Toward the formation of crossed laser-induced periodic surface structures

The formation of a new type of laser-induced periodic surface structures using a femtosecond pulsed laser is studied on the basis of the Sipe–Drude theory solved with a finite-difference time-domain scheme. Our numerical results indicate the possibility of coexisting structures parallel and perpendicular to the polarization of the incident light for low reduced collision frequency ($\gamma /\omega \lesssim 1/4$, where ω is the laser frequency). Moreover, these structures have a periodicity of $\Lambda \sim \lambda $ in both orientations. To explain this behavior, light–matter interaction around a single surface inhomogeneity is also studied and confirms the simultaneous presence of surface plasmon polaritons and radiation remnants in orthogonal orientations at low $\gamma /\omega $ values