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Physics Seminar

Spin-orbit coupling in nanophotonics

Speaker: Prof. Anatoly V. Zayats (King’s College London)
Date: Wednesday 23 January 2019
Time: 15:00
Venue: Queens Buildings N/3.28

Spin-orbit coupling of light describes how spin angular momentum of light (associated with circular polarisation of an electromagnetic wave) is coupled to orbital angular momentum of light (associated with the energy flow and propagation direction). This effect provides interesting applications in polarisation-enabled control of optical signals, or in reverse, controlling light polarisation, sensing applications and quantum optical processes. Near the nanostructures capable of supporting waveguided modes, the spin-orbit coupling is mediated by the transverse spin carried by guided modes: electric field spins around an axis perpendicular to the wavevector, with the spinning sense determined solely by the propagation direction. The spin-orbit coupling in such type of modes, results in the so-called photonic spin-Hall effect, in analogy to spin-Hall effect for electrons. The use of polarisation (spin) of light to control interaction of light with nanostructures, waveguides, metamaterials and metasurfaces provides exquisite route to manipulation sub-wavelength optical signals with high precision in classical and quantum optical domains. Due to the momentum conservation, the waveguided modes can be used to engineer polarisation-controlled forces on nano-objects near a waveguide and repulsion of nanoparticles from metamaterials and metasurfaces. Circularly polarised dipoles are also responsible for counterintuitive lateral van der Waals forces on symmetric nanoparticles located near a surface. In this talk we will overview the effects associated with the photon spin when circularly polarised light interacts with plasmonic nanostructures and metamaterials. Spin-dependent directional excitation of guided modes, spin-orbit coupling in surface plasmon scattering associated with the unusual, transverse spin of surface polaritons, and spin-dependent optical forces will be discussed. Photonic spin-orbit interactions provide an additional and important tool for harvesting functionalities and applications of circularly polarised light in numerous photonic technologies.