Fig. 1. Schematic of material removal process under temperature field by millisecond laser

Fig. 2. Stress field effect. (a) Schematic of interaction between recoil pressure and material^[27]; (b) molten material penetrates into Al₂O₃ pores due to recoil pressure^[28]

Fig. 3. Thresholds of Al₂O₃ during millisecond laser processing^[32]. (a) Melting threshold; (b) vaporization threshold

Fig. 4. Relationship between millisecond laser pulse duration and hole diameter^[33-34]. (a) Al₂O₃ with thickness of 2.2 mm; (b) Al₂O₃ with thickness of 10 mm( laser peak power of 6 kW)

Fig. 5. Relationship between millisecond laser power and hole diameter^[33-34]. (a) Al₂O₃ with thickness of 2.2 mm; (b) Al₂O₃ with thickness of 10 mm

Fig. 6. Cross-section images of the holes on Al₂O₃ drilled by millisecond laser^[36] (Al₂O₃ with thickness of 10.5 mm, laser peak power of 6 kW)

Fig. 7. Relationship between of millisecond laser energy and hole depth. (a) Relationship between laser power and hole depth^[36], Al₂O₃ with thickness of 10.5 mm, and pulse duration of 2 ms; (b) cross-section image of the holes on Al₂

Fig. 8. Relationship between millisecond laser action time and hole depth^[24,36]. (a) Al₂O₃ with thickness of 1 mm, pulse duration of 15 ms, and laser energy of 600 mJ; (b) Al₂O₃ with thickness of 10.5 mm, pulse duration of 2 ms, peak power of 8 kW, and repetition rate of 10 Hz

Fig. 9. Relationship between millisecond laser repetition rate and hole diameter and depth. (a) Al₂O₃ with thickness of 10.5 mm, pulse duration of 2 ms, peak power of 8 kW, and focal plane position of -2 mm; (b) cross-section images of the holes on Al₂O₃

Fig. 10. Relationship between millisecond laser pulse duration and hole taper (Al₂O₃ with thickness of 10 mm)^[34]

Fig. 11. Relationship between millisecond laser peak power and hole taper, and schematic of ejected particles resolidified around hole entrance^[34]. (a) Hole taper versus laser peak power; (b) schematic of ejected particles resolidified around hole entrance

Fig. 12. Relationship between millisecond laser focal plane position and hole taper. (a) Al₂O₃ with thickness of 1 mm, pulse duration of 15 ms, laser energy of 600 mJ, and repetition rate of 5 Hz^[24]; (b) Al₂O₃ with thickness of 10.5 mm, pulse duration of 2 ms, peak power of 8 kW, and repetition rate of 10 Hz^[36]

Fig. 13. Ablation depth per pulse of Al₂O₃ versus nanosecond laser fluence (pulse duration of 10 ns and repetition rate of 1 Hz)^[47]

Fig. 14. Material removal mechanism of nanosecond laser processing aluminum nitride, and morphology of hole wall^[48-49]. (a) Chemical reaction for AlN drilled by nanosecond laser; (b) SEM image of hole cross-section on AlN

Fig. 15. Element content in different parts of hole exit on AlN by nanosecond laser processing (laser power of 8 W, repetition rate of 50 kHz, scanning speed of 20 mm/s, and repeat counts of 40)

Fig. 16. Relationship between nanosecond laser power and hole diameter (Al₂O₃ with thickness of 0.8 mm and repetition rate of 5 Hz)^[50]

Fig. 17. Relationship between hole entrance diameter and scanning speed for nanosecond laser processing (Al₂O₃ with thickness of 0.12 mm, laser power of 8 W, and repetition rate of 50 kHz)

Fig. 18. Influence of nanosecond laser processing parameters on etching depth of Al₂O345. (a) Laser fluence;

Fig. 19. Relationship between shot number and ablation depth (Al₂O₃ with thickness of 0.6 mm and laser fluence of 600 J/cm²)^[51]

Fig. 20. Relationship between laser power and hole taper(Al₂O₃ with thickness of 0.12 mm, repetition rate of 50 kHz, and repeat counts of 100)