Light carries spin angular momentum (SAM) in its left- or right-handed circular polarization, and orbital angular momentum (OAM) in spiralling wavefronts that form a vortex. Here we report on how interactions between two types of light fields – one spinning and the other rotating as a plasmon vortex – excite electrons from a gold surface. We demonstrate the spin-orbit mixing between the two forms of angular momenta of these optical fields.
Figure 1. Experimental Concept and Results Schematic. (A) Plasmonic vortex of order l=4 (green) revolving on a gold surface and interacting with right or left circularly polarized light pulses (s=+1 or -1) (red helix). Blue circles represent the photoemitted electrons resulting from two-photon absorption in gold. (B, C) Raw experimental data of electron emission patterns exhibiting an angular distribution of order 5 (B) and 3 (C), indicating the subtraction (mixing) of the plasmon (orbital) and light (spin) angular momenta. The scale bar on all data images is 1 µm.
This mixing allowed us to resolve new spectroscopic information on specific electronic transitions in the gold and may enhance current techniques such as Raman spectroscopy. Additionally, the possibility to control light-matter interactions could lead to exciting advances in quantum information science. OAM could be used to encode more information than SAM and potentially realize higher-order qubits for nanoscale integrated devices.
Publication Title: Mixing the light spin with plasmon orbit by nonlinear light-matter interaction in gold
Authors: Grisha Spektor, Deirdre Kilbane, Anna-Katharina Mahro, Michael Hartelt, Eva Prinz, Martin Aeschlimann and Meir Orenstein
Journal: Physical Review X 9, 021031 (2019) https://journals.aps.org/prx/abstract/10.1103/PhysRevX.9.021031