Generation of high spatial frequency ripples on silicon under ultrashort laser pulses irradiation
Periodic high spatial frequency ripples structures have been generated in silicon under femtosecond laser pulses irradiation. The period of the ripples is wavelength dependent. It increases from 110 up to 160 nm when the wavelength varies from 700 to 950 nm, respectively. We propose a refined model of the second harmonic generation ripples spacing theory =/2 n* taking into account the modified femtosecond laser excited silicon refractive index n* related to the Drude model. Good agreement is found between experimental results and the presented revisited model.