Skyrmions are topological defects in vector fields that exhibit a characteristic vector structure. When excited by electro-magnetic near fields on thin metal films, they are called plasmonic skyrmions. These fields exist at the sub–100-nm scale, oscillate with periods of a few femtoseconds, and thus are difficult to measure. So far, two-photon photoemission electron microscopy was able to image local plasmon fields with femtosecond time resolution. We now extend this technique to obtain time-resolved vector information that enables us to compose entire movies on a subfemtosecond time scale and a 10-nm spatial scale of the electric field vectors of surface plasmon polaritons (SPPs). We use this technique to image complete time sequences of propagating surface plasmons, demonstrating their spin-momentum locking, as well as plasmonic skyrmions on atomically flat single-crystalline gold films that have been patterned using gold ion beam lithography [1].
Plasmonic microcavities are compact systems having the capability to confine light in an extremely small volume. Light
matter interactions can therefore be mediated very effectively by them. In this report we demonstrate experimentally that
dispersion of photonic cavity modes can be tuned to a large degree in a plasmonic microcavity with two identical
corrugated metallic films as resonant mirrors. The modification of the dispersion is induced by interactions between the
photonic and plasmonic modes. Additionally, the excited surface waves are strongly enhanced by the gratings, which is
important for coupling and enhancing evanescent fields. To realize such a cavity, we employed self-assembled
monolayer nanosphere crystals as a prepatterned substrate. Metal/dielectric/metal films were subsequently deposited on
it. The cavity length was used to tune the interaction strength. As a result, the original positively dispersive FP mode, i.e.,
the resonance frequency is increased with the incident angle, becomes independent or even negatively dependent on the
incident angle. Due to the hexagonal textured corrugation of the metal film and the existence of some line defects in a
large area, the optical response is isotropic and independent of the specific polarization. This behavior can have potential
applications for light emission devices, plasmonic color filters and subwavelength imaging.
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