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Ablation laser par double impulsion pico-femtosecondes, mono-bi-chromatique, et multi-perforation de la silice fondue

Abstract : This thesis work is part of a project aiming at drilling glass with an ultrafast laser pulse. The objective is to multi-perforate glass for interposers used in the manufacture of electronic components such as processors or memory units, with holes of a characteristic size of about ten microns. This drilling results from : the ablation of the material induced by the deposition of laser energy, which is mainly governed by the electronic dynamics. The latter involves various processes (ionization, free electron heating and electronic recombination), whose contribution depends on the characteristics of the pulse in terms of wavelength, time shape, duration, polarization and fluence. This research work has made it possible to explore different ways to increase ablation efficiency and reduce drilling time, while maintaining the machining quality of femtosecond laser pulses. It is based on two work axes. The first axis aims to optimize energy deposition by temporal pulse shaping, which consistsof dividing the initial laser pulse into two sub-pulses. Experimental work was initially carried out with two sub-pulses of the same wavelength, varying various parameters such as delay, total fluence and polarization state. The ablation efficiency is maximal for a zero delay. Polarization also has a significant influence on the ablation efficiency. In a second step, the work was conducted with two sub-pulses of different wavelengths, varying the delay, the total fluence, the energy distribution between the two sub-pulses and the duration of the second pulse. The optimum delay is1 ps. The analysis of these experimental results was supported by the development of an electronic dynamics model. The second axis consists in reducing the drilling time by simultaneous irradiation of several points. However, laser drilling induces in the glass a significant thermal load whose relaxation can lead to the appearance of residual mechanical stresses, or even to glass break by cracking. The parallelization of the process can introduce cooperative effects between the sub-beams that can amplify these undesirable phenomena. To study these phenomena and determine the limits of the process, experimental results obtained with different geometries produced by a phase modulator were compared to those predicted by a thermo-elastic model. The probability of cracking increases strongly at high fluence (several tens of J/cm²) and for a distance between holes of the order of the diameter of these holes. Other than this configuration, the parallelization of the process does not introduce any risk of cracking. This work has made it possible, on the one hand, to clarify the interest of the double pulse mono and bi-chromatic process for laser drilling, and on the other hand, to identify the limits of parallelization of the laser drilling process.
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Kévin Gaudfrin. Ablation laser par double impulsion pico-femtosecondes, mono-bi-chromatique, et multi-perforation de la silice fondue. Physique [physics]. Université de Bordeaux, 2020. Français. ⟨NNT : 2020BORD0280⟩. ⟨tel-03329603⟩

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