Impacts of SiO2 planarization on optical thin film properties and laser damage resistance
2016
Lawrence Livermore National Laboratory (LLNL) and Colorado State University (CSU) have co-developed a
planarization process to smooth nodular defects. This process consists of individually depositing then etching tens of
nanometers of SiO 2 with a ratio of 2:1, respectively. Previous work shows incorporating the angular dependent ion
surface etching and unidirectional deposition reduces substrate defect cross-sectional area by 90%. This work
investigates the micro-structural and optical modifications of planarized SiO 2 films deposited by ion beam sputtering
(IBS). It is shown the planarized SiO 2 thin films have ~3x increase in absorption and ~18% reduction in thin film
stress as compared to control (as deposited) SiO 2 . Planarized SiO 2 films exhibit ~13% increase in RMS surface
roughness with respect to the control and super polished fused silica substrates. Laser-induced damage threshold
(LIDT) results indicate the planarization process has no effect on the onset fluence but alters the shape of the
probability vs fluence trace.
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