Optimizing the process parameters of laser-induced periodic surface structures to the highest production rate

Pioneered by Birnbaum in the mid-twentieth century, laser-induced periodic surface structures (LIPSS) have been produced on a wide range of materials including semiconductors, metals, polymers and ceramics. They are generally periodic nanoscale structures that develop on top of surfaces processed by a (ultra-) short pulsed laser beam. Up to now, several types of laser-induced periodic surface structures have been developed in the form of ripples, pillars, cones, and grooves. In particular, low spatial frequency-LIPSS have recently attracted significant research attention. They are periodical surface ripples parallel or perpendicular to the laser polarization direction and thus exhibiting potential applications in various areas.

Different laser parameter i.e. the angle of incidence of the laser beam relative to the surface substrate and the laser wavelength among others have exhibited significant influence on the morphology and dimension of the laser-induced periodic surface structures. Therefore, there is a high need to homogenously cover surface areas larger than the laser spot size using one type of laser-induced periodic surface structures. Unfortunately, establishing laser processing parameters capable of inducing uniform homogenous areas have remained a challenge due to the relatively small process windows. This hinders achieving high production rates. Presently, various approaches have been proposed to derive laser process parameters for homogenous areas. However, these approaches face numerous challenges as they are majorly iteratively based. To this end, the development of closed mathematical models for processing optimal parameters producing homogenous areas of laser-induced periodic surface structures are highly desirable.

To this note, Marek Mezera (PhD candidate) and Professor Gert-willem Römer from the Faculty of Engineering Technology at University of Twente in the Netherlands developed a non-iterative closed mathematical model for calculating the optimized laser processing parameters to manufacture large homogenous areas of laser-induced periodic surface structures. Technically, the approach was based on laser-materials dependent parameters, the geometrical pulse-to-pulse overlap and the peak laser fluence. Additionally, the authors aimed at determining the optimal processing conditions favorable for the fabrication process. The research work is currently published in the research journal, Optics Express.

The authors successfully used the proposed model to calculate the optimized laser parameters considering the material-dependent parameters. For instance, the material-dependent parameters were used to determine a range of peak fluence levels and pulse-to-pulse overlap values that allowed the production of homogenous areas of laser-induced periodic surface structures. Additionally, the model can be used to calculate processing parameters for the highest possible production rate. To actualize the study, the model was successfully validated over a large range of fluence levels and geometrical pulse-to-pulse overlap values on silicon using a picosecond laser source. The experimental results were observed to agree well with the proposed mathematical model. Therefore, the Mezera-Römer study will lead to accurate prediction of the laser processing parameters which will advance production of large homogeneous surface areas on laser-induced periodic surface structures at much higher production rates.

Acknowledgments

The Laser4Fun project leading to this study has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie Grant Agreement No. 675063.