Towards obtaining high-quality surfaces with nanometric finish by femtosecond laser ablation: a case study on coppers

Femtosecond laser ablation is an essential technology for the fabrication of functional surfaces. However, the ablation quality in femtosecond laser processing is influenced by the excessive energy deposition and the heat accumulation, which results in a low ablated surface quality and even defects on the surface. This study performed femtosecond laser ablation to obtain surfaces with a nanometric finish. Different pulse overlap rates and multiple scanning strategies of the femtosecond laser to machine surfaces with reduction of debris, periodic striped micro-grooves, and micrometric ripples were investigated, which allowed an access to a high-quality surface with a nanometric finish. A mathematical model of femtosecond laser ablation was established to study the formation mechanism of ablated surface characteristics. The effects of the pulse overlap rate and scanning strategy on the generation of debris and microstructures were investigated. Experiments were carried out to verify the method by controlling the pulse overlap rate and scanning strategy of the laser. A femtosecond laser ablated copper workpiece with a surface roughness Sa of 0.056 μm was achieved.