北京大学高平均流强光阴极电子枪驱动激光系统

DC-SC超导光阴极注入器将直流光阴极电子枪和超导加速腔结合在一起,其特点之一是适合于提供高平均流强电子束.文中介绍了直流光阴极电子枪的驱动激光系统的研制.该驱动激光系统的主机为瑞士TBP公司的GE-100-XHP型激光器,是采用可饱和吸收镜技术的被动锁模激光器,其工作晶体为Nd:YVO₄,输出波长为1064nm,脉冲重复频率为81.25MHz,平均功率10W.该驱动激光系统配套的CLX-1100同步控制器可以将激光脉冲与射频参考信号严格锁定,随机抖动不大于1ps.根据使用要求,作者研制了高效的激光倍频器,获得了大于1W的266nm紫外激光.同时,激光到光阴极的传输设计中,采用了傅立叶光学技术,在紫外激光功率650mW左右的条件下,从自行研制的Cs₂Te光阴极上实现了大于500μA的光电流引出     

Lixiscope及几种材料的X射线吸收特性研究

介绍Lixiscope及模拟系统,测量了钛片(Ti)、玻璃板、镍片(Ni)和铝片(Al)对峰值能量为40keV的X射线的吸收持性,指出平板式X射线像增强器输入窗口材料选择的原则。     

Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

紫外光对MCP增益特性测量的影响

介绍用ＵＶ光电法测量ＭＣＰ电子增益时，ＵＶ透过金薄膜的附加输出给测量带来的影响，给出了实验结果并进行初步分析，最后指出确保增益测量结果可靠性的途径。     

改进的TESLA式高阶模衰减器的实验研究

讨论了TESLA型高阶模耦合器的改进, 对所设计的改进型TESLA式高阶模耦合器进行实验, 对理论计算与实验结果进行详细分析, 结果表明改进的高阶模耦合器理论计算和实验结果符合得较好.     

2-cell超导腔的高阶模分析

 阐述了2-cell Telsa腔的设计。用3维程序HFSS分析了其高阶模的特点，给出了高阶模的主要参数频率、品质因数、分路阻抗以及模式的电场分布，并且π模的电场分布与Superfish的模拟结果相比较，两者是一致的。最后，简要分析了各高阶模对电子加速的影响，分析表明高阶模降低了电子加速效率和束流的稳定性。     

Concerted Ring Opening and Cycloaddition of Chiral Epoxy Enolsilanes with Dienes

Silyl‐triflate‐catalyzed (4+3) cycloadditions of epoxy enolsilanes with dienes provide a mild and chemoselective synthetic route to seven‐membered carbocycles. Epoxy enolsilanes containing a terminal enolsilane and a single stereocenter undergo cycloaddition with almost complete conservation of enantiomeric purity, a finding that argues against the involvement of oxyallyl cation intermediates which have been previously proposed for these types of reactions. Reported are theoretical and experimental investigations of the cycloaddition mechanism. The major enantiomers of the cycloadducts are derived from S_N2‐like reactions of the silylated epoxide with the diene, in which stereospecific ring opening and formation of the two new C? C bonds occur in a single step. Calculations predict, and experiments confirm, that the observed small losses of enantiomeric purity are traced to a triflate‐mediated double S_N2 cycloaddition pathway.     

Hydrothermal synthesis,crystal structure and photoluminescence of two homochiral zinc(II) coordination polymers

Metal–organic frameworks (MOFs) have potentially useful applications and an intriguing variety of architectures and topologies. Two homochiral coordination polymers have been synthesized by the hydrothermal method, namely poly[(μ‐N‐benzyl‐L‐phenylalaninato‐κ⁴O,O′:O,N)(μ‐formato‐κ²O:O′)zinc(II)], [Zn(C₁₆H₁₆NO₂)(HCOO)]_n, (1), and poly[(μ‐N‐benzyl‐L‐leucinato‐κ⁴O,O′:O,N)(μ‐formato‐κ²O:O′)zinc(II)], [Zn(C₁₃H₁₈NO₂)(HCOO)]_n, (2), and studied by single‐crystal X‐ray diffraction, elemental analyses, IR spectroscopy and fluorescence spectroscopy. Compounds (1) and (2) each have a two‐dimensional layer structure, with the benzyl or isobutyl groups of the ligands directed towards the interlayer interface. Photoluminescence investigations show that both (1) and (2) display a strong emission in the blue region.     

A turn-on fluorescent probe for selective and sensitive detection of hydrogen sulfide

An imidazolethione based turn-on fluorescent probe was synthesized for the detection of hydrogen sulfide, a biologically relevant molecule and an important air pollutant. The probe rapidly and selectively reacted with hydrogen sulfide to produce a strongly fluorescent product, resulting in the fluorescence enhancement of the system. The detection limit was determined to be 30 nM at the probe concentration of 1.0 μM. An indicating paper for visual detection of hydrogen sulfide gas has been fabricated by immobilizing the probe on a piece of appropriate paper substrate, and the detection limit of the visual method reached as low as 0.7 ppm. Moreover, the fluorescence turn-on/off of the system showed good reversibility when exposed alternately to hydrogen sulfide and mercuric ion, which was utilized to make an INHIBIT logic circuit for the presence of the two species.