Spiral surface plasmon modes inside metallic nanoholes.

Area of Science:

• Condensed Matter Physics
• Nanophotonics
• Plasmonics

Background:

• Surface plasmon polaritons (SPPs) are electromagnetic waves confined to the interface between a dielectric and a metal.
• Spiral surface plasmon (SSP) modes offer unique light-matter interaction properties within nanostructures.
• Understanding SSP mode behavior in silver (Ag) nanoholes is crucial for developing advanced plasmonic devices.

Purpose of the Study:

• To investigate the formation and propagation characteristics of SSP modes within Ag nanoholes.
• To analyze how nanohole geometry (uniform vs. tapered) and dimensions influence SSP mode properties.
• To explore the potential of composite structures for manipulating SSP modes and enhancing field energy density.

Main Methods:

• Numerical simulations were employed to model SSP mode propagation and behavior.
• Theoretical analyses were conducted to understand the underlying physics of SSP mode formation.
• Investigations included uniform and tapered Ag nanoholes, as well as a composite fiber-nanorod structure.

Main Results:

• SSP modes are formed by the superposition of two rotating SP eigenmodes in the fast-wave branch.
• The handedness and number of strands of SSP modes depend on the component eigenmodes and their rotation.
• SSP mode pitch is tunable by nanohole radius and incident wavelength; tapering affects pitch and energy density.
• A composite Ag-clad fiber capped by a tapered Ag nanorod demonstrated SSP mode handedness reversal and significant field energy density enhancement at the nanorod tip.

Conclusions:

• The study elucidates the fundamental principles governing SSP modes in Ag nanoholes.
• Geometric engineering of nanoholes provides a pathway to control SSP mode characteristics.
• Composite nanostructures offer promising avenues for enhancing and directing plasmonic energy for applications in sensing, imaging, and nanoscale optics.