Substrate and coating defect planarization strategies for high-laser-fluence multilayer mirrors

Abstract

a b s t r a c t a r t i c l e i n f oAvailable online xxxx Keywords: Nodular defect Laser damage testing 1064-nm laser Nanosecond pulse length Thin film Multilayer mirror Ion beam sputtering PlanarizationPlanarizing or smoothing over nodular defects in multilayer mirrors can be accomplished by a discrete depositand-etch process that exploits the angle-dependent etching rate of optical materials. Typically, nodular defects limit the fluence on mirrors irradiated at 1064 nm with 10 ns pulse lengths due to geometrically-and interference-induced light intensification. Planarized hafina/silica multilayer mirrors have demonstrated N 125 J/cm 2 laser resistance for single-shot testing and 50 J/cm 2 for multi-shot testing for nodular defects originating on the substrate surface. Two planarization methods were explored: thick planarization layers on the substrate surface and planarized silica layers throughout the multilayer in which only the silica layers that are below one half of the incoming electric field value are etched. This paper also describes the impact of planarized defects that are buried within the multilayer structure compared to planarized substrate particulate defects.Published by Elsevier B.V.

Waterproof coatings for high-power laser cavities

“…3a1. Since there are always extrinsic defects in real multilayer coatings 19 , water molecules in HfO 2 layers could reach and corrode the Nd:Glass substrate along defect-induced channels, which could be linked to the Nd:Glass surface.

Fig. 3Schematic of water diffusion in nanopores; optical photographs; cross-sectional SEM images of HfO 2 /SiO 2 and Ta 2 O 5 /SiO 2 multilayers prepared by an IAD process

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Growth defects in CrN/NbN coatings deposited by HIPIMS/UBM techniques

“…shows the schematic diagram of localised corrosion related to coating defects. In optical coatings, nodular defects were found to influence laser-induced damage [105][106][107][108]. Electric-field modelling had shown that the light intensified at the defect spots due to the geometric and interference nature of these defects [106].…”