Accurately Predicting the Radiation Enhancement Factor in Plasmonic Optical Antenna Emitters

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Plasmonic optical antennas (POAs) enhance emitter radiation efficiency, crucial for applications like surface-enhanced Raman spectroscopy (SERS) and light-emitting devices.
• Radiation enhancement factors (REFs) for POA-emitter systems have historically been approximated, with their validity being an open question in SERS theory.
• Previous methods indirectly predicted REFs by assuming plane wave illumination without emitters, limiting accuracy.

Purpose of the Study:

• To develop a rigorous method for accurately calculating REFs of emitters coupled to POAs.
• To address the long-standing challenge of direct REF calculation in POA-emitter systems.
• To investigate the validity of the plane wave approximation in predicting REFs.

Main Methods:

• Development of a method based on the rigorous optical reciprocity theorem.
• Accurate calculation of REFs for emitters in nanoparticle-substrate nanogaps (single-molecule SERS).
• Accurate calculation of REFs for emitters in scanning probe-substrate nanogaps (tip-enhanced Raman spectroscopy).

Main Results:

• The developed method provides accurate REF calculations for POA-emitter systems.
• Demonstrated breakdown of the plane wave approximation when high-order plasmonic modes are excited.
• Identified limitations of indirect REF prediction methods.

Conclusions:

• The optical reciprocity theorem offers a robust approach for precise REF determination.
• Accurate REF calculation is essential for understanding and optimizing POA performance.
• The new method facilitates the design of advanced POA nanostructures for enhanced luminescence and SERS applications.