Probing of Ultrafast Plasmon Dynamics on Gold Bowtie Nanostructure Using Photoemission Electron Microscopy**Supported by the National Basic Research Program of China under Grant No 2013CB922404, the National Natural Science Foundation of China under Grant Nos 11474040 11274053, 11474039 and 61178022, and the Project under Grant No 14KP007.

Abstract

We report the direct imaging of plasmon on the tips of nano-prisms in a bowtie structure excited by 7 fs laser pulses and probing of ultrafast plasmon dynamics by combining the pump-probe technology with three-photon photoemission electron microscopy. Different photoemission patterns induced by the plasmon effect are observed when the bowties are excited by s- and p-polarized femtosecond laser pulses. A series of images of the evolution of local surface plasmon modes on different tips of the bowtie are obtained by the time-resolved three-photon photoemission electron microscopy, and the result discloses that plasmon excitation is dominated by the interference of the pump and probe pulses within the first 13 fs of the delay time, and thereafter the individual plasmon starts to oscillate on its own characteristic resonant frequencies.