Ultrafast Laser‐Induced Sub‐100 nm Structures on Tungsten Surfaces: Stretched Liquid Dynamics Insights

The origin of high‐spatial‐frequency laser‐induced periodic surface structures, known as HSFLs, has always been a controversial topic. HSFLs of sub‐100 nm periodicity and sub‐20 nm amplitude are generated on tungsten by Ti:sapphire femtosecond laser irradiation under four different processing environments (ambient, air at 10 mbar, Ar at 10 mbar, and vacuum at 10 −7 mbar). The topography and subtopography analysis together with two‐temperature model–molecular dynamics simulations reveal that HSFLs formation originates from laser‐induced thermal stresses, implying both surface tension and tensile forces are involved. The experimental observation of subsurface cavitation confirms a hydrodynamics‐based origin for these nanostructures.