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

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 m2 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.