Mode matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation

Area of Science:

• Nano-optics
• Plasmonics
• Nonlinear optics

Background:

• Boosting nonlinear frequency conversion in confined volumes is crucial for nanomedicine, photocatalysis, and biosensing.
• Existing nanoplasmonic systems often struggle with symmetry-induced quenching of second harmonic generation and phase matching.
• Enhancing electromagnetic field intensity is a common strategy, but symmetry issues persist.

Purpose of the Study:

• To overcome symmetry limitations in plasmonic materials that quench second harmonic generation.
• To develop doubly-resonant single-crystalline gold nanostructures with no axial symmetry.
• To achieve efficient nonlinear frequency conversion at the nanoscale.

Main Methods:

• Fabrication of single-crystalline gold nanostructures with no axial symmetry.
• Designing nanostructures for spatial mode overlap at both excitation and second harmonic wavelengths.
• Utilizing doubly-resonant effects to enhance nonlinear phenomena.

Main Results:

• Attained a nonlinear coefficient for second harmonic generation of approximately 5 × 10⁻¹⁰ W⁻¹.
• Achieved a second harmonic photon yield exceeding 3 × 10⁶ photons per second.
• Demonstrated enhanced nonlinear performance by overcoming symmetry-induced quenching.

Conclusions:

• The developed nanostructures significantly boost nonlinear frequency conversion in confined volumes.
• These nonlinear plasmonic nanoantennas show promise for efficient label-free molecular sensing.
• The study provides a pathway towards brighter nanoscale nonlinear light sources.