Ultrafast vector imaging of plasmonic skyrmion dynamics

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].