Microsphere Assisted Super-resolution Optical Imaging of Plasmonic Interaction between Gold Nanoparticles

Area of Science:

• Nanophotonics
• Plasmonics
• Optical microscopy

Background:

• Far-field microscopy is limited in resolving sub-diffraction phenomena.
• Localized surface plasmons in metal nanostructures are crucial for many optical applications but difficult to image directly.

Purpose of the Study:

• To develop a method for imaging the spatial distribution of localized surface plasmons beyond the diffraction limit.
• To map the origin of enhanced two-photon photoluminescence in plasmonic nanodimers.

Main Methods:

• Utilized barium titanate (BaTiO3) microspheres as far-field superlenses to collect near-field signals.
• Employed a conventional far-field microscope setup.
• Investigated gold nanosphere and nanorod dimers.

Main Results:

• Successfully mapped the enhanced two-photon photoluminescence signal originating from the gap regions of nanodimers.
• Observed photoluminescence intensity varying with a cos^4(theta) function, correlating with structural axis and laser polarization.
• Achieved an optical resolution of approximately lambda/7 in the dimer gap region.

Conclusions:

• Barium titanate microspheres can function as effective far-field superlenses for near-field optical measurements.
• The developed technique allows for sub-diffraction imaging of plasmonic hotspots.
• Quantitative agreement with numerical simulations validates the experimental approach and findings.