Nature of resonator mirror damage in high-power industrial electron-beam-controlled CO2 lasers

An investigation was made of the nature of damage to resonator mirrors and of the change in the microstructure of the mirror material as a result of prolonged operation of a general-purpose industrial electron-beam-controlled CO₂ laser with on output power ~ 10 kW. It was found that the damage to the mirror surfaces occurred at considerably lower radiant flux densities than in the case when radiation is focused on a mirror surface in vacuum. Characteristic forms of surface damage were classified according to the following basic scheme: damage to the surface by incandescent particles formed in the laser active medium from the materials in the discharge chamber and resonator; damage by pitting; appearance of deep craters resulting from breakdown at the mirrors; damage to and crystallization of an oxide film, accompanied by the formation of a dendritic structure. An analysis was made of deformation effects in the material of the mirrors.