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We apply ultrafast nanoscale microscopic imaging and analytical modeling to investigate the coherent field and spin textures of dual plasmonic vortices as a means to design the momentum flow, and spin topology by interaction of their gyrating fields. The ultrafast laser normal incidence illumination by circularly polarized light of two vortex generator structures with variable separations in silver films launches structured surface plasmon polariton fields. Two distinct primary vortices and a third emergent vortex, generated by interaction of the primary vortices and tunable by design of their separation, form through the spin–orbit interaction of light. The gyration of plasmon fields and the consequent vectorial Poynting momentum flow is imaged with sub-optical cycle phase and spatial resolution by interferometric time-resolved two-photon photoemission electron microscopy (ITR-2P-PEEM). The ultrafast imaging and analytical modeling of the interaction of the dual plasmonic vortices examines the nanoscale control of plasmon spin topology and momentum driven transport.
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Ultrafast Microscopy of Plasmonic Vortex Fields
Surface Plasmon Polariton (SPP), as a novel information carrier, offers unprecedented opportunity for confining electromagnetic fields that carry orbital angular momentum (OAM) to subwavelength dimensions. In this thesis, I focus experimentally on the generation, manipulation, and spatio-temporal evolution—and theoretically on the analytical modeling—of plasmonic phase singularities, known as plasmonic vortices, at the silver (Ag)/vacuum interface. I image and study the dynamics of plasmonic vortices by interferometric time-resolved multi-photon photoemission electron microscopy (ITR-mP-PEEM). Firstly, I report on the generation, evolution, and topological properties of plasmonic vortices carrying pure geometrically induced orbital angular momentum (OAM), generated by illuminating Archimedean spiral coupling structures with normally incident, linearly polarized light. Next, I present an analytical model describing the generation and evolution of these plasmonic vortices, and based on this model, I further analyze their spatial structure and dynamics. I also derived the spin angular momentum (SAM) of plasmonic vortices, whose textures reveal transient plasmonic spin-Skyrmion topological quasiparticles. In parallel, I also record images of plasmonic vectoral vortex field evolution on the nanometer spatial and femtosecond temporal scale, from which I derive the plasmonic spin Skyrmion boundary and topological charge. The excellent agreement between analytical model and experimental results confirms the topological spin texture at surface plasmon polariton vortex core. To extend the understanding of ITR-PEEM imaging, I perform a simple experiment withv double line coupling structure at the silver/vacuum interface, which reveals an asymmetric cross term between the different components of the SPP field that also appear in the ITR-PEEM imaging. Finally, I approach a novel method to manipulate momentum transport between two plasmonic vortices analytically and experimentally. By tuning the relative distance between two vortex generator structures with same sign and sign of the geometric charge, a conveyor belt-like field could be observed at the center of the device, which can be applied to transport the field, momentum, and energy between two plasmonic vortices.
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- Award ID(s):
- 2303197
- PAR ID:
- 10637302
- Publisher / Repository:
- University of Pittsburgh
- Date Published:
- Page Range / eLocation ID:
- 1-122
- Subject(s) / Keyword(s):
- Orbital angular momentum Surface Plasmon Polariton Plasmonic vortices emergent plasmonics
- Format(s):
- Medium: X
- Institution:
- University of Pittsburgh
- Sponsoring Org:
- National Science Foundation
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