Fig. 1. Particle size distributions of SiO₂ in sol with different concentrations

Fig. 2. Optical properties of fourth harmonic generation SiO₂ antireflective films. (a) Transmittance curves; (b) transmittance values at 266 nm

Fig. 3. Refractive index of fourth harmonic generation SiO₂ antireflective films

Fig. 4. Surface roughness (root-mean-square) of fourth harmonic generation SiO₂ antireflective films

Fig. 5. Schematic of laser damage resistance of sol-gel SiO₂ film

Fig. 6. Scanning electron micrograph of 1# film surface

Fig. 7. Laser damage test of fourth harmonic generation SiO₂ antireflective films. (a) Laser-induced damage threshold; (b) damage morphology of 1# film

Fig. 8. Properties of fourth harmonic generation SiO₂ antireflective films in high humidity environment. (a) Transmittance change at 266 nm; (b) contact angle change