Fig. 1. Timescales of various electron and lattice processes in laser-excited solids^[36]

Fig. 2. Multi-temporal/spatial-scale processes during femtosecond laser irradiation of materials^[37-38]

Fig. 3. Nonlinear ionization mechanisms of femtosecond laser materials interaction^[48]. (a) Tunneling ionization; (b) mixture of tunneling and multiphoton ionization; (c) multi-photon ionization; (d)－(e) impact ionization (avalanche ionization)

Fig. 4. Femtosecond laser-induced plasma radiation and shockwave propagation. (a) Plasma radiation of fused silica^[61]; (b) external shockwave propagation of fused silica^[62]

Fig. 5. Development of femtosecond laser pumping detection technology

Fig. 6. Phase shift and amplitude ratio evolution with time delay during femtosecond laser processing in water^[85]

Fig. 7. Femtosecond laser pump-probe multi-scale observation system^[88]

Fig. 8. Four-dimensional (4D) femtosecond laser pump-probe and transient absorption pump-probe. (a) Carriers evolution and electrons dynamics by 4D femtosecond laser pump-probe technology with high spatial-temporal resolution^[28]; (b) transient absorption microscopy probe of ZnO nanowire^[89]

Fig. 9. Separation of femtosecond laser pulses based on different methods for ultrafast continuous imaging^[32]. (a) Schematic illustration of ultrafast imaging based on spatial division; (b) generation of time-delayed probe pulses through an echelon method; (c) schematic illustration of ultrafast imaging principle based on temporal wavelength division; (d) schematic of plasma dynamics observation and continuous imaging of phonon dynamics with sequentially timed all-optical mapping photography (STAMP)

Fig. 10. Electron dynamics response of materials excited by femtosecond laser. (a) Reflectivity/transmissivity evolution of femtosecond laser during processing fused silica^[95]; (b) free electrons evolution with laser fluence under different polarized laser irradiation^[96]; (c) absorptivity of probe pulse and self-trapping excitons evolution over time under different laser fluences^[98]

Fig. 11. Transient electron density evolution of femtosecond laser-induced fused silica. (a) Transient phase shift evolution over time and space measured by frequency domain interferometry^[99]; (b)(c) transmissivity and interference images of fused silica inner measured with interferometric pump-probe technology^[100]; (d) electron density evolution with time delay^[101]；(e) electron relaxation time evolution with electron density^[101]

Fig. 12. Internal optical response of silicon processed by femtosecond laser with transmission pump-probe technology. (a) Temporal and spatial evolution of transmissivity of femtosecond laser induced silicon^[106]; (b) time evolution of central axis transmissivity of laser induced plasma^[106]; (c) focusing imaging of solid infiltration^[107]; (d)－(f) optical characterization of silicon internal modified structure morphology^[107]

Fig. 13. Femtosecond laser excited material phase transition process. (a) Transient reflectivity evolution of LiNbO₃ crystal excited by femtosecond laser^[111]; (b) evolution of Al₂O₃ relative reflectivity with electron density and electron scattering rate^[18]

Fig. 14. Laser-induced ultrafast phase transition mechanism of novel materials. (a) Schematic of MoS₂ ablation mechanism by femtosecond laser pump-probe technology^[112]; (b) optical microscopy morphology and transient reflectivity spatial distribution comparison of MoS₂^[112]; (c) internal quantum efficiency improvement mechanism of GaN excited by femtosecond laser^[113]; (d) transient reflectivity evolution of GaN surface induced by femtosecond laser at different fluences^[113]

Fig. 15. Evolution of shockwave induced by femtosecond laser. (a) Time-resolved images of jets and shockwave expansion after femtosecond laser pulse ablation of aluminum^[72]; (b) direct observation of laser-induced air ionization and shockwave evolution assisted by crater^[120]

Fig. 16. Study on temperally-shaped femtosecond laser ultrafast dynamic process. (a) Evolution of energy deposition in fused silica with double pulse delay^[125]; (b) comparison of shockwave evolution morphologies during single-pulse and double-pulse irradiating silicon^[16]; (c) phase transformation process and spallation layer formation mechanism of fused silica by double-pulse ablation^[127]

Fig. 17. Study on spatially-shaped femtosecond laser ultrafast dynamic. (a) Shockwave evolution of PMMA drilling by Bessel laser^[128]; (b) evolution of time-resolved transient transmissivity of synchronous spatial-temporal focusing femtosecond laser processing^[129]; (c) optical path of synchronous spatial-temporal focusing femtosecond laser processing^[129]