Laser ablation of graphite with near infrared microsecond pulses

Laser processing of polycrystalline porous graphite through micro- to millisecond pulses with 1 mu m wavelength is investigated. The study aims at finding the best compromise between the efficiency of the process (ablation rate) and the quality (reduced heat-affected zone) for drilling and cutting applications. Our experimental approach is based on experiments involving a monomode kW ytterbium fibre laser (1080 nm) coupled with a laser scanning system. This system is used for parametric studies on pulse duration, power, repetition rate and scanning speed on samples that are analysed with scanning electron microscopy. To improve the understanding of the underlying physical phenomena and processes involved, a finite element numerical model is developed, taking into account energy deposition through optical ray tracing, heat transfer, sublimation of the material and crater formation. Based on these experimental and numerical tools, we identify some optimum parameters to fabricate high aspect ratio shapes in graphite samples of 1.5 mm thickness with excellent edge quality and minimal heat-affected zone. Laser processing under vacuum atmosphere is also studied and exhibit no difference in behaviour compared to ambient atmosphere.