Formation of corrugated and porous steel surfaces by femtosecond laser irradiation

Novel interaction regime of femtosecond laser pulses with steel surface at high peak irradiation fluences (0.82–10 J/cm2) has been observed and thoroughly investigated. This interaction regime allows the generation of well defined microrough surfaces. To investigate the mechanisms involved in the formation of sub-focus microscale cavities and protrusions, the influence of key structuring parameters has been analyzed using a multi-pulse/multi-point layout. Threshold-like appearance of large amplitude sub-focus corrugations and micropores with the variation of laser fluence, hatch spacing, and radiation exposure has been observed. The dependencies of these threshold values on ambient gas pressure and focal spot size have been verified. The established experimental background has been applied for the fabrication of ordered rough-porous patterns with the feature sizes in the range of 1–25 μm.