Mapping plasmonic near-field profiles and interferences by surface-enhanced Raman scattering

Area of Science:

• Nanophotonics
• Plasmonics
• Optical Engineering

Background:

• Sub-wavelength mapping of surface plasmon polaritons (SPPs) is essential for understanding their behavior and for developing nanoscale photonic devices.
• The short effective wavelength of SPPs necessitates high-resolution imaging techniques beyond the diffraction limit.

Purpose of the Study:

• To develop and demonstrate a sub-wavelength scale mapping technique for the near-field profiles and dynamics of SPPs.
• To investigate the spatial distribution of the perpendicular component of surface plasmon fields in a metal nanoparticle-film system.

Main Methods:

• Combined total internal reflection excitation with surface-enhanced Raman scattering (SERS) imaging.
• Utilized spectrally selective and polarization-resolved excitation of the vertical gap mode.
• Employed a focused radially polarized beam to generate a spot size of approximately 0.355 free-space wavelengths (λ0).

Main Results:

• Achieved sub-wavelength scale mapping of the dominant perpendicular component of surface plasmon fields.
• Demonstrated that the lateral field-extension at the junction is sufficiently small to resolve fine details.
• Successfully traced near-field nano-focusing and interferences of SPPs generated by plasmon lenses with high reproducibility.

Conclusions:

• The developed SERS-based technique provides high-resolution mapping of SPP near-field profiles and dynamics.
• This method is crucial for advancing the fundamental understanding of SPPs and for the design of miniaturized photonic devices.
• The technique allows for the observation of complex plasmonic phenomena like nano-focusing and interference patterns.