<title>Effect of SiO2 overcoat thickness on laser damage morphology of HfO2/SiO2 Brewster's angle polarizers at 1064 nm</title>

HfO₂/SiO₂ Brewster's angle polarizers are being developed at Lawrence Livermore National Laboratory for the National Ignition Facility. Damage threshold studies using a 3-ns pulse length 1064-nm laser have revealed a number of different damage morphologies such as nodular ejection pits, plasma scalds, and overcoat delaminations. Of these laser damage morphologies, delaminations have the most negative impact on fusion laser performance. By increasing the thickness of the SiO₂ overcoat, the delamination morphology is eliminated without significantly modifying the spectral characteristics of the coating. A model of the thermal mechanical response of the overcoats is presented for various SIO₂ overcoat thicknesses. The overcoat thickness influences the electric-field profile resulting in different thermal gradients between the outer SiO₂ and HfO₂ layers. This modeling effort attempts to understand the relationship between the thermal stress distribution in the overcoat and the occurrence of delamination.