介质加载复合光栅结构的色散特性研究

提出了一种用于Smith-Purcell器件的介质加载金属光栅周期慢波结构.通过采用本征函数法和单模近似法求解了介质加载金属光栅的"热"色散方程,在同步点得到了注-波互作用的一阶和二阶增长率,分析了光栅槽宽和槽深对色散特性的影响,并研究了电子注参数及其与光栅表面距离等主要参数对增长率特性的影响.结果表明:通过介质加载金属光栅有利于减弱色散,随着介质相对介电常数、槽宽度以及深度的增大,色散曲线变平缓且向低频区移动;当电子注参数变化时,一阶增长率曲线从整体上粗略地描述增长率变化趋势,二阶曲线则更精细地描述增长率相应值的变化.利用软件MAGIC对该结构的色散特性进行了二维模拟,模拟结果与理论计算值符合良好.     

金属柱平板慢波系统高频特性研究

对于离散的金属柱结构构建的周期性平板慢波系统,本文利用3维FDTD方法结合HFSS仿真软件深入分析了该慢波系统的高频特性.研究了金属柱高度、周期长度对色散特性的影响,计算了耦合阻抗,并与传统光栅慢波系统特性进行了对比分析.分析表明金属柱慢波系统既有与传统光栅慢波系统相似的高频特性,又具有独自的特点,位于离散的金属柱周期间隙中的电子注互作用耦合阻抗具有对称性;金属柱结构用作真空电子器件的高频系统可增加发生有效互作用的电子注厚度,降低起振电流密度,提高器件效率.本文的分析结果为设计低电流密度工作的多电子注短毫 关键词： 金属柱平板慢波系统 3维FDTD算法 色散特性 耦合阻抗     

螺旋坐标系下考虑厚度的螺旋线行波管小信号研究(英文)

采用螺旋坐标系对有限厚度的螺旋带行波管进行了注波互作用的线性理论分析,利用自洽场理论得出了此结构中引入电子注后的"热"色散方程,数值计算了其小信号增益,分析了电子注参数和螺旋线厚度对于螺旋线慢波系统的色散特性的影响。结果表明:螺旋线厚度的增加,行波管的小信号增益也会增加,且带宽也略有增加。该结论为高增益宽频带的螺旋线行波管放大器的设计提供了理论基础。     

有限引导磁场下相对论环形电子注色散特性的研究

采用等效媒质处理方法来研究有限引导磁场下沿纵向运动的相对论环形电子注.首先建立运动坐标系以电子注纵向速度匀速运动,在运动坐标系中电子注可以被考虑成静止的磁化等离子体,再通过四维空间的洛伦兹变换得到电子注在静止的实验室坐标系下可以被等效为双各向异性媒质,其不仅具有张量形式的电导率和磁导率,还具有手征特性.在此基础上同时考虑了由于电子注表面波动所引起的表面电流密度.采用该方法研究了有限引导磁场下圆柱波导中沿纵向运动的相对论环形电子注,推导出该模型的色散方程,并进行了数值计算.计算结果表明该研究方法能够得到更准 关键词： 相对论环形电子注 磁化等离子体 色散特性     

凹面光栅型波长解复用器的标量波动分析

利用标量波动衍射理论，通过对光栅槽面的数值积分，计算了罗兰圆型集成二维凹面光栅像点的光强分布。给出了光线追变法难以得到的光栅槽面沿光栅圆不同方位刻划所引起的成像点对于光栅方程计算位置的偏离；在对色散和分辩力的分析上，获得了与光线追迹法很好的一致性；分析了光栅的槽面波、光源的模场宽度以及因工艺产生的槽面圆角对光栅成像的影响；最后给出了光栅的波像差和光线像差的计算。     

矩形槽光栅矢量模式理论的数值计算

本文根据矩形槽光栅的矢量模式理论进行了数值计算。对于任意入射方向及任意偏振态的入射场，计算了其衍射效率和偏振特性变化，并详细研究了光栅结构参数（周期、槽宽、槽深等）对衍射场的影响。     

双间隙谐振腔的高频分析

 从麦克斯韦方程组出发,运用电磁场的匹配条件,导出了双间隙谐振腔等效周期结构横磁模的色散关系及场分布表达式。然后通过数值计算,求出了双间隙谐振腔的谐振频率和场分布,并分析了谐振腔的结构尺寸对频率的影响,为C波段双间隙输出腔的设计提供了理论依据。     

