Fig. 1. Schematic of WJGL processing system ^[9]

Fig. 2. Coupling principle of laser beam and water jet. (a) Schematic diagram of laser coupling with water jet^[22]; (b) schematic diagram of laser beam propagation^[23]; cross-sectional views of propagation paths of (c) meridional rays and (d) skew rays; (e) coupling errors between water jet and laser, with aligned coupling, axial deviation, radial deviation, and angular deviation shown from left to right^[25]

Fig. 3. Factors affecting coupling of laser and water jet. (a) Numerical apertures under different states^[27]; (b) electric field distributions at different stages of water jet with contraction, cavitation, development of cavitation, and hydraulic flip^{shown from left to right[28]}

Fig. 4. Laser energy distributions^[31]. (a) Water-jet guided laser; (b) Gaussian laser

Fig. 5. Simulation of temperature field in material processing with water-jet guided laser. (a) Temperature distribution and diffusion under different pulse durations^[34]; (b) temperature variations of high-temperature alloy surface material of thermal barrier coating^[35]

Fig. 6. Principles and material removal mechanisms of water-jet guided laser, underwater laser, and water-assisted laser processing technologies. (a) Cooling and remelting process during water-jet guided laser processing^[36]; (b) heat-affected zone in cross-section of nickel-based alloy^[36]; (c) principle of water-jet guided laser processing^[37]; (d) oxidation process in water-jet guided laser processing^[37]; (e) cross section of alloy^[37]; (f) schematic diagram of underwater laser processing^[38]; (g) material removal mechanism of underwater laser processing^[38]; (h) upper surface of blind hole^[38]; (i) schematic diagram of water-assisted laser processing^[39]; (j) material removal mechanism of water-assisted laser processing^[39]; (k) upper surface of microgroove^[39]

Fig. 7. Characteristics of water jet^[42]. (a) Four stages of water jet; (b) various nozzle structures

Fig. 8. Water jet lengths under different conditions. (a) Different water flow velocities^[11]; (b) different nozzle diameters^[11]; (c) different atmospheres^[47]

Fig. 9. Influence of laser wavelength on material. (a) Absorption coefficients of water for different laser wavelengths^[24]; (b) 355 nm water-jet guided laser processing of wafer^[48]; (c) transmission efficiency of 1064 nm water-jet guided laser at different nozzle diameters^[52]; (d) comparison of simulated and experimental transmission efficiencies for 1064 nm water-jet guided laser^[25]; (e) processing of 0.75 mm thick silicon wafer using 1064 nm water-jet guided laser ^[25]

Fig. 10. Influence of duty cycle on material processing. (a) Process of material ablation by water-jet guided laser^[26]; (b) variation in hole depth under different duty cycles ^[54]

Fig. 11. Temperature field simulation of water-jet guided laser. (a) Temperature field simulations of conventional laser and water-jet guided laser^[56]; (b) heat affected zone distribution in 304 stainless steel substrate under different average laser powers^[58]; (c) drilling depths and heat affected zone distributions in nickel-based superalloy under different pulse numbers ^[61]

Fig. 12. Schematic diagrams of water-jet guided laser equipment^[62]. (a) Schematic diagram of high-pressure water circulation system; (b) schematic diagram of laser and water jet coupling device

Fig. 13. Influence of scanning speed on processed material. (a) Surface morphologies of processed LTCC at different scanning speeds^[64]; (b) widths and tapers of upper and lower surfaces of LTCC processed at different scanning speeds^[64]; (c) widths and surface morphologies of upper and lower surfaces of CFRP processed at different scanning speeds^[65]; (d) effects of different paths on material removal rate ^[65]

Fig. 14. Advantages of water-jet guided laser in processing efficiency. (a) Comparison of cross sections of monocrystalline silicon processed by water-jet guided laser and water-assisted laser^[66]; (b) comparison of surface morphologies of diamond processed by conventional laser and water-jet guided laser^[67]; (c) comparison of surface morphologies of CMCs processed by femtosecond laser and water-jet guided laser^[68]; (d) comparison of cross sections of microgrooves in Ti-6Al-4V alloy processed by gas-assisted laser and water-jet guided laser^[69]; (e) simulation and experimental results of water-jet guided laser processing at different scanning speeds^[70]; (f) morphologies and temperature distributions of water-jet guided laser processed groovings under different pulse numbers ^[71]

Fig. 15. Advantages of water-jet guided laser in processing accuracy. (a) Water-jet guided laser processed monocrystalline silicon at different powers^[72]; (b) water-jet guided laser machining of monocrystalline diamond micro-milling cutters^[74]

Fig. 16. Advantages of water-jet guided laser in depth-to-diameter ratio. (a) Drilling of 10 mm thick 7075 alloy^[76]; (b) drilling of 10 mm thick CFRP seam section^[65]; (c) drilling of 3 mm thick DD6 alloy^[78]

Fig. 17. Advantages of water-jet guided laser in processing flexibility. (a) TBC skew hole and skew hole quality^[80]; (b) FCHs of nickel-based single-crystal turbine blades^[81]; (c) CMC skew hole^[82]