Soutenance de thèse – LOZAN

La soutenance de thèse d’Olga Lozan a eu lieu le jeudi 26 février 2015 à 13h30 à l’Université de Bordeaux, dans l’amphithéâtre du Labri (bâtiment A30).
Le sujet de la thèse est « Surface Plasmons and Hot Electrons Imaging with Femtosecond Pump-Probe Thermoreflectance ».
La thèse a été soutenue en anglais.

The defense of the thesis of Olga Lozan, took place on Thursday, 26/02/2015 at 13h30 in the amphitheater of Labri (building A30).
The topic of the thesis is « Surface Plasmons and Hot Electrons Imaging with Femtosecond Pump-Probe Thermoreflectance« .
The defense has been held in English.

Résumé/Summary :

The field of plasmonics encompasses the science and engineering of optical interaction with nanostructures. Prospects of subwavelength confinement and enhancement of optical fields near properly designed nanoscale objects has been a motivation to extensively investigate a variety of plasmonic optical phenomena in recent years.
The particular interest in this field resides on the fact that plasmonics builds a bridge between two different length scales by confining light in subwavelength regions. For the further development and implementation of plasmonic devices, important limiting factors are the losses which the plasmon undergoes. Thus, the focus of this thesis is to measure these losses in metallic sub-wavelength surfaces (or plasmonic devices).
The measurement of the heat dissipated in plasmonic structures is of fundamental importance, but it is also a daunting task. The existent high-resolution techniques for measuring the dissipated plasmon heat reveal a temporally- and spatially-broadened profile of the local heat source because of the energy carriers diffusion transport in the metal. The mechanism of plasmon energy absorption in metals is mediated by hot electrons. The surface plasmons and hot electrons interact in metals over a time scale of a few tens of femtoseconds. In this time range, we detect electronic temperature variation accompanying the plasmon propagation. In such a time scale all diffusion processes (electrons and phonons) have not started yet and can be neglected. The temperature profile is therefore the perfect image of the power density distribution (absorption) induced by the plasmon losses.
In this thesis we propose to take advantage of femtosecond pump-probe technique, capable of measuring electronic temperature variation with femtosecond time resolution. Losses can be seen as a plasmon-to-hot-electron energy conversion. This energy conversion is measured by launching femtosecond surface plasmon pulses and by probing the permittivity variations induced by the hot-electron gas. The variations are recorded a few hundred femtoseconds after the plasmon was launched. They reveal the image of the local heating source with a weak broadening.

Ces travaux ont donné lieu à la publication :

Anomalous light absorption around tiny apertures in metal films
Olga Lozan, Mathias Perrin, Buntha Ea-Kim, Jean-Michel RampnouxStefan Dilhaire, Philippe Lalanne
Physical Review Letters, American Physical Society, 2014, 112, pp.193903.

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