The precise understanding of the spatiotemporal characteristics of ultrafast surface plasmons is a prerequisite for applications of plasmonics. Here, we report on the investigation of near-field imaging and dynamics of propagating and localized surface plasmons (PSPs and LSPs) using photoemission electron microscopy (PEEM) of the trench on the silver film and gold bowtie nanostructure. The actual propagation direction of PSPs is directly obtained by reading PEEM images via the non-collinear exciting method by the trench. The results have demonstrated that the trench structure is potential as a 2D plasmonic dispersion element. Moreover, we experimentally obtain diﬀerent LSPs dephasing times in the tips of the bowtie nanostructure by interferometric time-resolved PEEM. Experimental result reveals the dynamics of the LSP field initially oscillate at the laser field frequency and finally develop into its eigenfrequency after experiencing a few periods of frequency ﬂuctuation.
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.