Dynamic Evolution Of The Coupled Plasmon Field

Compared with a single plasmon field,a coupled plasmon field formed by the coupling or hybridization of multiple single plasmons in a nanostructure has higher adjustment freedom and stronger near-field enhancement,has become an important research content in the field of plasmon research.The dynamic evolution of plasmon and its nano-scale characterization of dephasing time are the foundation for people to understand and use plasmon in depth,However,the current research on the nanoscale characterization of coupled plasmon field dynamics and its dephasing time is seriously insufficient.To this end,this paper conducts nanoscale characterization studies on the dynamic evolution of coupled plasmon fields and their dephasing times in several typical nanostructures(nanorod dimers,nanocross and nano-bowtie structures).The research content and results are as follows:(1)The research on the dynamic evolution of single excited hot-spot coupled plasmon field in nanorod dimer structure and its dephasing time are carried out.The results show that when the two rods in the dimer have different lengths,only the dynamic evolution curve corresponding to the short rod shows a beat frequency signal,that is,only the short rod exhibits the coupled plasmon field characteristic.Comparing the dephasing time of a single rod and an equal-length double rod,it is found that the equal-length double rod results in greater radiation damping due to the coupling effect,so the dephasing time is shorter(110nm single rod 5.5fs,110 nm equal-length double rod 3.6fs).(2)The dynamic evolution of a single excited hot spot coupled plasmon field in an asymmetric nanocross structure and its dephasing time have been studied.The results show that in the cross structure,only the short arm dynamic evolution curve will show a beat frequency signal,that is,only the short arm shows the characteristics of the coupled plasmon field.In addition,changing the polarization of incident light does not affect the frequency and coupling properties of the plasmon field of the nanocross structure,but only changes the oscillation intensity.By using the coupled harmonic oscillator model,it is found that the dephasing time range of the plasmon field of the cross structure is about 4fs to 14 fs.Further investigation revealed that as the length of the structural arm changes,the dephasing time corresponding to the long arm changes from 4fs to 5fs,the dephasing time corresponding to the high frequency field in the short arm change from 14 fs to 7fs,and the dephasing time corresponding to the low frequency field from 4.5fs change to 9fs.(3)The research on the dynamic evolution of coupled plasmon field and its dephasing time in bowtie nanostructure was carried out.The results show that when the size of the bowtie nanostructure is 89 nm and 107 nm,there is only a single plasmon mode in the structure,and its dephasing time is 2fs and 2.5fs,respectively.When the structure size is increased to 124 nm,the top position of the bowtie nanostructure still shows only a single plasmon mode,its dephasing time is 2fs,and the coupled plasmon field signal appears at the outer corner position of the structure,its dephasing time is 2fs and 4fs.In addition,by means of interference time-resolved photoemission electron microscopy,a high-temporal and spatially resolved in-situ characterization of the dynamic evolution process of the nano-bowtie plasmon field.