Controlling of surface ablation threshold of fused silica by double-pulsed femtosecond laser
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Controlling of surface ablation threshold of fused silica by double‑pulsed femtosecond laser Xiaoyan Sun1 · Kaifan Cheng1 · Dongkai Chu1 · Youwang Hu1 · Zhuolin Dong1 · Ji’an Duan1 Received: 25 November 2019 / Accepted: 2 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Femtosecond laser (fs) ablation is an effective method to processing waveguide, microfluidic channel and other functional devices in fused silica glass. The accuracy of ablation is critical for high-performance devices. In this paper, a double-pulse femtosecond laser was used to control the surface ablation threshold of fused silica. It was found that, when the delay time of the double pulses ranged from 0 to 100 ps, with the increasing of delay time, the ablation threshold first rapidly increased to the maximum value, then fell to a stable value. And the overall threshold was higher than the threshold at 0 ps, which means the processing accuracy could be significantly improved. By simulating the relationship between the maximum electron density of conduction band and the time delay, it can conclude that the modification of threshold was caused by the difference of maximum electron density. In addition, to find the more optimized processing parameters, we also studied the weights of the two sub-pulses at 10 ps. These results provide an important reference for ultra-precision machining. Keywords Femtosecond laser · Double pulses · Surface ablation threshold · Accuracy
1 Introduction During the past several decades, micro/nano-structures in glass have gained increasing attention, due to their wide applications in chips [1–3], biochemical analysis [4], gratings [5–8], waveguides [9–11], couplers [12, 13], and Fresnel zone plates [14], etc. The structural accuracy is an important parameter, which is crucial for achieving the desired performance [15]. For example, in micro-fluidic chip, the microchannel size must be quite precise for realizing the precise control of minimal amount of fluid [16, 17]. In optical waveguide, the precision of waveguide structure directly affects the characteristics of the device [10]. Traditionally, the high-accuracy micro/nano-structures can be obtained by lithography [18–20], vapour deposition [21], and etching techniques [22, 23], and so on. However, these methods have some drawbacks, such as high cost and complicated processing procedures, and the coatings are prone * Youwang Hu [email protected] 1
The State Key Laboratory of High Performance Complex Manufacturing, College of Mechanical and Electrical Engineering, Central South University, 932 South Lushan Street, Changsha 410083, China
to degradation. What is more important is that, it is difficult to obtain three-dimensional structure directly. Compared to these methods, femtosecond laser, with extremely short pulse width, high peak power and quite small thermal effect, has shown great promising for high-accuracy micro/nanostructure processing. A number of works using femtosecond laser to process glass have been conducted, and th
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