【作者】 张雅鑫；

【导师】 刘盛纲；

【作者基本信息】 电子科技大学 ， 物理电子学， 2009， 博士

【摘要】 在太赫兹科学技术的研究工作中,太赫兹辐射源是一个急待解决的问题。无论是从科学研究的角度还是从应用角度看,一个便于使用又具有良好性能的太赫兹辐射源就是科学家们追求的目标。因此本论文主要研究电子束在各向异性Hermitian介质中以及新型圆柱型亚波长孔阵列结构中的辐射特性以及互作用机理,旨在为相关太赫兹源的研究、发展提供理论依据及新思路。本论文主要从理论到模拟研究、从基础到应用,通过对各向异性Hermitian介质Cherenkov辐射理论体系的建立引申到电子在亚波长孔阵列结构中的辐射现象,再将电子束与亚波长孔阵列结构相结合研究该结构中注波互作用过程。本论文主要研究内容及所得到的成果如下：1.本文对电子在Hermitian介质中的Cherenkov辐射进行了详尽的讨论,建立了较为完整的理论体系,得到了辐射场解析表达式、辐射功率表达式等,对其辐射条件、特征值、相速、群速、辐射功率进行了研究。结果表明带电粒子在各向异性介质中激发的Cherenkov辐射必须要考虑电荷和电流同时对辐射场的贡献；Hermitan介质中的Cherenkov辐射能向外辐射出两个模式,一个是通常可以向外辐射的“o”模,一个则是往往以局域场出现的“e”模。当满足特殊条件时,两个模式仍然可以同时向外辐射,这个结果有别于传统的在各向同性色散介质中的Cherenkov辐射。此外,Hermitan介质中Cherenkov辐射的辐射场相速大于群速。2.本文研究了Hermitian介质中的Cherenkov辐射精细结构出现的原因,得出该现象是带电粒子在有损Hermitian介质中Cherenkov辐射固有的一种特殊物理现象,它的出现主要因为辐射场群速比相速小。3.本文研究了运动Hermitian介质中的Cherenkov辐射,讨论了介质运动速度对辐射场特征值、辐射条件、辐射功率的影响,结果表明在运动Hermitian介质中的Cherenkov辐射同样存在两个不同的辐射模式。并且介质运动速度对“e”模影响十分大,随着速度的增加“e”模场强迅速减小,而“o”模影响则较小。并且在运动介质中同样存在辐射场相速大于群速的情况,当考虑损耗时也同样存在精细结构现象。4.基于Hermitian介质中Cherenkov辐射的研究本文对电子在圆柱型亚波长孔阵列结构中辐射现象进行了研究。发现,电子在这种结构中辐射场分布明显与传统光栅有所不同,其角向场分布由于周期孔阵列的出现也呈周期分布。鉴于此我们对电子束在这种结构中的互作用以及该结构高频特性也进行了研究。5.本文分析了圆柱亚波长孔阵列结构色散特性、模式分布以及耦合阻抗,并通过线性理论分析得出了电子束在该结构中互作用色散方程、计算出了互作用增长率,并通过3D粒子模拟软件仿真了该互作用过程。结果发现电子束在这种结构中的互作用能有效降低起振电流密度。更多还原

【Abstract】 Terahertz Science and Technology is a very important and rapidly developing area of modern science. Nowadays, in order to fill the "THz gap", the exploration of THz radiation sources turns to be the highest priority. Although strong efforts have been made and some progresses have been achieved in this aspect, there are still many problems associated with the THz radiation sources. In this dissertation, the Cherenkov radiation in Hermitian medium, radiation and interaction between electron beam and cylindrical mimicking surface plasmons wave have been studied.The following results have been achieved in this dissertation:1. Detailed theoretical investigation and computer calculations on Cherenkov Radiation by an electron bunch that moves in a Hermitian medium (CRH) with and without absorption are presented in the paper. The theory shows that in CRH, not only the current density but also the charge density of the particle contributes to the Cherenkov Radiation (CR). It has been found that there are two modes in the CRH; in general, only one of them is radiative mode, another one is local field, and the area where both of these two modes are radiative modes simultaneously is studied, the comparison of the two modes is given in the paper and the relation of the existence of these two modes has been improved. The comparison of the calculations shows that the radiation power of mode "o" is larger than that of mode "e". And it indicates that the group velocity in the CRH is slower than the phase velocity. Detailed computer calculations are given in the paper, and some interesting physical phenomena of CR have been revealed.2. The theory gives a simple physical interpretation of the inner fine structure of the CRH; it concludes that the mechanism of the appearance of the inner fine structure of CR is that in the absorptive Hermitian medium the group velocity is less than the phase velocity.3. Detailed theoretical investigation and computer calculations on the Cherenkov Radiation (CR) in moving Hermitian medium (CRMH) are presented in this paper. It has been found that, similar to that in stationary Hermitian medium (CRH) case, there are two modes in the CRMH; in general, only one of them is radiative mode, another one is local field, and the comparison of the two modes is given in the paper. The small absorption of CRMH mainly results in the Gaussian-like field intensity pattern. And the group velocity in the CRMH is always slower than the phase velocity in the moving HM, so the fine inner structure occurs. Comparing the behaviors of CRMH and CRH, we have found that the movement of the Hermitian medium (HM) brings significant influences on the CR, so there are some interesting characteristics of CRMH, such as in the CRMH, the radiation power of the "o" mode is much higher than that of "e" mode. And because of the relativistic Doppler Effect, the frequency region where both modes are radiative becomes quite different from that for CRH.4. Based on the study of Cherenkov radiation in Hermitian Medium, the study on the radiation in the cylindrical sub-wavelength holes array is presented. It is found that the contour of this radiation is different from traditional grating-radiation. So the works on the dispersion characteristics and interaction have been carried out.5. The coupling impedance and modes distribution of this cylindrical structure is presented and studied theoretically and by computer simulation. More importantly, the mimicking surface plasmons modes are proposed to interact with electron beam to generate terahertz radiation. The results given in the paper show that the cylindrical MSP has distinct characteristics and the efficiency of this cylindrical MSP-electron beam interaction can reach an attractive value with reasonable current density of electron beam at THz regime.更多还原