Dépôt numérique

Magneto-photonic phenomena at terahertz frequencies.

Shalaby, Mostafa (2013). Magneto-photonic phenomena at terahertz frequencies. Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, Doctorat en sciences de l'énergie et des matériaux, 157 p.

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Magneto-terahertz phenomena are the main focus of the thesis. This work started as supporting research for the science of an X-ray laser (SwissFEL). X-ray lasers have recently drawn great attention as an unprecedented tool for scientific research on the ultrafast scale. A potential terahertz-pump / X-ray-probe experiment is foreseen to reveal the fundamentals of magnetic systems on the ultrafast time scale and benefits the ultrafast magnetic storage industry. The main objective of this work was to find the conditions and prove that a suitable terahertz pulse can induce ultrafast magnetization dynamics on the picoseconds scale. To answer this fundamental question, we performed original numerical simulations using a coupled Landau- Lifshitz-Gilbert Maxwell model. Calculations showed us that terahertz pulses can trigger ultrafast dynamics, but highlighted the requirements of properly shaped pulses and beyond-current-technology peak field intensities. Those requirements werethe motivations for the experiments performed in the second part of the thesis. To shape the terahertz pulses, we used time-resolved optical-pump / terahertz-probe of free carriers in semiconductors. We managed to temporally shape the terahertz pulses and even extend the technique to spectral shaping as well. Regarding the field intensities, we followed two approaches. The first deals with field enhancement in nanoslits arrays. We designed a sub-wavelength structure characterized by simultaneous high field enhancementand high transmission at terahertz frequencies to suit nonlinear sources. The second approach depended on up-scaling the generation from laser-induced plasma by increasing the pump wavelengths. Numerical calculations have also brought to our attention the importance of linear magneto-terahertz effects. In particular, the simulations showed that the ultrafast dynamics could lead to significant rotation of the polarization plane of the triggering terahertz pulse. Motivated by this finding, we focused in the last part of the thesis on the linear effects. We performed three original studies coming out with first demonstrations of broadband non-reciprocal terahertz phase retarders, terahertzmagnetic modulators, and the non-reciprocal terahertz isolators. In the first two experiments, we extended the unique properties of the magnetic liquids (Ferrofluids) to the terahertz regime. In the latter experiment, we used a permanent magnet (Ferrite) to experimentally show complete isolation (unidirectional transmission) of the terahertz waves.

Type de document: Thèse
Directeur de mémoire/thèse: Morandotti, Roberto
Co-directeurs de mémoire/thèse: Peccianti, Marco
Mots-clés libres: magnétophotonique; magnétisation; fréquences térahertz; THz
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 09 juill. 2014 20:53
Dernière modification: 16 mars 2016 14:53
URI: http://espace.inrs.ca/id/eprint/2163

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