Toward the formation of crossed laser-induced periodic surface structures

TL;DR

This paper investigates the formation of crossed laser-induced periodic surface structures using femtosecond lasers, revealing conditions for coexisting structures with different orientations and their underlying physical mechanisms.

Contribution

It introduces a theoretical and numerical analysis of crossed laser-induced periodic surface structures, highlighting the coexistence of structures in orthogonal orientations at low collision frequencies.

Findings

Coexisting structures parallel and perpendicular to laser polarization are possible.

Structures have a periodicity approximately equal to the laser wavelength.

Surface plasmon polaritons and radiation remnants are involved in structure formation.

Abstract

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 FDTD 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 $\omega$ 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.