Advantages of evaporation of hafnium in a reactive environment formanufacture of high-damage-threshold multilayer coatings by electron-beam deposition

摘要

Abstract: Electron-beam deposition is the current method to produce large-aperture high laser-induced damage threshold coatings for the National Ignition Facility, a 1.8 MJ fusion laser. The e-beam process is scalable to large optics up to 0.25 m$+2$/ and with laser conditioning has relatively benign coating defect ejections resulting in high damage threshold thin films. The latest technological breakthrough in manufacturing high damage threshold coatings is e-beam deposition of hafnia by evaporation from a metallic instead of an oxide source in a reactive environment. Although the damage threshold is not significantly increased, a 3-10x defect reduction occurs resulting in significantly less coating modification during laser conditioning. Additional benefits of this technology include improved interfaces for the elimination of flat-bottom pits and up to 3x reduction in plume instability for improved layer thickness control and spectral performance. !16