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.
Strong coupling of metallic nanoparticles results in interaction of the plasmonic properties of individual nanoparticles
and forms a new hybridized response that can be controlled through nanoparticle geometry and excitation field
parameters. In this report, we show controlled excitation and enhancement of gap plasmon responses in closely spaced
and differently aligned gold nanoparticles of various sizes and shapes. Our numerical results reveal that the spectral,
spatial, and temporal intensities of coupled nanoparticles can be hugely enhanced by controlling the geometry,
morphology, and alignment of the nanoparticles. Besides, shaping the temporal profiles of the excitation field gives an
unprecedented control over the spectral and temporal responses of the gap plasmons. These findings might have
implications for designing and fabrication of metallic nanoparticles for surface-based applications.