Laser induced damage characteristics of optical thin film with ion assisted planarization and annealing*

Ion beam sputtering growth of amorphous oxides coupled with processing using Ar ion assist is termed \textit{planarization}. This process was introduced by our team reducing defect cross-section on pre-patterned substrates by up to 90{\%} and increasing laser damage performance by 10x The effects of SiO$_{\mathrm{2}}$ planarization processing on the laser damage resistance of single, bilayers, and multilayer coatings of HfO$_{\mathrm{2}}$ and SiO$_{\mathrm{2}}$ is investigated at pulse durations of 9ps and 220ps. Planarized samples experience a large increase in absorption loss at 1\textmu m wavelength, which is reduced after in-air annealing suggesting presence of oxygen point defects. It is shown the laser damage threshold reduces with planarized SiO$_{\mathrm{2}}$ layers directly implemented compared to control samples at both pulse durations. In-air annealing instead shows a recovery of the laser damage threshold.