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Laser nanostructuring of thin films with ultrashort laser pulses is widely used for nanofabrication across various fields. A crucial parameter for optimizing and understanding the processes underlying laser processing is the absorbed laser fluence, which is essential for all damage phenomena such as melting, ablation, spallation, and delamination. While threshold fluences have been extensively studied for single compound thin films, advancements in ultrafast acoustics, magneto-acoustics, and acousto-magneto-plasmonics necessitate understanding the laser nanofabrication processes for functional multilayer films. In this work, we investigated the thickness dependence of ablation and delamination thresholds in Ni/Au bilayers by varying the thickness of the Ni layer. The results were compared with experimental data on Ni thin films. Additionally, we performed femtosecond time-resolved pump-probe measurements of transient reflectivity in Ni to determine the heat penetration depth and evaluate the melting threshold. Delamination thresholds for Ni films were found to exceed the surface melting threshold suggesting the thermal mechanism in a liquid phase. Damage thresholds for Ni/Au bilayers were found to be significantly lower than those for Ni and fingerprint the non-thermal mechanism without Ni melting, which we attribute to the much weaker mechanical adhesion at the Au/glass interface. This finding suggests the potential of femtosecond laser delamination for nondestructive, energy-efficient nanostructuring, enabling the creation of high-quality acoustic resonators and other functional nanostructures for applications in nanosciences. [ABSTRACT FROM AUTHOR]

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]

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]