新型史密斯-帕塞尔自由电子激光实验

介绍一种新型的Smith PurcellFEL实验 ,实验中利用中等能量级的相对论电子束激励 ,由衍射光栅和三反射镜组成的新型准光学系统 ,可以产生可调短毫米波、远红外波段的辐射。主要实验参数为 :电子注能量为 40 0～ 5 0 0keV ,电压脉冲宽度 70ns ,同步脉冲磁场强度 1.2T ,成功地检测到 3mm波段的毫米波信号 ,其峰值功率达到数十千瓦     

新型史密斯-帕塞尔效应可调辐射源研究

提出采用中等能量的相对论环状电子注激励轴对称三曲面反射镜、绕射光栅系统，产生毫米波、远红外波段辐射的新型准光学可调辐射源实验方案，这是一种基于史密斯一帕塞尔效应的自由电子激光。由于引入新型准光学谐振腔系统，可以改变能量输出方向的角度，从原理上讲，可制造一系列模型，产生可调频率的短毫米波、远红外波段相干辐射。采用环状电子注比带状电子注稳定性高，便于成型和聚焦；采用新腔体后增长了电子注与高频场的互作用范围；新型准光腔具有较小的绕射损耗。新方案的这些特点，进一步提高器件的输出功率，改善了高频特性。介绍这种新辐射源在3mm波段的粒子模拟计算初步结果，其输出功率达数百千瓦以上；同时给出准光学谐振腔高频系统的模拟计算和冷测实验的典型曲线。     

开放光栅中史密斯－帕塞尔超辐射机理研究

采用理论分析和粒子模拟相结合的方法,对连续电子注通过平板矩形光栅产生毫米波段史密斯-帕塞尔(SP)超辐射机理进行了研究.研究结果表明:选择恰当的电子注与光栅尺寸参数,光栅表面慢波将与电子注互作用,使电子注产生群聚,群聚的电子束团将在光栅表面产生史密斯-帕塞尔超辐射,其辐射频率为电子注与光栅表面慢波互作用同步点频率的整数倍,其辐射角度方向与史密斯-帕塞尔公式所预期的基本一致, 表面慢波由于光栅的有限长度也能在其端头以一定的形式辐射出去.     

光栅—谐振腔复合结构中的史密斯—帕塞尔辐射（英文）

提出了光栅—谐振腔复合结构.利用光学理论和粒子模拟方法研究了这种光栅—谐振腔复合结构中的史密斯—帕塞尔辐射的输出特性.结果显示:利用这种装置可以产生太赫兹波段的可调谐相干史密斯—帕塞尔辐射.这种光栅—谐振腔复合结构具有下列优点:它可以把一定发射角和任意方位角的史密斯—帕塞尔辐射同相位反馈到电子束,对电子束进行调制.     

W波段双光栅准光学谐振腔Q值计算与分析

采用衰减测试法,对双光栅准光学谐振腔的 Q值进行数值计算与分析,得到匹配槽高度和宽度、光栅槽深度等参数对Q值的影响。通过分析 W波段谐振腔各参数与Q值的关系,总结出 W波段双开槽准光学谐振腔Q值的经验公式,为准光学谐振腔的设计提供了理论依据。同时模拟计算分析了双光栅结构的加入对谐振腔 Q值的影响。结果表明,相比普通准光腔,双光栅准光学谐振腔能够降低光栅引入对Q值的影响。     

预群聚电子束团辐射特性

研究了预群聚电子束团沿周期性理想金属光栅表面平行移动时产生的史密斯-帕塞尔辐射(SPR).详细分析了电子束团能量、束团群聚长度、具有不同电流密度分布的电子束团以及光栅结构对辐射特性的影响,同时研究了多个群聚束团的辐射.分析发现,电子束团能量增加、束团群聚尺寸变小以及光栅周期变短,辐射能量角分布峰值所对应的频率明显向高频方向移动;光栅周期与电子束团参量相同的条件下,三角形光栅辐射能量角分布峰值所对应的频率明显高于正弦光栅;群聚束团尺寸越小辐射能量越大,并且束团的纵向群聚长度对辐射能量与辐射频率起主要作用.研究结果表明,通过合理选择光栅尺寸与束团参量,可获得工作频率锁定的太赫兹(THz)波段辐射.     

太赫兹频段一维介质光子晶体中的史密斯-帕塞尔辐射特性模拟

基于Smith-Purcell(SP)效应,采用粒子模拟的方法探讨了电子束团激发一维介质光子晶体中的SP辐射特性.模拟研究了单个束团激发一维介质圆柱光子晶体产生的SP辐射现象,并对周期束团激发的THz频段的相干SP辐射进行了模拟分析.研究表明,提高介质的相对介电常数和增加光子晶体的层数都可使辐射强度增加,选择合适的参数能够有效地增强THz频段的相干SP辐射强度.     

