Study of the Surface of Al/MgF2 Mirrors after Exposure to High-Intensity VUV Radiation

The degradation of the surface of the Al/MgF2 mirror coating under the influence of ultraviolet radiation from a high-intensity broadband plasma erosion source was investigated. The discharge was carried out in different gases (neon, argon, and air) to control the spectral composition of the radiation. The surface of the samples was examined using a micro-nanoprofilometer, measuring the roughness and the depth of cracks that occurred after irradiation. It was found that, when the sample was exposed to quanta with energy not exceeding 6 eV, the sample experienced minimal roughness losses, and no cracks were observed. When the sample was exposed to quanta with energy ≈6–15 eV, the MgF2 layer near the radiation source began to evaporate, and the depth of cracks reached 55 nm. When the sample was exposed to quanta with energy up to 21 eV, in addition to complete evaporation of the coating, severe degradation of the substrate was observed, with cracks reaching a depth of 200 nm.