Aluminum Cayley trees as scalable, broadband, multi-resonant optical antennas

TL;DR

This paper demonstrates that aluminum Cayley trees, as self-similar fractal structures, can serve as broadband, multi-resonant optical antennas capable of supporting multiple plasmonic resonances across a wide spectral range, from ultraviolet to mid-infrared.

Contribution

The study introduces aluminum Cayley trees as scalable, broadband optical antennas with multiple resonances, verified through electron energy loss spectroscopy.

Findings

Single aluminum Cayley tree sustains multiple plasmonic resonances.

Resonance spectral positions are scalable over two decades.

Structures are effective for applications in non-linear optics and sensing.

Abstract

An optical antenna can convert a propagative optical radiation into a localized excitation, and reciprocally. Although optical antennas can be readily created using resonant nanoparticles (metallic or dielectric) as elementary building blocks, the realization of antennas sustaining multiple resonances over a broad range of frequencies remains a challenging task. Here, we use aluminum self-similar, fractal-like structures as broadband optical antennas. Using electron energy loss spectroscopy, we experimentally evidence that a single aluminum Cayley tree, a simple self-similar structure, sustains multiple plasmonic resonances. The spectral position of these resonances is scalable over a broad spectral range spanning two decades, from ultraviolet to mid-infrared. Such multi-resonant structures are highly desirable for applications ranging from non-linear optics to light harvesting and photodetection, as well as surface-enhanced infrared absorption spectroscopy.