Femtosecond-laser-induced nanostructure formed on nitrided stainless steel

► Femtosecond-laser-induced periodic surface nanostructures formed on nitrided stainless steel were investigated. ► The mean spacing D in the nanostructure showed the minimum size of 250 nm, corresponding to the size of ∼λ/3. ► The phenomenon where an irradiated area on the nitrided surface swells arose. ► D observed for the nitrided surface was 10-20% smaller than that for the untreated surface.