We report on surface structuring of sapphire, silicon carbide, and silicon by femtosecond laser pulses in multipulse
irradiation mode. The formed ripples on the flat surface or on the vertical walls with hierarchical structures
whose feature sizes are ranging from the irradiation wavelength down to ~ 50 nm are prospective templates for
surface enhanced Raman scattering after coating with plasmonic metals. We study complex patterns of fine
ripples with periods Λr, as small as λ/Rp, where Rp (see manuscript) 3 - 5. The mechanisms suggested for such Rp values
are discussed: temperature and density of breakdown plasma, angle of incidence, mechanism of second harmonic
generation (SHG) and absorption. Predictions of the surface and bulk models of ripple formation are compared
with experimental values of Rp-factor. We propose a model of ripple formation on the surface, which is based on
the known in-bulk sphere-to-plane formation of breakdown plasma in the surface proximity. In semiconductor
4H:SiC normal ripples with periods 190 and 230 nm were recorded with 800 nm and 1030 nm fs-laser pulses
respectively. We show that the period of ripples is defined by the dielectric properties of crystalline (solid) phase
rather than the molten phase in the case of silicon. Generation of SHG on the surface of sample and plasma
nano-bubbles are discussed: surface-SHG is found not important in ripples' formation as revealed by comparative
study of periods on Al2O3 and TiO2 at 800 nm wavelength of irradiation. We propose that ripple periodicity is
pinned to the smallest possible standing wave cavity (λ/n)/2 inside material of refractive index n.
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