Silica thin films have been deposited by a dual-ion-beam sputtering technique using argon or xenon ions mixed with oxygen ions in the assisting beam and the role of the assisting-ion-beam parameters on the laser-damage-threshold at 308 nm (XeCl laser) has been investigated. It is shown that a proper choice of these parameters allows a considerable increase of the laser-induced damage threshold. Lower damage thresholds (1 J/cm(2)) were found for the xenon/oxygen assisted samples. Whereas, the highest damage threshold (8 J/cm(2)) was found for the argon-ion assisted sample and its value was also much higher than that (2.9 J/cm(2)) of the non-assisted films. Damage thresholds have been determined by the photoacoustic mirage technique and it is demonstrated that this technique can provide useful information on the mechanisms responsible for laser damage.