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.

Effects related to the use of high repetition rate lasers in ablation of metals (aluminum, copper, stainless steel) and silicon were investigated. The multi-pulse irradiation with the laser beam significantly lowered the ablation threshold and led to a relative increase in the ablation rate at the higher repetition rate. The reason of alteration could be accumulation of structural defects on the metal surface formed by irradiation with a laser of the sub-threshold fluence. The mean volumetric ablation rate in laser milling experiments was a non-linear function of the pulse energy. Plasma shielding was the main limiting factor in processing efficiency of metals with the high power picosecond lasers. Increasing the repetition rate keeping the pulse energy below the plasma formation threshold is a way to increase the efficiency of material removal with nanosecond lasers. Thermal management of the specimen could be a problem at high repetition rates because of the laser energy wasted in the bulk. The reduction in the ablation threshold by irradiation with a series of laser pulses might be useful in application of the high- repetition-rate lasers with the low pulse energy.

Here, to the best of our knowledge, for the first time we report an in-depth experimental study of high ultrafast laser ablation efficiency for processing of copper and steel with single-pulses, MHz, GHz, and burst-in-the-burst (biburst) regimes. The comparison of burst, biburst, and single-pulse ablation efficiencies was performed for beam-size-optimised regimes, showing the real advantages and disadvantages of milling and drilling processing approaches. Highly efficient ultrashort pulse laser processing was achieved for ∼1 µm optical wavelength: 8.8 µm³/µJ for copper drilling, 5.6 µm³/µJ for copper milling, and 6.9 µm³/µJ for steel milling. We believe that the huge experimental data collected in this study will serve well for the better understanding of laser burst-matter interaction and theoretical modelling.

Results on the manipulation of the wetting properties of stainless steel alloy surface by ultrashort pulse laser texturing are presented.