SiO2 and HfO2 thin films have been deposited on polished fused silica substrates by the ion assisted electron beam evaporation technique in different deposition conditions. The role of the assisting ion beam parameters either on the optical and structural film properties and the film damage threshold at 308 nm (XeCl excimer lasers) has been investigated. Laser damage thresholds have been determined by the photoacoustic mirage technique.