Linear and Non-linear Response of Lithographically Defined Plasmonic Nanoantennas

TL;DR

This study combines numerical, fabrication, and optical characterization to demonstrate that gold bowtie nanoantennas significantly enhance electric fields and exhibit nonlinear optical effects, promising advancements in nanophotonic applications.

Contribution

The paper provides a comprehensive analysis of bowtie nanoantennas, including optimized designs, fabrication techniques, and experimental validation of their nonlinear optical responses.

Findings

Mean intensity enhancement factors >2300x in feed-gap

Blue shift of surface plasmon resonance from 1.72eV to 1.35eV

Observation of two-photon photoluminescence and second harmonic generation

Abstract

We present numerical studies, nano-fabrication and optical characterization of bowtie nanoantennas demonstrating their superior performance with respect to the electric field enhancement as compared to other Au nanoparticle shapes. For optimized parameters, we found mean intensity enhancement factors >2300x in the feed-gap of the antenna, decreasing to 1300x when introducing a 5nm titanium adhesion layer. Using electron beam lithography we fabricated gold bowties on various substrates with feed-gaps and tip radii as small as 10nm. In polarization resolved measurement we experimentally observed a blue shift of the surface plasmon resonance from 1.72eV to 1.35eV combined with a strong modification of the electric field enhancement in the feed-gap. Under excitation with a 100fs pulsed laser source, we observed non-linear light emission arising from two-photon photoluminescence and second harmonic generation from the gold. The bowtie nanoantenna shows a high potential for outstanding conversion efficiencies and the enhancement of other optical effects which could be exploited in future nanophotonic devices.