Role of two-photon absorption in Ta_2O_5 thin films in nanosecond laser-induced damage

Laser-induced damage in the nanosecond domain has been connected to the heating and breakdown of local defects within the thin film and the various interfaces. Within the femtosecond regime, the damaging events can be traced back to multiphoton-based excitation into the conduction band. When critical electron density is exceeded, an optical breakdown will occur. In this Letter we report on evidence that two-photon absorption also significantly triggers laser-induced damage in Ta(2)O(5) thin films at 532 nm and 8 ns pulse duration. For experimental verification, single layers of Ta(2)O(5)/SiO(2) mixtures have been analyzed.