基于同步辐射的快速扫描X射线微束荧光成像方法

在上海光源硬X射线微聚焦光束线站(BL15U1)上, 基于EPICS软件平台, 集成运动控制, 光强探测, 荧光探测等功能, 实现了"飞行"模式 (on-the-fly) X射线扫描微束荧光成像方法. 用"飞行"扫描X射线荧光成像法获得了标准镍网, 以及微量元素Cu, Zn,K, Fe在样品老鼠脾内的分布图像, 结果显示该方法不但在速度上有了极大的提高, 而且获得的元素分布图像具有高质量. 关键词： 快速扫描X射线微束荧光成像 同步辐射 微量元素分布     

Anomalous lattice dynamics near the ferroelectric instability in PbTe

A recent report of highly unusual ferroelectric fluctuations in PbTe by E. S. Bo?in et al. [Science 330, 1660 (2010)] raises fundamental questions about the nature of underlying lattice dynamics. We show by first-principles calculations that the reported results can be attributed to abnormally large-amplitude thermal vibrations that stem from a delicate competition of dual ionicity and covalency, which puts PbTe near ferroelectric instability. It produces anomalous properties such as partially localized low-frequency phonon modes, a soft transverse optical phonon mode, and a positive temperature coefficient for the band gap. These results account for experimental findings and resolve the underlying atomistic mechanisms, which have broad implications for materials near dynamic instabilities.     

High-power 880-nm diode-directly-pumped passively mode-locked Nd:YVO₄ laser at 1342 nm with a semiconductor saturable absorber mirror

A high-power 880-nm diode-directly-pumped passively mode-locked 1342 nm Nd:YVO? laser was demonstrated with a semiconductor saturable absorber mirror (SESAM). The laser mode radii in the laser crystal and on the SESAM were optimized carefully using the ABCD matrix formalism. An average output power of 2.3 W was obtained with a repetition rate of 76 MHz and a pulse width of 29.2 ps under an absorbed pump power of 12.1 W, corresponding to an optical-optical efficiency of 19.0% and a slope efficiency of 23.9%, respectively.     

Design and end chamfer simulation of PEFP beam line curved dipole magnets

The design, fabrication and field measurement of 11 DC curved dipole magnets for the PEFP Beam Line have been completed. In this paper, a design method for a complex end chamfer using OPERA-3D is proposed. The conventional method for estimating chamfer shape is extended and applied to a curved dipole magnet by a coordinate transformation. Using the interface with CAD software, the complex end chamfer is modeled and fully determined by 3D simulation to meet the field uniformity requirement. The magnetic field measurement results are in good agreement with the simulation. The design considerations, field simulation results, end chamfer development process and measurement results are presented in detail.