Planarization of nodular defects was investigated in order to improve the laser-induced damage threshold (LIDT) of high-reflection coatings. Monodisperse SiO<sub>2</sub> microspheres were first deposited on the substrate surface by a spin coating process. Using a dual ion beam sputtering system, these engineered seeds were used to create artificial nodules in 1064nm HfO<sub>2</sub>/SiO<sub>2</sub> high-reflection coatings and Ta<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub> high-reflection coatings. These SiO<sub>2</sub> microspheres were then smoothed by a single thick SiO<sub>2</sub> planarization layer, where the relationship between the thickness of the planarization layer and the size of the microspheres was investigated. When the planarization layer (etching layer) thickness is slightly larger than the diameter of the seeds, the seeds could be completely planarized to obtain smooth thin films. In addition, the LIDT of the high-reflection coatings with different coating materials and different planarization layer thicknesses were tested. The results showed that the nodular defects planarization could noticeably improve the damage resistance of high- reflection coatings. In addition, the surface roughness of Ta<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub> high-reflection coatings was shown to decrease after the planarization, while the surface roughness of the 1064nm HfO2/SiO2 high-reflection coatings was shown to increase.
For the sol-gel method, it is still challenging to achieve excellent spectral performance when preparing antireflection (AR) coating by this way. The difficulty lies in controlling the film thickness accurately. To correct the thickness error of sol-gel coating, a hybrid approach that combined conventional sol-gel process with ion-beam etching technology was proposed in this work. The etching rate was carefully adjusted and calibrated to a relatively low value for removing the redundant material. Using atomic force microscope (AFM), it has been demonstrated that film surface morphology will not be changed in this process. After correcting the thickness error, an AR coating working at 1064 nm was prepared with transmittance higher than 99.5%.