电子束激励TM模虚阴极振荡器的分析

 从理论上对实心电子束和空心电子束激励轴向虚阴极振荡器产生高功率微波的情况进行了比较分析。通过数值计算比较了在相同的结构参数条件下输出微波功率的大小。分别讨论了在激励TM₀₁和高阶TM₀₂,TM₀₃模式时电子束半径的优化值。用KARAT软件进行粒子模拟初步验证了数值计算的结果。数值计算和粒子模拟结果均表明：要在轴向虚阴极振荡器中有效地激励TM₀₁主模式,应采用实心电子束;而空心电子束则在激励高阶TM_0n模式时,可能更为有效。     

克尔介质中超连续谱的产生与自聚焦的抑制

 从（3+1）维非线性薛定谔方程出发,理论上分析了超短脉冲频谱展宽与自聚焦的影响因素。分析得出：通过改变泵浦光的功率和光束口径,可以实现光谱的极大展宽并避免自聚焦成丝。数值模拟了小口径强泵浦光束在BK7玻璃中的传输过程并进行了实验验证。模拟结果显示在超连续谱产生的同时小尺度调制被完全抑制。实验结果表明：降低泵浦光功率,使光束不会因为全光束自聚焦而发生塌陷,同时还能控制除自聚焦外的其它非线性效应,进而改善近场光束质量。由于自相位调制是超短超强脉冲产生超连续谱的重要机制之一,需要维持传输过程中的泵浦光功率,由此最佳的入射光功率应选在全光束自聚焦功率阈值附近。     

The effects of induced heat loads on the propagation of Ince-Gaussian beams

Thermal effects are very much influential in high power beam generators. Their impacts on special types of beams such as Helmholtz-Gauss beams have attracted special attentions. This work reports thermal effects on the generation and propagation of Ince-Gaussian beams. The results show considerable beam spot size variations for near fields under various induced heat loads. As Ince-Gaussian beams are directly related to cavity symmetry breaking, the results can greatly help system designers for circumventing these types of symmetry breaks usually encountered in high power lasers.     

相对论返波管振荡器齿状阴极

研究了一种齿状阴极的电子束产生传输过程以及对相对论返波管振荡器产生高功率微波的影响。基于SINUS881加速器,利用束流轰击金属靶观测齿状阴极产生电子束在不同轴向位置上的角向分布,并开展了基于环形阴极和齿状阴极的X波段相对论返波管振荡器的实验研究。对不同齿数及尺寸对电子束流特性、器件输出微波功率和脉冲宽度的影响进行了分析。实验结果表明：当阴极的齿数增加到一定数量时,电子束的横向运动使得电子束在径向逐渐趋于分布均匀;与均匀环形阴极的打靶结果近似,此时,电子束对于相对论返波管振荡器产生微波的功率和脉宽影响不大。     

相对论返波管振荡器齿状阴极

研究了一种齿状阴极的电子束产生传输过程以及对相对论返波管振荡器产生高功率微波的影响。基于SINUS881加速器,利用束流轰击金属靶观测齿状阴极产生电子束在不同轴向位置上的角向分布,并开展了基于环形阴极和齿状阴极的X波段相对论返波管振荡器的实验研究。对不同齿数及尺寸对电子束流特性、器件输出微波功率和脉冲宽度的影响进行了分析。实验结果表明:当阴极的齿数增加到一定数量时,电子束的横向运动使得电子束在径向逐渐趋于分布均匀;与均匀环形阴极的打靶结果近似,此时,电子束对于相对论返波管振荡器产生微波的功率和脉宽影响不大。     

Optimization of the parameters of a virtual-cathode oscillator with an inhomogeneous magnetic field

A two-dimensional numerical model is used to study the generation of powerful microwave radiation in a vircator with an inhomogeneous magnetic field applied to focus a beam. The characteristics of the external inhomogeneous magnetic field are found to strongly affect the vircator generation characteristics. Mathematical optimization is used to search for the optimum parameters of the magnetic periodic focusing system of the oscillator in order to achieve the maximum power of the output microwave radiation. The dependences of the output vircator power on the characteristics of the external inhomogeneous magnetic field are studied near the optimum control parameters. The physical processes that occur in optimized virtual cathode oscillators are investigated.     

Generation of a radially polarized laser beam by use of the birefringence of a c-cut Nd:YVO4 crystal

We demonstrated the generation of a radially polarized laser beam from an extremely simple laser resonator including a c-cut Nd:YVO4 crystal as a laser medium. The oscillation in the radial polarization was based on the optical path difference between an extraordinary ray and an ordinary ray induced by the birefringence of the crystal. By simply adjusting the distance between two cavity mirrors, only the extraordinary ray became stable for the oscillation, resulting in the generation of a radially polarized beam. The beam was very stable even at low power output and is expected to be a promising radially polarized laser source because of its excellent simplicity.     

