The orbital angular momentum (OAM) of light could be exploited in a number of applications from data storage and quantum cryptography to enantiomer determination and optical tweezing. Recent work has demonstrated the potential role of surface plasmon polaritons for confining and controlling light carrying OAM in plasmonic vortices. Now a collaboration of researchers in Israel, Germany and Ireland have used time-resolved two-photon photoemission electron microscopy to show how plasmonic vortices are generated and evolve with femtosecond temporal and nanoscale spatial resolution.

The researchers shone circularly polarized light on nanostructured single-crystalline gold flakes on silicon substrates. Incident light gives rise to surface plasmon polaritons – quantized oscillations of the electrons in the metal, “surface plasmons”, coupled with electromagnetic waves bound at interfaces. By incorporating Archimidean spiral slits on the gold nanostructures the researchers could encourage the generation of plasmonic vortices from incident circularly polarized light.

Harald Giessen at the University of Stuttgart, Frank Joachim Meyer zu Heringdorf at the University of Duisburg–Essen, Meir Orenstein at Technion–Israel Institute of Technology, Martin Aeschlimann at the University of Kaiserslautern and their collaborators probed the system with time-resolved two-photon photoemission electron microscopy. This allowed them to follow the ultrafast dynamics of the plasmonic vortices on a subfemtosecond time scale and nanometre lateral scale as they evolve, giving unprecedented insights into how the light spin to plasmonic OAM takes place. The researchers conclude in their report, “The study reveals the nature of the plasmonic OAM and vortex formation and these observations open new avenues for designing and directly measuring exciting applications of OAM in the nanoworld.”

Full details are reported in Science.