Femtosecond laser pulse induced breakdown in dielectric thin films

Laser-induced breakdown of a high-quality mirror consisting of alternating λ/4 layers of Ta₂O₅ and SiO₂ and a single 500-nm thin film of Ta₂O₅ were studied with amplified and unamplified femtosecond pulses. The experimental data can be fitted with a model taking into account multiphoton absorption, impact ionization, and local intensity enhancements due to interference effects in the films. Incubation effects are observed when the coatings are damaged with multiple pulses from a femtosecond oscillator. The results indicate that state of the art, high-quality thin films show a damage behavior that is similar to bulk materials. Defects and impurities play a negligible role.