Transverse spin angular momentum of space-time surface plasmon polariton wave packet

TL;DR

This paper investigates the properties of space-time surface plasmon polariton wave packets, revealing their ability to carry controllable three-dimensional spin textures and topological charges during propagation, with potential applications in spinphotonics and topological photonics.

Contribution

It introduces the concept of space-time SPP wave packets that maintain complex spin textures and topological charges while propagating at arbitrary velocities, expanding understanding of plasmonic wave dynamics.

Findings

Wave packets propagate with 3D spin textures.

Spatial distribution of spin and topological charge is controllable.

Propagation deformation is negligible.

Abstract

In addition to longitudinal spin angular momentum (SAM) along the axis of propagation of light, spatially structured electromagnetic fields such as evanescent waves and focused beams have recently been found to possess transverse SAM in the direction perpendicular to the axis of propagation. In particular, the SAM of SPPs with spatial structure has been extensively studied in the last decade after it became clear that evanescent fields with spatially structured energy flow generate threedimensional spin texture. Here we present numerical calculations of the space-time surface plasmon polariton (ST-SPP) wave packet, a plasmonic bullet that propagates at an arbitrary group velocity while maintaining its spatial distribution. ST-SPP wave packets with complex spatial structure and energy flow density distribution determined by the group velocity are found to propagate with accompanying three-dimensional spin texture and finite topological charge density. Furthermore, the spatial distribution of the spin texture and topological charge density determined by the spatial structure of the SPP is controllable, and the deformation associated with propagation is negligible. ST-SPP wave packets, which can stably transport customizable three-dimensional spin textures and topological charge densities, can be excellent subjects of observation in studies of spinphotonics and optical topological materials.