Fano coupling between Rayleigh anomaly and localized surface plasmon resonance for sensor applications

Area of Science:

• Optics and Photonics
• Plasmonics
• Nanotechnology

Background:

• Fano coupling describes a resonance phenomenon where a narrow resonance interferes with a broad underlying resonance.
• Localized surface plasmon resonance (LSPR) occurs when light interacts with metallic nanoparticles, leading to collective oscillations of electrons.
• Rayleigh anomalies are diffracted modes that arise from periodic structures, exhibiting sharp spectral features.

Purpose of the Study:

• To investigate the Fano coupling between Rayleigh anomaly and LSPR in aluminum nanostructures.
• To explore the excitation mechanisms of LSPR in both nanoparticles and nanolines.
• To demonstrate the application of this coupled mode in refractive-index-sensing.

Main Methods:

• Fabrication of diffractive grating structures with aluminum nanolines composed of aggregated aluminum nanoparticles on photoresist.
• Excitation of LSPR using differently polarized light.
• Analysis of optical extinction spectra to observe spectral features of Fano coupling.
• Characterization of the diffracted and scattered light properties.

Main Results:

• Observed Fano coupling between Rayleigh anomaly and LSPR in the aluminum nanostructures.
• LSPR was excited in both individual nanoparticles and the nanolines.
• Surface propagation modes were strongly diffracted by the plasmonic grating, resulting in narrow-band light.
• Sharp dips in the broad-band reflective optical extinction spectrum confirmed the Fano coupling.

Conclusions:

• The observed Fano coupling provides a novel mechanism for light manipulation in plasmonic nanostructures.
• The coupled mode exhibits excellent sensitivity, making it suitable for refractive-index-sensor applications.
• This study highlights the potential of engineered plasmonic gratings for advanced optical sensing.