Modulation Of Terahertz Radiation By Electron Beam Excited Metamaterials

Terahertz(THz)wave usually refers to the wavelength in the range of 0.03 mm to3 mm,and it is also known as submillimeter waves or T rays.Terahertz wave not only has high transmission and low energy,but also has unique physical properties such as transient,water absorption and coherence.Therefore,it has important application in the fields of food safety,radar,public safety,communication,etc.The current methods for generating terahertz waves include electronics methods and photonics methods.Although each type of radiation source has made great progress,there are still some problems.In this paper,we propose to use the metamaterial groove structure and grating structure to realize the miniaturization of terahertz vacuum electronics radiation source,that is,the Smith-Purcell terahertz radiation source based on metamaterials.This paper uses CST to design and analyze the metamaterial groove structure,discuss its cold cavity transmission and reflection characteristics and thermal cavity resonance characteristics,then place the metamaterial groove structure above the grating.Under the excitation of electron beams,we explore its radiation characteristic and finally realize the modulation and enhancement of Smith-Purcell radiation by using the geometric parameters of the groove structure.The specific content is as follows:(1)Design of metamaterial groove structureBased on the existing metamaterial structure,we design a structure that can be laid on the top of the grating and it has a specific frequency response.The characteristics of the cold cavity are explored in the CST Microwave Studio,and the length,width and thickness of the groove are optimized to adjust the resonant frequency and match the grating frequency.(2)Research on the radiation characteristics of the structure of laying grooves above gratingBy adjusting and optimizing the parameters of the groove structure,the frequency matching with the negative primary or negative second harmonic radiation of the grating Smith-Purcell under the excitation of a single bunch of Gaussian electron beams is realized to form the structure of laying grooves above grating to achieve specific radiation with controllable frequency angle enhancement.(3)Optimization and experimental design of Smith-Purcell radiation characteristics of the structure of laying grooves above grating,(a)Based on the above simulation and design,the Smith-Purcell radiation characteristics of the metamaterial structure are studied under the stimulation of several Gauss electron beams,and the efficiency of the metamaterial structure is compared with the side-wall grating.Furthermore,the metamaterial structure is optimized to maximize radiation efficiency.(b)According to the preliminary design and consider the factors in the experiment,we carry on the simple experiment design to provide the thoughts and methods for the follow-up researchers.