Gradient periodic structure with feature sizes in the micrometer range have gained attention since when produced on a certain material, it can lead to anisotropic surface functions. Such topographies can be produced for instance using Direct Laser Interference Patterning, in case that the spatial period is locally varied depending on the position where the laser power is applied. Furthermore, in the low or moderate fluence ranges (laser energy per unit of area), also the local grain orientation can affect the laser-matter interaction and thus can lead to irregularities in the resulting topography.

In this study, DLIP method is applied for producing periodic surface structures with gradual variation of the period (from 2 to 4 µm) by locally changing the intercepting angle between the laser beams, and thus changing the periodic intensity distribution of the laser energy interacting with the material’s surface. For the structuring experiments, a ps laser (10 ps) emitting at infrared wavelength was used, with a laser fluence level of approximately 0.7 J/cm². The results show an important influence of the existing crystallographic structure of the steel sample on the produced topographies, depending on the grain orientation. In addition, Laser Induced Periodic Surface Structures (LIPSS) are reported with different morphologies.