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.