Fig. 4: Laser-induced damage testing of diamond and dielectric mirrors.

a Optical image of a diamond mirror mounted on a water-cooled stage that was taken prior to testing. b–e Thermal images of the diamond mirror irradiated by 0.5, 2.5, 5, and 10 kW, respectively, of continuous-wave laser power. Color bar shows the temperature of the setup with varying scale for each image. Temperature accuracy is ±2°. Hot spot corresponds to the position of the beam (on the diamond mirror). At increased power levels a small fraction of optical power leaking through the backside of the diamond mirror results in heating of the stage. f Wide-area SEM image of the diamond mirror shows no damage after testing. Scale bar is 5 μm. g Optical image of a corresponding dielectric mirror mounted on the water-cooled stage. h–k Thermal images of the dielectric mirror irradiated by 0.5, 2, 6, and 10 kW, respectively, of CW laser power. Damage ensues at 10 kW of power due to thermal stress. l Image of damage region of dielectric mirror taken after testing shows a several mm-sized hole where the laser beam ablated the dielectric. Photo Credit for panels (a), (g) and (l): S. DeFrances, Penn State EOC.