Extreme Nonlinear Optics with Field Enhancing Metamaterials

The THz part of the electromagnetic spectrum, which lies between microwaves and the mid-infrared, encompasses the frequencies of many important excitations in condensed matter such as phonons, excitons and plasmons. In the last few years there has been increasing interest in strongly driving such excitations with pulses of very intense THz radiation in order to create, for example, non-equilibrium phases with different properties or strongly coupled light-matter states. This interest is driven by recent developments in generating intense pulses of THz radiation in the laboratory [1], although there is a need to create more spectrally tailored terahertz fields that are an order of magnitude or more greater than can currently be achieved easily but still below the threshold for dielectric breakdown. This is necessary to explore extreme nonlinear optical effects resulting from large perturbations of lattice or band structure and strong light-matter coupling.

This project aims to experimentally and computationally evaluate concepts and optimisation procedures for using nano-fabricated, thin film metal-dielectric ‘antennas’ to both enhance and spectrally control the local electric or magnetic components of the THz field [2,3], Optimised structures will be used to explore strong field effects predicted in bulk and low dimensional semiconductors. Simple examples of field concentrating structures described in the literature are nano-scale slots in thin metal sheets and micron scale patch antennas and split ring resonators. Such structures can be fabricated on thin film samples of interest using fairly standard material processing techniques such as those available in the department’s nanofabrication laboratory and can be studied computationally using commercial finite element modelling software. The group’s existing facilities for conducting nonlinear THz experiments in fields up to ~1 MV/cm will be used for the experimental parts of the project.

You will have access to extensive laser spectroscopy facilities together with the opportunity to benefit from in-house expertise in the underlying theory of nonlinear systems and the wider interactions and training opportunities offered by the group’s affiliations with the Bath-Bristol Centre for Doctoral Training in Condensed Matter Physics.