Research On Terahertz Superradiant Smith-Purcell Radiation Source

Terahertz(THz)waves are electromagnetic waves whose frequency is between 0.1 THz and 10 THz and wavelength is between 30 ?m and 3 mm.The wavelength of the terahertz wave is between the millimeter wave and the infrared ray,which is a spectrum band that has not been fully exploited,and because of the unique properties of terahertz waves with high resolution,low energy and high penetration.The development and exploration of terahertz have great scientific significance and application prospects.The terahertz radiation source is an important link in the transformation of terahertz science and technology into real productivity.At the same time,the research of vacuum electronic terahertz source with characteristics of high power,high efficiency and working at room temperature is great significant to promote the development of terahertz technology.However,with the increase of the frequency of the vacuum electronic terahertz radiation source,the size of structure is greatly reduced,and the starting current density is greatly increased.Therefore,increasing the frequency of the existing vacuum electronic terahertz radiation source and reducing the starting current density become the main research goals.Based on the above reasons,this paper will delve into the dispersion characteristics of open grating structures,expanding the application of Smith-Purcell radiation(SPR),exploring the dispersion characteristics of two-dimensional periodic columns,and focusing on super-radiate Smith-Purcell radiation(SSPR)which is exciting by electron beams in the two-dimensional periodic columns.Finally,follow-up related experimental researches are carried out.The specific contents of the study are as follows:a.Based on the open grating to study the mechanism of higher harmonic super-radiate Smith-Purcell radiation.Dispersion characteristics are the most important parameters of the structural system.It is related to a series of important indicators such as working voltage,frequency bandwidth,working frequency and working stability of vacuum devices.Since the radiation power of the high-order harmonic super-radiate Smith-Purcell radiation is too small,the existing research has focused on the second-harmonic super-radiate Smith-Purcell radiation.By theoretically analyzing the dispersion characteristics of open grating structures,this paper proposes a new mechanism to improve the output power of the third harmonic super-radiation by suppressing the second harmonic super-radiation,and verify its feasibility by PIC simulation.The operating frequency of the radiation source has increased significantly.b.Study on multi-electron beams injection two-dimensional periodic columns for excitation of super-radiation Smith-Purcell radiation.The terahertz radiation source operating in the terahertz band has a sharp increase in the current density of the electron injection with increasing frequency.The two-dimensional periodic columns allow electron beams to pass inside the structure,increasing the interaction area between the surface wave and the electron beams,while allowing coupling between multiple electron injections.In this paper,the chromatic dispersion characteristics of the two-dimensional periodic column structure are analyzed,and then the structural size of the best two-dimensional periodic columns is discussed by PIC simulation.Finally,the simulation are carried out to verify the two-dimensional periodic columns to reduce the starting current density and increase the radiant power.c.Study on coupled-output super-radiated Smith-Purcell radiation of three mirror quasi-optical cavity.Super-radiate Smith-Purcell radiation is a coherent radiation with a radiation angle.The three-mirror quasi-optical cavity has a unique position and role in coupling-output super-radiate Smith-Purcell radiation,since it has the advantages of high Q value and adjustable angle.In this paper,based on the theory of free electromagnetic oscillation,the electromagnetic field distribution in the three mirrors is theoretically analyzed,and the resonance condition of the cavity is obtained.The model of the two-dimensional periodic column coupled with three mirrors is simulated to verify the applicability of three mirror quasi-optical cavity in the coupled-output super-radiate Smith-Purcell radiation.d.Preliminary experiment of super-radiated Smith-Purcell radiation.The previous work has carried out in-depth research on the open grating and the super-radiate Smith-Purcell radiation in the two-dimensional periodic columns.The experimental verification is the basic step of turning the theory into practice.This paper has completed the preliminary stage of experimental study of the super-radiate Smith-Purcell radiation.