Optimization of the ablation process using ultrashort pulsed laser radiation in different burst modes

Abstract

The authors report on a solid-state burst mode amplified laser source capable of varying the pulse duration in the range of 0.24–10 ps and generating pulse trains (bursts) with an intraburst pulse repetition rate of 65 MHz (MHz burst mode) and 2.5 GHz (GHz burst mode). Furthermore, every pulse of a burst in the MHz burst mode can be divided into another GHz burst, called BiBurst. In this study, a laser radiating at 1030 nm wavelength is used to generate ablation areas and investigate the efficiency, the surface quality, and the process stability on stainless steel with different total fluences per burst, numbers of pulses per burst, and pulse durations in the MHz, GHz, and BiBurst modes. In the investigated parameter range, the highest efficiencies were obtained in the MHz burst mode with femtosecond pulses, but in this burst regime, the burst mode induced smoothing effect is dependent of the number of scans. In contrast, the process stability and the quality in the GHz and BiBurst are granted over a wide range of parameters. Thus, the actual advantages of the GHz and BiBurst regimes in terms of a high process stability and quality could be established.

Review on Experimental and Theoretical Investigations of Ultra-Short Pulsed Laser Ablation of Metals with Burst Pulses

“…The results show that the energy specific volumes for peak fluences of 0.5 J/cm 2 , 1.5 J/cm 2 , and 2.5 J/cm 2 mainly depend on the pulse duration, but follow identical trends when the number of pulses per burst is increased. Depending on the pulse duration and the peak fluence, regimes where a melt film is formed leading to smooth surfaces can be identified [ 131 ]. Similar smoothing effects were already reported for steel 1.4301 (AISI 304) in [ 14 , 60 ] and for cobalt and titanium alloys in [ 78 , 132 ].…”

“…In a comprehensive study, Metzner et al compared the smoothing effects using a MHz burst, a GHz burst, and a biburst (a combination of MHz and GHz bursts) on stainless steel [ 131 ]. It was found that the smoothing process shows a higher stability and reproducibility when using GHz bursts compared to MHz bursts.…”

“…Brenner et al [ 203 ] demonstrated another interesting application by combining ablation processing in burst mode followed by a cleaning and an additional polishing process for large-format 3D mold tools. Another new approach of combining MHz and GHz bursts, the bi-burst mode, was recently presented in [ 24 , 131 ], but, in milling applications for copper and steel, this mode did not reveal higher removal rates compared to single pulses. In the field of laser burst processing, a comparison of literature data regarding roughness and energy specific volumes for different metals is a challenging task due to different study designs.…”

Optimization mechanism and applications of ultrafast laser machining towards highly designable 3D micro/nano structuring

“…56 Metzner and co-workers reported a solidstate pulsed mode amplication laser source with an intraburst pulse repetition rate of 65 MHz and 2.5 GHz. 57 The research on the GHz laser and burst mode is still in progress. Bonamis et al emphasized the importance of experimental parameters to determine the optimal conditions of burst.…”

MHz burst mode processing as a tool for achieving removal rates scalability in ultrashort laser micro-machining

“…Nevertheless, the MHz burst mode processing with a temporal sub-pulse distance of few nanoseconds had be employed in some applications to smoothen surfaces at low fluence level [30]. Combinations of GHz and MHz burst mode processing were proposed as a potential solution to benefit from the advantages offered by both processes [31][32][33][34]. Although, the reported results showed that there were no efficiency gains in comparison to the single pulse mode, the surface roughness was improved and did not depend on the number of processed layers.…”