Research On Tunable Terahertz Radiation Source Based On Two-dimensional Material

Terahertz radiation is a new type of excellent electromagnetic radiation,which has a very broad application prospect in the fields of terahertz imaging,terahertz communication,and biomedical spectrum analysis.The design and production of efficient and stable terahertz radiation source is a key core technology to promote the progress of terahertz science and technology.The terahertz radiation device based on the principle of Smith-Purcell radiation has become a hot research topic both at home and abroad as an effective terahertz source.In the current research,the Smith-Purcell radiation on the metal grating structure is a classic electromagnetic radiation.Electromagnetic radiation is generated when the moving electron beam passes through the surface of the periodic metal grating.However,the electromagnetic radiation generated in the metal grating structure will be emitted in all directions,which is inconvenient to control in practical applications,and the dispersion of the metal grating structure is strong.The radiation intensity is low.On the other hand,once the traditional metal grating structure use efficient,stable,and tunable terahertz radiation sources.The main research contents and results of this article are as follows:(1)Aiming at the problem of strong dispersion of metal gratings,a new type of metasurface structure is designed which can generate directional and high-intensity terahertz radiation.The radiation source is a three-layer structure composed of a metal patch,a dielectric,and a metal.The electron beam cluster generated by a free electron laser excites the metasurface structure to generate a Smith-Purcell radiation field in the terahertz band.The results show that the Smith-Purcell radiation produced by the metasurface structure has a 90-degree directional radiation characteristic,and its radiation intensity can reach 5 times the terahertz radiation intensity generated by the traditional metal grating.When the electromagnetic wave is incident perpendicularly,the metasurface structure strongly resonates at 0.5 THz,and the Smith-Purcell radiation spectr?m intensity at the resonance frequency is significantly increased and the bandwidth is narrow.The Smith-Purcell radiation at this resonance frequency is strong and narrow,which cannot be generated by traditional metal gratings.The research on the metasurface structure will provide important guidance and reference value for the development of terahertz radiation sources driven by electron beams with high intensity and directional radiation.(2)Based on the tunability of the chemical potential of the new two-dimensional material graphene,a tunable graphene metasurface terahertz radiation source structure was designed.By adjusting the chemical potential of graphene,not only the frequency of Smith-Purcell radiation can be controlled,but also the amplitude and direction of the radiation wave can be completely controlled.The radiation frequency is always the same as the resonance frequency of the graphene metasurface structure when it is perpendicularly incident.At the resonance frequency,higher radiation will be obtained for higher absorption.The intensity of the irradiated hypersurface structure can reach 2.4 times the intensity of terahertz radiation produced by traditional metal gratings.When a periodic electron beam excites the graphene metasurface structure,the radiation will be greatly enhanced.In addition,the graphene metasurface structure adopts a symmetrical design and has the characteristics of polarization insensitivity,which can be applied in various occasions.(3)Based on the tunable characteristics of MoS2,a tunable medi?m-loaded metal grating radiation structure in the near-infrared band was designed.The radiation source is a three-layer structure composed of molybden?m disulfide sheet-dielectric-metal base plate.The initial energy of the moving electron beam is reasonably designed.The metal grating can be excited by the medi?m to generate radiation at a frequency of 550 THz.In the case of molybden?m sulfide and without the introduction of molybden?m disulfide,the results show that the structure with the introduction of molybden?m disulfide can generate higher intensity radiation,and by changing the applied grid voltage of molybdenum disulfide,a tunable terahertz radiation source can be obtained.In addition,changes in the groove depth,width,and dielectric constant of the dielectric-loaded metal grating will affect the dispersion curve of the structure,that is,the frequency of the plasmon on the surface of the molybdenum disulfide,and then the frequency of the terahertz radiation.