A compact free electron laser investigation

An electron beam source based on pseudospark discharge was successful in operation at the beam voltage of 200keV and beam current of 2kA. The detailed design of a compact free electron laser using an electron beam by a pseudospark discharge is described. The compact free electron laser consists of a smaller Marx generator with 6 capacitors and switches, a water capacitance of 6nF and a beam source with a high brightness of 3×10¹¹ A/(m rad)². The computer simulation shows that an output power of 101MW is expected at a frequency of 38GHz with a beam energy of 300keV, a current of 2kA and a beam emittance of 48mm mraa.     

自由电子激光器谐振腔内电子束和激光脉冲的时间同步

研究自由电子激光器谐振腔内电子束和辐射的时间同步问题.这是激光器谐振腔设计中的一个重要问题.本文讨论了腔内布儒斯特窗片对光路的影响.研制出由微机控制谐振腔的精密微调装置,扫描范围为±3cm,微调精度达1μm.     

太赫兹自由电子激光波荡器的设计、测量与优化

波荡器电子轨迹中心偏移和磁场误差对CTFEL装置性能影响很大,通过前期设计和后期测量与优化将其限制在指标要求范围内。在前期设计中尽量避免引入全局性的系统误差：磁结构具有平面反对称结构,保证电子轨迹中心和波荡器磁轴重合;磁结构端部的特殊设计减弱了间隙对出口磁场二次积分的影响;机械系统的大梁和立柱具有良好的刚性,闭环控制系统保证了高的波荡器间隙控制精度,这些措施降低了间隙不一致引入的磁场误差。在后期测量与优化中削弱了磁场的残存全局系统误差和局部随机误差：利用磁场点测台测量了波荡器磁场的纵向和横向分布,通过调节标准单元组件位置对磁场进行了垫补和优化,优化后电子轨迹中心偏移、峰峰值误差、相位误差、好场区及其误差均满足指标要求。     

北京自由电子激光器的光学速调管结构

采用KMR方程,结合即将运转的北京自由电子激光器总体实验参数,对其光学速调管结构研究.详细分析计算输入功率、电子束能散度、色散磁场、漂移空间长度及位置、以及电子束流等参数对光学速调管增益的影响.基于北京自由电子激光器的振荡器结构,提出一组对电子束能散度要求适中的实用化光学速调管参数.并对其饱和功率、功率谱以及渐变摆动器进行分析.     

Degradation in gain for a free electron laser amplifier due to electron momentum spread

A finite spread in axial momentum for the electron beam in a free electron laser amplifier is shown to decrease the small-signal gain. For millimeter and sub-millimeter wave amplifiers, where exponential growth dominates the gain, it is shown that the gain is approximately 3 db below that for a cold beam if the relative momentum spread (u/u)_1/2 = (G_o/248)^1/2 (_o/L), where G_o1 is the gain in db for the cold-beam case, _o is the magnetic wiggler period, and L is the amplifier length. Exact numerical examples are given for representative FEL amplifiers at 35 and 550 GHz.This research was sponsored by the U.S. Office of Naval Research, and by the U.S.-Israel Binational Science Foundation.     

1.19米相互作用长度的喇曼自由电子激光器实验

利用新研制的1.3米双螺线波荡器以及与此相配合的引导场磁体,使自由电子激光相互作用长度从308mm可以最大增加到1190mm.总体实验证明,最大的激光辐射峰值功率达12MW电子转换效率是3.7%.     

自由电子激光器的掠射环形谐振腔

研究一种新型自由电子激光谐振腔结构.采用双曲面-抛物面非球面镜组合的扩束系统,使振荡光束在腔内口径扩大6倍.提高了反射膜层抗激光破坏能力.本文讨论了扩束倍数、非球面参量、谐振腔长度和掠射光斑尺寸等参量对光学系统像差的影响.     

The effects of self-fields on the electron trajectory in a two-stream free electron laser with a helical wiggler and an axial guiding magnetic field

A theory for the two-stream free-electron laser(TSFEL) with a helical wiggler and an axial guide magnetic field is developed.In the analysis,the effects of self-fields are taken into account.An analysis of the two-stream steady-state electron trajectories is given by solving the equation of motion.Numerical calculations show that there are seven groups of orbits in the presence of self-fields instead of two groups reported in the absence of self-fields.The stability of the trajectories is studied numerically.     

Effects of self-fields on gain in two-stream free electron laser with helical wiggler and an axial guiding magnetic field

The theory for the two-stream free electron laser （FEL） consisting of a relativistic electron beam transporting along the axis of a helical wiggler in the presence of an axial guiding magnetic field is proposed and investigated. In the analysis, the effects of self-fields are taken into account. The electron trajectories and the small signal gain are derived. The characteristics of the linear-gain and the normalized maximum gain are studied numerically. The results show that there are seven stable groups of orbits in the presence of self-fields instead of two groups reported in the absence of the self-fields. It is also shown that the normalized gains of three groups decrease while the rest increase with the increasing of normalized cyclotron frequency g20. Furthermore, it is found that the two-stream instability and the self-field lead to a decrease in the maximum gain except for group 3. The results show that the normalized maximum gain is enhanced in comparison with that of the single stream.     

Investigation of mechanism of free electron laser through spontaneous radiation spectrum

In this paper, the mechanism of free electron laser with a guide magnetic field is investigated by analyzing spontaneous radiation spectrum of electrons. The physical relation between spontaneous radiation and stimulated radiation in FEL with a guide magnetic field is studied. It is found that this relation in FEL is similar to that in quantum lasers. The spontaneous radiation spectrum is discrete. The frequency of stimulated radiation in FEL is oneselected and amplified in the radiation spectrum.     

