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Title: Gain and plasmon dynamics in active nanoplasmonic metamaterials
Author: Wuestner, Sebastian Marc
ISNI:       0000 0004 2732 4996
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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Optical metamaterials are composite media that can be made to exhibit striking optical properties, some of which are not observed in nature, such as a negative refractive index. This advanced control over the electromagnetic response is enabled by subwavelength building blocks, most often based on metals. While metallic structural features provide the necessary resonant interaction with light, they also give rise to dissipative losses, which can interfere with the desired performance in applications. The incorporation of optical gain has emerged as a promising way to improve the loss-encumbered operation. It is this enhancement of metamaterials by gain, which is at the heart of this thesis. Three relevant topics will be considered: loss compensation, coherent amplification and lasing dynamics. The numerical studies presented here focus on the double-fishnet structure, a metamaterial exhibiting a negative refractive index at optical wavelengths. First, it is shown that loss compensation via optical gain is possible and that, in addition, it constitutes a practical means to overcome dissipative losses. Compensation of losses in combination with a negative refractive index is observed, disproving theoretical claims that rule out such behaviour. As a natural continuation, the characteristics above the threshold of amplification are investigated, i.e., when dissipative losses are overcompensated. By defining and analysing an effective rate balance, radiative outcoupling is found to be non-negligible. Hence, contrary to quasistatic predictions for nanoplasmonic metamaterials, a window of amplification opens. Beyond the regime of amplification, when gain exceeds both dissipative losses and radiative outcoupling, lasing instabilities occur. Nonlinear mode dynamics arise and it is shown that sole bright emission can be achieved despite the strong competition from a dark plasmonic mode. The numerical studies performed here shed new light on the complex physics arising from the nonlinear dynamic interaction of optical gain and resonant modes in nanoplasmonic metamaterials.
Supervisor: Hess, Ortwin Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral