CC BY
32HiLASE-I-10
Nano-ablation by femtosecond laser-metal interactions
S. Sakabe1,2, M. Hashida1,2, S. Inoue1,2 1Kyoto University,
Institute for Chemical Research- Advanced Research Center for Beamc Science, Uji- Kyoto, Japan
2Kyoto University, Graduate School of Science- Department of Physics, Kyoto, Japan
Lasers are widely used in the industry as modern processing tools for drilling, cutting, fluting grooving, peening, and so on. All the processing is based on laser ablation. Major processing has been done with rather long pulse lasers (several tens picoseconds to microsecond pulse duration, here simply we call it "nanosecond laser"), and the physics of nanosecond laser ablation has been abundantly studied to be understood well by thermohydrodynamics and laser plasma physics. Recent significant developments of femtosecond laser technologies are opening new aspects in the laser-matter interactions and their applications. In the femtosecond laser interaction with matter, we are observing distinguishing phenomena, which are never seen in nanosecond laser interactions. For femtosecond laser ablation, extremely small amount of ablation less than some nanometer depth is observed even with rather small laser fluence, resulting in discriminative morphology on the matter surface. We name it "nanometer-ablation (simply, nano-ablation)".
In this presentation, first comparing of laser fluence dependence of ablation rate for femtosecond laser with that for nanosecond laser, the term of nano-ablation is defined with the classification of laser fluence into three (high, middle and low) and distinguish features of femotosecond laser ablation for metals are overviewed. Femtosecond laser nano-ablation is discussed from three aspects, those are, (i) ablation rate, (ii) ion emission, and (iii) surface morphology. Multiple thresholds seen in laser fluence dependence on ablation rate can be interpreted by multiphoton processes and optical field ionization [1]. Ions emitted from the ablation process in low fluence are not distributed in the energy spectrum of Maxwell Boltzmann but in that of Coulomb explosion of nano particles [2]. Laser induced periodic surface structure, so-called LIPSS, is seen in middle fluence [3]. From the observed phenomena, laser produced surface plasma seems to play an important role in LIPSS formation [4]. Even in low fluence nano structure can be seen, but is not LIPSS. We have interpreted it to be formed by aggregation of nano particles in the laser-induced near field around some initial nano hollow and cracks [5].
Finally, potential of nano-ablation with femtosecond lasers to some applications are introduced.
References
[1] M. Hashida, et al.,Physical Review B 81, 115442(2010); Y. Miyasaka et al., Applied Physics Letters 106, 013101 (2015).
[2] Y. Miyasaka, et al., Physical Review B 86, 075431 (2012).
[3] S. Sakabeet al.,Physical Review B 79, 033409(2009), (ERATA) 91, 159902(E) (2015); K. Okamuro, et al.,Physical Review B 82, 165417 (2010); M. Hashida, et al.,Physics Letters 102, 174106 (2013).
[4] M. Hashida, et al., Applied Physics A 122, 484 (2016); K.Takenaka, et al., Applied Surface Science 478, 882 (2019).
[5] M. Shimizu, et al., Applied Physics Letters103, 174106 (2013).
