Fig. 1. Experimental setup for femtosecond laser processing

Fig. 2. Software interface of femtosecond laser processing system

Fig. 3. Results of the focus evaluation functions (fun 1‍‒‍fun 4 correspond to gray-level fluctuation function, gradient square function, Laplace gradient function, and quadratic gradient squared function)

Fig. 4. Schematic of correction by sub-regional plane fitting. (a) Original machining path; (b) sample surface; (c) corrected machining path; (d) flow chart of proposed method

Fig. 5. Schematic of sub-region division and sample points selection. (a) Divide into one rectangle region; (b) schematic of error calculation; (c) divide into rectangle regions by 2×2

Fig. 6. Schematic of correction by two-dimensional interpolation. (a) Original machining path; (b) sample surface; (c) corrected machining path; (d) flow chart of proposed method

Fig. 7. Schematic of femtosecond laser processing. (a) Single direction machining in Y direction; (b) double direction machining in XY directions

Fig. 8. Surface sampling point of sample 2 and results of plane fitting in each sub-region

Fig. 9. Surface microstructure machining results. (a) Photograph of experimental sample after machining; (b) schematic of characterization locations by SEM; (c) SEM image of sample 1; (d) SEM image of sample 2

Fig. 10. Groove width machining at different Z distances (Δz=0 represents machining at the focal point)

Fig. 11. Surface sampling point of sample 4 and intermediate points calculated by interpolation

Fig. 12. Result of micro-bulges machining. (a) Photograph of experimental sample after machining; (b) schematic of characterization locations by SEM; (c) SEM image of sample 3; (d) SEM image of sample 4