Control of ablation morphology on Cu film with tailored femtosecond pulse trains
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Control of ablation morphology on Cu film with tailored femtosecond pulse trains Jiannan Deng1 · Hongxia Qi1,2 · Liang Zhao1 · Xinyi Liu1 · Zhenzhong Lian1 · Qiunan Tong1 · Juntong He1,2 · Chuanlin Jin1,2 · Juan Li1 · Jinqiu Bo1 · Dehou Fei1 · Zhou Chen1,2 · Zhan Hu1,2 Received: 19 December 2019 / Accepted: 27 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The ablation morphology of Cu film is investigated using tailored femtosecond pulse trains. The width, depth, and structure of ablation craters are systematically analyzed as the function of sub-pulse interval. Two distinct ablation sub-structures are observed. The gentle slope irradiated by low fluence emerges from the peripheral region of the ablation crater, and the steep slope formed in the central region is irradiated by high fluence. The ablation morphology can be controlled by manipulating the shaped pulse trains. We demonstrate that the ablation depth modulation is significant with the ablation width almost unchanged. By fitting the depth curves, we define a coefficient K to characterize the plasma shielding effect between subpulses with the increase in sub-pulse interval. For three fluences, the coefficient K using two kinds of pulse trains are extracted experimentally. The results reveal that the plasma shielding effect can be modulated by changing sub-pulse interval, and the corresponding physical interpretation is proposed. Keywords Shaped pulse train · Plasma shielding · Ablation substructures
1 Introduction Femtosecond laser ablation has been investigated experimentally [1–3] and theoretically [4–6] since the 1990s, and has been widely used in many fields, such as dental surgery [7], eye surgery [8], nanoparticle formation and growth [9], micromachining [10–12]. The duration of femtosecond pulse is significantly shorter than that of picosecond pulse. Since the typical time scale of electron–phonon thermal equilibrium is several picoseconds [13], the absorption process of femtosecond pulse energy in metal ablation is considered to be non-thermal and the ablation threshold is normally lower than that of longer pulses. Such characteristics make femtosecond laser an irreplaceable tool for micromachining. In the * Zhou Chen [email protected] * Zhan Hu [email protected] 1
Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
Advanced Light Field and Modern Medical Treatment Science and Technology Innovation Center of Jilin Province, Jilin University, Changchun 130012, China
2
theoretical studies on femtosecond laser ablation of metal, most of the works focus on the use of two-temperature model [14], or hydrodynamic model [5] to illustrate the ablation mechanisms. In the experimental studies, the influences of different laser parameters on laser ablation have been investigated, e.g., laser fluence [15], pulse duration [16], incident angle [17]. In addition, several groups have experimentally studied the influence of environmental parameters, such as the temperature [18] and the
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