Dependence of Laser-Induced Damage Threshold of Anti-Reflection Coatings on Substrate Surface Roughness

The geometrical shapes of damage sites in 5-layer SiO 2 /ZrO 2 anti-reflection (AR) coatings generated by 1 µm laser irradiation have been accurately determined. The damage can be classified into two types: deep damage and shallow damage, the former having a lower threshold. The dependence of the damage threshold of deep damage on the substrate surface roughness is given. It is suggested that the presence of absorption centers embedded in the pores or scratches on the surface of the substrate is responsible for determining the damage threshold. Possible approaches that will lead to stronger AR coatings are proposed.