Advanced laser scanning for highly-efficient ablation and ultrafast surface structuring: experiment and model

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.

Evolution of microstructures on stainless steel induced by ultra-short pulsed laser ablation

“…In detail, the material removal in terms of one layer is presented and the discussed structures after laser machining pointing to clear growth regimes. The contour plot points to a saturation in terms of material removal rate at increasing fluence with adjacent layer depth z layer , where the slope of the iso-ablation depth lines decreases at about 10 ⋅ F th ≈ 0.65 J cm −2 in good agreement with proposed models in literature concerning efficient laser ablation [17,21]. At low feed rates and small distance between two pulses starting from moderate fluence of 0.3 J cm −2 , bumps due to heating and melting are formed, where the characteristic semispherical morphology with several 10 μm of size covers the surface [49].…”

“…The threshold fluence F th , defined by the power density where ablation starts for the multi-pulse regime, of stainless steel was determined for the used samples by considering the assumption for the ablation efficiency [17,21]. An optimal fluence F opt = e 2 F th follows from a logarithmic ablation law and using a Gauss intensity distribution with a beam waist w 0 the dependency of the applied peak fluence F 0 can be studied.…”

“…Defined ablation conditions are a prerequisite for low roughness and efficient laser ablation [17]. In principle the fluence, pulse-to-pulse distance from laser repetition rate and scan speed leads to a certain overlap linked with the focal beam waist, which are the main parameters [18].…”

Glass Fiber Reinforced Polycarbonate Composites for Laser Direct Structuring and Electroless Copper Plating

“…The results showed that the resolution increases with laser repetition, and it also increases as the scanning speed decreases. This could also be explained by laser fluence theory, which assumed that at low scanning speed a high number of pulses per spot were achieved because of high pulse overlap, while small laser spot size resulted in laser fluence high above the ablation threshold and large ablation depths .…”

Evolution of Microstructures on Stainless Steel induced by Ultra-Short Laser Ablation

“…Defined ablation conditions are a prerequisite for low roughness and efficient laser ablation [7]. In principle the fluence, laser repetition rate, and scan speed are interdependent [8] and no global optimum can be reached.…”