On solid material under irradiation of linear polarized femtosecond laser pulses, the periodic surface structures are self-organized and oriented perpendicular or parallel to the laser polarization direction. For laser fluence levels near the ablation threshold, periodic structures have an interspace of ～0.1 λ L‒～ λ L , which is shorter than the laser wavelength λ L. The interspaces of the periodic structures depend on laser fluence and laser wavelength, and these phenomena have been explained by such models as the parametric decay model, the bidirecrtional surface plasma wave model, the plasmon polariton excitation model, and the second harmonic generation model. However, since the mechanism of the periodic structures remains unclear, further investigation is required. In this paper, we summarize the current study of the periodic surface structure induced by femtosecond laser pulses and review the several models proposed for the formation mechanism.
