Control of microstructure and laser induced damage threshold of antireflective silica films

Polyvinyl butyral (PVB) modified antireflective silica films were deposited on fused silica substrates by sol-gel process. The effect of PVB on the microstructure and laser induced damage threshold (LIDT) of the films was investigated. The results of nanoparticle analyzer, and scanning probe microscope show that PVB molecules surround and control the growth of silica particles, resulting in a stable sol with uniformly distributed silica particles. As a result, the film deposited from these PVB modified sols possesses uniform microstructures. The optimal PVB modified silica film has surface roughness of 3.25 nm. The adhesive-resistance test exhibits that the strength of PVB modified silica film increases due to the bond reaction between PVB molecules and silica particles. The addition of PVB to silica sol increases the LITD of films. By adding 1.0% PVB to silica sol, the LIDT of films increases from 30.0 J/cm2 to 40.1 J/cm2. The increase in LIDT is attributed to the increase in film strength and uniformity of film microstructures as an effect of PVB modification.