光纤光栅非线性时延对啁啾的电视信号的影响

分析了有线电视系统中,用作色散补偿的光纤光栅因色散抖动对信号载波互调比产生的影响,结果显示色散抖动对有线电视信号互调比的影响随拦动幅度、抖动周期、信道数目的加而增加,信道频率的分布也对其的影响。对光栅的色散特性进行数值估算,发现常耦合系数线性啁啾光栅不能用的有线电视系统中进行色散补偿。     

回旋管同轴谐振腔模式的选择

 为了研究回旋管工作模式的选择机理,分析了圆柱波导开放式谐振腔、光滑同轴谐振腔和纵向内开槽同轴谐振腔相应波导的色散特性,进而研究了这些谐振腔内模式竞争的问题。对同轴结构波导色散方程作了相应的数值计算,结果表明,同轴谐振腔利用自身色散曲线与谐振腔内外半径比值的数值关系,能够使在开放式谐振腔内无法工作的高阶模式在其内部稳定工作。最后,以德国卡尔斯鲁厄理工学院(KIT)研制的同轴回旋管为例,进行了相应的分析计算,结果表明纵向内开槽同轴谐振腔相对于光滑同轴谐振腔更适合高阶模式的稳定工作。     

S波段多注相对论速调管放大器的数值模拟

利用3维电磁场与粒子模拟软件对S波段多注相对论速调管放大器进行了分析设计和模拟计算。通过对谐振腔本征模的计算确定腔体的冷腔高频特性,采用3维的粒子模拟软件（PIC）模拟分析速调管各腔及整管的束波互作用过程。模拟结果表明:通过引入同轴谐振腔结构,使电子注不必集中在谐振腔中心通过,降低了电场不均性对束波互作用的不利影响;通过引入多电子注,电子在相对较低的轴向聚焦磁场下依然拥有较高的通过率,降低了速调管对聚焦磁场的要求。模拟中采用3个同轴谐振腔进行束波互作用,在输入电压700 kV、束流5.8 kA和聚焦磁场0.4 T的情况下,得到了功率1.4 GW的输出微波,效率为35%。     

太赫兹波段Smith-Purcell辐射的介质加载光栅高频特性

提出了一种用于Smith-Purcell效应器件的介质加载光栅慢波结构,通过研究该结构的注-波互作用过程,推导出带电子注的色散方程,并数值求解出波的线性增长率.利用色散方程,结合电磁场传播的边界条件,推导出Smith-Purcell效应振荡器工作所需的起振电流.详细研究了高频结构长度、电子注主要参数和介质相对介电常数对起振电流的影响,并与普通金属光栅结构进行了比较.结果表明:保持其他参数不变时,高频结构长度越短,起振电流越大;保持高频结构参数不变时,起振电流随电子注厚度和注-栅距离的增大而增大,随电子注电压的增大而减小;与金属光栅相比,介质的引入提高了注-波互作用的增长率,有效减小了振荡器的起振电流.理论计算结果与软件CHIPIC的模拟结果比较符合.     

Fabrication of high-frequency electron beam moiré grating using multi-deposited layer techniques

This paper proposed new ways for producing multi-layer model grids for electron beam moiré method. An electron beam lithography system was set up under scanning electron microscope which was equipped with a beam blanking device and a pattern generator. The two-deposited-metal layers method was used to manufacture electron beam grating for high-temperature use. The results verify that the Zr–Pt-type grating possesses heat resistance up to 1100°C in vacuum. A new type of composite grating with frequencies 100 lines/mm and 1000 lines/mm using three deposited layers was produced. A 10 000 lines/mm two-deposited-metal layers grating was successfully fabricated using electron beam lithography.     

Research on target uniform irradiation method using linearly modulated light and special grating dispersion

In indirect-drive laser fusion research, filamentation instability (FI) severely influences laser injection efficiency and beam pointing accuracy in hohlraum. Experiments indicate that high frequency modulations on the far field of the laser driver are responsible for the filamentation. To solve this problem, a new smoothing technique is proposed using linear modulation and special grating dispersion. The linear modulation was realized by stacking a series of 100 ps chirped pulses in fiber delay lines. The temporal smoothing characteristics of the focal spot adopting star and circular grating dispersion were studied. Simulation results indicate that both kinds of grating investigated restrained the high frequency modulations. The star grating has a better smoothing effect when compared to circular grating. The insertion of the star grating could realize “color” variation across the beam in the azimuthal direction and make the far-field pattern rotate with time. Therefore, the time-integrated focal spot would be smoothed in a more comprehensive way. This smoothing method bears the advantage of simple configuration, two-dimensional angular spectral dispersion and not enlarging the far field too much.     

