The Mechanism of Formation of Nanostructures of Hexagonal Symmetry on Surfaces of Metals by a Sequence of Doubled Ultrashort Pulses of Radiation of Orthogonal Polarization

Abstract

Recent experimental results on formation of ordered surface nanostructures of hexagonal symmetry on metals under the action of a series of scanned doubled collinear femtosecond pulses of orthogonal polarization and variable time delay are analyzed. It is demonstrated that the appearance of structures is related to the formation of a dynamic grating by the first pulse and excitation of two pairs of surface plasmon–polaritons by the second pulse in directions symmetric with respect to its vector of polarization and forming an angle of π/3 with each other. This leads to the formation of corresponding dynamic gratings and fourfold degeneracy of the first grating. Three dynamic gratings symmetric with respect to the surface normal form a residual surface relief of hexagonal symmetry that can be observed experimentally.