Periodic Grating Structures on Metal Self-organized by Double-pulse Irradiation

The formation of periodic grating structures has been demonstrated on a titanium surface irradiated by a double-pulse beam with a time delay of 160 fs. The first-pulse fluence F PP was varied and always kept below the threshold F TH = 60 mJ/cm 2 for forming periodic grating structures on Ti and the delayed pulse fluence F LP was kept above F TH . The grating structure interspaces were 0.5 L to 0.85 L and decreased with F PP for all values of F LP . This tendency suggests that variation in surface plasma density, which is associated with the fluence of the first pulse, led to variation of the grating interspaces. We found that the interspaces produced by double-pulse irradiation agreed relatively well with those produced by single-pulse irradiation and those predicted by a parametric decay model. To visualize the surface plasma wave induced by the femtosecond laser, two-dimensional particle-in-cell simulation was conducted for a preformed plasma on a metal. The simulation results suggest that the preformed plasma density led to the variation in the grating interspaces.