Study Of Radiation And Interaction In Te Hermitian Medium And Cylindrical Subwavelength Holes Array

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.