Periodic Micro-nano Structures And Their Applications In THz Radiation Sources

Terahertz technology has shown great potential in modern communications,biomedical engineering,materials science,biological research,and other fields.Terahertz radiation sources are the key to terahertz technology.Terahertz radiation sources excited by the electron beam are one of the important types.It depends on electron-matter interaction,and the structure of matter depends on micro/nanofabrication.micro/nanofabrication is gradually becoming more reliable and stable,promoting the development of terahertz radiation sources excited by the electron beam.How to obtain the maximum radiation has become the focus of research and attention.This thesis investigates terahertz radiation based on photonic crystals and their derived structures and subwavelength hole arrays under free electron excitation,in which the radiation characteristics and mechanisms are focused.The main works are as follows.1.The oscillating dipole effect and resonant effect in photonic crystals are studied.The radiation mechanism and simulation results of grating with different rows are discussed and analyzed in detail.The increase of grating rows will increase the number of dipole oscillations,thus enhancing radiation.For four rows of grating,the resonance characteristics may narrow the radiation band.The period increases,and the resonant frequency decreases.Increasing the grating tooth width and decreasing the pillar distance can enhance resonance and radiation.In a specific range,electron velocity does not affect the resonant effect in the photonic crystal.The enhancement of radiation by electron trajectories and loading defects is studied using the dipole oscillation effect.Controlling the position of incident electrons can adjust radiation’s spatial and frequency distribution and improve energy conversion efficiency.Loading rectangular defects can enhance the radiation of the grating.2.Based on the fluid dynamics theory,the composite grating was studied to become a discrete upwind or downwind structure by changing the lateral displacement.Their radiation response under free electron excitation was analyzed.Adjust lateral displacement to achieve unequal radiation energy distribution in the upper and lower spaces.3.The extraordinary transmission of subwavelength rectangular hole arrays in the terahertz band was studied,the interpretation of Bloch mode at the macro level and quasi cylindrical wave at the micro level were analyzed,and the effect of structural parameters on transmission was studied.The relationship between the cutoff frequency and the period is obtained.4.The influence of structural parameters of subwavelength hole arrays on radiation was studied.The structural parameters of the subwavelength hole array with optimal radiation at the corresponding frequency are obtained by periodic normalization.The hole’s long side affects the radiation peak’s distribution and intensity.To a certain extent,the short side decreases,and the frequency band narrows.The thickness increases,the intensity increases,and the frequency band narrows.When the long side of the hole is1.6-1.75,the short side is 0.2-0.35,and the thickness is 0.75-1.25 times the period,a subwavelength hole array with a narrow frequency band and intense radiation can be obtained.Therefore,a radiation source operating at 650 GHz was designed.