大面积均匀电子束产生实验研究

在电子束泵浦气体激光实验中,大面积均匀电子束是获得高效能激光输出的必要条件。介绍了利用SPG-200脉冲功率源产生大面积均匀电子束的实验。SPG-200是基于SOS的全固态重复频率脉冲功率源,其开路电压大于350 kV。用于产生电子束的真空二极管阴极长294 mm,宽24 mm,两端均为半径为12 mm的半圆,栅网平面为阳极面,两者之间的距离在0~49 mm可调,阴极发射的电子束通过用于隔离激光气室和二极管真空室的压力膜及其支撑栅网引出。分别以石墨和天鹅绒为阴极材料,获得了大面积电子束输出,给出了二极管参数的测量结果,并对电子束发射均匀性进行了诊断。实验结果表明：在阴极材料为石墨、阴阳极间隙为5~9 mm时,二极管电压为240~280 kV,二极管电流为0.7~1.8 kA,输出的电子束很不均匀;在阴极材料为天鹅绒、阴阳极间隙为31~46 mm时,二极管电压为200~250 kV,二极管电流为1.5~1.7 kA,输出的电子束均匀性较好。     

Effective use of the electron beam in pulse-periodic electron-beam-controlled CO2 lasers and comprehensive optimization of their excitation parameters

Results are presented of experimental and theoretical investigations aimed at obtaining a maximum average generation power of pulse-periodic electron-beamcontrolled lasers at a limited average electron-beam current density. The conditions for the evolution of the post-pulse breakdown of the discharge gap are investigated and the parameters of the discharge circuit are optimized. Excitation regimes that ensure the most effective use of the electron beam are calculated with allowance for the beam divergence. Promising methods of improving the effective use of the laser beam and of increasing the output power of pulse-periodic electron-beam-controlled C0₂ lasers are considered.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 142, pp. 3–45, 1983.     

大面积均匀电子束产生实验研究

 在电子束泵浦气体激光实验中,大面积均匀电子束是获得高效能激光输出的必要条件。介绍了利用SPG-200脉冲功率源产生大面积均匀电子束的实验。SPG-200是基于SOS的全固态重复频率脉冲功率源,其开路电压大于350 kV。用于产生电子束的真空二极管阴极长294 mm,宽24 mm,两端均为半径为12 mm的半圆,栅网平面为阳极面,两者之间的距离在0~49 mm可调,阴极发射的电子束通过用于隔离激光气室和二极管真空室的压力膜及其支撑栅网引出。分别以石墨和天鹅绒为阴极材料,获得了大面积电子束输出,给出了二极管参数的测量结果,并对电子束发射均匀性进行了诊断。实验结果表明：在阴极材料为石墨、阴阳极间隙为5~9 mm时,二极管电压为240~280 kV,二极管电流为0.7~1.8 kA,输出的电子束很不均匀;在阴极材料为天鹅绒、阴阳极间隙为31~46 mm时,二极管电压为200~250 kV,二极管电流为1.5~1.7 kA,输出的电子束均匀性较好。     

Transients and efficient generation of electron beams in the pulsed wide-aperture glow discharge

The quasi-continuous wide-aperture glow discharge in helium at pressures from 1.2 to 6.0 Torr is studied. It is found that electron beam generation efficiency η is higher than 96% in the pressure range 1.2–3.0 Torr at voltages from 1.0 to 2.6 kV. The maximum power was ≈ 0 kW at 6 Torr and a voltage across the discharge gap of 2.6 kV. Under these conditions, the beam generation efficiency is about 80%. The pressure and voltage dependences of main parameters of the discharge are explained from the standpoint of its photoemission nature.     

Active formation of an antiguide structure in a photorefractive polymer for enhanced second-harmonic generation

An antiguide structure for enhanced second-harmonic generation was actively constructed in a photorefractive polymer by use of a pump beam. Irradiation of a pump beam enhanced second-harmonic power, and blocking the pump returned the power to the initial value. The electric-field dependence of the degree of enhancement of the second-harmonic power confirmed that the antiguide structure was constructed through a photorefractive-index change in the medium. The photorefractive-index change accompanied molecular reorientation induced by the pump-generated space charges. The thermo-optic effect on formation of the structure is also discussed.     

Second harmonic generation of high power Cosh-Gaussian beam in cold collisionless plasma

The purpose of this study is to explore the second harmonic generation (SHG) of a high power Cosh-Gaussian beam in cold collisionless plasma. The ponderomotive force causes carrier redistribution from high field to low field region in presence of a Cosh-Gaussian beam thereby producing density gradients in the transverse direction. The density gradients so produced the results in electron plasma wave (EPW) generation at the frequency of the input beam. The EPW interacts with the input beam resulting in the production of 2nd harmonics. WKB and paraxial approximations are employed for obtaining the 2nd order differential equation describing the behavior of the beam's spot size against normalized distance. The impact of well-established laser-plasma parameters on the behavior of the beam's spot size and SHG yield are also analyzed. The focusing behavior of the beam and SHG yield is enhanced with an increase in the density of plasma, the radius of the beam and the decentred parameter, and with a decrease in the intensity of the beam. The results of the current problem are really helpful for complete information of laser-plasma interaction physics.     

