Due to its flexible applications, functional laser surface texturing using Direct Laser Interference Patterning (DLIP) has developed into a powerful tool to fabricate well-defined micro-textures that mimic natural surfaces, such as the lotus effect for self-cleaning properties or the structure of shark skin for reduced friction [1]. On the other hand, the fabrication of surface patterns using DLIP with micro- and submicrometer resolution necessitates advanced monitoring strategies to control the ablation quality as well as ensure DLIP-pattern repeatability. Furthermore, the employed monitoring systems require in-line capabilities to allow closed-loop control ap-proaches. A possible method, already applied to direct laser writing, is the use of structure-borne acoustic emis-sion (AE) generated by the laser-interaction with the surface [2].

This work describes the pre-processing and analysis of the acoustic information extracted from the AE using a contact microphone during laser-material interaction. The process-inherent characteristics such as the size of the interaction area, the influence of the laser pulse energy and changes in the spatial period during DLIP processing are examined. The results show that the working position, defined as the position of the target surface along the vertical extent of the volume of interference between the beams, can be correlated with the amplitude and spec-tral shape of the AE. This provides important information for the possibility to develop a monitoring system using only the signals from the acoustic emission for 3D processing, as well as the possibility to predict devia-tions in the DLIP processing parameters.

[1] A. F. Lasagni, “Laser interference patterning methods: Possibilities for high-throughput fabrication of periodic surface pat-terns”, Advanced Optical Technologies, 6 (2017) 3–4, 265–275, doi: 10.1515/aot-2017-0016.
[2] E. V. Bordatchev, S. K. Nikumb, “Informational properties of surface acoustic waves generated by laser-material interactions during laser precision machining”, Measurement Science and Technology, 13 (2002) 6, 836–845, doi: 10.1088/0957-0233/13/6/303.