Laser damage properties of broadband low-dispersion mirrors in sub-nanosecond laser pulse

Broadband low dispersion (BBLD) mirrors are an essential component in femto-second (fs) pulse laser systems. We designed and produced Ta₂O₅-HfO₂/SiO₂ composite quarter-wave and non-quarter-wave HfO₂/SiO₂ BBLD mirrors for the 30fs petawatt laser system. The laser damage properties of the BBLD mirrors were investigated in an uncompressed sub-nanosecond laser pulse. It showed that the Ta₂O₅-HfO₂/SiO₂ composite BBLD mirror possessed higher LIDT due to the low electric-field intensity (EFI) in the case of the coating without artificial nodules. Nevertheless, the LIDT of the composite mirror was significantly lower than the non-quarter-wave HfO₂/SiO₂ mirror when the nodules exist. The EFI simulation and damage morphology of the nodules analysis demonstrated that the nodule leading to the light intensification in the middle of the boundary between the nodular and the surrounding coating, thus the outermost HfO₂/SiO₂ layers cannot protect the Ta₂O₅/SiO₂ layers, and resulting to the significantly low LIDT. This study shed some light on the development of high-laser-damage BBLD mirrors for pulse compression laser systems.