Gain and Plasmon Dynamics in Active Nanoplasmonic Metamaterials
Author(s)
Wuestner, Sebastian Marc
Type
Thesis
Abstract
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.
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.
Date Issued
2012-08
Date Awarded
2012-11
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Hess, Ortwin
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)