强磁场混合型短周期摇摆器研究

对混合型短周期摇摆器磁场进行了解析求解,给出了与摇摆器周期、间隙、磁块性能、磁场尺寸以及磁极尺寸等相关的二维解析表达式。根据该公式,作者讨论了混合型短周期摇摆器产生强磁场的潜在能力,提出了一系列改进方法,并分别进行了模型实验,实验结果与理论分析相符合。目前,在1cm周期、5mm间隙的短周期摇摆器模型试验中,中心轴峰值磁感应强度已达到0.45T。另外,该短周期摇摆器可进行单磁场磁场调节,最大峰峰值磁场相对误差小于1％。     

永磁类直线阵列摇摆器的磁场计算与场形分析

从电磁场基本理论出发，导出了计算永磁体磁场的基本公式，在此基础上得出了二维和三维永磁体直线周期阵列摇摆器的磁场计算公式。对二维摇摆器进行了场形分析，得到了单组元永磁体直线阵列摇摆器磁场的解析表达式。用此表达式给出了六种典型的单元型摇摆器的场形公式。     

毫米波自由电子激光的数值模拟和实验的比较

从波导管毫米波自由电子激光器的设计要求出发,根据Livermore实验室FRED程序的物理思想,编制了空间三维的数值模拟程序(WAGFEL)。为了检验程序的可靠程度,结合ELF装置的实际参数,进行了数值模拟并和实验结果进行了比较。结果表明,把Wiggler磁场B_w增大300 Gs后,WAGFEL程序的模拟结果和Livermore实验室的实验结果基本符合。模拟使用的全部参数,除B_w增大300Gs外,都是ELF的实际参数。模拟时峰值磁场B_w=4050Gs,实验测量峰值磁场B_w=3720Gs,相差在8％左右。WAGFEL程序可以用来从事毫米波自由电子激光器的设计以及基本物理问题的研究。     

电磁铁摇摆器磁场的二维数值计算

本文根据泊松方程用数值计算给出了电磁铁摇摆器的二维磁场分布,定量地讨论了磁极形状、磁隙大小、周期长短和电流大小等因素对峰值磁场强度的影响,重点讨论了如何根据二维磁场分布选择磁极形状才能提高峰值磁场强度和抑制磁饱和的问题。将计算的二维磁场分布和摇摆器磁场的理想波形相比较,可以帮助我们确定进入摇摆器的束流半径应该控制的范围。在对电磁铁摇摆器磁场二维数值计算的基础上,还探讨了适用ATA电子束的PALADIN摇摆器用于ETA电子束带来的结构设计和材料选择等问题。     

100μmFIR-FEL摇摆器的改进

经过几年实验发现，摇摆器的磁场强度、峰值误差和好场区宽度对束波作用效率有很大影响。为了提高摇摆器性能对摇摆器如下改进：（1）提高磁场强度：永磁块材料采用北京钢研院的钕铁硼N39SH，其风达到11．6kOe（10e≈79．578A／m），B，达到12．3kGs（1Gs=10^-4T），（BH）max为36MGOe；摇摆器周期长度由30mm改为32mm，磁块与磁极宽度的比值由9：6改为11：5；（2）减小峰值误差和增加好场区宽度：改进永磁块、磁极的形状和固定方式，从机械上消除不规则磁块、磁极形状带来的负面影响。通过上述改进可以提高单电子小信号增益与理想增益的比率，即提高整个摇摆器品质。精密的磁场自动测量系统是摇摆器调试过程中所必须的装置，该系统经过改进，具有高精度、高稳定度、可同时监测x、y、z方向磁场值、操作方便等优点，为摇摆器的研制打下良好基础。     

不用导引磁场的虚火花束源拉曼自由电子激光器的数值计算

采用非线笥模型对拉曼自由电子激光器进行数值模拟,发现虚火花束源自由电子激光器苛以去掉导引磁场,用小周期摇摆器,实现器件的小型化和高功率。     

短波长自由电子激光器电子运动特性研究

短波长自由电子激光器的电子束在摇摆器中的传输通道长而狭窄, 须得电子具有良好的运动特性, 避免在传输过程中产生横向发散. 本文研究短波长自由电子激光器中超相对论电子在磁场具有横向分布的平面摇摆器中的三维运动特性, 用逐次逼近法推导相对论运动方程的解析表达式, 非线性数值计算模拟传输过程, 采用科尔莫 戈罗夫熵 方法分析运动的稳定性. 结果表明: 摇摆器磁场除使电子做周期性摇摆运动外, 还迭加了偏离轴线的横向漂移运动, 在没有外置的磁场聚焦系统情况下, 电子将偏离轴线横向发散; 但是, 恰当选取电子的横向初始速度, 可有效地防止电子运动的横向发散, 即使没有外置的磁场聚焦系统, 也能在长达10 m 的摇摆器中顺利传输, 横向位移范围不超过0.09 mm, 而且其运动是稳定的. 关键词： 短波长自由电子激光器 平面摇摆器 超相对论电子运动 运动稳定性     

双向聚焦电磁铁摇摆器磁场的数值模拟

 应用磁矢量势公式导出了螺线圈绕组的磁场计算公式，应用标量磁势并对电磁铁作局部均匀磁化近似，给出了电磁铁摇摆器磁场的积分方程式和相应的耦合系数。通过求解积分方程得到了摇摆器磁场的空间分布及摇摆器两端非均匀区的磁场分布。本方法可以为双向聚焦电磁铁摇摆器的设计提供参考数据。     

六层加侧混合型摇摆器磁场的理论计算与数值模拟

 利用文献[1，2]给出的结果，提供了六层加侧混合型摇摆器中永磁体磁场的计算公式和软铁磁场计算的积分方程式。对周期长度lw =1.6cm，磁极间隙g=0.5cm的情况，计算了单向聚焦和双向聚焦两种不同构形的磁场分布，并得到了g /lw =1/3条件下，峰值磁场Bw超过1特斯拉的设计指标。     

新型高谐波分量摇摆器的研究

分析了提高摇摆器中谐波场分量的方法，提出了一种新型谐波摇摆器Ｕ形谐波摇摆器，并对其参数进行了优化。讨论了在Ｕ形谐波摇摆器中的电子轨迹和自发辐射谱。设计和制作了６个周期的模型以验证理论，并对模型进行了测量。     

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.     

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.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.