Development of high-power laser ablation process for polycrystalline diamond polishing: Part 3. processing with an ultra-short-pulsed laser up to 1kW

Ultra-short pulse laser machining has been applied to the polishing of polycrystalline diamond (PCD) wafers in order to generate a smooth surface finish and reduce mechanical polishing time. Past studies were first carried out with a 5W laser highlighting the difference in ablation rates between PCD grades and the possible graphitization of diamond on the surface of micrometric PCD grades over a fluence threshold. Some upscaling work was undertaken at 80W with a 3-pulse burst reducing the Sa of a micrometric PCD grade lapped surface by 50% with a volume removal rate double that of the conventional mechanical polishing technique. From these previous base investigations, an ultra-short pulse laser delivering an average power of 1kW at 500fs via state-of-the-art thin disk multi-pass amplification is implemented here to achieve a higher ablation rate for high throughput processing. This is the first time that such an average power is applied on polycrystalline diamond in the ultra-short pulse regime. A burst mode is also implemented which is demonstrated to reduce the Sa by 10% and 55% on fine and coarse grade surfaces respectively compared to single pulse processing. From 80W to 1kW, the ablation rate is increased by a factor of 70 on micrometric PCD grades while the Sa of the initial lapped surface is reduced by 14% without any graphitization of the diamond structure. However, no improvement of the Sa is performed on the initial surface of coarser grades due to the formation of cavities (∼5μm wide) potentially caused by the spallation of diamond grains.