LIPSS and DLIP: From hierarchical to mutually interacting, homogeneous, structuring

Abstract

Direct Laser Interference Patterning (DLIP) and Laser Induced Periodic Surface Structures (LIPSS) are two distinct, key technologies for texturing of surfaces with structures in the range comprised between some hundreds of nm and few µm. Based on different physical phenomena, they enable structures often showing distinct morphologies and pitches. It has been shown the possibility of superposing LIPSS over DLIP with a final multi-scale, hierarchical morphology where the two structures coexist. Here, we report an experimental study showing that it is possible to turn from a hierarchical to mutual interacting texturing where DLIP and LIPSS give rise to a novel, uniform texturing having a homogeneous morphology with highly regular periodicity and low orientation dispersion. Moreover, we show that our approach makes possible an unexpected, significant reduction of the LIPSS period from the conventional values (roughly comprised between 0.7λ – 0.9 λ) to ∼0.45λ. In addition, for all the tests an industrial set-up has been used including an IR, ps laser, an f-theta lens with relatively high NA and a galvo scanner making possible the extension of the process over large area. Results are discussed in the light of different LIPSS generation models. We believe that our results represent a significant step forward through the further miniaturisation of laser induced morphologies opening the possibility for innovative surface functionalisations (anti-reflective, wide spectrum antimicrobial activity) to be exported in an industrial environment.