Determination of the interference spot size using photo-acoustic emission in direct laser interference patterning

Direct laser interference patterning (DLIP) has emerged as a versatile tool for producing well-defined microstructures that mimic natural surfaces with the aim of obtaining functionalized surfaces on relevant technological materials. On the other hand, the fabrication of surface patterns with micro- and submicron resolution features necessitates of advanced monitoring and setup strategies in order to ensure repeatability as well as quality control. In addition, the monitoring systems also allow inline capabilities to enable a closed-loop control approach. A possible strategy, that has been already applied to different laser processes, is the utilization of the sound pressure generated by the laser beam hitting the surface and producing ablation that can be detected and analyzed using commercially available microphones. In this frame, this work focuses on the analysis of the acoustic information extracted from the audio signal for determining process-inherent characteristics in DLIP, allowing the calculation of interference volume using stainless steel and titanium as reference materials. The results show that the acoustic emission measured at the ablation spot can be correlated to the interference volume shape and thus allowing to approximate the size of the interference spot. The possible utilization of this approach as an auto-focus and auto-setup method during DLIP is discussed.