Simple model of saturable localised surface plasmon.

Area of Science:

• Plasmonics
• Nanophotonics
• Quantum Optics

Background:

• Localized surface plasmons (LSPs) are crucial for applications like bio-sensing and solar cells.
• Experimental observations reveal that LSPs optically saturate under high-intensity light.
• The conventional boson model fails to explain this saturation, indicating strong optical nonlinearity.

Purpose of the Study:

• To propose a new theoretical model for saturable localized surface plasmons (LSPs).
• To explain the nonlinear optical response of LSPs using an effective dipole approximation.
• To validate the model by analyzing the optical response of ellipsoidal nanometals.

Main Methods:

• Developed a simple model of saturable LSPs based on effective dipole approximation.
• Compared the classical linear optical response of LSPs with a saturable quantum two-level system.
• Performed second quantization by replacing classical polarizability with a quantum dipole operator.
• Analyzed the optical response of a single ellipsoidal nanometal numerically.

Main Results:

• The proposed model successfully describes saturable LSPs, accounting for strong optical nonlinearity.
• Numerical simulations show that plasmon resonance frequency and spectral linewidth decrease with increasing ellipsoid aspect ratio.
• Observed size-dependent behavior in nanometals aligns with previous experimental findings.

Conclusions:

• The effective dipole approximation provides a viable framework for understanding saturable LSPs.
• The model accurately predicts the optical response of nanometals, including frequency and linewidth dependencies.
• This work offers a new perspective on the nonlinear optical properties of plasmonic nanostructures.