Preparation and damage of wideband chirp mirrors

The HfO2/SiO2 and Ta2O5/SiO2 chirped mirrors with different electric field distribution were fabricated by electron beam evaporation with good damage characteristics and stress features. The laser-induced damage test of samples was performed by laser pulses with duration 350fs, center wavelength 1 030 nm. The results show that the material characteristics and electric field distribution are the key factors which can influence the damage threshold. Ta2O5/SiO2 chirped mirror, which has much wider GDD bandwidth and has the same damage threshold as HfO2/SiO2 chirped mirror can be fabricated by reducing the peak intensity of field in the film stack. This phenomenon was illustrated by the theoretical model of conduction band electron density while the breakdown mechanism of chirped mirrors was explained and damage morphologies of samples were analyzed.