提取光栅耦合的高电子迁移率晶体管中的太赫兹辐射

借助于傅立叶光谱仪,在具有耦合光栅的高电子迁移率晶体管中观察到了波长在400um左右的微弱的太赫兹辐射。同时使用了一种调制探测技术,从而使得太赫兹辐射的绝对功率能够被提取计算出来。并且发现器件的太赫兹辐射功率正比于源漏电流,而黑体辐射功率则与器件电功率有密切关系。此外,太赫兹辐射对于源漏偏置电压及栅压的依赖性,说明太赫兹辐射是由加速电子与光栅的相互作用而引起的。     

GaAs远红外探测器中的辐射复合特性研究

借助光致发光技术对n-GaAs同质结内发射远红外探测器结构进行了详细的辐射复合特性研究.根据发光特性和高密度理论计算,观察和确认了来自探测器发射层中的光致发光信号.提出了光生载流子转移模型,很好地解释了发射层中光致发光信号与温度和激发功率的依赖关系.根据得到的辐射复合特性,提出了进一步提高探测器工作温度的方案.     

Smith-Purcell radiation from a narrow tape helix

A theoretical investigation of a narrow tape helix excited by a modulated electron beam gives quantitative results which can be used to estimate the strengths of interactions obtainable in experimental configurations. Extensive results are presented for the radiation emitted by a single fast space harmonic when a slow beam is in synchronism with the azimuthally symmetric space harmonic. The effects of beam velocity, frequency, beam diameter, tape width, and pitch angle are illustrated. The analysis also demonstrates the influence of the synchronism or electromagnetic resenance condition on the interaction and, further, points out the usefulness of the complex Brillouin (k - β) diagram in predicting some of the quantitative as well as most of the qualitative properties of this influence.     

Stimulated coherent Smith-Purcell radiation from a metallic grating

A relativistic electron beam with velocity ν_bz passing over a metallic grating, with deep periodic depressions of wavenumber k₀z, excites a slow wave (ω, k_z) via Cerenkov interaction, ω=(k_z+k₀)ν_b. The beam bunches induce currents in the fins of the grating that act as a phased radiating dipole array, thereby generating coherent radiation at a wavelength λ=(2π/k₀l)(c/ν_b-sin&thetas;) where l is an integer and &thetas; is the angle of emission measured from the normal of the grating. The current threshold for the instability and radiation power scaling with beam current are discussed     

Leaky space-charge waves II: Smith-Purcell radiation

This paper contains a new theoretical approach for analyzing Smith-Purcell radiation. The new theory is self-consistent, i.e., it takes into account the effect of the radiation back on the beam. This approach is not only more precise than the previously available one, but it brings to light a number of new effects. It shows that two kinds of waves contribute to radiation, namely, slow and fast space-charge waves, and demonstrates that these waves are of leaky nature. The numerical results show in detail that there is an optimum beam thickness and an optimum beam velocity.     

Output of Super-radiant Smith-Purcell radiation: A theoretical analysis

A two-section grating system for Smith-Purcell free-electron lasers is investigated. The system is composed of two open gratings with different geometrical parameters. It is expected that the originally continuous electron beam is bunched in the first section by interaction with the evanescent wave near the grating surface, and enhanced radiation can be extracted at the second section in the form of super-radiant Smith-Purcell radiation at a designed angle. With the help of particle-in-cell simulation, the electron beam bunching and directed output of the fundamental radiation and higher order harmonics are demonstrated.     

Smith—Purcell型自由电子激光的辐射

基于电子与光栅表面电势场相互作用的模型，用经典的单粒子理论研究了Ｓｍｉｔｈ－Ｐｕｒｃｅｌｌ效应的辐射过程，得到了自发辐射谱。讨论了自发辐射与受激辐射之关系，即Ｍａｄｅｙ定理在该类激光器中的对应形式。结果对于高能电子束同样适用。     

Investigation of a Novel Smith-Purcell Tunable Radiation Source

A novel Smith-Purcell tunable radiation source with relativistic electron beam of middle energy and a quasi-optical resonator composed of diffraction grating and three-mirror reflector is reported. Theoretical analyses and numerical simulation results indicate that coherent radiation with peak power of a few MW order can be achieved from this experimental model. The typical curve of PIC simulation and cool testing experiment is also given.     

Smith-Purcell Radiation in the Sub-mm Wavelength Region

Spontaneous Smith-Purcell radiation at wavelengths of 100 and 220μm has been observed. The angles of observation were 17° and 28° and the electron beam energies 1.9 and 1.56MeV, respectively. The radiated power was about 320nW at 17° and 92nW at 28°. These values are in reasonable agreement with what is theoretically expected if the emission process is due to the acceleration of image charges induced on the grating surface by the electrons of the beam.