Investigations of surface processing of functional ceramics applying ultrashort laser pulses

Abstract

The development of ultrashort pulse lasers has enabled many new process technologies in the past few years. The nonlinear absorption caused by high peak intensities and the nonthermal ablation are two of the most attractive benefits of pulse durations in the pico- and femtosecond regime, which allow for the processing of a wide variety of materials. Even dielectric, brittle-hard substrates can be processed precisely and gently without cracking or inducing stresses. For this reason, the technology is particularly suited to open up new processing possibilities in the field of functional ceramics. These materials offer many opportunities to set up complex microsystems and multisensor systems. However, the options to structure and shape functional ceramics were limited in the past and had to be solved by elaborate mechanical processes so far. By means of ultrashort pulse laser processing, new applications in the fields of precise shape formation and microstructuring of functional ceramics become accessible. In order to reveal and optimize the processes occurring during surface ablation, investigations with different laser systems have been executed and evaluated by applying various characterization techniques. The results show how the properties of the bulk material and the process parameters such as pulse energy, wavelength, and pulse overlap influence the removal rate as well as the material characteristics, for instance, roughness and morphology. Thereby, the attention is focused on the dependence of the process on the pulse duration. In contrast to the homogenous surface profile that is created during picosecond ablation, the femtosecond process exhibits material modifications in terms of melting patterns. This effect is strongly dependent on the pulse duration, the fluence, and the pulse overlap. It leads to an increase in roughness, which affects the precise material removal. Nevertheless, the investigations also show that the material melting can be utilized to achieve a smoothing effect of the surface if the parameters are well adjusted. The experimental investigations result in optimized process strategies to realize user-defined aims like high ablation rates, high accuracy, or low damage.