Theoretical Study Of Novel Terahertz Sources Based On Special Smith-Purcell Radiation

Due to its unique physical properties,terahertz waves have tremendous application prospects in the fields of biomedicine,materials research,security check,and commu-nication.However,the lack of compact,high-efficiency,high-power terahertz radiation sources have always been one of the main obstacles restricting the practical application of terahertz waves.This thesis proposes and studies a series of terahertz source schemes based on special Smith-Purcell radiation for this key scientific and technical problem.The working mechanism and the physical problems involved are discussed in detail,including:1)A kind of terahertz radiation model based on two cascading grating and utiliz-ing high harmonic coherent radiation generated by continuous electron beam is studied.It consists of two models:the first model is a cascading structure formed by adding a grating operating in special Smith-Purcell radiation mode behind a grating operating in ordinary Smith-Purcell radiation mode.The first grating is used to pre-bunch the electron beams,and then the second grating is used to generate higher harmonic coher-ent terahertz Smith-Purcell radiation.In the second model,both gratings operate in the ordinary Smith-Purcell radiation mode.This model can produce multicolor coherent terahertz Smith-Purcell radiation from multi-bunched electron beams.2)A model for generating multi-color coherent terahertz radiation from double-bunched electron beams was studied.The periodic bunched electron beam generated by photocathode electron gun is used to interact with the surface wave of the grating.Electrons in each bunch is further micro-bunched,and the multi-color coherent terahertz radiation is generated on the superimposed harmonic components.The spectrum of the radiation frequency is widely tunable by adjusting the laser pulse repetition frequency within a certain range.3)In order to achieve the manipulation of the radiation direction in three-dimensional space,a terahertz radiation model which generates special Smith-Purcell radiation by using a sheet electron beam to excite a two-dimensional sub-wavelength rectangular hole array is studied.By changing the relevant structural and physical pa-rameters,the model can produce coherent terahertz radiation with multi-colors,multiple radiation directions,and adjustable radiation directions.The above research could provide new ideas for the development of new com-pact,high-power,tunable terahertz sources,and also provide theoretical support for the development of practical devices.