铌钛超导体的非合金化制备

本文研究了Nb片和Ti片在不同温度下的扩散行为,并利用Nb片和Ti片交替组配加工,经过扩散反应制备出了NbTi超导线.运用扫描电镜(SEM)观察了Nb/Ti界面的扩散形态及微结构,并对热处理工艺的合理选择进行了讨论.结果表明:经800℃,5小时扩散可得到厚度最大,Ti含量最高的NbTi超导相.该工艺制备出的NbTi超导线材的临界电流密度Jc可达到2800A/mm2(5T、4.2K)和4200A/mm2(3T、4.2K),与传统工艺制备出的超导体的性能相当.     

铌钛超导体的非合金化制备

本文研究了Nb片和Ti片在不同温度下的扩散行为，并利用Nb片和Ti片交替组配加工，经过扩散反应制备出了NbTi超导线．运用扫描电镜（SEM）观察了Nb／Ti界面的扩散形态及微结构，并对热处理工艺的合理选择进行了讨论．结果表明：经800℃，5小时扩散可得到厚度最大，Ti含量最高的NbTi超导相．该工艺制备出的NbTi超导线材的临界电流密度Jc可达到2800A／mm^2（5T、4．2K）和4200A／mm^2（3T、4．2K），与传统工艺制备出的超导体的性能相当．     

NbTi50/Cu复合超导材料中Cu-Ti扩散层的研究

NbTi50/Cu的加工性能受加工过程中由Cu和Ti的互扩散形成的脆性Cu-Ti化合物所影响.为选择最佳的热处理制度和加工工艺,我们用高温金相观察了在高温和加压条件下扩散层的行为.发现扩散层的厚度与时间的平方根成正比.电子探针测到它随温度按指数规律变化.对单芯和多芯导体作机械性能(σ_b和δ％)测量表明:400—500℃的热处理温度是合适的。Nb-Ti-Cu的共晶点为780℃.     

不同Ti含量对NbTi超导体临界电流密度的影响

利用Nb片和Ti片交替组配加工,经扩散反应制备了Ti含量从43WT%到57WT%之间的三种不同成份的NbTi超导线.测量了三种不同成份的临界电流密度Jc,讨论了在磁场下不同Ti含量对NbTi线临界电流密度Jc的影响,并对磁通钉扎机制进行了分析.通过扫描电镜(SEM)观察了Nb/Ti界面扩散形态及微结构,并运用多源标度分析法[1]对不同成份的NbTi超导线进行了磁通钉扎力密度随磁场变化曲线的拟合.结果表明:随着含Ti量的增加,其临界电流密度在低场时很高,而在高场时的性能偏低,且下降迅速,而含Ti量低的超导线在高场时的性能更具有优势;超导线在不同磁场下的性能是由点钉扎和面钉扎两种钉扎机制共同作用决定的.     

多芯NbTi超导复合线中扩散隔层的研究

研究了两次组合工艺中NbTi与Cu间的扩散隔层对NbTi—Cu界面扩散和复合线性能的影响.发现,NbTi芯棒外加入Nb、Ni、CuNi10、CuNi30等扩散隔层后能有效地减少Nb-Ti-Cu化合物的生成.但在有Ni元素的试样中同时存在Nb-Ti-Ni等高硬度扩散生成物;加入Nb扩散隔层后能减缓了它们间的扩散,又不生成高硬度化合物,因而复合线的塑性极好.实验结果表明,采用NbTi-Nb-Cu复合锭坯在挤压加热温度升高到600℃的情况下,仍可得到塑性良好、载流能力高的多芯超导复合线.     

热等静压对NbTi/Cu多芯超导线加工过程的影响

采用传统方法生产的NbTi/Cu多芯超导线在生产芯数较多的超导线时存在填充系数较大的问题,这直接影响了芯丝的整齐排布,所以组装完成后加入热等静压过程.研究了经过热等静压和未经过热等静压的NbTi/Cu多芯超导线的加工性能.经过试验证明,经过100～150MP,2小时热等静压处理的NbTi/Cu多芯超导线坯锭在加工过程中具有良好的加工性能,提高了超导线复合坯锭的成品率;而未经过热等静压处理的NbTi/Cu多芯超导线坯锭加工性能较差,坯锭内部缺陷较多.     

NbTi-Cu界面扩散对多芯NbTi超导复合线的机械性能和载流能力的影响

研究了用不同挤压加热条件制得的芯径小于10μm的NbTi-cu多芯超导复合线的界面扩散情况及线材的机械性能和载流能力.发现NbTi-Cu界面存在互扩散现象,元素的扩散速度按Nb、Ti、Cu次序递增,并随温度升高而加剧.扩散物为硬度比基体高得多的Nb-Ti-Cu复杂化合物.研究指出:附着在界面上的硬而脆的扩散物颗粒及无氧铜的“污染”是导致复合线的机械性能、载流能力和稳定性下降的重要原因。实验证明:要制得芯径小于10μm的多芯NbTi超导复合线,必须严格控制其界面扩散程度.     

范性形变对NbTi合金超导转变温度的影响

研究了时效热处理的Nb50wt％Ti和Nb46.5wt％Ti合金在经历不同程度最终冷变形后,它们的超导转变温度的变化。研究发现:当最终真应变≥2.5时,NbTi合金(420℃×40h三次热处理)的超导转变温度随最终真应变增加而线性下降。针对该实验结果,本文在理论机制上进行了探讨。     

Nb-50wt%Ti超导合金的临界电流及钉扎机构

采用多次时效工艺制成了最佳性能的NbTi 50超导多芯线.给出了在4.2 K下,场强接近B_c_2时的临界电流,以及透射电镜的观察结果.结合上述结果对其中的磁通钉扎机构作了详细的讨论.从而弄清了多次时效工艺的理论根据.作者指出:为了进一步提高NbTi 50合金的高场临界电流密度J_c,除了有细化的亚带和αTi沉淀外,还必须控制高场下磁通的切交流动.     

(111)择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜的制备及研究

选用不同浓度的Pb(Zr0.52Ti0.48)O3溶胶,用Sol-gel法在Pt/Ti/SiO2/Si基片上沉积一层厚度不同的Pb(Zr0.52Ti0.48)O3(PZT52)过渡层,经400℃烘烤、550℃退火等程序后,再用Sol-gel法在PZT52过渡层上沉积Pb(Zr0.52Ti0.48)O3薄膜.XRD分析表明,有PZT52过渡层的Pb(Zr0.52Ti0.48)O3薄膜具有(111)择优取向的钙钛矿结构,且随着过渡层厚度的增加,Pb(Zr0.52Ti0.48)O3薄膜的(111)择优取向程度越高.SEM分析表明,当PZT52过渡层的厚度达到14nm以上,Pb(Zr0.52Ti0.48)O3薄膜结晶程度得到明显改善,平均晶粒尺寸大大增加.介电、铁电性能测试表明,与没有过渡层的Pb(Zr0.52Ti0.48)O3薄膜相比,有PZT52过渡层的Pb(Zr0.52Ti0.48)O3薄膜具有较大的介电常数和剩余极化强度,而介电损耗则较小.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.