Second harmonic generation in metallic nanostructured arrays

Abstract

The desire to incorporate optical and photonic components into miniaturised devices provides the impetus for the eld of nanophotonics to control light at ever decreasing length scales. Traditional optical elements, for instance, lenses, are described by macroscopic properties such as refraction. Designing and building optical elements using these macroscopic properties results in relatively large components that need to be multiple wavelengths thick. This size limitation hinders their integration into small form factor products. One approach to controlling light at the nanoscale is to use plasmonics.

Plasmons are coherent oscillations of the free electrons in a metal and allow light to be confined to nanoscopic volumes. Conning light to small volumes drastically enhances the local electric eld, which is particularly favourable for nonlinear optical processes. Utilising nonlinear frequency mixing provides control over the wavelength of light. Therefore, plasmonics is an advantageous platform for nanophotonic control of wavelength. However, engineering plasmonic nanomaterials for nonlinear applications is extremely challenging and would greatly bene t from robust nonlinear characterisation techniques.

This thesis presents the nonlinear characterisation of two metallic nanostructured arrays. The analyses of these characterisations are then related to different physical origins. Presented first are arrays of anisotropic nanoscale helices. The nonlinear chiral optical response of the helices is investigated and how it is affected by anisotropy. It is found that nonlinear chirality cannot be thoroughly characterised without considering sample anisotropy. Secondly, the nonlinear response of nanoparticle arrays that support surface lattice resonances is studied. The electric eld enhancements caused by the surface lattice resonances greatly boosts the second harmonic generation of the arrays. Furthermore, the surface lattice resonance dispersion is used to tune this effect.

By providing comprehensive characterisations of these nanomaterials and identifying the physical origins responsible for their nonlinear optical behaviour, this thesis contributes to establishing design rules needed to create practical nonlinear plasmonic nanophotonic systems. The growing body of work on nonlinear plasmonics in nanophotonics will serve as reference guides for future design schemes, enabling the miniaturisation of photonic components able to control the wavelength of light.

Date of Award	2019
Original language	English
Awarding Institution	University of Bath
Supervisor	Simon Bending (Supervisor) & Ventsislav Valev (Supervisor)