Défense de thèse de doctorat en sciences physiques : "electromagnetic absorption"

Super absorbers : a metamaterial approach

Jury

Benoit HACKENS (UCL), Philippe TASSIN (Chalmers Goteborg), Olivier DEPARIS, co-promoteur (UNamur), Philippe LAMBIN (UNamur), Robert SPORKEN, président (UNamur), Luc HENRARD, promoteur (UNamur)

Résumé

Electromagnetic absorption is paramount for a range of daily applications wheter for photovoltaic/photothermic devices or in order to reduce the electromagnetic pollution coming from an increasing number of emitters. Electromagnetic absorption also raise a fundamental question in physics: "How is it possible to conceive a material able to trap all the incident electromagnetic radiation in the most efficient way?" This thesis aims to provide ways to answer to this question. Therefore, several photonic devices are under investigation.

The first approach is using the concept of metamaterials. Owing to the dissipative characteristic of metals in the visible range, reinforced by the shaping of plasmonic resonances, a metal/dielectric pyramidal metamaterial is studied. This device is able to perform ultra-broadband super absorption from 0.2 µm to 5.8 µm with an integrated absorption of 98 %.

The second approach uses the high conductivity of graphene in the GHz range. Due to this property, graphene/polymer heterostructures are shown to be able to absorb incident radiation up to 50% once impedance matching conditions are fulfilled. Electrodynamics of conducting bidimensional layers as well as the refractive index of 2D materials are investigated and generalized Fresnel formula for a conducting 2D material are derived.

Finally, hybrid graphene-metamaterials structures are studied to perform electromagnetic absorption. Second harmonic generation activity of graphene-coated gold photon sieve is examined as well as its plasmonic absorption properties. A graphene/polymer heterostructure lying on a epsilon-near-zero metamaterial is shown to be able to reach perfect electromagnetic absorption under certain conditions.

This work consequently results in a variety of modern approaches to answer the fundamental electromagnetic absorption question.

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