太赫兹自由电子激光的受激饱和实验

中国工程物理研究院基于半导体光阴极高压直流电子枪和超导直线加速器的高平均功率太赫兹自由电子激光达到了受激饱和,并实现了太赫兹光输出频率可调.在1.99,2.41和2.92 THz三个频率点上进行测试,测得太赫兹宏脉冲内平均功率大于10 W,最高达17.9 W.本文介绍了太赫兹自由电子激光装置的主要组成部分及受激饱和实验的结果.     

Effects of self-fields on dispersion relation and growth rate in two-stream electromagnetically pumped free electron laser with axial guide magnetic field

A theory for a two-stream free-electron laser （FEL） with an electromagnetic wiggler （EMW） and axial guide magnetic field is developed. In the analysis, the effects of self-fields are taken into account. The growth rate is derived. The characteristics of the growth rate are studied numerically. The dependence of the normalized wave number, which corresponds to the maximum growth rate, on the cyclotron frequency is presented. The comparisons between the normalized maximum growth rate and its corresponding wave number normalized by employing the axial magnetic field, for the cases with and without self-fields in the two-stream FEL are studied numerically.     

X射线自由电子激光晶体学在结构生物学中的应用

X射线晶体学是获得生物大分子三维空间结构最主要的方法。基于X射线自由电子激光的晶体学——串行飞秒晶体学方法的出现,以其独特的优势为结构生物学研究提供了一种全新的研究手段。文章主要介绍了串行飞秒晶体学方法在结构生物学领域的应用及所取得的成果。这些成果表明该方法是在亚纳米空间尺度和飞秒时间尺度、在接近于自然状态下进行生物大分子静态和动态结构研究的强有力手段。     

Orbit stability in free electron lasers

Helical magnetic wigglers for free electron lasers can produce non-helical electron trajectories if a uniform axial guide magnetic field is imposed. Friedland's necessary criterion for the existence of helical orbits is reviewed and shown to apply for non-relativistic electron energies. An experiment designed to test this criterion is described and results are compared with theory.This research was ponsored by the U.S. Office of Naval Research, and by the U.S.-Israel Binational Science Foundation.     

UP-conversion of terahertz radiation induced by photon drag effect

An all-optical approach to convert terahertz radiation (THz, wavelength λ₁) into infrared (IR, peak wavelength λ₂) is presented. We show that this up-conversion process is due to the photon drag effect induced by the THz radiation in intrinsic narrow-gap semiconductors followed by spatial redistribution of current carriers and band-to-band radiative recombination. The process results in non-selective high-speed (ns range rise/fall times) IR imaging of positive (conventional luminescence) and/or negative (negative luminescence) contrasts. Estimates made for an InSb pixelless converter at 300 K and moderate THz intensity (kW/cm²) show that this up-conversion process (with λ₁/λ₂>10²) can be observed with a conventional thermal imaging camera.     

Smith-Purcell free electron laser based on the semi-elliptical resonator

A novel Smith-Purcell(S-P) free electron laser composed of an electron gun,a semi-elliptical resonator,a metallic reflecting grating and a collector,is presented for the first time.This paper studies the characteristics of this device by theoretical analysis and particle-in-cell simulation method.Results indicate that tunable coherent S-P radiation with a high output peak power at millimeter wavelengths can be generated by adjusting the length of the grating period,or adjusting the voltage of the electron beam.The present scheme has the following advantages:the semi-elliptical resonator can reflect all radiation with the emission angle θ and random azimuthal angles,back onto the electron beam with same-phase and causes the electrons to be modulated,so the output power and efficiency are improved.     

Proposal for Efficiency Enhancement of a Far Infrared Free Electron Laser

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半导体量子阱材料的自由电子激光辐照效应及OTCS测试研究

利用低温光荧光谱(PL)和光瞬态电流谱(OTCS)研究了自由电子激光辐照对GaAs/AlGaAs多量子阱材料的光学性质以及缺陷能级的影响。用波长为8.92μm,光功率密度相应于电场强度为20kV/cm的自由电子激光辐照多量子阱60min,分析PL谱发现量子阱特征峰(797nm)经过辐照后峰值发生红移至812nm,波形展宽,峰高降低。分析OTCS谱发现自由电子激光辐照引入了新的缺陷能级,量子阱结构发生变化, 对此结果进行了讨论,并与电子辐照的情况做了比较。     

自由电子激光相干强太赫兹源装置鬼脉冲初步研究

研究中国工程物理研究院自由电子激光相干强太赫兹源(FEL-THz)装置上鬼脉冲产生的原因及其对装置调试测量的影响,通过束流动力学模拟、热分析、蒙特卡罗模拟以及初步实验结果分析,证明了鬼脉冲将会明显破坏阻拦型测量,并会在束线管道上造成温度升高和辐射强度增大。研究表明:鬼脉冲成为限制FEL-THz装置正常工作的重要原因,为保证FEL-THz顺利出光,鬼脉冲必须予以消除,并简要讨论了鬼脉冲的消除方法。     

半导体量子阱材料的自由电子激光辐照效应及OTCS测试研究

利用低温光荧光谱(PL)和光瞬态电流谱(OTCS)研究了自由电子激光辐照对GaAs/AlGaAs多量子阱材料的光学性质以及缺陷能级的影响。用波长为8.92μm,光功率密度相应于电场强度为20kV/cm的自由电子激光辐照多量子阱60min,分析PL谱发现量子阱特征峰(797nm)经过辐照后峰值发生红移至812nm,波形展宽,峰高降低。分析OTCS谱发现自由电子激光辐照引入了新的缺陷能级,量子阱结构发生变化, 对此结果进行了讨论,并与电子辐照的情况做了比较。