Rémi MEYER : "Contrôle du dépôt d'énergie par laser femtoseconde dans les diélectriques par faisceaux de Bessel"

PhD works of Rémi MEYER : "Energy deposition control by femtosecond laser in dielectrics using Bessel beams "

Abstract : 

The use of ultrashort pulses for laser ablation allows for a precise energy deposition thanks to a highly confined laser-matter interaction. The non-linear effects causing this confinement are also usually responsible of beam profile distorsions along propagation and intensity instabilities. High cone angle Bessel beams have shown to be excellent candidates for dielectrics processing since they are robust to non-linear effects. In femtosecond regime, they are able to generate in single shot high aspect ratio nanochannels in transparent media. However the ablation dynamics and the coupling with the laser-induced plasma remain partially unclear in this case. The current model describing such interaction is uncompatible with experimental observations.

This thesis investigates the laser-plasma interaction and follows two axes of work. First part is focused on the laser-plasma interaction characterization in transparent media and in the case of femtosecond Bessel beam, by developping and exploiting an interferometric pump-probe experiment. We measure the plasma dynamics through the plasma-related complex refraction index modifications, which we resolve in space and time. Preliminary results show a confined plasma (radius < 1 µm) in the transverse direction and whose density approaches the critical density for a pulse energy approaching the nanochannel formation threshold. In a second part, we investigate the effect of aligned nanochannels on the fracture ability of glass samples and its application to glass cleaving. Here we solve two limiting problems to high quality cleaving by spatial beam shape engineering: we demonstrate a signification improvement of 150 µm-thin glass cleaving by the use of elliptical-core Bessel beams; and we establish a proof of principle of 10 mm-thick glass single-pass cleaving thanks to a 3 axicons-based setup.

Composition of jury :

Yves Bellouard, Reporter, Associate Professor , École Polytechnique Fédérale de Lausanne (EPFL), Neuchâtel (CH)

Jean-Pierre Wolf, Reporter, Professor, Université de Genève (CH)

Fabien Quéré, Reviewer, Research Director, Commissariat à l'Energie Atomique (CEA), Paris-Saclay

John M. Dudley, Reviewer, Professor, Université de Bourgogne-Franche-Comté, Besançon

François Courvoisier, PhD Director, Researcher, Institut FEMTO-ST, Besançon

Localization : Auditorium JJ Gagnepain - Bâtiment TEMIS - 15B, Avenue des Montboucons - Besançon