Diffraction Radiation From The Peridical Waveguide Structure Excited By A Uniformly Moving Electron Beam

Terahertz wave, electromagnetic radiation in the frequency from0.1THz to10THz (wavelength of3mm to0.03mm), has attracted extensive interests of scientistsfrom different disciplines for its great potential applications in varieties of ifelds ofmodern science. Yet till now, it is still an urgent problem to develop the compact, roomtemperature, and relatively high power terahertz radiation source, even though greatefforts have been made.The primary obstacle for the traditional vacuum electronic devices, such as BWOand EIO，to generate high frequency (higher than0.5THz) terahertz radiation is therequirement of extremely high starting beam current density. The diffraction radiationfrom the periodical waveguide structure (PWS) excited by a uniformly moving electronbeam, which is newly found in the recent years, may offer a good opportunity to thevacuum electronics and bring attractive prospects to develop the compact and tunablefree-electron-radiation-source in the high frequency terahertz regime since it avoids therequirement of starting current density. Detailed theoretical analysis as well asnumerical simulations on this kind of radiation are carried out in this dissertation. Therequirements for the coherent radiation from the electron bunch and the train of bunchesare found. And the influence of the charge distribution on the radiation characteristicsare studied. The results I obtained are of great signiifcances for the development of thehigh frequency terahertz radiation sources based on this mechanism.I also propose, in the dissertation, a kind of free electron terahertz wave radiationsource with two-section periodical waveguide structure (PWS), where the first section(section-I) is used to pre-modulate the electron beam and the second section (section-II)is for terahertz wave generation. By means of theoretical analysis and numericalsimulations, I demonstrate that the starting current density of the beam-wave interactionin section-II can be signiifcantly reduced provided that its operation frequency is theharmonic of electron beam’s pre-modulation frequency. This kind of source can generaterelatively high power terahertz wave radiation but only need a moderate beam current density. And it may have great potential application in developing the compact and highpower terahertz wave radiation source.Besides, the detailed theoretical analysis and computer simulations on theelectromagnetic waves propagating in the nano-scale periodical waveguide structurewith Surface Plasmon Polaritons (SPPs) taken into consideration are carried out in thisdissertation. The results show that the presence of SPPs will signiifcantly influence theelectromagnetic characteristics of the structure. More importantly, when the operatingfrequency lies in the radial conifnement region，the electromagnetic waves will becompletely conifned within the longitudinal waveguide and propagate along it with littleattenuation. And the radial energy loss is greatly reduced. These results are of greatsigniifcance for increasing the eiffciency of the radiation sources based on this structure,as well as for the development of high eiffciency transmission waveguides andwide-band iflters in the infrared and visible region.