Influence of SiO2 overcoat layer and electric field distribution on laser damage threshold and damage morphology of transport mirror coatings

Four mirror coatings were designed for transporting 1064 nm light, and prepared under the same process parameters. The laser induced damage threshold (LIDT), electric field distribution, as well as the damage morphology of the prepared transport mirror coating was investigated. The results indicate that the SiO2 overcoat layer and electric field distribution have a great impact on the LIDT and damage morphology of the transport mirror coating. A thicker SiO2 overcoat layer can suppress the delamination damage morphology, and significantly increase the LIDT. For the designs with similar SiO2 overcoat layer thickness, the nano-absorbing defects can survive at higher laser fluence in the design with lower electric field intensity. In addition, the HfO2 over SiO2 interface has a better interfacial strength and less “invisible” nano-absorbing defects than the SiO2 over HfO2 interface, suggesting that improving the SiO2 over HfO2 interfacial quality will be an effective way to enhance the laser damage performance of the transport mirror coating.