Helium Ion‐Induced Degradation Mechanisms in Optical Coatings for Space Applications

ABSTRACT Low‐energy helium ions represent a significant source of degradation for optical coatings operating in space environments, especially in Geostationary Earth Orbit (GEO). Despite their relevance, the mechanisms responsible for ‐induced degradation remain largely unexplored. This work systematically investigates the effects of irradiation on metallic and dielectric thin films for space optical applications, including single‐ and bi‐layer coatings based on Al, Au, Ag, , , and . More than 150 samples were irradiated at different fluences, fluxes, and ion energies (4, 16, and 100 keV) under conditions covering both 15‐year GEO baseline fluences and intentionally above such levels. The selected energies allow a comparative investigation of both ion penetration effects in single layers and interface‐stressing mechanisms in multilayer structures. Radiation‐induced modifications were characterized through optical and structural analyzes, including reflectance/transmittance measurements, Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM). The results reveal distinct degradation mechanisms associated with implantation and interface damage, highlighting effects that differ significantly from those typically observed under proton irradiation. In addition, empirical reference fluences without observable optical degradation were determined for the investigated coating systems, providing an empirical baseline for assessing coating stability in space environments.