Fig. 1. Changes in reflectivity and transmittance caused by the Kerr effect of different thin films^[31]. (a) (b) Nb₂O₅/SiO₂; (c) (d) Ta₂O₅/SiO₂

Fig. 2. Two-photon absorption phenomenon in Ta₂O₅/SiO₂ and HfO₂/SiO₂ thin films^[14]. (a) The trend of thin film reflectivity with varying incident light power density; (b) the reversibility of observed nonlinearity

Fig. 3. A schematic representation of the third harmonic generation in a medium with length l, an incident wave with intensity I0 and frequency ω^[28]

Fig. 4. Schematic diagram of a frequency tripling mirror^[28]

Fig. 5. The pulse energy of the generated third harmonic for different fundamental pulse energies^[45]

Fig. 6. Typical single-beam Z-scan setup (the inset shows the characteristic Z-scan curves for closed and open apertures)^[63]

Fig. 7. Normalized transmittance and its fitting curves of HfO₂ thin films under irradiation at different wavelengths^[35]. (a) 343 nm; (b) 515 nm

Fig. 8. Closed aperture Z-scan curves of ITO films under excitation of 1440 nm at different input fluences^[65]

Fig. 9. The interferometric setup for the determination of the nonlinear refractive index^[66]

Fig. 10. Spectral technique characterization of third-harmonic generation effect^[28]. (a) Third-harmonic measurement setup; (b) spectral intensity distribution of the generated third harmonic

Fig. 11. Typical light limiting effect^[67]

Fig. 12. Dependence of normalized transmittance of ITO films (asdeposited and annealed) on optical intensity using different pump sources^[65]. (a) 1030 nm; (b) 1440 nm

Fig. 13. Experimental results of different thin-film designs^[69]. (a) The thin film structure before optimization; (b) the thin film structure after optimization; (c) reflectance versus incident light intensity; (d) temperature versus time curve

Fig. 14. Intensity-dependent performance of high-dispersion HD58 and HD1631 chirped mirrors^[70]. (a) (d) Measured reffectance as a function of incident laser peak intensity; (b) (e) power loss on reffection as a function of peak intensity on a log-log scale; (c) (f) SHG signal generated with the reffected laser beam, as a function of the reffected laser energy density on a log-log plot

Fig. 15. Chirped mirror simulation experimental results^[70]. (a) (e) The structures of thin film; (b) (f) a thermal image of the mirror when illuminated by 30 fs pulse after optimization; (c) (g) the electric field intensity distribution within thin films; (d) (h) the volume integrated peak intensity ratio between Ta₂O₅ and SiO₂

Fig. 16. Optical switch effect diagram^[28]. (a) Spectral shift caused by Kerr effect; (b) transmittance of incident pulses with different energies

Fig. 17. Photo of the experimental setup demonstrating the operation of a frequency tripling mirror^[74]

Fig. 18. TH signal of frequency tripling mirrors as a function of the number of layers^[74]

Fig. 19. Detailed study of the THG inside an FTM^[39]. (a) The conversion efficiency of THG from a 1-nm thick probe layer inside layer 9 of an FTM with N = 27; (b) the conversion efficiency of THG from a 1-nm thick probe layer inside layer 11 of an FTM with N = 27

Fig. 20. The enhancement of THG conversion efficiency.