Research On Smith-Purcell Radiation By Free Electron Beam Excited Periodic Micro-Nano Structure

After a long period of development,electronics and photonics have made rapid progress in their respective fields,but with the increasing demand of people in recent years,the development of radiation sources using only one of the two related technologies has encountered a huge bottleneck.Therefore,it is of great significance to explore the research direction of combining electronics and photonics.In these directions,the combination of electronics and photonics to produce electromagnetic radiation is a very important research direction.With the development of electron beam source and micro-nano processing technology in recent years,it is possible to use free electrons to stimulate metal to produce electromagnetic radiation.In this context,surface plasmons(SPPs)excited by free-electron in metal micro-nano structures and Smith-Purcell radiation generated by SPPs in periodic grating structures are investigated in depth.In this paper,The physical process of electron beam parallel crossing the metal film is analyzed in detail.In this paper,we study two modes of SPPs excitation,symmetric and asymmetric,and find the the effect of thickness of metal film,the energy of electron beam,and the property of metal material on surface plasma by changing parameters.On the basis of stimulating SPPs in metal structures,we hope to explore the electromagnetic radiation generated by SPPs and its enhancement through specific physical mechanisms.Then,we studied the physical process of parallel electron beam passing through PEC grating,verified the description of the radiation property of Smith-Purcell in the theoretical formula by numerical calculation and simulation,and the surface wave and smith-purcell radiation in the far field are analyzed meanwhile.The effects of parallel electron beam energy,grating parameters such as grating period,grating depth and grating duty ratio on surface wave and far-field radiation are investigated by changing relevant parameters.It is shown that the frequency of Smith-Purcell radiation can be tuned by the period of the PEC grating and the acceleration voltage of the excited electron beam.As the period increases,the radiation frequency decreases gradually.The acceleration voltage of electron beam increases and its frequency increases correspondingly.The duty ratio and grating depth can only affect the radiation efficiency.For surface waves,the frequency can be tuned by changing the parameters of the PEC grating itself(such as the grating period P and gap depth h)and the acceleration voltage of the electron beam.In metal gratings,SPPs,smith-purcell radiation and surface waves can be excited by parallel electron beams simultaneously.In this paper,the physical process of parallel electron beam excited gold gratings is reasoned and proved.Through the previous study of PEC grating,we learned that a similar physical process occurred in the excitation process of gold grating,and the material change did not change Smith-Purcell radiation.But at the same time,with the change of energy of electron beam and the change of grating depth,SPPs experienced a series of changes,and the frequency difference between the two modes of SPPs also became larger and larger.Numerical analysis and simulation show that if the structural parameters of the metal grating and the energy of the electron beam match each other,the Smith-Purcell radiation enhanced by SPPs can be obtained.Finally,according to the analysis of simulation results,we designed a suitable gold grating and carried out experimental research by modified SEM and spectrometer.Scanning electron microscopy(SEM)provides a cluster of electron beams,a spectrometer is used to analyze the radiation field generated by the excitation received by an optical fiber to obtain the corresponding spectrum map by post-processing the signal.The presence of-2~-4 harmonics of Smith-Purcell radiation was found in the spectra generated by scanning electron microscopy(SEM)using bunched electrons to excite the structure of the gold grating with anoxic copper as the substrate,and receiving angle of far-field radiation are changed by scanning electron microscope to verify the previous numerical and simulation results.