It is widely known that metals, such as gold and silver, when suitably structured at the nanometre scale, are able to focus light into very small (sub-wavelength) volumes, greatly enhancing its local intensity. For this unique capability such metallic nanostructures are often referred to as “nanoantennas”. In the last decades, metallic nanoantennas have opened up a wide range of applications in numerous fields, spanning (bio)imaging and sensing to the development of optoelectronic hybrid devices. However, since the mechanism of light confinement relies on the collective oscillation of free electrons, generation of heat via Joule dissipation is inherent to the process and detrimental effects arise for several uses, such as ultrafast and nonlinear optics.
The central objective of this project was to circumvent this issue through the use of dielectric nanoantennas, which have been proposed recently as low-loss alternatives with relatively high light confinement capability. Specifically, this research focused on investigating dielectric-based resonators for high-efficiency infrared-to-visible light conversion, as well as ultrafast optical modulation, including the study of hybrid arrangements of dielectric and metallic nanostructures to combine the best of both worlds. Dielectric ultra-thin novel perovskite materials were also analysed.
The project found that a silicon nano-disk surrounded by a gold nano-ring delivers a record nonlinear light-conversion efficiency close to 0.01%. The nano-system uses a third harmonic generation process, which involves tripling the energy of the incident photons. Slightly less efficient, but still very promising, sub-100 nm thickness lead halide perovskites were also found to produce significant third harmonic emission. In addition, this investigation discovered that these structures can produce sub-20 fs all-optical switching, enabling modulation speeds over 20 THz. The results of this work could have potential impact in solar cell technology, nano-medicine, and the development of photonic and optoelectronic nano-devices.
