Quantitative spectroscopy on individual wire, slot, bow-tie, rectangular, and square-shaped optical antennas

Area of Science:

• Nanophotonics
• Plasmonics
• Optical Metamaterials

Background:

• Optical antennas are crucial for manipulating light at the nanoscale.
• Understanding the scattering, absorption, and extinction properties of individual antennas is essential for device optimization.
• Previous methods often lacked the precision to quantify these properties for single antennas.

Purpose of the Study:

• To quantitatively measure the extinction, scattering, and absorption cross-section spectra of individual optical antennas.
• To compare the performance of various antenna designs, including thin-wire, slot, bow-tie, rectangular, and square-shaped antennas.
• To investigate antenna behavior near the 1.4 μm wavelength resonance.

Main Methods:

• Utilized a recently introduced approach combining a focus-modulation technique with a common-path interferometer.
• Performed quantitative spectral measurements on individual optical antennas.
• Analyzed experimental results for five distinct antenna geometries.

Main Results:

• Demonstrated increased resonant scattering cross sections for slot, bow-tie, rectangular, and square-shaped antennas compared to thin-wire antennas.
• Observed that the square-shaped antenna's resonant extinction cross section approaches the theoretical limit of a coherent point dipole.
• Found the highest ratio of resonant extinction cross section to geometrical cross section for the simple thin-wire antenna.

Conclusions:

• The study provides quantitative insights into the optical performance of various individual antenna designs.
• Different antenna geometries offer distinct trade-offs between scattering, absorption, and extinction efficiency.
• The thin-wire antenna remains highly efficient in terms of extinction relative to its physical size.