Alternative coating materials and treatments for the manufacture of ultraviolet sol-gel mirrors

Previous studies of for sol-gel coated multilayer UV mirrors have shown a significant decrease in laser induced damage threshold (LIDT) between the single component layer coatings and ten pair multilayer coatings. Further investigation has shown that the LIDT decreased rapidly after the first two pairs however no further decrease was seen with the subsequent deposition of more layers. In this paper, the effect on the LIDT of starting and finishing with high index material was assessed as a function of the number of layers. The effects on LIDT and environmental stability, i.e. the reaction to changes in temperature and pressure, of using a silica or Teflon half wave overcoat were also investigated. Different coating treatments, e.g. baking each layer applied to the substrate, were also investigated with the aim of improving both the LIDT and the number of layers which could be deposited, and hence the reflectivity of the mirrors, without the occurrence of crazing. Investigations into the damage morphologies were made and differences between the samples compared.