Precision measurement of ablation thresholds with variable pulse duration laser
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Precision measurement of ablation thresholds with variable pulse duration laser Takashi Takahashi1,2 · Shuntaro Tani1 · Ryunosuke Kuroda2 · Yohei Kobayashi1,2 Received: 13 March 2020 / Accepted: 22 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The laser ablation threshold’s dependence on the pulse duration is a powerful tool that can be used to aid in understanding the mechanism of laser ablation. To determine the expected value of the ablation threshold accurately, it is essential to increase the number of data points available for analysis. In this study, we developed an automatic pulse-duration-tunable laser processing system with an in situ monitor that can collect more than 10,000 data points in a few hours. The laser system was operated at a wavelength of 1050 nm with a repetition rate of 1 MHz, and the pulse duration was tuned from 0.53 to 31 ps. Multi-shot ( 105 pulses) ablation thresholds for silicon were measured with an average error of less than 1%. We found that there were two ablation thresholds, at a fluence of 0.22 J∕cm2 with a pulse duration below 4 ps and at an intensity of 24 GW∕cm2 of intensity with a pulse duration above 13 ps. Keywords Laser ablation · Ablation threshold · Automated system · Energy dissipation · Silicon
1 Introduction Ultrafast laser pulses can realize high-quality materials processing because of the suppression of thermal degradation [1, 2]. High-precision processing with little heating of the surrounding material is important for microfabrication and biomaterials processing applications [3, 4], and more precise processing with reduced thermal effects is required for some industrial applications. To minimize heating effects for various materials, it is necessary to clarify the physical phenomena that occur within materials during laser ablation to enable selection of appropriate laser parameters, including the fluence, pulse duration and wavelength. Laser ablation
* Yohei Kobayashi [email protected]‑tokyo.ac.jp Takashi Takahashi taka‑[email protected]‑tokyo.ac.jp 1
The Institute for Solid State Physics, The University of Tokyo, 5‑1‑5 Kashiwanoha, Kashiwa, Chiba 277‑8581, Japan
AIST‑UTokyo Advanced Operando‑Measurement Technology Open Innovation Laboratory (OPERANDO‑OIL), National Institute of Advanced Industrial Science and Technology (AIST), 5‑1‑5 Kashiwanoha, Kashiwa, Chiba 277‑8589, Japan
2
via ultrashort laser pulses involves thermal and non-thermal processes, such as phase transitions, spallation and coulomb explosion [5, 6]. Numerous studies have been performed over more than three decades to reveal the various aspects of the laser ablation mechanism induced by ultrashort laser pulses. One fundamental value that characterizes the laser ablation process is the ablation threshold. At the ablation threshold, a target material is subjected to irreversible separation. Determination of the threshold value can reveal how the material responds to ultrafast optical energy injection at the point of no return. The value should depend on the
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