微秒长脉冲有磁场高功率微波二极管真空界面设计

介绍了一种微秒长脉冲有磁场的真空二极管界面的设计和实验结果。采取了三种措施来抑制沿面闪络:一是阴极电子束挡板,用来拦截来自阴极和电子束漂移管的回流电子束;二是接地屏蔽板,使电场等势线和界面成约45°角,使阴极三结合点处发射的电子远离绝缘板;三是降低阴极三结合点处的场强,并使用一悬浮电位的金属环阻止电子倍增过程。计算了二极管内电场、磁场分布和电子束的运动轨迹并据此优化了真空界面的结构,实验验证了该二极管真空界面可以在400 kV、800 ns条件下正常工作,可以支持长脉冲高功率微波器件的研究。     

一种陶瓷径向绝缘强流二极管耐压结构设计

 对外径230 mm的陶瓷绝缘板，依据强流真空二极管径向绝缘的设计思想，设计加工了“锥-柱”型阳极外壳，并在传输线内筒和阴极杆末端位置增加了均压罩和屏蔽环结构。利用静电场有限元程序计算了陶瓷-真空界面电场分布，通过对外壳细节结构以及均压罩、屏蔽环形状和位置的调整，使得真空界面上沿面场强和三结合点处场强均得到了有效控制。在单线长脉冲加速器上进行了实验研究，结果显示，二极管能够耐受400 kV、脉宽大于200 ns的脉冲电压，运行稳定，达到了理论设计要求。     

强流电子束二极管陶瓷真空界面

从绝缘和机械强度两方面优化设计了一种应用于强流电子束二极管的陶瓷真空界面。首先,依据真空沿面闪络机理及其影响因素,针对外径220mm的陶瓷板,应用ANSYS静电场模拟,通过对阴极电极形状和阳极外壳尺寸的调整,使得陶瓷沿面电场和阴、阳极三结合点场强均得到了有效控制。模拟结果显示:陶瓷沿面电场分布均匀,阴、阳极三结合点场强小于30kV/cm,电场线与陶瓷表面所成角度基本保持在45°;其次,针对陶瓷与电极的约束结构,通过静力和瞬态冲击分析,确定了该陶瓷界面可承受的最大静压和冲击波最大峰压分别为4.8MPa和60MPa;最后,在脉宽200ns的脉冲功率驱动源上进行了实验研究,陶瓷真空界面平均绝缘场强达到44kV/cm,二极管运行稳定,机械性能可靠,实验结果与理论设计相符。     

百焦耳级KrF准分子激光装置设计与调试

首先用解析方法分析了提高激光输出能量的途径。其次用分析和反应动力学模拟计算相结合方法给出激光腔设计参数。并给出二极管、电子束传输系统以及变阻抗线预脉冲开关等设计参数。根据这些参数对百焦耳准分子激光器进行了工程设计。在安装调试时,采用单元安装、逐级调试然后总调。在调试中解决了阴极边缘电子发射和沿径向有机玻璃绝缘板表面的沿面滑闪等问题。在Marx电压1.1MV,主膜为50μmTi箔,二极管电压为620kV,电子束流为160kA,束能8kJ条件下,当腔内总气压为0.25MPa、气体混合比为F_2Kr:Ar=0.4:10:89.6,谐振腔全反镜反射率为96％,输出镜透射率为75％时,获得稳定、重复100JKrF激光输出能量。     

真空中A-B-A绝缘结构的电场分析

提出了一种变插入层电导率和介电常数的三层(A-B-A)绝缘结构。分析了插入层(A)电导率和介电常数对三层绝缘结构真空-绝缘子-阴极三结合点处和真空-插入层绝缘子(A)-主绝缘子(B)三结合点处电场的影响,结果发现通过控制插入层电导率和介电常数可以有效降低真空-绝缘子-阴极三结合点处的电场又不至于使真空-插入层绝缘子-主绝缘子三结合点处电场过高。考虑了介质表面带电的情况,分析插入层介质表面带不同极性电荷对真空-绝缘子-阴极和真空-插入层绝缘子-主绝缘子两个三结合点电场分布的影响。估计了三层绝缘结构真空沿面闪络电压的变化趋势,发现在插入层电导率或介电常数不断增大时,真空沿面闪络电压会呈现先上升后下降,最后趋于稳定。     

电子束泵浦三原子Kr_2F准分子激光的一维动力学研究

应用一维动力学模型，对电子束泵浦Ａｒ／Ｋｒ／Ｆ２混合气体产生的三原子Ｋｒ２Ｆ准分子激光进行了理论模拟研究，指出了提高三原子Ｋｒ２Ｆ准分子激光能量的实验方向，激光能量输出可达毫焦耳量级。     

电子泵浦KrF准分子激光的一维动力学研究

对电子束泵浦KrF准分子激光进行了一维动力学模拟研究,考虑了24种粒子,119种反应通道。较为细致地研究了一维模型的物理机制及数学处理方法。运用该模型对国外实验结果作了模拟计算,结果符合较好。对原子能院电子束泵浦百焦耳级准分子激光器进行了模拟计算,给出了一些激光参数随时间、纵向位置的变化规律。最后对零维模型和一维模型的计算结果作了比较。     

百焦耳级XeCl准分子激光辐照靶材的光学诊断

在百焦耳级ＸｅＣｌ准分子激光器上，开展了强紫外激光辐照ＬＹ—１２铝靶和碳纤维靶的光学诊断实验。研究了靶面对激光的反射系数随入射激光功率密度的变化规律，获得了激光等离子体光谱及蒸汽羽积分图象等实验结果。     

真空中聚乙烯膜在纳秒脉冲电压下的沿面闪络特性

 在高功率离子束二极管中，当利用阳极膜沿面闪络产生的等离子体作为离子束引出源时，其特性对产生离子束的大小和品质有着很大的影响，因此要深入研究阳极膜的沿面闪络特性。主要介绍了所研制的一套适用于沿面闪络特性研究的实验装置和测量诊断系统。对离子束二极管中使用的三种厚度聚乙烯薄膜在脉冲电压下的沿面闪络特性进行了实验研究，并对沿面闪络过程中薄膜表面的发光现象作了初步的诊断。     

圆形平板电极与薄膜层叠结构的沿面闪络性能

强电磁脉冲模拟装置中用于脉冲压缩的陡化电容器常采用电极与薄膜介质层叠的结构，其主要绝缘失效模式为沿面闪络。采用圆形平板电极，在SF₆绝缘环境中和加载电压为前沿约30 ns的纳秒脉冲电压的条件下，实验研究了陡化电容器关键结构参数和气压对沿面闪络性能的影响。结果表明:（1）电极厚度、气隙和表面涂覆均不能明显改变层叠结构的沿面闪络电压；（2）气压可以提高层叠结构的沿面闪络性能，但是存在饱和趋势；（3）薄膜介质层数与沿面闪络电压近似线性比例关系；（4）增长薄膜介质伸出长度能显著提高沿面闪络电压。基于流注理论对上述结果进行了探讨，认为极不均匀场中，闪络起始主要由高场强区域决定，但是闪络通道的形成和发展主要由闪络路径上的背景电场决定，因此减小层叠结构三结合点处电场对闪络性能影响不大，但减小闪络通道发展路径上的背景电场，可以有效提高层叠结构的沿面闪络电压。     

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.     

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.     

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.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.