Figure 1.

SEM images of the three LIPSS structures produced in steel under different laser irradiation conditions, distinguished fundamentally by the laser fluence and pulse number N_{eff_2D} (parameters given in the text): A) ripples with a periodicity Λ_y = 850 nm, B) grooves, Λ_y = 840 nm, Λ_x = 2.6 µm, and C) spikes. D) Highly irregular (“damaged”) morphology (optical micrograph) obtained at high fluence and N_{eff_2D} values. E) Schematic distribution of the different structures found with one single scan, depending on the laser fluence and the effective number of pulses in an area (N_{eff_2D}). The positions on this plot for the structures shown in A–D are represented accordingly. The scanning direction and laser polarization for all the images shown are included in A.