Femtosecond‐Laser Irradiation onto Sapphire Substrates in an N2 Ambient Atmosphere

Herein, a new technique is proposed for forming nitrogen‐related bonds anywhere on a substrate using a femtosecond laser. Laser‐induced periodic structures with a minimum periodicity of <50 nm are formed on a sapphire substrate. Nitrogen‐related bonds are formed at the sapphire surface by laser irradiation in N2 ambient. This technique is applicable to periodic polarization inversion in nitride semiconductors for nonlinear optical devices.