Abstract
Ultra-short laser pulses are frequently used for material removal (ablation) in science, technology and medicine. However, the laser energy is often used inefficiently, thus, leading to low ablation rates. For the efficient ablation of a rectangular shaped cavity, the numerous process parameters such as scanning speed, distance between scanned lines, and spot size on the sample, have to be optimized. Therefore, finding the optimal set of process parameters is always a time-demanding and challenging task. Clear theoretical understanding of the influence of the process parameters on the material removal rate can improve the efficiency of laser energy utilization and enhance the ablation rate. In this work, a new model of rectangular cavity ablation is introduced. The model takes into account the decrease in ablation threshold, as well as saturation of the ablation depth with increasing number of pulses per spot. Scanning electron microscopy and the stylus profilometry were employed to characterize the ablated depth and evaluate the material removal rate. The numerical modelling showed a good agreement with the experimental results. High speed mimicking of bio-inspired functional surfaces by laser irradiation has been demonstrated.
Highlights
Our simulation results at each value of the laser fluence were in good agreement with the ablation rate measurements
The complete model of laser ablation incorporating the accumulation effect and the saturation of ablation depth, if many pulses are applied to a single spot, is presented
The model assumes that laser beam has a Gaussian intensity profile, the ablation depth per pulse is proportional to the logarithm of fluence applied with a certain ablation threshold, the beam is scanned on a flat target material surface by parallel overlapping lines, the inter-pulse distance is equal to the distance between scanned lines, and the ablation volume per pulse is calculated by summing ablated depths from surrounding pulses within cut-off radius
Summary
Ultra-short laser pulses have shown their applicability for high-quality laser micromachining of metals[1,2,3,4,5], semiconductors[6,7,8] and insulators[9,10,11] in scientific[3,12,13], technological[14,15,16,17,18,19,20,21], and medical[22,23,24,25] applications. The maximum volume of the paraboloid and most efficient ablation are achieved when the applied peak laser fluence is e2 times higher than the ablation threshold This model is in good agreement with most of experimental works[27,28,29,30,31,32,33,34,35]. It suggests that an optimal beam scanning speed on the sample should be zero for the maximal material removal rate This fact is in a contradiction with the experimental results, because ablation depth saturates for multi-pulse treatment[43,44,45] and maximum trench depth is achieved for a non-zero scanning speed[47]. Proof-of-principle experiments on copper by various processing parameters sets demonstrate that an optimal point for highest ablation rate can be predicted by our theoretical model
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