Formation of highly organised, periodic microstructures on steel surfaces upon pulsed laser irradiation

We present results on the growth of highly organised, reproducible, periodic microstructure arrays on a stainless steel substrate using multi-pulsed Nd:YAG (wavelength of 1064 nm, pulse duration of 7 ns, repetition rate of 25 kHz, beam quality factor of M (2)similar to 1.5) laser irradiation in standard atmospheric environment (room temperature and normal pressure) with laser spot diameter of the target being similar to 50 mu m. The target surface was irradiated at laser fluence of similar to 2.2 J/cm(2) and intensity of similar to 0.31x10(9) W/cm(2), resulting in the controllable generation of arrays of microstructures with average periods ranging from similar to 30 to similar to 70 mu m, depending on the hatching overlap between the consecutive scans. The received tips of the structures were either below or at the level of the original substrate surface, depending on the experimental conditions. The peculiarity of our work is on the utilised approach for scanning the laser beam over the surface. A possible mechanism for the formation of the structures is proposed.