxygen partial pressure has been analyzed. At P-O2 = 2.85 x 10(-19) and 1.06 x 10(-15) MPa, the surface tension decreases linearly with the increase of temperature and its temperature coefficients are -0.151 and -0.094 mNm(-1) K-1, respectively. However, at high P-O2 (3.17 x 10(-10), 8.56 x 10(-6) MPa), the surface tension increases with the temperature near the melting point (505 K) and decreases above 723 K. The surface tension decrease with increasing P-O2 is much larger near the melting point than at temperatures above 823 K. The contact angle between the molten tin and the alumina substrate is 158-173degrees, and the wettability is poor.

Microstructure Study Of Laser Welding Cast Nickel-Based Superalloy K418

Experiments of laser welding cast nickel-based superalloy K418 were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness. The corresponding mechanisms were discussed in detail. Results show that the laser welded seam have non-equilibrium solidified microstructures consisting of Cr-Ni-Fe-C austenite solid solution dendrites as the dominant and some fine and dispersed Ni-3(Al,Ti) gamma' phase as well as little amount of MC needle carbides and particles enriched in Nb, Ti and Mo distributed in the interdendritic regions, cracks originated from the liquation of the low melting points eutectics in the HAZ grain boundary are observed, the average microhardness of the welded seam and HAZ is higher than that of the base metal due to alloy elements' redistribution of the strengthening phase gamma'. (C) 2008 Elsevier B.V. All rights reserved.

NUMERICAL ANALYSIS OF THE FLOWFIELD IN A SUPERSONIC COIL WITH AN INTERLEAVED JET CONFIGURATION AND ITS EFFECT ON THE GAIN DISTRIBUTION

In a supersonic chemical oxygen-iodine laser (COIL) operating without primary buffer gas, the features of flowfield have significant effects on the Laser efficiency and beam quality. In this paper three-dimensional, multi-species, chemically reactive CFD technology was used to study the flowfield in mixing nozzle implemented with a supersonic interleaving jet configuration. The features of the flowfield as well as its effect on the spatial distribution of small signal gain were analyzed.

横流CO_2激光器中介质的流速对激活特性的影响

以横流、放电、CO_2激光器为例,用物理力学的方法,联系器件中流动的非平衡激光介质各能态间传能变化的微观动力学机制,分析研究其输出和激活特性随介质流速变化的规律.