Numerical simulation of periodic surface structures created by direct laser interference patterning

Abstract

Surface structuring using nano-second lasers can be used to enhance certain properties of a material or even to introduce new ones. One way to create these structures efficiently is direct laser interference patterning using different polarization vector orientations of the interfering beams. However, experimentally measuring the fabrication process of these structures is very challenging due to small length and time scales. Therefore, a numerical model is developed and presented for resolving the physical effects during formation the predicting the resolidified surface structures. This three-dimensional, compressible computational fluid dynamics model considers the gas, liquid, and solid material phase and includes various physical effects, such as heating due to the laser beam for both parallel and radial polarization vector orientations, melting, solidification, and evaporation, Marangoni convection, and volumetric expansion. The numerical results reveal a very good qualitatively and quantitatively agreement with experimental reference data. Resolidified surface structures match both in overall shape as well as crater diameter and height, respectively. Furthermore, this model gives valuable insight on different quantities during the formation of these surface structures, such as velocity and temperature. In future, this model can be used to predict surface structures based on various process input parameters.

Diffraction-based approach for real-time monitoring of nanosecond direct laser interference patterning structure formation on stainless steel

“…Regarding the decrease in the structure depth, in particular for the laser fluences of 5.3 and 4.2 J/cm 2 , further investigations are necessary. This behavior was observed in the FEM simulations reported in 49 . In the published report, the authors also considered a DLIP process with ns-pulses and fluence levels similar as the ones presented in this work.…”

“…This effect can be explained by two possible reasons: the increase in the voltage signal can be attributed to an increase of the reflectivity of the material when cooling (as reported in 42 for stainless steel 17246), or due to a decrease in the structure depth. In the last case, a recent publication by Heinrich et al which focused on numerical simulations of the structure formation in three-beam DLIP, reported on such possible temporal morphological changes 49 .…”