Material structuring by a train of spatially chirped femtosecond laser pulses

• Main Author: Quinoman, Paul
• Other Authors: Centre d'Etudes Lasers Intenses et Applications (CELIA), Université de Bordeaux (UB)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), Université de Bordeaux, Hervé Jouin, Guillaume Duchateau
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2023
• Subjects: Dielectric materials; Femtosecond laser pulses; Train of laser pulses; Beam shaping; Matériaux diélectriques; Impulsions laser femtosecondes; Train d'impulsions laser; Mise en forme de faisceaux; [PHYS.PHYS]Physics [physics]/Physics [physics]; Arctic
• Online Access: https://theses.hal.science/tel-04301586; https://theses.hal.science/tel-04301586/document; https://theses.hal.science/tel-04301586/file/QUINOMAN_PAUL_2023.pdf

Nowadays, femtosecond laser pulses are widely used to induce structural modifications within dielectric materials. Because of their large bandgap, those materials are transparents to visible light, and become absorbing for high intensities. This nonlinear feature of the interaction is responsible for a threshold intensity during the interaction, and allow one to induce localized energy deposition in the volume of the material. However, the control of both localization and geometry of the energy deposition requires a fine adjustment of the laser parameters. Currently, the influence of the laser energy and numerical aperture are well known. However, the spatio-temporal shaping of the laser energy distribution, through a spatial chirp in a direction transverse to the laser propagation, is a promising approach still to be investigated. The present work aims at studying the shaping of femtosecond laser pulse train, for intensity around the interaction threshold, and moderate focusing conditions. First, spatially chirped laser pulses are studied using the 3D Maxwell solver ARCTIC. Relevant laser configuration are identified and implemented in ARCTIC. The results demonstrate the possibility to control the direction of the ionization front and the shape of the energy deposition. A model has been developed to evaluate the geometry of the resulting structure. Then, in order to study multiple laser pulses interacting with a material, a propagation model based on NonLinear Schrödinger equation is developed. Using analytical optimization, 3D results are correctly predicted with very low computation cost. The influence of laser induced defects in the material is introduced as well as the incubation effect during multi-pulse irradiation. The model is validated against experimental results. Parametric studies are done for a train up to a hundred of laser pulses. It is shown that the energy deposition can be controlled by tuning the intensity distribution within the train. Les lasers femtosecondes sont aujourd'hui largement ...