Fig. 1. In-situ observation platform for picosecond laser processing. (a) Schematic; (b) actual platform

Fig. 2. Morphologies of porous glass. (a) Appearance; (b) morphology by CT scanning; (c) SEM morphology

Fig. 3. Morphologies of K9 glass and porous glass under different N with laser removal range shown by dashed line and spot irradiation range shown by solid line. (a)‒(d) K9 glass; (e)‒(h) porous glass

Fig. 4. Comparison of groove processing between porous glass and K9 glass. (a) Schematic of single scanning route; (b) morphology of porous glass after two times of ablation; (c) morphology of K9 glass after 50 times of ablation; (d) removal volume by single pulse and surface roughness after processing

Fig. 5. Ultrafast laser processing of porous glass and K9 glass under different moments. (a)(d) 0 ms; (b)(e) 2 ms; (c)(f)4 ms

Fig. 6. Removal mechanisms of porous glass and dense glass by ultrafast laser. (a) Laser-induced particle spalling; (b) laser ablation

Fig. 7. Schematics of microcone array machining. (a) Geometric features of microcone array; (b) scanning strategy with constant feeding direction; (c) scanning strategy with feeding from edge of microcone to center

Fig. 8. Microcone array machined under constant feeding direction. (a) Local 3D morphology of microcone array when D_th=100 μm; (b) statistics of cone apex size and cone height error under different machining allowances

Fig. 9. Microcone array machined under scanning strategy with feeding from edge of microcone to center. (a) Local 3D morphology of microcone array when D_th=100 μm; (b) statistics of cone apex size and cone height error under different machining allowances

Fig. 10. SEM images of top morphology of microcone

Fig. 11. Fabrication, assemblage and test of emitter. (a) Geometric structure of emitter; (b) physical image of machined emitter and 3D morphology of typical microcone; (c) appearance of electrospray thruster and its working situation