Spatial Variations in Femtosecond Field Dynamics within a Plasmonic Nanoresonator Mode

Abstract

Plasmonic resonators can be designed to support spectrally well-separated discrete modes. The associated characteristic spatial patterns of intense electromagnetic hot-spots can be exploited to enhance light−matter interaction. Here, we study the local field dynamics of individual hot-spots within a nanoslit resonator by detecting characteristic changes of the photoelectron emission signal on a scale of ∼12 nm using time-resolved photoemission electron microscopy (TR-PEEM) and by excitation with the output from a 20 fs, 1 MHz noncollinear optical parametric amplifier (NOPA). Surprisingly, we detect apparent spatial variations of the Q-factor and resonance frequency that are commonly considered to be global properties for a single mode. By using the concept of quasinormal modes we explain these local differences by crosstalk of adjacent resonator modes. Our findings are important in view of timedomain studies of plasmon-mediated strong light−matter coupling at ambient conditions.

Ultrafast Photoemission Electron Microscopy: Imaging Plasmons in Space and Time

“…With effort, the pulse duration can be further decreased to <10 fs range. , The IR fiber laser pulses can also be converted in atomic gases to generate directly high harmonics in the VUV range . The broad tunability, short pulse duration, high power, and high repetition rates make the Yb-doped fiber laser pumped NOPA systems particularly well suited to study a broad spectrum of plasmonic phenomena in a variety of materials by ITR-mPP and ITR-PEEM methods. ,,,,,, …”

“…Experimental PEEM instruments equipped with broadly tunable excitation sources, however, are still sparse and available only in a few laboratories. ,,, Nevertheless, narrower tunability around a central wavelength of the laser output (usually in the range 720–920 nm) has been successfully utilized to explore the spectral properties of Au nanostructures. In particular, Yu et al has spatially resolved coupled bonding and antibonding plasmon modes within Au dolmen structure .…”

Space- and time-resolved UV-to-NIR surface spectroscopy and 2D nanoscopy at 1 MHz repetition rate

“…In previous work, we had demonstrated a minimum length scale of 12 nm using fs pulse excitation. 51 Fig. 5c) and the single-pulse multiphoton photoemission image (third column in Fig.…”

Speeding up Nanoscience and Nanotechnology with Ultrafast Plasmonics

“…Furthermore, Zeuner and co-workers used a coupled three-nanorod structure and phase-dependent ultrafast excitation to achieve coherent control of the nonlinear response of plasmonic modes by tuning the phase relation between two orthogonally polarized light fields via damping effects . While Fourier-limited pulse duration in pump–probe experiments can allow the best temporal resolution, to improve the spatial resolution and access information on the nanometer scale, Hensen and co-workers proposed a time-resolved interferometric photoemission electron microscopy scheme, where the dynamics of the local plasmonic modes has been resolved on the fs time-scale and on a 12 nm size-scale . With this approach, they were able to resolve the spatial variations of the quality factor of single plasmonic resonances, and showed, by using the theory of quasi-normal modes, that these variations are due to crosstalk between spectrally adjacent resonances.…”

“…3 While Fourier-limited pulse duration in pump−probe experiments can allow the best temporal resolution, to improve the spatial resolution and access information on the nanometer scale, Hensen and co-workers proposed a time-resolved interferometric photoemission electron microscopy scheme, where the dynamics of the local plasmonic modes has been resolved on the fs time-scale and on a 12 nm size-scale. 4 With this approach, they were able to resolve the spatial variations of the quality factor of single plasmonic resonances, and showed, by using the theory of quasi-normal modes, that these variations are due to crosstalk between spectrally adjacent resonances. The nanometer engineering of plasmons through a proper nanostructure design is indeed fundamental to develop future plasmonic nanodevices.…”