The vacuum effect of femtosecond LIDT measurements on dielectric films

Abstract

At ~10 -7 Torr, the multiple femtosecond pulse LIDT, F( ), is about 10% of the single pulse damage fluence for hafnia and silica films compared to ~75% at 630 Torr. The 1-on-1 LIDT is pressure independent. The decrease of F( ) is related to the water vapor and oxygen content of the ambient gas with the former having the largest effect. The decrease of F( ) is associated with a change in damage morphology. In air, the damage "crater" starts at the center of the beam and grow in diameter as the fluence increases. In contrast, the damage starts at random "sites" within the exposed area under vacuum. Absorbing centers are created by the removal of oxygen from predisposed sites (for example grain boundaries) on the film surfaces, producing absorbing states.