Fig. 1. Schematic diagram of femtosecond laser processing system

Fig. 2. Schematic diagram of femtosecond laser ablation experiment. (a) Single pulse ablation; (b) multipulse ablation

Fig. 3. Physical image of a digital 3D video microscope

Fig. 4. Energy density distribution of the Gaussian beams

Fig. 5. Fitting curve of D² and ln P

Fig. 6. Fitting curve of h_max and ln P

Fig. 7. Effect of defocusing amount on micro-hole processing. (a) Positive defocus; (b) no defocus; (c) negative defocus

Fig. 8. Schematic diagram of the defocus variation

Fig. 9. Profile and energy distribution of ablation pits. (a) P=1 W; (b) P=3.2 W

Fig. 10. Fitting curve of D and N

Fig. 11. Residual form of melt in ablation pits. (a) Remain in the pit bottom; (b) remain in the pit wall

Fig. 12. Morphology of residual melt in ablation pits. (a) Single pulse ablation pits; (b) multipulse ablation pits

Fig. 13. Morphologies of ablation pits under different laser powers. (a) 1 W; (b) 1.7 W; (c) 2 W; (d) 2.7 W; (e) 3.2 W

Fig. 14. Effect of N and P on the ablation pit depth h_max