Linear and ultrafast nonlinear plasmonics of single nano-objects

Area of Science:

• Nanophotonics and Plasmonics
• Single-Particle Spectroscopy
• Materials Science

Background:

• Ensemble measurements obscure fundamental properties of nano-objects.
• Single-particle optical techniques offer higher resolution and avoid averaging effects.
• Correlating optical data with imaging (e.g., electron microscopy) enables quantitative interpretation.

Purpose of the Study:

• To review single-particle optical techniques for nano-object investigation.
• To quantitatively study surface plasmon resonance (SPR) in metallic nano-objects.
• To elucidate optical nonlinearities and relaxation processes in nano-objects using ultrafast spectroscopy.

Main Methods:

• Single-particle optical techniques (near-field, dark-field, spatial modulation, photothermal).
• Linear and ultrafast optical spectroscopy.
• Analytical models and numerical simulations.
• Electron microscopy for morphological information.

Main Results:

• SPR positions and areas agree with theory, but widths are affected by quantum confinement and surface scattering.
• Size and geometry effects on SPR in confined metals quantified for silver nanospheres and gold nanorods.
• Ultrafast spectroscopy models the optical nonlinearities and relaxation dynamics of gold nanorods.
• Fano interferences observed in bimetallic heterodimers.

Conclusions:

• Single-particle optical methods provide crucial insights into nano-object behavior.
• Quantum effects significantly influence SPR in small metallic nanoparticles.
• Ultrafast spectroscopy is key to understanding complex plasmonic phenomena and relaxation dynamics.