Role of multiple shots of femtosecond laser pulses in periodic nanostructure formation on silicon surface

Self-organized periodic nanostructures much smaller than the laser wavelength are often produced on solid surfaces in femtosecond (fs) laser ablation [1]. It is well known that the nanostructure formation is sensitive to the experimental conditions, and superimposed multiple shots of low-fluence fs laser pulses are especially effective for the nanostructuring. However, the role of multiple shots of fs pulses, as well as the fundamental physics, in the nanostructuring is insufficiently understood, resulting in the difficult control of the interaction. Here we report the experimental study to make clear the effect of multiple shots of fs laser pulses on nanostructuring. The pump-probe reflectivity measurements for silicon (Si) have shown that the superimposed multiple shots of low-fluence fs pulses are crucial to the excitation of surface plasmon polaritons (SPPs) for the periodic nanoscale ablation through the non-thermal interaction [2].