Fig. 1. AFM images of the prepared W metals: (a) polished surface, (b) non-polished surface.

Fig. 2. SEM pictures of periodic ripples induced by the fs laser on W metal surfaces: (a) polished, (b) non-polished.

Fig. 3. SEM pictures of periodic ripples induced by a fs laser on a metal surface with defects.

Fig. 4. SEM pictures of ripples achieved with different scanning times on the polished W surface: (a) one time, (b) two times, (c) three times, (d) four times, (e) five times, and (f) six times.

Fig. 5. Curve of ripple depth changes with scanning times.

Fig. 6. Overview of the experimental setup for nano-structures experiments using two beams with crossed light polarizations. BS is non-polarizing 50/50 beam splitter, PP is polarizing prism, Re is reflecting mirror, and TDL is a motorized time-delay-line.

Fig. 7. SEM images of nano-gratings produced by pulses with different crossed angles: (a) the electric field E01 and E02 is orthogonal, (b) the angle between E01 and E02 is 45°. The period of the gratings is about 610–630 nm.