| Terahertz(THz)electromagnetic waves refer to electromagnetic waves with a frequency range between 0.1 THz and 10 THz and a wavelength between 0.03 mm and 30 mm.It is also called terahertz wave,T-ray.Because terahertz waves are in a special position in the electromagnetic spectrum,they have unique properties such as high permeability,transient properties,low energy,and coherence,which have great potential in academics and applications.Therefore,it has very important application results in the fields of biomedicine,communication,food safety,public safety and so on.The key to the development of terahertz technology is the development of terahertz radiation sources.Vacuum electron radiation source has attracted much attention due to its high efficiency and high power.However,due to the scale effect,such devices have encountered bottlenecks in the research of upgrading from the microwave frequency band to the terahertz frequency band.It is difficult to increase the frequency of the vacuum electron radiation source only by reducing the size of the device.The Smith-Purcell superradiation effect can increase the frequency of electromagnetic waves by radiating higher harmonics.In order to achieve the miniaturization of the terahertz vacuum radiation source,the theoretical and simulation research of Smith-Purcell super-harmonic super-radiation effect is carried out in this paper,and the experimental platform of the Smith-Purcell super-radiation verification experiment is set up,and part of the experimental work is completed.Among them,the study of Smith-Purcell’s higher harmonic superradiation.This paper theoretically analyzes the dispersion characteristics of the periodic structure,adjusts and optimizes the structural parameters,and designs a system that can stimulate Smith-Purcell’s third harmonic superradiation and fourth harmonic superradiation.Two flat grating periodic structures.In the verification experiment,Smith-Purcell superradiation simulation and experimental design were completed,and an experimental platform was set up according to the experimental design.The details are as follows:(1)Simulation study of Smith-Purcell higher harmonic superradiationBased on the characteristics of the periodic structure,the dispersion equation of the flat grating is derived through theoretical calculations,and the influence of various parameters of the flat grating structure on its dispersion curve is analyzed.By adjusting the structural parameters,the mechanism of Smith-Purcell higher harmonic superradiation was analyzed.(2)Simulation study of Smith-Purcell higher harmonic superradiationBy adjusting and optimizing the parameters of the periodic structure,the low-order harmonic super-radiation is suppressed,and the output power of the high-order harmonic super-radiation is enhanced.A flat grating structure capable of exciting the third harmonic super-radiation of Smith-Purcell,a flat grating structure capable of exciting the fourthharmonic super radiation of Smith-Purcell,and openings suitable for the Smith-Purcell super-radiation verification experiment based on a scanning electron beam source are designed.Channel grating structure.(3)Experimental study of Smith-Purcell higher harmonic superradiation(a)Using laboratory equipment,an experimental platform suitable for Smith-Purcell second harmonic superradiation was established.According to the simulation data of Smith-Purcell’s second harmonic superradiation,the designed electron gun is processed and assembled.The electron beam current density and beam spot size were measured.The reasons for the failure of the experiment were analyzed and the experimental scheme was improved.(b)Experimental study of Smith-Purcell superradiation based on scanning electron beam source.The high-frequency structure designed based on the electron gun will be processed,and the experimental scheme and the platform required for the experiment will be designed.These include translation stages,Faraday cups,and more. |
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