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For the laser drilling of aluminum nitride (AlN) ceramic the influence of the laser parameters and material properties on the drilling rate, quality of the holes and the effects related to plasma formation are investigated. The ablation is performed by pulsed irradiation of Nd:YAG laser at wavelengths of 1064, 532 and 355 nm, at pulse duration of 6 ns (FWHM) in air. The SEM scans of the processed surface reveal regular, cylindrically shaped holes of diameter of about 100 μm obtained under conditions of constant fluence at all wavelengths applied. Holes are surrounded by circular zones which are colored different than the non-processed surface, and of a much larger diameter. Comparison of the original material composition with that of the processed one made by EDX shows a decrease of the N concentration in the affected area. The zones are identified as heat-affected due to the high thermal conductivity of the ceramic material and change of the photon distribution due to multiple reflections into the material. In the LIBS spectra recorded in order to obtain the composition of the ablated material the presence of ions and neutrals depends on the laser intensity applied. At intensity values close to the ablation threshold the ejected material consists mainly of neutrals and doubling the intensity results in appearance of single-ionized Al species. The ionized species dominate over neutrals under conditions of higher drilling rate (15 GW/cm2 at 532 nm). Their existence in the plasma plume together with clusters is confirmed by the TOF-MS spectra. It also corresponds to the characteristic spatial structure of the plume. The investigation of the decomposition reactions of AlN in dependence on the applied laser intensity is based on numerical solving of the three dimensional heat-transfer equation. A solution consistent with the experimental observation indicates that at threshold the ceramic decomposes into gaseous nitrogen and solid Al particulates, while at higher fluences the Al vaporizes and influences the drilling quality.
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