Pulse duration dependence of ablation threshold for fused silica in the visible femtosecond regime
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S.I. : CURRENT STATE-OF-THE-ART IN LASER ABLATION
Pulse duration dependence of ablation threshold for fused silica in the visible femtosecond regime E. Terasawa1,2 · T. Shibuya3 · D. Satoh2,3 · Y. Moriai2 · H. Ogawa2,3 · M. Tanaka2,3 · R. Kuroda2,3 · Y. Kobayashi2,4 · K. Sakaue1,5 · M. Washio1 Received: 15 October 2019 / Accepted: 15 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this study, we investigated the variation of the femtosecond pulse duration of the threshold fluence of fused silica by a single-shot irradiation at a wavelength of 400 nm. The single-shot threshold fluence was obtained from the relationship between the crater area based on the crater shape and the irradiation fluence. The crater shape was divided into two affected regimes depending on the pulse duration and the laser fluence. The crater depth and each threshold fluence for the corresponding two affected regimes were also measured. We have found that shorter pulse duration provides more energy-efficient results. Keywords Laser ablation · Femtosecond laser · Ablation threshold · Pulse duration dependence · Fused silica · Visible wavelength
1 Introduction The ablation phenomenon induced by ultrashort laser pulses has attractive properties and is an important research area both scientifically and industrially [1, 2]. Compared to conventional laser processing by the heat melting process, the main advantage of the ablation phenomenon is high-precision and high-quality processing caused by a significant reduction in the heat-affected zone [1, 2]. Fused silica is a dielectric material, for which highquality processing is expected by the ultrashort laser pulse. Several studies on the ablation phenomenon mechanism of * E. Terasawa [email protected] 1
Waseda Research Institute for Science and Engineering, Waseda University, 3‑4‑1 Okubo, Shinjuku, Tokyo, Japan
2
OPERANDO‑OIL, National Institute of Advanced Industrial Science and Technology (AIST), 5‑1‑5 Kashiwanoha, Kashiwa, Chiba, Japan
3
RIMA, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1‑1‑1 Umezono, Tsukuba, Ibaraki, Japan
4
The Institute for Solid State Physics, The University of Tokyo, 5‑1‑5 Kashiwanoha, Kashiwa, Chiba, Japan
5
Photon Science Center, Graduate School of Engineering, The University of Tokyo, 7‑3‑1 Hongo, Bunkyo, Tokyo, Japan
dielectrics containing fused silica by ultrashort laser pulses were conducted [3–6]. The ultrashort laser ablation of the dielectric can be classified into two types [7–15]: (1) a ‘gentle’ ablation phase, where the ablation efficiency is low, and (2) a ‘strong’ ablation phase, where the ablation efficiency is high, and the melting traces (e.g. droplets) are confirmed. The gentle ablation is caused by the Coulomb explosion [8, 9, 11, 12] or material densification [13], whilst the strong ablation is caused by phase explosion [16, 17]. The threshold fluence is used in a manner similar to the critical points for a laser-induced breakdown of optical
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