On the formation of nano and micro scale surface features induced by femtosecond filament laser ablationFriday (26.06.2020) 11:50 - 12:10 Room 2
The formation of laser-induced periodic surface structures, which are also referenced to as LIPSS or rather ripples in the literature, is a universal phenomenon occurring when using linearly polarized laser beams in materials processing. It has been thoroughly demonstrated during the past that the unique LIPSS feature characteristic can easily be controlled by the wavelength, fluence, pulse duration, polarization state, etc. of the impinging laser beam. However, the first evidence of ripples developing from multi-shot femtosecond filament irradiations was observed on copper during long-distance laser-induced breakdown spectroscopy operations . Since then, only a few initial studies report on filament-induced metallic ripples and a systematic study on feature formation has not been provided so far.
In this study, we report on the development of nano and micro scale surface features on stainless steel and silicon induced by femtosecond filament laser irradiations. The filament was initiated by an ultrashort pulse laser beam of 800 nm wavelength, 120 fs pulse duration and 5.2 mJ pulse energy (Astrella, Coherent). The filament laser ablation could be investigated within a range between 50 m and 55 m target distance from the laser beam exit. At different positions of the substrates in the filament, the number of irradiations, the pulse repetition frequency and the laser beam incidence angle were varied, namely, in the range between single pulses and up to 2000 pulses, 50 Hz and 500 Hz as well as vertical beam incidence and 60°. On stainless steel, as shown in Figure 1 a, nano craters, nano spikes and high spatial frequency LIPSS (HSFL) have been found in areas of low overlapping filament ablations. For a larger number of overlapping filaments, however, high-regular low spatial frequency LIPSS (LSFL) emerged, such as shown in Figure 1 b by the example of 100 pulses.
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