Cross-sectional study of high spatial frequency ripples performed on silicon using nanojoule femtosecond laser pulses at high repetition rate

We report on investigations of fine cross-sectional cuts performed by focused ion beam on periodic high spatial frequency ripples generated on large areas of silicon in air under ultrashort low energy pulses irradiation at high repetition rate. The morphology, depth profile, and aspect ratio which was found to be of 1:1 are quite independent from the energy and number of pulses applied even if a slight decrease of the aspect ratio was found at high energies and high number of applied pulses. Furthermore, even if the orientation of the HSFL is perpendicular to the polarization the profile and aspect ratio of the cross sections are not influenced by the rotation of the polarization.