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In times of digitalization, multilayer composite materials became central components in an increasing number of application fields. Thus, there is a need for optimization of the cost-intensive and time-consuming processing of multilayer composites. In this contribution, an ultrashort pulse laser-based method is presented for precise and flexible ablation of a printed circuit board base material. Therefore, an 800 nm Gaussian laser beam was transformed into a Bessel beam by an axicon to get a small spot size and an ablation result with a high aspect ratio. The influence of the average laser power, the number of exposure cycles, and the pulse duration on the geometry as well as the surface quality of ablated structures was investigated and compared to Gaussian beam ablation. Furthermore, it is shown that the results can be transferred to microdrilling processes. With the presented method, it was possible to ablate the copper top layer of the printed circuit boards as well as the FR4 layer below with a precisely adjustable depth. [ABSTRACT FROM AUTHOR]

We report on an optical setup to generate multi-Bessel beam profiles combining a refractive axicon and a spatial light modulator. Based on their particular beam profile, Bessel beams offer advantageous properties for micro drilling processes and internal volume processing, especially for transparent materials. In addition, the laser power of industrial, ultrashort pulsed lasers has increased significantly over the last few years, offering the possibility for highly efficient processes using multi-spot profiles. Our optical concept combines the dynamic possibilities of beam splitting using a spatial light modulator with the benefits of Bessel beams, which facilitates multi-Bessel beam processing. Beside the simulation and experimental evaluation of the generated multi-Bessel beams, we exemplify the applicability of the developed module for the perforation of thin metal foils by micro drilling. [ABSTRACT FROM AUTHOR]

This paper reports on combining non-diffracting Bessel beams and ultra-short pulsed laser ablation for the generation of micro-channels. The small focal spot and the long focus depth make Bessel beams suitable as an ideal tool for fabricating sharp-edged channels. In this context, we present a study on the generation of rectangular micro-channels that are highly interesting for future investigations on material properties of additive manufactured and cast aluminum samples, e.g., using them as initial notches or defects, respectively, for fatigue and damage tolerance assessment. In order to achieve the highest quality of rectangular microchannels, optimal processing conditions were achieved by analyzing the influence of the laser power, the number of exposure cycles, and the axial position of the sample on the ablation process. Similar experiments using a Gaussian Beam were performed to compare the different beam shapes regarding the resulting channel geometry and ablation efficiency. Nevertheless, the walls of the Bessel beam processed channels are almost perpendicular to the surface and the bottom of the channel is almost flat. Thus, the Bessel beam generated micro-channels are more rectangular than the ones processed with the Gaussian beam. [ABSTRACT FROM AUTHOR]

Spatial Light Modulators are widely used for creating multiple laser spots with a flexible spatial distribution. This work presents an optical setup for multi-spot laser micro-drilling on stainless steel. For decreasing the hole diameter and getting high laser spot intensities, Bessel beams were generated. A phase only SLM was used as a beam splitter and a physical axicon was added to the setup. This separation of beam splitting and shaping is due to the higher diffraction efficiency of the axicon compared to holographic generated Bessel beams, especially for high cone angles. Minimizing the intensity losses is important due to the low damage threshold of SLM displays. Furthermore, additional lenses has been added for increasing the spot intensity. An ultra-short pulse Ti:Sa-laser (800 nm, 100 fs) was used for the experiments. Possible Bessel spot distributions for metal processing and the impact of the mutual influence of the spots were investigated. [ABSTRACT FROM AUTHOR]