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Abstract
The uniform energy distribution of top-hat laser beams is a very attractive property that can offer some advantages compared to Gaussian beams. Especially, the desired intensity distribution can be achieved at the laser spot through energy redistribution across the beam spatial profile and, thus, to minimize and even eliminate some inherent shortcomings in laser micro-processing. This paper reports an empirical study that investigates the effects of top-hat beam processing in micro-structuring and compares the results with those obtainable with a conventional Gaussian beam. In particular, a refractive field mapping beam shaper was used to obtain a top-hat profile and the effects of different scanning strategies, pulse energy settings, and accumulated fluence, i.e., hatch and pulse distances, were investigated. In general, the top-hat laser processing led to improvements in surface and structuring quality. Especially, the taper angle was reduced while the surface roughness and edge definition were also improved compared to structures produced with Gaussian beams. A further decrease of the taper angle was achieved by combining hatching with some outlining beam passes. The scanning strategies with only outlining beam passes led to very high ablation rates but in expense of structuring quality. Improvements in surface roughness were obtained with a wide range of pulse energies and pulse and hatch distances when top-hat laser processing was used.
Highlights
Direct laser micro-structuring is an attractive solution for fabricating micro-scale features due to advantages offered in overcoming some material and dimensional limitations of conventional machining methods
This paper reports an empirical study that investigates the effects of top-hat beam processing in micro-structuring and compares the results with those obtainable with a conventional Gaussian beam
The drop of peak power when the Gaussian profile was transformed into a top-hat one while keeping the pulse energy the same led to a reduction of the average surface roughness
Summary
Direct laser micro-structuring is an attractive solution for fabricating micro-scale features due to advantages offered in overcoming some material and dimensional limitations of conventional machining methods. The majority of commercially available laser micro-processing systems employs Gaussian beams (TEM00) due to their intensity profile and their consistency along propagation direction. This makes Gaussian beams much easier to use and calibrate. Their spatial intensity distribution leads to an energy waste at the “tails” of the beam profiles as the intensity is lower than ablation thresholds and is just sufficient to melt/heat the material. This increases the heat affected zone (HAZ) while decreasing the processing efficiency of delivered pulse energies. Gaussian spatial intensity can be transformed into top-hat, donut, or reverse Gaussian distribution by employing beam shapers
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