Fig. 1. Surface wettability model. (a) Young's state; (b) Wenzel model; (c) Cassie model; (d) angle of droplet is advancing angle when droplet is added and contact line remains stationary; (e) contact angle of droplet is receding angle when droplet is drawn and contact line remains stationary; (f) sliding angle of droplet

Fig. 2. Surface periodic fringe structure induced by femtosecond laser and wettability regulation. (a) (b) Change direction of stripe by adjusting polarization direction of laser and control surface wettability^[65]; (c)-(f) periodic stripe structure obtained by scanning on stainless steel^[66]; (g)-(j) surfaces are superhydrophilic and underwater superoleophobic

Fig. 3. Micro/nano composite structure designed by femtosecond laser and its intelligent wettability. (a)-(d) Micro/nano array structure on zinc surface prepared by femtosecond laser^[70]; (e) EDXS results before and after femtosecond laser processing; (f) reversible surface wettability of femtosecond ablated Zn surface; (g)-(j) titanium surface becomes superhydrophobic after femtosecond laser ablating and PDMS modification^[

Fig. 4. Controllable microcone and microtooth structures fabricated by ethanol and sucrose solution assisted femtosecond laser irradiation[74

Fig. 5. Biological surfaces of anisotropic structures in nature. (a)(b) Microstructure of rice leaf surface; (c)(d) microstructure of reed leaf surface^[75]; (e)(f) scale structure of butterfly wing surface^[7]; (g)(h) micro-cavity structure of nepenthes pitcher plant^[77]

Fig. 6. Bidirectionally/tridirectionally anisotropic sliding superhydrophobic PDMS surfaces fabricated by femtosecond laser^[85]. (a) Anisotropic processing step; (b)-(e) rice-leaf-like bidirectionally anisotropic microstructures; (f)-(i) butterfly-wing-like tridirectionally anisotropic microstructures

Fig. 7. Microporous array structure on aluminum foil surface by femtosecond laser ablation. (a) Control spacing and size of micro-hole by adjusting laser scanning pitch and energy^[87]; (b) Ren et al. prepare micro-hole arrays by femtosecond laser ablation and study gradient of wettability of inner wall of conical holes^[88]; (c) Zhang et al. use microporous structure for oil-water separation.

Fig. 8. Schematic diagram of preparation process for slippery PET surface by femtosecond laser directwriting^[90]. (a) Photo of nepenthes; (b) preparing interconnected porous microstructures by femtosecond laser ablation; (c) fluoroalkylsilane modification used to reduce surface free energy; (d) micropores for infusion of silicone oil; (e) droplet slides down smooth surface

Fig. 9. Laser-grown smart structures of polystyrene film mimicking sunflower^[91]. (a) Polystyrene film fabricated by femtosecond laser processing. Ring in left picture is scanning path,and right pictures show growing mode of structure; (b) four stages during laser-induced polymer self-growing; (c) tuning growth direction in situ

Fig. 10. Realizing structural color based on femtosecond laser induced stripe structure. (a)-(c) Colorizing aluminum sheets with femtosecond laser pulses^{[94, 100]}; (d) relationship between laser induced stripe and color^[101]; (e) relationship between laser wavelength and fringe period^[102]; (f) relationship between

Fig. 11. Self-cleaning and antifouling properties of femtosecond laser processed surfaces^[104]. Roll-off tests of (a) water droplets and (b) oil droplets were performed on untreated side (left side) and laser-treated side (right side), respectively; (c) (d) liquid adhesion tests

Fig. 12. Janus oil barrel with tapered microhole arrays for spontaneous high-flux spilled oil absorption and storage^[89]. (a) Five-step preparation of Janus oil barrel; (b) (c) fast absorption of oil floating on water by Janus oil barrels. Blue part is water, and red part is oil

Fig. 13. Imitation pitcher plant slippery surface fabricated by femtosecond laser for self-transportation and efficient capture of underwater bubble^[111]. (a) Preparation flow chart of imitation pitcher plant slippery surface; (b) mechanical analysis of bubble on surface; (c) bubble slides up surface under buoyancy; (d) (e) double funnel device for gas capture

Fig. 14. Diversified structural surfaces for droplet transfer and transport. (a) Fish scale inspired design for droplet transfer^[112]; (b) processing strategy for mimicking rice leaf groove structure^[83]; (c) groove structure of PDMS for directed transport of droplets; (d) processing strategy of tridirectionally anisotropic step-like microstructure; (e) slightly directional movement of droplets by extrusi

Fig. 15. Various structures prepared by femtosecond lasers for water droplet/optical switches. (a) Change bubble’s contact angle by controlling surface tension of liquid for light path switching application^[116]; (b) left and right bending of microplate by controlling magnetic field; (c) color conversion of surface by coloring left and right sides of microplates; (d) controlling microplate bending by magnetic field for droplet roll-off and retention; (e)