Two types of laser-induced periodic surface structures (LIPSS) formed on titanium by femtosecond (fs) laser pulses (lambda= 800 nm, tau = 180 fs, nu =1 kHz) in air were investigated experimentally. At a laser fluence F above the ablation threshold, LIPSS with a minimum mean spacing of D < lambda 2 were observed perpendicular to the laser polarization direction. In contrast, for F slightly below than the ablation threshold, ultrafine LIPSS with a minimum value of D

Keywords:Femtosecond-laser processing;Laser-induced periodic surface structures;Titanium;XPS;ToF-SIMS;Cellulose derivative