G波段500 W带状注扩展互作用速调管设计研究

针对太赫兹频段实现高功率面临物理机制上的难题,设计了一个G波段带状注速调管,展示了基于非相对论带状电子注和扩展互作用技术所能达到的功率水平以及影响性能的物理因素。文中设计基于电压24.5 kV、电流0.6 A,1 mm×0.15 mm的椭圆电子注,以及与之相匹配的互作用系统,即横向过尺寸哑铃型多间隙谐振腔,可以实现高功率和高增益。三维PIC仿真结果显示,在考虑实际腔体损耗的情况下,能够获得超过500 W的功率,电子效率和增益分别达到3.65%和38.2 dB。研究发现,输出功率和效率的提升很大程度上受到多间隙腔模式稳定性以及电路欧姆损耗的制约;输出腔的欧姆损耗对输出功率影响尤为显著,工程设计需要特别考虑。本文的研究为高频段带状注扩展互作用器件的研发打下了良好的基础。     

41 mW high average power picosecond 177.3 nm laser by second-harmonic generation in KBBF

We report on the generation of high average power, high repetition rate, and picosecond (ps) deep-ultraviolet (DUV) 177.3 nm laser. The DUV laser is produced by second-harmonic generation of a frequency-tripled mode-locked Nd: YVO₄ laser (<15 ps, 80 MHz) with KBBF nonlinear crystal. The influence of different fundamental beam diameters on DUV output power and KBBF-SHG conversion efficiency are investigated. Under the 355 nm pump power of 7.5 W with beam diameter of 145 μm, 41 mW DUV output at 177.3 nm is obtained. To our knowledge, this is the highest average power for the 177.3 nm laser. Our results provide a power scaling by three times with respect to previous best works.     

High-power microwave generation using a ferroelectric cathodeelectron gun

A two-stage 500 kV 200-A ferroelectric electron gun has been designed, fabricated, tested, and used in a high power microwave amplifier experiment. We report on the operational characteristics of the gun including measurements of the beam dynamics. The optimum conditions for application of the trigger and its timing are also reported. Faraday cup measurement shows that the beam radius is 4.1 mm, in good agreement with simulation. The gun is designed for use in traveling-wave tube amplifiers, and testing of an X-band amplifier driven by the gun is reported. A peak output power of 5.9 MW has been observed from a single stage amplifier driven by a 100 A. 450 kV beam. This corresponds to energy converging efficiency of 13.1% and is the first observation of high power (~MW) microwave generation using the beam generated from a ferroelectric cathode,     

飞秒平顶光束经微透镜阵列在熔融石英中的成丝及其超连续辐射

实验研究了平顶激光光束经微透镜阵列在熔融石英中成丝的演化以及超连续辐射的产生,并进一步与高斯光束的成丝和超连续辐射进行了对比研究.分别对这两种光束的多丝传输进行了横向和纵向成像.结果表明,使用平顶光束可以获得更为均匀的多丝分布,成丝的起点也更为一致;尤其重要的是,相对于高斯光束,平顶光束可以使用更高的入射激光脉冲能量而不会造成介质的损伤,从而可以获得更高脉冲能量和更高转换效率的超连续辐射.     

一种新型周期永磁聚焦系统过渡区的设计

 分析了过渡区中电子注调节的基本原理,设计了一种渐变式的过渡区结构,其注腰半径为0.8 mm,周期均匀磁场峰值为0.29 T,周期为4.5 mm,压缩比为22。该结构能够在减小电子枪压缩比的情况下对电子注进行再压缩,得到符合互作用要求的电子注。将采用渐变式过渡区结构的电子注匹配与采用传统方法的电子注匹配进行了比较,模拟结果表明：采用渐变式过渡区结构匹配电子注不仅能有效改善电子注的层流性（波动性为8%）,还能够提高电子光学系统的稳定性。根据此方法对Ku波段6 kW行波管的电子光学系统进行了模拟计算,得到了良好的设计结果。     

一种新型周期永磁聚焦系统过渡区的设计

分析了过渡区中电子注调节的基本原理,设计了一种渐变式的过渡区结构,其注腰半径为0.8 mm,周期均匀磁场峰值为0.29 T,周期为4.5 mm,压缩比为22。该结构能够在减小电子枪压缩比的情况下对电子注进行再压缩,得到符合互作用要求的电子注。将采用渐变式过渡区结构的电子注匹配与采用传统方法的电子注匹配进行了比较,模拟结果表明：采用渐变式过渡区结构匹配电子注不仅能有效改善电子注的层流性（波动性为8%）,还能够提高电子光学系统的稳定性。根据此方法对Ku波段6 kW行波管的电子光学系统进行了模拟计算,得到了良好的设计结果。