Dr. Sebastian Wuestner Profile

Dr. Sebastian Wuestner

Research Associate at Imperial College London

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Proceedings Article | 7 September 2011 Paper

Dynamics of light amplification and gain in nano-plasmonic fishnet metamaterials

Sebastian Wuestner, Andreas Pusch, Kosmas Tsakmakidis, Joachim Hamm, Ortwin Hess

Proceedings Volume 8095, 809504 (2011) https://doi.org/10.1117/12.895163

KEYWORDS: Metamaterials, Plasmonics, Refractive index, Absorption, Electromagnetism, Picosecond phenomena, Dielectrics, Metals, Silver, Surface plasmons

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Plasmonic metamaterials form an exciting new class of engineered media that promise a range of important applications, such as subwavelength focusing, cloaking and slowing/stopping of light. At optical frequencies, using gain to overcome potentially not insignificant losses has recently emerged as a viable solution to ultralow-loss operation that may lead to next-generation active metamaterials. Here, we employ a Maxwell-Bloch methodology for the analysis of these gain-enhanced optical nanomaterials. The method allows us to study the dynamics of the coherent plasmon-gain interaction, nonlinear saturation, field enhancement as well as radiative and non-radiative damping such as tunnelling and F¨orster coupling. Using numerical pump-probe experiments on a double-fishnet metamaterial with dye-molecule inclusions we investigate the build-up of the inversion and the formation of the plasmonic modes in the low-Q fishnet cavity. We find that loss compensation occurs in the negative-refractiveindex regime and that, due to the loss compensation and the associated sharpening of the resonance, the real part of the refractive index of the metamaterial becomes more negative compared to the passive case. Furthermore, we investigate the behaviour of the metamaterial above the lasing threshold, and we identify the occurrence of a far-field lasing burst and gain depletion when higher dye densities are used. Our results provide deep insight into the internal processes that affect the macroscopic properties of active metamaterials. This could guide the development of amplifying and lasing plasmonic nanostructures.

Proceedings Article | 11 September 2010 Paper

Gain in negative-index metamaterials and slow-light waveguides

S. Wuestner, E. Kirby, A. Pusch, K. Tsakmakidis, J. Hamm, O. Hess

Proceedings Volume 7754, 775414 (2010) https://doi.org/10.1117/12.871948

KEYWORDS: Metamaterials, Refractive index, Waveguides, Cladding, Absorption, Heterojunctions, Geometrical optics, Light wave propagation, Finite-difference time-domain method, Silver

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We investigate on the basis of a full three-dimensional spatio-temporal Maxwell-Bloch approach the possibility of complete loss compensation in non-bianisotropic negative refractive index (NRI) metamaterials. We show that a judicious incorporation of optically pumped gain materials, such as laser dyes, into a double-fishnet metamaterial can enable gain in the regime where the real part n^′ of the resulting effective refractive index (n = n^′ + in^″) is negative. It is demonstrated that a frequency band exists for realistic opto-geometric and material (gain/loss) parameters where n^′ < 0 and simultaneously n^″ < 0 hold, resulting in a figure-of-merit that diverges at two distinct frequency points. Having ensured on the microscopic, meta-molecular level that realistic levels of losses and even gain are accessible in the considered optical frequency regime we explore the possibility of compensating propagation losses in a negative refractive index slow-light metamaterial heterostructure. The heterostructure is composed of a negative refractive index core-layer bounded symmetrically by two thin active cladding layers providing evanescent gain to the propagating slow light pulses. It is shown that backward-propagating light - having anti-parallel phase and group velocities and experiencing a negative effective refractive index - can be amplified inside this slow-light waveguide structure. Our results provide a direct and unambiguous proof that full compensation of losses and attainment of gain are possible on the microscopic as well as the macroscopic level in the regime where the non-bianisotropic refractive index is negative - including, in particular, the regime where the guided light propagates slowly.

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