Imaging Of Plasmon Field By Two-color Photoemission Electron Microscopy

Plasmon has characteristics such as high near-field enhancement and breakthrough of diffraction limit convergence,and it is widely used in many fields such as sensing,communication and solar energy.The accurate characterization of the near field of plasmon is an important prerequisite for people to understand and use plasmon in depth.Photoemission electron microscopy(PEEM)has the characteristics of no probe interference,fast full-field imaging and time-resolvable integration,and has become one of the powerful tools for plasmon near-field characterization.In particular,the two-color photoemission electron microscopy developed in recent years can realize flexible control of the photoemission electron order and yields,and significant optimization of the near field PEEM image of the plasmon,so it will play an increasingly important role in the plasmonic field distribution imaging in the future.The specific research contents are as follows:In this paper,two-color photoemission electron microscopy is used to study the near-field imaging of the plasmonic field in gold nanoring structure and its corresponding influencing factors.The findings are as follows:(1)The simulation of the optical response of the plasmon field of gold nanoring structure was carried out.FDTD is used to simulate the extinction spectrum and its near-field distribution of plasmonic field under the excitation conditions of incident light with different polarization directions.The near-field distribution of gold nanorings excited by 800 nm resonant wavelength light and 400 nm non resonant wavelength light at the same time was simulated,then the feasibility of imaging 800 nm light corresponding to the plasmonic field under the irradiation of two-color light(800 nm + 400 nm)is explored.(2)The plasmonic field of the gold nanoring in two-color PEEM imaging was studied.The high spatial resolution characterization of the plasmonic field in the gold nanoring structure was studied by using two-color PEEM,and it was compared with the near-field PEEM image of the gold nanoring under monochromatic excitation.The results show that the photoelectron emission yield under the two-color excitation condition is increased by about 10 times compared with the 800 nm single-color excitation condition.The light emission electron order of the nanoring structure decreased from 3.8 under 800 nm monochromatic excitation to 1.85 under two-color excitation.But for the defect location,the order of the photoemission electron decreased from 3.72 to 2.52.The effects of the position,shape and size of structural defects on the plasmonic field of the gold nanoring structure were studied in depth,and the reasons for the strong interference of defect excitation on the PEEM image of the gold nanoring structure were analyzed.(3)The effect of two-color light parameters on the plasmonic field PEEM image was studied.The results show that when the relative delay time of dichroic light is 0 and the polarization angle of two-color light is 0°,the photoelectron yield is the largest and theopening degree of two-color quantum channel is the largest.In addition,it is found that when the polarization direction of 800 nm resonant wavelength light is unchanged,the opening degree of the two-color quantum channel decreases gradually with the shift of 400 nm non-resonant wavelength light polarization to S-polarization.Further,the influence of the polarization direction of the two-color light on the opening degree of the two-color quantum channel was explored,and the corresponding physical mechanism was analyzed.