Figure 4.

(a) 2D scanning electron microscopy (SEM) images presenting the influence of the $N_{DPS}$ in enhancing nanostructures at a fixed time delay. (b) 2D SEM images of growing nanopatterns by decreasing the time delay at a fixed peak fluence of 0.24 J/cm${}^2$ and $N_{DPS}$ = 25. (c) 2D SEM image of the gaussian laser spot at a fixed laser parameters (0.18 J/cm${}^2$; 10 ps; $N_{DPS}$ = 44). (d) The left region of the gaussian laser spot, showing the significant role of laser fluence in controlling different types of nanostructures.