Plateau–Rayleigh instability as the seed process in the self-organization of a photonic crystal at the surface of crystalline silicon in a femtosecond laser field

In a Si(111) surface exposed to tightly focused multipulse scanning 1.95-$\mu$m infrared femtosecond laser radiation, anomalous (i.e., oriented parallel to the polarization of radiation) nanostrip gratings with a period of about 0.4 $\mu$m are formed either along or across the irradiated area, depending on the mutual orientation of the scanning direction and polarization of radiation. With an increase in the radiation energy density or exposure intensity, the strips are transformed by the Plateau–Rayleigh mechanism into periodic linear chains of resolidified nanodroplets (nanospikes) with a period of about 0.7 $\mu$m. With a further small increase in the energy density or exposure intensity, the surface-plasmon-assisted near-field scattering of infrared laser radiation by nanospike chains causes the formation of a two-dimensional photonic crystal slightly elongated in the direction of laser polarization consisting of densely packed nanospikes with subwavelength crystal constants.