The use of a concave grating in pulsed dye laser cavities

The concept of using a concave diffraction grating for both beam expansion and spectral dispersion in a pulsed dye laser cavity is introduced. A simple, aberration free design based on a double pass Wadsworth configuration is suggested and its characteristics are discussed.     

W波段带状注矩形单栅返波振荡器模拟研究

提出并研究了一种带状电子注矩形单栅返波振荡器。首先研究了矩形单栅慢波结构的色散特性和耦合阻抗特性,然后粒子模拟并优化设计了带状注矩形单栅高频结构,预群聚腔及输出一体化结构。研究结果表明:利用电压200kV、电压2kA、截面为24mm×0.5mm的带状电子注,驱动该矩形单栅返波振荡器,能够产生42 MW的输出功率,工作频率86GHz,效率为10.5%。     

Numerical analysis of radiation by a relativistic electron beampropagating parallel to a reflection grating

Two-dimensional radiation by a relativistic sheet electron beam propagating parallel to a reflection grating composed of a sinusoidally corrugated conducting surface is studied rigorously using the mode-matching method. Accurate dispersion curves for the eigenmodes that govern the Smith-Purcell radiation and the instability of the electromagnetic surface wave are presented. The imaginary parts of the eigenwavenumber and eigenfrequency give the leakage coefficient of space-charge waves and the growth rate of electromagnetic surface waves. Their dependences on the dimensions of the radiating structure are discussed. Optimum parameters for achieving the maximum leakage coefficient and the growth rate are determined. The method is general and can be applied to any two-dimensional system of electron beam coupled to an open periodic structure of arbitrary profile     

速调型相对论返波管理论研究

对速调型相对论返波管慢波结构色散特性及束波相互作用进行了理论研究。色散特性研究表明:器件工作模式为TM01模,近点,耦合阻抗较高。色散特性预测的工作频率与粒子模拟结果非常接近。慢波结构峰值增长率相对较小,这与电子束与慢波结构相距较大有关,因而器件从起振到饱和的时间较长。在束波相互作用理论中,全面考虑了电子束与慢波结构前向波基波、反向波－1次空间谐波及空间电荷场相互作用、谐振反射器对电子束进行的束流调制和能量调制作用,以及调制腔和提取腔处引入的耦合阻抗及轴向波数突变。稳态和非稳态计算结果均获得了超过40%的束波转换效率。     

Numerical Analysis of the C-Band Klystrode with Annular Electron Beam

A klystrode oscillator cavity is designed using annular electron beam in the C-band frequency that can be easily scaled to S and X bands. Beam electrons are assumed pre-modulated and injected into the toroidal cavity in the shape of thin reentrant resonator with the grid structure built in the beam entrance. We optimize the beam conversion efficiency via the MAGIC code in the range of sixty to seventy percent with the fundamental TM₀₁-mode which is fine tuned by the 3D HFSS code. The annular electron beam has a merit to permit the center coupling to the adjacent cavity to enhance and stabilize the beam pre-modulation in addition to increased power handling capability.     

A High Efficiency Yb3+-doped Fiber Ring Cavity Laser with Narrow Line-widthRound-trip Dispersion Calculation for Martinez Pulse Stretcher

A novel Yb3+-doped fiber ring cavity laser pumped by a 977 nm laser diode is presented with its output laser wavelength of 1060 nm. Based on a fiber Bragg grating (FBG), the laser exhibits 0.20 nm line-width, 7.5 mW laser output power, 40 dB signal-to-noise ratio (SNR) and 66% slope efficiency.This paper proposed a ray-tracing model for the Martinez stretcher, derived the calculation formulae for the stretcher of a grating-spherical mirror system and discussed the error for the total dispersion resulted from the spatial dispersion. The calculated results show that the error could be ignored for the beam returned to the stretcher for the second pass in the wavelength range of 750 nm and 850 nm.