Spatio-temporal topology of plasmonic spin meron pairs revealed by polarimetric photo-emission microscopy

TL;DR

This paper introduces a novel polarimetric PEEM technique to visualize and analyze the three-dimensional topology and time evolution of plasmonic spin meron pairs formed by surface plasmon polaritons, revealing complex electromagnetic field structures.

Contribution

The work extends topological analysis of electromagnetic fields to spin quasi-particles, demonstrating a new microscopy method for full 3D field measurement at sub-wavelength resolution.

Findings

Revealed the 3D topology of plasmonic spin meron pairs.

Showed the in-plane vectors follow the Poincare-Hopf theorem.

Captured the time evolution of the spin field with femtosecond resolution.

Abstract

Topology is the study of geometrical properties and spatial relations unaffected by continuous changes, and has become an important tool for understanding complex physical systems. Although recent optical experiments have inferred the existence of vector fields with the topologies of merons, the inability to extract the full three dimensional vectors misses a richer set of topologies that have not yet been fully explored. In our work, we extend the study of the topology of electromagnetic fields on surfaces to a spin quasi-particle with the topology of a meron pair, formed by interfering surface plasmon polaritons, and show that the in-plane vectors are constrained by the embedding topology of the space as dictated by the Poincare-Hopf theorem. In addition we explore the time evolution of the three dimensional topology of the spin field formed by femtosecond laser pulses. These experiments are possible using our here developed method called polarimetric photoemission electron microscopy (polarimetric PEEM) that combines an optical pump-probe technique and polarimetry with photo-emission electron microscopy. This method allows for the accurate generation of surface plasmon polariton fields and their subsequent measurement, revealing both the spatial distribution of the full three-dimensional electromagnetic fields at deep sub-wavelength resolution and their time evolution.