Control of material removal of fused silica with single pulses of few optical cycles to sub-picosecond duration

Abstract

International audienceSurface ablation of a dielectric material (fused silica) by single femtosecond pulses is studied as a function of pulse duration (7-450 fs) and applied fluence (F (th)< F < 10F (th)). We show that varying the pulse duration gives access to high selectivity (with resolution similar to 10 nm) for axial removal of matter but does not influence the transverse ablation selectivity, which only depends on the normalized applied fluence F/F (th). The ablation efficiency is shown to be inversely dependent on the pulse duration and saturates with respect to the applied fluence earlier at ultra-short pulse durations (a parts per thousand currency sign30 fs). The deduced optimal fluence F (opt) corresponding to the highest ablation efficiency for each pulse width defines two regimes of laser application. Below F (opt), the removed material depth can be accurately adjusted in a large range (similar to 40-200 nm) as a function of the applied fluence and the morphology of the ablated pattern almost reproduces the Gaussian beam distribution. Above F (opt), the material removal depth tends to saturate and the morphology of the ablated pattern evolves to a top-hat distribution. The coupled evolution of depth and morphology is related to the dynamics of formation of dense plasma at the surface of the material, acting as an ultra-fast optical shutter

First-principles calculations for initial electronic excitation in dielectrics induced by intense femtosecond laser pulses

“…Red-circle shows the theoretically estimated crater depth, while blue-square shows the experimental result. 3 One sees that the theoretical crater-depth fairly reproduces the experimental result. The crater depth drastically increases just above a threshold.…”

“…We determined F max and w 0 so that the calculated diameter and the central depth of the In Table 1, we show the chosen beam parameters that are determined to reproduce the experimental values. 3 The experimental beam parameters 3 are also shown. For the weaker laser case, the beam parameters from our analysis are reasonably consistent with the experimental ones.…”

“…Because of this unique feature, the femtosecond laser-induced damage has been attracting much interest as a novel micro-materials-processing technique. [1][2][3][4][5] However, the fundamental mechanism of laser-induced damage has not been clearly understood yet.…”

Front-surface fabrication of moderate aspect ratio micro-channels in fused silica by single picosecond Gaussian–Bessel laser pulse

“…As the free electron density goes above a critical value, plasma gradually turns highly absorbing yielding to optical breakdown and further to material ablation when the deposited energy is sufficiently high [4]. In surface ablation regime, for Gaussian beam with pulse duration especially below 100 fs, a plasma shielding effect (solid density plasma mirror) may take place transiently, which contributes to self-limiting the ablation depth to hundreds of nanometers at most [5]. This offers excellent control of making modest-depth craters with high regularity in the front opening.…”

ASUR : plateforme d'applications des sources laser ultra-rapides pour l'imagerie X et l'interaction laser-matière

“…Dans le cadre de nouvelles recherches, nous menons une étude résolue en temps de l'absorption et de la dynamique de création d'une population d'électrons libres, afin de définir la fraction d'énergie laser réellement absorbée par le matériau ainsi que la dynamique de ce phénomène. Cela permet de déterminer les propriétés transitoires du matériau et leur influence sur l'impulsion excitatrice elle-même et de définir des informations utiles (seuils, efficacité d'ablation, morphologie et qualité d'ablation) pour le développement de procédés de micro-usinage [6].…”