Properties of SiO2 antireflective films for SG II in atmospheric pressure humidity environments

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.