Diffraction gratings for high-energy-laser (HEL) systems

High diffraction-efficiency nonpolarizing gratings with CW damage thresholds in the range of 100 kW/cm² and higher are necessary for scaling Spectral-Beam-Combined (SBC) High-Energy Laser (HEL) systems to MW powers and above. We present the results of a campaign to improve capabilities of multilayer dielectric gratings for these applications. Current capabilities are demonstrated by showing the peak temperature, damage threshold, defect density, and diffraction efficiency (where applicable) of 51 MLD gratings and 17 coatings when illuminated at 1070 nm at intensities up to 3 MW/cm².