Publication database

Laser polishing offers numerous advantages, one of which is the convenience of using the same system for the
whole manufacturing process. In this work, an ultrashort pulse laser operating in a GHz burst regime was used to polish
stainless steel. The aim was to minimise surface roughness, characterised by the average roughness parameter R_a. Different
laser processing parameters (average laser power, number of pulses per burst, scanning speed, hatch size) were varied to polish
samples that were covered in laser-induced periodic surface structures (LIPSS). Thermal effects, such as melt layer formation,
were noticed and discussed. It was demonstrated that LIPSS can be erased and the initial surface roughness of 73 nm was
reduced to 41 nm using 100 pulses per burst and burst fluence of F_B = 0.15 J/cm².

Results of in-depth experimental analysis of the laser-assisted local copper deposition on commercial Polyamide 6 (PA 6) are presented. Pico- and nanosecond lasers were validated for surface modification of the polymer followed by silver (I) activation and finished by autocatalytic electroless copper plating on the laser-modified areas. Detailed investigations were dedicated to finding out the origin of selective metal plating, including the surface profiling and wettability dynamics, XPS analysis and electric resistance measurements of the deposited copper layer. Based on the experimental data, the mechanism of the polymer surface activation by the laser modification is proposed.

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.

New results on development of the Direct Laser Interference Patterning (DLIP) technique using the interference of several beams to directly ablate the material are presented. The method is capable of producing sub-wavelength features not limited by a beam spot size and is an effective method of forming two-dimensional periodic structures on relatively large area with just a single laser shot. Surface texturing speed of DLIP method and the direct laser writing was compared. Fabrication time reduction up to a few orders of magnitude using DLIP was evaluated. The sub-period scanning technique was applied for formation of the complex periodic structures. A new method of laser scanning for fabrication of periodic structures on large areas without any visible stitching signs between laser irradiation spots was tested.

The picosecond laser-induced ripple formation on the stainless steel surface upon irradiation with linearly-polarized single-pulse and dual-wavelength cross-polarized double-pulse trains in air was studied experimentally. The characteristic switching of the ripple period and orientation were observed depending on the inter-pulse delay in the dual-wavelength cross-polarized double-pulse train irradiation experiments.