The plasmon effect is of great significance for photoemission in metallic nanostructure. We introduced the photoemission electron microscope (PEEM) in detail, and used it to study the effects of polarization on the far-field and near-field of the plasmon. We further investigate the photoelectron energy spectrum obtained by PEEM and demonstrated the spatial distribution of photoelectrons with different energies. These experimental results help us to further understand the mechanism of photoemission and laid the foundation for the future development of plasmon device and technology.
Accurately grasping and controlling the plasmon dynamics and dephasing time is a prerequisite for the application of plasmons. Here, we report on the investigation of dynamics and dephasing time of different plasmonic hot spots in a single bowtie structure under varied light polarization using time-resolved photoemission electron microscopy (PEEM). In contrast to those previous global-parameter descriptions, we here report the experimental observation of apparently spatially diverse plasmon dynamic characteristics and spatially different dephasing time within a plasmonic bowtie. We experimentally obtain different plasmon dynamics in the tips of the bowtie nanostructure with different light polarization and actively control dephasing time by changing the light polarization which transforms the plasmon mode. Experimental results got the minimum dephasing time of 8.5fs and the maximum dephasing time of 17fs, which has a large adjustment range. In addition, we found that structural defects can prolong the dephasing time, and we analyzed its role in the influence of plasmon dynamics and dephasing time.
Subwavelength imaging and control of localized near-field distribution under off-resonant excitation within identical gold bowtie structure, and of dark mode distribution within nanoring were demonstrated. The near-field control was established by coherent control of two orthogonally polarized fs laser pulses in bowtie and by varying polarization direction and wavelength of single femtosecond laser beam in the nanoring structure. We found that the hot spot under off-resonant wavelength illumination mainly distributed along the edges of the nanoprism in the bowtie and quadruple mode formation in the nanoring. The obtained results show that the PEEM images correspond generally to the simulated patterns of the plasmonic modes for the both structures and difference exists between experimental and simulated images. The responsible reasons for difference are discussed in terms of band structure near Fermi level and of surface imperfects of the structure. Our finding for the near field control of the nanostructure provides a fundamental understanding of the non-radiative optical near field and will pave the ways for the applications such as sensing, SERS, biomedicine and plasmonic devices.
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. 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. On the other hand, control of the near-field distribution was realized by variation of the phase delay of two orthogonally polarized 200fs laser pulses. The experimental results of the optical near-field distribution control are well reproduced by finite-difference time-domain simulations and understood by linear combination of electric charge distribution of the bowtie by s- and p- polarized light illumination. In addition, an independent shift of the excitation position or the phase of the near-field can be realized by coherent control of two orthogonally polarized fs laser pulses.