Probing the Photonic Spin–Orbit Interactions in the Near Field of Nanostructures.

Photonic spin–orbit interactions (SOI) provide a new design paradigm of functional nanomaterials and nanostructures, and have especially accelerated advances in spin–orbit photonics. The berry phase or the geometric phase, a salient property of SOI, plays a vital role in this process. Thus, the characterization of photonic SOI processes together with the Berry phase is highly demanded for studies such as the optical spin‐Hall effect, spin‐to‐vortex conversion, and Rashba effect. Here, a spin‐selective and phase‐resolved near‐field microscopic method is proposed and experimentally demonstrated for real‐time probing and direct visualization of photonic SOI at mesoscale, and a 3D tomographic technique for imaging the spatial evolutions of the optical phases is also properly realized. By analyzing a metallic metasurface as a spin‐to‐vortex conversion platform, the abrupt geometric phase and the spatially evolutional dynamic phases are directly measured and intuitively illustrated. This work provides a powerful tool for the study of spin–orbit phenomena in near‐field optics, and can hold the promise for directly exploring the spin‐dependent surface states in plasmonics and photonic topological insulators. [ABSTRACT FROM AUTHOR]