Sol-gel SiO2 antireflective (AR) film is an important part of the components in "SG II" high power laser device, which plays a technical support in the inertial confinement fusion experiment. Due to its high porosity and large specific surface, it is susceptible to complex environmental conditions during the operation of the device, including humidity change, which will lead to uncertainty in the results of physical experiments. The degree of influence about humidity conditions on the various key properties of SiO2 AR film can be systematically understood by tracking and testing the changes in water contact angle (WCA), transmittance, laser induced damage threshold (LIDT), etc. of that under different humidity conditions for about 24 weeks. Results show that the contact angles and transmittances of SiO2 AR films decrease with increasing humidity. The WCA of the films decrease from 120° to 89.2°, and the peak transmittances decrease by about 0.2% when the relative humidity is 49%, the films had a trend of hydrophilic and becoming thinner. SiO2 AR films have an improving effect on the surface roughness of components, the surface roughness of the components with SiO2 AR film is less than 1 nm, and basically not affected by humidity environment. While the LIDTs of SiO2 AR films increase with the increasing humidity. In order to ensure the long-term stability of the key properties of the components with SiO2 AR films, the ideal storage and working humidity environment for components with SiO2 AR films is 24%~49% based on the test results of various performance factors.
Silica antireflective films were prepared on flat glass substrates by spraying method. By adding n-propanol, isopropanol, n-butyl alcohol and low vapor pressure solvent 1,3-butanediol to form gradient volatilization solvents, the “whitish” in color of coating was solved. Spray coating is a single side coating technology which is suitable for flat or weakly bent substrates. This method can be flexibly applied to single-side coating, double-side heterogeneous coating and rapid coating of large-scale components. The results show that the antireflection coating prepared by spraying method has good optical properties, the transmittance can reach 99.61%, the root mean square roughness is 1.22 nm and the uniformity of the coating was smooth. The spraying method has been successfully applied to the preparation of antireflection films on flat substrates.
Modified antireflective thin films for optical crystals are developed by sol gel chemistry. Hexamethyldisilazane is added
to silica sol to prepare modified sol by the Stöber method. The particle size distribution of the modified sol is found to
have good uniformity, with an average particle diameter of about 42.14 nm. This sol can be used to prepare antireflective
films with low refractive index of about 1.2. Homogeneous double layered films of antireflective and moisture resistant
properties are demonstrated to coat small square sized KH2PO4/KD2PO4 crystals through a combination of dip and spin
coating. The modified antireflective films display residual reflectivity close to zero, and laser induced damage threshold
of 10.9 J/cm2 (pulse wavelength: 355nm, pulse width: 3ns) measured by raster scan method.
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