AR Nanotextured YAG for High Energy Laser Systems

The Air Force utilizes YAG laser crystals for critical applications including target designation, range finding, guidance, and directed energy weaponry; but has identified that thin film antireflection coatings on the laser facets reduce the pulsed laser-induced damage threshold (LiDT) of the crystal and are a primary limiting factor in achieving desired power levels. The Air Force recognizes that these coatings can by be replaced with a surface nanotexture that is etched directly into the critical laser facet, providing a rugged, low absoprtion solution with superior optical performance and pulsed laser damage resistance. In the Phase I effort, YAG crystals will be nanotextured and characterized, showing bandwidth, reflections levels, and angular properties exceeding the capabilities of coatings. Absoprtion measurements on the etched surfaces will confirm the absence of the absorptive defects that lead to premature laser damage. Standardized pulsed laser damage testing will demonstrate that the damage threshold of nanotextured YAG surfaces are comparable to as-polished surfaces. The fabrication process will be shown to be both reproducible and cost-effective, critical milestones on the path to providing the U.S. Department of Defense with an industry base for nanotextured infrared materials, and a path to advancing power scaling in high energy lasers.