Plasmonic nanostructures for shrinking structured light to access forbidden transitions

Area of Science:

• Nanophotonics and Light-Matter Interactions
• Plasmonics and Nanoscale Optics

Background:

• Plasmonic nanostructures offer strong light confinement and enhancement for light-matter interactions.
• Nanogap structures enable precise control over electric field distributions at the nanoscale.

Purpose of the Study:

• To demonstrate a plasmonic tetramer structure capable of squeezing structured light into a nanoscale area.
• To investigate the generation of a quadrupole-profiled structured light via plasmonic eigenmodes.
• To explore lattice resonance effects for enhancing quadrupole fields in array architectures.

Main Methods:

• Numerical simulations of a gold tetramer structure on a glass substrate.
• Fabrication using electron-beam lithography to achieve ~50 nm gap sizes.
• Investigation of plasmonic resonance in the near-infrared regime.

Main Results:

• A plasmonic tetramer structure was shown to generate structured light with a quadrupole profile in the nanogap.
• Electron-beam lithography enabled the creation of nanogaps supporting plasmonic resonance.
• Array architecture demonstrated collective lattice resonance, enhancing quadrupole field intensity.

Conclusions:

• Plasmonic nanostructures can generate structured light with specific profiles (quadrupole).
• This capability allows access to forbidden optical transitions via strong field gradients.
• The findings suggest new platforms for spectroscopy, sensing, and light sources leveraging multipolar transitions.