Formation mechanism and inhibition strategies of surface tool marks in multi-layer laser ablation of fused silica microstructures

Laser ablation has been widely applied in the functional microstructure manufacturing due to its high efficiency and non-contact processing properties with reduced risk of surface/subsurface defects. However, tool marks formed by the superposition of multi-pulse laser multi-line ablation seriously influence the surface roughness and service performance of the microstructures. To inhibit it, the formation mechanism of the multi-layer ablation tool marks was first revealed by multi-physics coupling simulation. An innovative staggered ablation strategy was proposed, and experimental results confirmed that the height of the tool marks could be reduced by more than 50%. Then, the laser ablation experiments were conducted to explore the influence of parameters on the tool marks and surface accuracy. Based on the experimental results, a variable-depth multi-step ablation strategy that could ensure ablation efficiency and improve processing precision was innovatively proposed. The tool marks could be reconstructed through deep-layer ablation, shallow ablation followed by thin-layer ablation combined with the staggered ablation strategy. Finally, the height of the ablation tool marks along track pitch direction was reduced from 320 nm to 75 nm, and the surface roughness was improved from 89 nm to 33 nm. Moreover, various functional microstructures for different purposes were manufactured, which verified the universality and effectiveness of the ablation strategies proposed. This work explored the formation mechanism of tool marks involved in laser multi-layer ablation and proposed processing strategies that can effectively improve the surface quality. It can provide significant theoretical and experimental guidance for the laser ablation technique of optical components.